Topic 1. General patterns of growth
1. General ideas about plant growth and development
2. Localization of growth
3. Cellular basis of growth
4. Growth phenomena
5. Irreversible growth disorders
6. Methods for accounting for growth rate
Ontogenesis (individual development or life cycle) is a complex of successive and irreversible changes in the life activity and structure of plants from emergence from a fertilized egg, embryonic or vegetative bud to natural death.
Height is the most important manifestation of the normal functioning of a plant - it is an irreversible increase in length, volume and general sizes plant, its individual organs, cells and intracellular structures. An increase in size and weight in plants continues throughout their life.
There is a distinction between apparent and true growth.
Visible growth is a balance of mutually opposite processes of neoplasm and destruction.
True growth is the process of new formation of structures.
But not every increase in mass can be called growth; for example, when seeds swell, there is an increase in mass, but this is not growth, since the phenomenon can be reversible.
Growth conditions are :
1. availability building material and energy;
2. the presence of special regulators - phytohormones.
The source of building material and energy is the process of photosynthesis. With its intensive flow, substances (reserve, mineral, water) are involved in growth processes.
Development according to D.A. Sabinin is a qualitative change in the structure and functional activity of the plant and its parts during ontogenesis.
Growth and development are closely related to each other and occur simultaneously. Growth is one of the properties of development, therefore, for development to begin, at least barely begun growth is necessary. In the future, development processes are decisive. However, rapid growth can be accompanied by slow development and vice versa. For example, winter crops grow quickly when sown in spring, but do not begin to flower, and when sown in autumn, they grow slowly and undergo a development process that determines the further appearance of flowers. Thus, the indicator of development is the transition of plants to reproduction, and the indicator of growth rates is the rate of accumulation of mass, volume, and size of the plant.
The processes of growth and development are determined by the heredity of the plant and are regulated by phytohormones and environmental factors.
Ontogenesis classification:
1. Phenological phases– these are clearly expressed morphological changes in the structure and functional activity of plants. They characterize, on the one hand, a change morphological characteristics plants associated with the appearance of new organs, on the other hand, they are often associated with a detailed description of economically important traits cultivated plants.
For example, in cereals, the following phases are distinguished: seed germination, shoots, third leaf, tillering (branching) from underground nodes of the stem, emergence into the tube (stemming, beginning of growth of the main shoot stem), heading (shooting), flowering, milky ripeness, waxy ripeness, complete ripeness.
In the apple tree, the following are noted: swelling of the buds, blooming of flower and leaf buds, unfolding of the first leaves, formation of inflorescences, flowering, fruit set, fruit ripening, autumn leaf coloring, leaf fall. In grapes, phenophases are distinguished: the beginning of sap flow, swelling of the buds, opening of the buds, unfolding of the first leaf, unfolding of the third leaf, flowering, ripening, technical ripeness, autumn coloring of leaves.
2. The life cycle of a plant consists of two periods - vegetative and reproductive. During the first period, the vegetative mass is intensively formed and grows rapidly root system, tillering and branching occur, woody branches grow, and flower organs are formed.
The reproductive period includes flowering and fruiting. After flowering, the humidity of the vegetative organs decreases, the nitrogen content in the leaves sharply decreases, the outflow of plastic substances to their containers occurs, and the growth of stems in height stops.
Michurin I.V. distinguished 5 stages or life phases in fruit trees: 1. seed germination;
2. the phase of the seedling’s youth and its first fruiting;
3. stabilization of the morphological and physiological characteristics of the body;
4. regular fruiting and the next 3-5 years;
5. aging and dying.
3. Age periods:
Embryonic – the period of zygote formation and embryo development;
Juvenile – the period of youth, characterized by the germination of the embryo and the formation of vegetative organs;
The period of maturity - the appearance of flower primordia, the formation of reproductive organs;
Reproduction (fruiting) – single and multiple formation of fruits;
Aging – the predominance of decay processes, the structures are inactive.
4. Stages of organogenesis, reflecting the morphophysiological changes occurring in the meristematic tissue (growth cone). The stages of organogenesis were proven by F.M. Cooperman and found that plants go through 12 stages during ontogenesis. Their assessment forms the basis for biological control of plant growth and development, which makes it possible to assess the influence of natural and climatic conditions, the level of agricultural technology, the implementation of the potential productivity of varieties and determine ways to increase their productivity. It has been established that at stages I-II, differentiation of the growth cone into vegetative organs occurs (the number of leaves, nodes, internodes, and plant habit are determined). At stages III-IV, the inflorescence axis is extended and inflorescence metameres are laid (spikelets in a spike, panicles in a panicle, lobes in a basket, etc.), at stages V-VIII, flower organs are laid and formed, IX - fertilization and formation of the zygote, X -XII – growth and formation of seeds. (The stages are discussed in more detail in practical classes).
