Modifications of roots and shoots. Modified shoots

1. What modifications of roots do you know? What functions do they perform?

The main functions of the root are to anchor the plant in the soil, absorb solutions of mineral compounds from the soil and transport them to its above-ground parts. However, the root can also perform some additional functions. At the same time, it acquires certain structural features called root modifications.

In many plants (for example, beets, carrots), reserve nutrients are deposited in the main root and base of the shoot. As a result, the main root thickens and turns into a root vegetable.

In other plant species (for example, dahlias, spring grass, sweet potatoes), reserve nutrients are deposited in additional or lateral roots, which take on a tuberous shape. Such modifications are called root tubers.

Some plants growing in swamps and waterlogged soils develop respiratory roots. These are lateral roots that grow upward and rise above the surface of the soil (or water). In waterlogged soils, due to the low oxygen content, respiration of the underground part of the plant becomes more difficult. Therefore, such modified roots absorb oxygen directly from moist air.

There are also roots-trailers. These are short additional roots that grow along the aboveground part of the stem. With their help, climbing plant stems cling to support. Remember ivy, which can even attach itself to the smooth vertical walls of houses.

There are also supporting roots that act as supports.

A special type of root modification is observed in orchids. Some species of these plants are able to settle on tree trunks in tropical rainforests. Their aerial roots hang freely and allow them to obtain water from moist air.

2. What modifications of leaves do you know? What is their function?

Leaf modifications are irreversible changes in leaf shape developed during evolution as a result of adaptation of plant organs to environmental conditions (i.e., with leaves performing new functions).

1. Spines are one of the most common modifications; they serve as protection against being eaten by animals (cacti, milkweed, barberry, white acacia, camel thorn).

2. Tendrils (in compound leaves of some plant species) cling to the support, carrying the entire shoot towards the light (peas, vetch).

3. The storage function is performed by juicy scales of bulbs (onions, garlic), aloe leaves, and heads of cabbage.

4. The covering scales of the buds protect the tender rudimentary leaves and the growth cone from unfavorable environmental conditions.

5. Trapping devices ensure the life of insectivorous plants in swamps in conditions of lack of nitrogen and other elements of mineral nutrition. The leaves of such plants have changed beyond recognition, turning into traps (Venus flytrap), pitchers (Nepenthes). The leaves of some plants, with their shiny, brightly colored droplets on the hairs, attract ants, flies, mosquitoes, and other small insects; The juice released during this process contains digestive enzymes (sundew).

3. What are the main functions of the stem?

Stems perform two main functions:

The stems carry the leaves towards the light (support function);

The stem transports substances between leaves and roots.

4. What is called an escape?

The stem with leaves and buds located on it is called a shoot.

Laboratory work

Tuber structure

2. Examine the eyes. What is their location on the tuber? Examine the buds in the eye using a magnifying glass.

On the surface of the tuber in the depressions there are 2-3 buds, called eyes. There are more eyes on that side of the tuber, which is called the top. On the opposite side - the base - the tuber is connected to the stolon.

3. Make a thin cross-section of the tuber. Hold it up to the light. Compare the cross section of the tuber with the cross section of the stem (Fig. 42).

4. Sketch a cross section of the tuber.

See answer to question #3.

5. Drop iodine onto the cut of the tuber. Explain what happened.

If you drop iodine onto a cut tuber, it will turn blue-violet, because... starch, when interacting with iodine, gives such a reaction. Potatoes contain starch in large quantities (this is the main storage substance of potato tubers).

6. Prove that the tuber is a modified underground shoot.

A cross section of a tuber is similar in structure to a cross section of a stem. Upon examination, you can distinguish cork, bast, wood and core.

Laboratory work

The structure of the bulb.

Consider the external structure of the bulb. What is the significance of dry scales?

The outer scales are dry and leathery - they perform a protective function.

2. Cut the onion lengthwise. Draw a longitudinal section of the bulb, indicate the scales, bottom, buds, adventitious roots.

3. Prove that the bulb is a modified underground shoot.

Like a ground shoot, the stem has apical and axillary buds and leaves.

Questions

1. What modified underground shoots do you know? Name the plants that have a rhizome, tuber, bulb.

Modified underground shoots - rhizomes, tubers and bulbs.

Many plants have a rhizome, for example, nettle, wheatgrass, iris, lily of the valley, and the houseplant aspidistra.

Tubers are found, for example, in potatoes, corydalis, and the food plant Jerusalem artichoke (earthen pear).

The bulbs form perennial plants - onions, lilies, tulips, daffodils, wild goose onions.

2. How does a potato tuber develop?

The underground shoots on which the tubers develop grow from the bases of the aboveground stems. These shoots are called stolons. Tubers are the apical thickenings of stolons.

Like a ground shoot, there are apical and axillary buds, from which young above-ground shoots develop in the spring.

A cross section of a tuber is similar in structure to a cross section of a stem. Upon examination, you can distinguish cork, bast, wood and core.

4. What is the structure of the bulb?

At the bottom of the onion bulb there is an almost flat stem - the bottom. On the bottom there are modified leaves - scales. The outer scales are dry and leathery, while the inner scales are fleshy and juicy. On the bottom there are buds located in the axils of the scales.

5. How to prove that the rhizome and bulb are modified shoots?

Like a ground shoot on the rhizome and bulb, there are apical and axillary buds, as well as modified leaves (membranous scales on the rhizome, succulent and dry scales on the bulb). Adventitious roots grow from