Rhythm of growth- alternation of slow and intense growth of a cell, organ, organism - sometimes daily, seasonal - is the result of the interaction of internal and external factors.
Frequency of growth characteristic of perennial, winter and biennial forms, in which the period of active growth is interrupted by a period of dormancy.
Law of Long Period of Growth- The rate of linear growth (mass) in the ontogenesis of a cell, tissue, any organ, or plant as a whole is not constant and can be expressed by a sigmoid curve (Sachs curve). The linear phase of growth was called by Sachs the great period of growth. There are 4 sections (phases) of the curve.
- Initial period of slow growth (lag period).
- Log period, long growth period according to Sachs)
- Growth deceleration phase.
- Stationary state (end of growth).
Growth correlations (stimulating, inhibitory, compensatory)- reflect the dependence of the growth and development of some organs or parts of the plant on others, their mutual influence. An example of stimulating correlations is the mutual influence of the shoot and the root. The root provides the above-ground organs with water and nutrients, and from the leaves the roots receive organic substances (carbohydrates, auxins) necessary for root growth.
Inhibitory correlations (inhibitory) - O days organs suppress the growth and development of other organs. An example of these correlations is the phenomenon a peak dominance– inhibition of the growth of lateral buds and shoots by the apical bud of the shoot. An example is the phenomenon of the “royal” fetus that sets first. Using in practice the method of removing apical dominance: crown formation by trimming the tops of dominant shoots, picking seedlings and seedlings of fruit trees.
TO compensatory correlations reflect the dependence of the growth and competitive relations of individual organs on the provision of their nutrients. In the process of growth of a plant organism, a natural reduction occurs (abscision, death) or artificially removes part of the developing organs (pinching, thinning of ovaries), and the remaining ones grow at a faster rate.
Regeneration - restoration of damaged or lost parts.
- Physiological - restoration of the root cap, replacement of the crust of tree trunks, replacement of old xylem elements with new ones;
- Traumatic - healing of wounds of trunks and branches; associated with callus formation. Restoration of lost above-ground organs due to the awakening and regrowth of axillary or lateral buds.
Polarity - specific differentiation of structures and processes in space characteristic of plants. It manifests itself in a certain direction of growth of the root and stem, in a certain direction of movement of substances.
Characteristics of factors determining patterns of plant growth and development.
All previously studied processes together determine, first of all, the implementation of the main function of the plant organism - growth, formation of offspring, preservation of the species. This function is carried out through the processes of growth and development.
The life cycle of any eukaryotic organism, i.e. its development from a fertilized egg to full formation, aging and death as a result of natural death is called ontogenesis.
Growth is the process of irreversible new formation of structural elements, accompanied by an increase in the mass and size of the organism, i.e. quantitative change.
Development is a qualitative change in the components of the body, in which existing forms or functions are transformed into others.
Both processes are influenced by various factors:
external abiotic factors environment, such as sunlight,
internal factors of the body itself (hormones, genetic traits).
Thanks to the genetic totipotency of the organism, determined by the genotype, a strictly sequential formation of one or another type of tissue occurs in accordance with the stage of development of the organism. The formation of certain hormones, enzymes, and tissue types in a certain phase of plant development is usually determined by the primary activation of the corresponding genes and is called differential gene activation (DAG).
Secondary activation of genes, as well as their repression, can also occur under the influence of certain external factors.
One of the most important intracellular regulators of gene activation and the development of one or another process associated with growth processes or the transition of a plant to the next phase of development are phytohormones.
The studied phytohormones are divided into two large groups:
growth stimulants
growth inhibitors.
In turn, growth stimulants are divided into three classes:
gibberellins,
cytokinins.
Auxins include substances of indole nature; a typical representative is indolyl-3-acetic acid (IAA). They are formed in meristematic cells and move both basipetally and acropetally. Auxins accelerate the mitotic activity of both apical meristems and cambium, delay the fall of leaves and ovaries, and activate root formation.
Gibberellins include substances of a complex nature - derivatives of gibberellic acid. Isolated from ascomycete fungi (genus Gibberella fujikuroi), which have a pronounced conidial stage (genus Fusarium). It is in the conidial stage that this fungus causes “bad shoots” disease in rice, characterized by rapid growth of shoots, their elongation, thinning, and, as a result, death. Gibberellins are also transported acropetally and basipetally in the plant through both the xylem and phloem. Gibberellins accelerate the cell elongation phase, regulate the processes of flowering and fruiting, and induce new formation of pigments.
Cytokinins include purine derivatives, a typical representative of which is kinetin. This group of hormones does not have such a pronounced effect as the previous ones, however, cytokinins affect many parts of metabolism and enhance the synthesis of DNA, RNA, and proteins.
Growth inhibitors are represented by two substances:
abscisic acid,
Abscisic acid is a stress hormone, its amount increases greatly with a lack of water (closed stomata) and nutrients. ABA suppresses the biosynthesis of nucleic acids and proteins.
Ethylene is a gaseous phytohormone that inhibits growth and accelerates fruit ripening. This hormone is secreted by the ripening organs of plants and affects both other organs of the same plant and plants nearby. Ethylene accelerates the fall of leaves, flowers, and fruits due to the release of cellulase from the petioles, which accelerates the formation of the separation layer. Ethylene is formed during the breakdown of ethrel, which greatly facilitates it practical application in agriculture.
Plant growth (patterns and types).
The term growth in plants refers to several processes:
cell growth,
tissue growth,
growth of the plant organism as a whole.
Cell growth is characterized by the following phases:
Embryonic phase (no vacuoles, other organelles are not large quantities).
Stretch phase (vacuole appears, cell wall strengthens, cell size increases).
Differentiation phase (appearance in the cell of tissue-specific organelles).
Tissue growth, depending on its specificity, can occur according to any of the following types:
Apical (shoot, root).
Basal (leaf).
Intercalary (stem in cereals).
The growth of a plant organism as a whole is characterized by the presence of the following phases:
Lag phase or induction growth (seed germination).
Log phase or phase of logarithmic growth (formation of the vegetative mass of the plant).
Slow growth phase (during the fruiting period, when the formation of new vegetative parts of the plant is limited).
Phase steady state(usually coincides with the aging and death of the plant).
Growth rate and relative growth or gain in plants are determined by measuring plant parameters in a certain time regime.
To determine growth, various methods are used, in particular:
using a ruler,
using a horizontal microscope,
using marks,
using an auxanograph,
using large-scale photography.
On average, the growth rate of plants is 0.005 mm/min, but there is fast growing plants and organs: stamens of cereals grow at a speed of 2 mm/min., bamboo - 1 mm/min.
Based on the results modern research(V.S. Shevelukha) the following classification of growth types is proposed:
sinusoidal type (the curve of the daily variation of the linear growth rate has the form of a sinusoid with a maximum phase in the daytime and a minimum phase in the early morning hours) (typical for cereals),
impulse type of growth (the curve of increasing the speed of growth processes and their inhibition occurs spasmodically under a straight line or acute angle for tens of minutes. The maximum growth rate occurs at 20-21 hours and persists all night; growth is inhibited during the day) (typical for root crops and tubers),
two-wave type (during the day the growth rate has two waves, twice reaching a maximum and a minimum),
leveled type of growth (the growth curve is smooth).
Types of movement in plants.
Despite the fact that plants, as a rule, are permanently fixed in the surrounding space, they are capable of a number of types of movement.
The main types of movement in plants:
tropisms,
Taxis are characteristic only of lower aquatic non-attached plants,
For higher plants The first three types are typical.
Nutations make growing apical shoots, rotating around their axis, and above-ground shoots make them only under the influence of hormones, and roots - both under the influence of hormones and with the help of special cells (statocytes (with organelles statoliths), which are able to use natural gravitational forces when implementation of this process.
The plant performs nasty under the influence of a uniformly acting abiotic factor (light, water, etc.).
A plant performs tropisms under the influence of an unevenly acting abiotic factor (light, water, gravity, etc.).
Plant development (types of ontogenesis, stages of ontogenesis, features of the evocation period, features of the resting phase).
Plant development or ontogenesis is characterized by the fact that a very large number of factors act on the transition of a plant from one phase of ontogenesis to another, and their combined action is often necessary.
The following types of plant ontogenesis are distinguished:
By life expectancy:
annuals,
biennials,
perennial;
By number of fruitings:
monocarpic,
polycarpic.
During the process of ontogenesis, any plant goes through the following stages of development:
embryonic phase (from fertilization of the ovule to the formation of the seed),
juvenile phase (from seed germination to emergence on the soil surface),
the phase of formation of aboveground vegetative organs,
phase of flowering and fruit formation,
maturation phase,
dying phase.
The most intense is the juvenile phase of development, which is divided into periods such as:
swelling,
pecking,
heterotrophic growth of seedlings in the dark,
transition to an autotrophic type of nutrition.
Almost every ontogenetic change occurs under the influence of internal and external factors. At the same time, of the external factors, the most important has sunlight. Transition to an autotrophic mode of nutrition, transition to the phase of budding and flowering, transition to a state of rest in perennial plants are directly related precisely to the influence of the duration of sunlight and are therefore called photomorphogenesis. Light is a signal not only for a change in the phase of development, but also directly affects growth, transpiration and other physiological processes in the plant. The direct effect of light is expressed in the ability of cells to form the appropriate hormones, in particular abscisic acid, which allows the plant to slow down its growth rate when transitioning to autotrophic nutrition. The indirect effect of light in the form of daylight hours determines the transition to the next phase of development, in particular to flowering.
Plant perception of impact sunlight occurs due to the presence of special photoreceptors and hormones.
Direct exposure to light is perceived by the plant using the “cryptochrome” photoreceptor and the “phytochrome” pigment. Particularly important is phytochrome, which is able to perceive various components of the spectrum of sunlight and, depending on the absorbed wavelength, turns into either the Fk form, which absorbs red light with a wavelength of 600 nm, or into the Fdk form, which absorbs far-red light with a wavelength of 730 nm. At normal conditions this pigment is found in both forms in equal proportions, however, when conditions change, for example to shaded ones, formation occurs more pigment F k, and this determines the elongation and etiolation of shoot tissues. Based on the action of these photoreceptors and pigments, the plant undergoes daily changes in a certain rhythm, which is called the circadian, or biological clock of the plant.
The light factor also causes the synthesis of certain hormones, which determine the transition of the plant to the flowering phase or the evocation phase, i.e. transition from a vegetative state to generative development. The main hormone acting at this stage of ontogenesis is the hormone “florigen”, consisting of two groups of hormones:
gibberellins, which cause the formation and growth of flower stalks,
anthesins that cause flower formation.
Understanding this point is very important in practice, especially in fruit growing, where the use of rootstock and scion in certain phases of ontogenesis will affect the rate at which the grafted plant enters fruiting. The flow of hormones, including florigen, goes from scion to rootstock, so it is important to use a rootstock from a plant that is in a certain phase of development. Floral morphogenesis is controlled by a complex system of many factors, each of which, in the required concentration and at the right time, triggers its own chain of processes leading to the initiation of flowers.
Second important factor The temperature factor plays a certain role in the formation of floral morphogenesis. It is especially important for winter and biennial crops, since it is low temperatures that cause in these crops those biochemical transformations that determine the synthesis of florigen and other associated hormones that determine the initiation of flowering.
It is on the effect of low temperatures that the vernalization technique is based, which is used in various experimental studies when it is necessary to accelerate the change of generations in winter crops. Treatment of plants with gibberellins also leads to the same results, thanks to which it is possible to accelerate the flowering of biennial plants.
In relation to photoperiod, plants are divided into three groups:
short-day plants (flowering when the day length is less than 12 hours) (chrysanthemum, dahlia, Jerusalem artichoke, millet, sorghum, tobacco),
long-day plants (flowering when the day length is more than 12 hours) (aster, clover, flax, onions, carrots, beets, spinach),
neutral plants (flowering does not depend on day length) (sunflower, buckwheat, beans, rapeseed, tomato).
In the ontogenesis of plants there is always a phase of weakening vital activity, which is called the dormant state. U annual plants this state occurs only once - during the formation of a seed; in perennial plants - many times during the transition to existence in unfavorable conditions environment (winter, drought). Dormancy is a state of a plant that is characterized by the absence of growth phenomena, an extreme degree of respiratory depression and a decrease in the intensity of transformation of substances.
There are summer and winter dormancy in perennials, deep and forced dormancy in all plants. Forced rest is possible only with the participation of a person who can provide special conditions for storing resting organs in special storage facilities using special methods. Very important point transition to a dormant state is the stage of post-harvest ripening, which helps prevent premature seed germination, concentrate maximum quantity spare substances.
Krenke's theory of plant aging and rejuvenation.
During the process of ontogenesis, the plant undergoes certain changes that are associated with the phenomenon of age-related variability. A theory explaining the patterns of this variability was proposed in the 40s of the last century by N.P. Krenke. The main postulates of this theory:
Every organism, starting from its origin, continuously ages until its natural death.
In the first half of life, aging is interrupted periodically by rejuvenation, i.e. the formation of new shoots, leaves, etc., which slows down the rate of aging.
Plants have an inherent physiological age, which determines the true age of the plant organ: the leaves of one-year and ten-year-old trees are unequal, and the leaves on the same tree are unequal, but on shoots of different orders. A distinction is made between the concepts of “age” (calendar age) and “age” (physiological age. Age is determined by the age of the organ and the mother plant. Within a fruit tree, leaves on shoots of higher orders of branching are physiologically older than leaves of the same age on shoots of lower orders of branching. Therefore, in terms of shape, anatomical structure, physiological and biochemical characteristics, the upper leaves, despite their younger age, show signs of greater aging; their lifespan is often shorter than that of the middle leaves on the same shoot.
The cyclical nature of ontogenetic development lies in the fact that daughter cells, when newly formed, are temporarily rejuvenated in relation to the maternal ones.
Aging rate and normal average duration life is determined by the initial potential of viability and is determined by the genetic characteristics of the species.
P.G. also dealt with the problem of aging and rejuvenation of fruit and berry crops. Schitt. In the 60s of the last century, he first established the presence of age-related qualitative changes in the roots. I.V. Michurin also pointed out the close connection between organoformative processes in organisms and age-related variability.
Established N.P. Krenke's patterns of changes in the morphology of leaves and shoots in connection with their age made it possible to develop recommendations for the early diagnosis of early maturity of plants within a species, to identify correlative connections between the quality of tubers and root crops and the early maturity of a variety. It has been established that early ripening varieties are characterized by a sharp change in the morphological characteristics of leaves (rapid yellowing and death of leaves), and in late ripening varieties changes occur gradually. This pattern is important in the process of selecting varieties for early ripening and quality.
Morphological characteristics are closely related to genetically determined precocity, which makes it possible to use them in the selection of fruit crops, for example:
in annual seedlings of early ripening varieties of apple trees, the internodes are shorter, the branching is stronger, the leaves are denser than in varieties that begin to bear fruit later,
in two-year-old apple tree seedlings, the intensity of the green color of leaves during the transition from the upper tiers to the lower ones in early-ripening forms changes more sharply than in late-ripening ones,
The higher up the stem of a fruit plant a cutting or bud is taken (during vegetative propagation), the sooner after rooting or budding the plant is able to bloom.
Based on Krenke's theory, plant pruning techniques, technology for selecting shoots and their parts of the required quality during vegetative propagation of plants, ensuring better rooting of cuttings, technology for achieving optimal combination vegetative and generative development of plants during cuttings and grafting.
Features of maturation of productive parts of plants.
Productive parts of plants are called both organs of generative reproduction (fruits, seeds) and organs of vegetative reproduction (tubers, bulbs). The remaining productive parts (leaves of green crops, stems, roots, etc.) do not perform the function of reproduction and therefore the patterns of growth and development are not so important.
seed protection,
seed distribution.
To carry out these functions, various fruits have appropriate adaptations (dry and juicy fruits, hooks, lionfish, attractive taste, etc.).
There are four phases in fetal development:
Formation of the ovary before pollination,
Growth due to cell division immediately after pollination and fertilization,
Growth due to cell stretching,
Maturation.
The growth of the ovary is stimulated by germinating pollen even before the formation of the zygote, and the intensity of this growth is directly proportional to the amount of germinating pollen. Even foreign pollen can contribute to the growth of the ovary, which is explained high content IAA in pollen.
Treatment of flowers with exogenous auxin in many plants with succulent fruits induces the growth of the ovary and the formation of parthenocarpic, i.e. seedless fruits. Treatment with gibberellin also causes fruit set in many plants (grapes, apple trees, tomatoes, etc.). The presence of cytokinin is necessary for the growth of young fruits, but exogenous cytokinins do not cause the formation of parthenocarpic fruits.
At the beginning of the formation of the ovary in a flower, its growth occurs as a result of cell division, which increases sharply after pollination. Then comes a longer phase of cell elongation. The growth pattern is highly dependent on the type of fetus.
Regulation of fruit growth is carried out by phytohormones. IAA enters the ovary first from the style and from germinating pollen. The developing ovule then becomes the source of IAA. In this case, the aging hormone (ethylene) also plays a certain role, which ensures the wilting of the flower after pollination. The resulting seeds supply auxin to the pericarp, which activates growth processes in it. With a lack of auxin (small number of seeds formed), fruit drop occurs.
Thus, in wheat grains, the maximum amount of cytokinins is observed immediately after flowering during the transition to the formation of endosperm. Then the content of gibberellins begins to increase, and later IAA, the concentration of which reaches its maximum value in the milky ripeness phase. During the transition to waxy ripeness, the level of gibberellins and auxins quickly decreases, but the ABA content increases, which promotes the deposition of reserve substances in the endosperm. When the increase in the dry mass of grains stops and dehydration of the seeds occurs (full ripeness), the ABA content decreases. The decrease in the amount of all phytohormones is explained by their transition to a bound state. This order of changes in the ratio of phytohormones in developing wheat grains is determined by the sequence of development of the embryo and endosperm. When the grains ripen, carbohydrates and proteins accumulate, changes occur in nucleic acid metabolism, and plastic substances actively move into the grains from the stems and leaves. The stems become woody (the content of fiber and lignin, which are converted into starch, decreases). As the grain ripens, the protein becomes more resistant to the action of proteolytic enzymes, the amount of monosaccharides decreases and the amount of starch increases.
Legumes accumulate significantly less starch and other carbohydrates than cereals.
When cultivating grain and leguminous crops, a separate harvesting method is often used, which makes it possible to better ensure the transfer of plastic substances from the stems to the seeds after mowing and ripening in windrows. Treatment of crops during the period of wax ripeness with a solution of ammonium nitrate accelerates the ripening of these crops by 5-7 days.
When oilseed seeds ripen, fats not only accumulate, but also change qualitatively. Unripe seeds contain more free and saturated fatty acids, while mature seeds increase the content of unsaturated fatty acids.
In juicy fruits greatest content gibberellins and auxin in the pericarp is observed at the beginning of its development. The level of these phytohormones then decreases and increases again during the last growth phase. Cytokinin content temporarily increases during the period of most intensive fetal growth. The cessation of pericarp growth coincides with the accumulation of ABA in its tissues.
The period of cell elongation in juicy fruits and especially the end of this period are characterized not only by intensive growth, but also by the accumulation organic matter. The content of carbohydrates and organic acids increases, and starch is deposited.
The ripening of some fruits correlates well with an increase in respiration rate. The period of increased carbon dioxide production by the fetus is called menopause, and during this period the fetus undergoes a change from immature to ripe. Treatment with ethylene stimulates this period and the ripening of ripe fruits. Ethylene increases the permeability of membranes in fetal cells, which allows enzymes previously separated from substrates by membranes to react with these substrates and begin to destroy them.
Auxin is also involved in fruit ripening, and during fruit ripening and leaf fall, auxin and ethylene act as antagonists. Which hormone dominates depends on the age of the tissue.
In a number of crops, the predominant method of reproduction has become precisely the method of reproduction using vegetative propagation organs (for example, potatoes). Therefore, the formation of these bodies, both performing and reproductive function, and, at the same time, serving as a source of nutrition for humans, requires separate consideration.
The process of tuberization in physiological terms is best studied in potatoes. With long days and high temperature(above 29 degrees) can turn into vertical leafy shoots, and at normal (lower) temperatures a tuber forms at the end of the stolon. Tuberization is always associated with inhibition of growth of both aboveground shoots and stolons. A short day promotes the entry of plastic substances into the tubers.
Tuber formation involves three stages;
preparatory - the appearance and growth of stolons,
laying and growth of the tuber itself,
ripening and dormancy of the tuber.
The formation of stolons from axillary buds is favored by their darkening (which is why hilling is mandatory in potato cultivation technology). IAA along with gibberellins entering the sufficient quantity from aerial parts, switch the genetic program for the development of the axillary bud from the development of a vertical leafy shoot to the formation of a stolon. Gibberellin is also necessary for the elongation of stolon internodes.
The initiation of tubers at the distal ends of stolons is associated with a sharp inhibition of their growth in length. Apparently, this suppression is caused by an increase in the concentration of ABA, which is formed in large quantities in leaves on short days. Under short day conditions, the synthesis and intake of IAA and gibberellins are reduced. At the same time, the ratio of cytokinins to auxins increases.
Tuber dormancy is associated with a sharp slowdown in respiration, decay and synthesis of biopolymers, and a stop in growth processes. In potato tubers, only meristematic tissues, primarily the eyes, are in a state of deep dormancy. Storage tissue is able to quickly activate in response to damage (a wound periderm is formed during mechanical damage).
The state of deep dormancy of the ocelli is due to the high content of ABA, caffeic acid and scopoletin.
The emergence of buds from a state of deep dormancy is associated with a decrease in ABA content (10-100 times) and an increase in the concentration of free gibberellins. Treatment with gibberellic acid-based stimulants breaks the dormancy state of the tubers and allows for summer planting of potatoes in the south.
In bulbs during the dormant period, growth processes do not stop, although they proceed very slowly. The dormant state is maintained by a high concentration of ABA. Before germination, the level of ABA decreases, and the content of cytokinins, gibberellin and auxins increases.
The processes of formation of rhizomes and stolons, as well as the ability of plants to take root using layering and cuttings, are subject to the same patterns in the change in the work of different phytohormones.
Use of growth regulators in practice agriculture.
Growth regulators are widely used in agricultural practice in the following areas:
At the stage of sowing, planting,
At the stage of controlling flowering, setting, crop formation,
At the cleaning stage,
At the resting stage.
At the sowing stage, plantings use:
for rooting cuttings that are difficult to root, such as grapes,
for better survival rate of vaccinations,
for better seed germination
At the stage of controlling flowering, setting, and crop formation, the following is used:
to stimulate the start of flowering,
to increase the number of fruits set,
to stimulate female flowering in dioecious species.
Gibberellins:
to increase fruit size,
to improve the quality of economically valuable organs (promote an increase in sugars in fruits, stems, stem crops, root crops, etc.),
to stimulate male flowering in dioecious species.
Ethylene and abscisic acid also stimulate female flowering in dioecious species.
At the cleaning stage use:
Ethylene and abscisic acid and a number of other growth inhibitors (for example: magnesium chlorate, hydrel, etrel):
to accelerate ripening, increase yield yield,
for defoliation,
for desiccation (pre-harvest drying of stems and leaves),
for senication (acceleration of ripening by 5-7 days in areas with a short warm period)
At the resting stage:
To prolong the dormant state, ethylene and abscisic acid are used to treat ware potatoes, root crops, and fruits (either sprayed with a 0.5% hydrel solution, or the composition of the atmosphere in the storage is adjusted),
To break the state of rest use:
etherization: for germination of shoots, rhizomes - treatment with sulfuric ether,
warm baths: for forcing lilacs for the New Year (dip the shoots of the bush into warm (30-35 o C) water for 9-12 hours),
gibberellins to obtain a second harvest of potatoes from freshly harvested tubers (soaked for 30 minutes in a mixture of 0.0005% gibberellin and 2% thiourea).
Every living organism undergoes constant quantitative and qualitative changes, which stop only under certain conditions with periods of rest.
Growth is a quantitative change during development, which consists of an irreversible increase in the size of a cell, organ or whole organism.
Development is a qualitative change in the components of the body, during which existing functions are transformed into others. Development is the changes that occur in a plant organism during its life cycle. If this process is considered as the establishment of form, then it is called morphogenesis.
An example of growth is the proliferation of branches due to the proliferation and enlargement of cells.
Examples of development are the formation of seedlings from seeds during germination, the formation of a flower, etc.
The development process includes a whole series complex and very strictly coordinated chemical transformations.
The curve characteristic of the growth of all organs, plants, populations, etc. (from the community to the molecular level) has an S-shaped, or signoid appearance (Fig. 6.1).
This curve can be divided into a number of sections:
– initial lag phase, the length of which depends on internal changes, which serve to prepare for growth;
– logarithmic phase, or period when the dependence of the logarithm of the growth rate on time is described by a straight line;
– phase of gradual decrease in growth rate;
– the phase during which the body reaches a stationary state.
Figure 6.1. S-shaped growth curve: I – lag phase; II – logarithmic phase; III – decrease in growth rate; IV – stationary state
The length of each of the phases composing the S-curve and its character depend on a number of internal and external factors.
The duration of the lag phase of seed germination is affected by the absence or excess of hormones, the presence of growth inhibitors, physiological immaturity of the embryo, lack of water and oxygen, lack of optimal temperature, light induction, etc.
The length of the logarithmic phase is associated with a number of specific factors and depends on the characteristics of the genetic development program encoded in the nucleus, the gradient of phytohormones, and the intensity of transport nutrients etc.
Growth inhibition may be the result of changes in environmental factors, and may also be determined by changes associated with the accumulation of inhibitors and specific aging proteins.
Complete inhibition of growth is usually associated with the aging of the organism, i.e., with the period when the rate of synthetic processes decreases.
During the completion of growth, the process of accumulation of inhibitory substances occurs, and plant organs begin to actively age. At the last stage, all plants or individual parts of it stop growing and may enter a dormant state. This final stage of the plant and the timing of the arrival of the stationary phase are often determined by heredity, but these characteristics can be modified to some extent by environmental influences.
Growth curves indicate the existence different types physiological regulation of growth. During the lag phase, mechanisms associated with the formation of DNA and RNA, the synthesis of new enzymes, proteins, and the biosynthesis of hormones function. During the logarithmic phase, active elongation of cells, the appearance of new tissues and organs, and an increase in their size are observed, i.e., stages of visible growth occur. The slope of the curve can often be a fairly good indication of the genetic pool, which determines the growth potential of a given plant and also determines how well the conditions match the plant's needs.
Growth criteria are used to increase the size, number, volume of cells, wet and dry weight, protein or DNA content. But to measure the growth of a whole plant, it is difficult to find a suitable scale. So, when measuring length, they do not pay attention to branching; it is hardly possible to accurately measure the volume. When determining the number of cells and DNA, they do not pay attention to the size of the cell, the definition of protein includes reserve proteins, the definition of mass also includes reserve substances, and the definition of wet mass also includes transpiration losses, etc. Therefore, in each case, the scale that can be used to measure the growth of a whole plant - this is a specific problem.
The growth rate of shoots averages 0.01 mm/min (1.5 cm/day), in the tropics - up to 0.07 mm/min (~ 10 cm/day), and for bamboo shoots - 0.2 mm/min (30 cm/day).
60. Phases of growth: embryonic, stretching, differentiation and their physiological characteristics. Differentiation of cells and tissues.
Embryonic phase or mitotic cycle The cell is divided into two periods: cell division itself (2-3 hours) and the period between divisions - interphase (15-20 hours). Mitosis is a method of cell division in which the number of chromosomes is doubled so that each daughter cell receives a set of chromosomes equal to that of the mother cell. Depending on the biochemical characteristics, the following stages of interphase are distinguished: presynthetic - G 1 (from the English gap - interval), synthetic - S and premitotic - G 2. During the G 1 stage, nucleotides and enzymes necessary for DNA synthesis are synthesized. RNA synthesis occurs. During the synthetic period, DNA duplication and histone formation occur. At stage G 2, the synthesis of RNA and proteins continues. Replication of mitochondrial and plastid DNA occurs throughout interphase.
Stretch phase. Cells that have stopped dividing begin to grow by extension. Under the influence of auxin, the transport of protons into the cell wall is activated, it loosens, its elasticity increases and additional water flow into the cell becomes possible. The growth of the cell wall occurs due to the inclusion of pectin substances and cellulose in its composition. Pectic substances are formed from galacturonic acid in vesicles of the Golgi apparatus. The vesicles approach the plasmalemma and their membranes merge with it, and the contents are included in the cell wall. Cellulose microfibrils are synthesized on the outer surface of the plasmalemma. An increase in the size of a growing cell occurs due to the formation of a large central vacuole and the formation of cytoplasmic organelles.
At the end of the elongation phase, lignification of cell walls increases, which reduces its elasticity and permeability, growth inhibitors accumulate, and the activity of IAA oxidase increases, which reduces the auxin content in the cell.
Cell differentiation phase. Each plant cell contains in its genome full information about the development of the whole organism and can give rise to the formation of a whole plant (the property of totipotency). However, being part of the body, this cell will realize only part of its genetic information. Signals for the expression of only certain genes are combinations of phytohormones, metabolites and physicochemical factors (for example, the pressure of neighboring cells).
Maturity phase. The cell performs the functions that are established during its differentiation.
Cell aging and death. As cells age, synthetic processes weaken and hydrolytic processes intensify. In organelles and cytoplasm, autophagic vacuoles are formed, chlorophyll and chloroplasts, endoplasmic reticulum, Golgi apparatus, and nucleolus are destroyed, mitochondria swell, the number of cristae in them decreases, and the nucleus vacuolates. Cell death becomes irreversible after the destruction of cell membranes, including the tonoplast, and the release of the contents of the vacuole and lysosomes into the cytoplasm.
Cell aging and death occurs as a result of the accumulation of damage in the genetic apparatus, cell membranes and the inclusion of genetic programmed cell death - PCD (programmed cell death), similar to apoptosis in animal cells.
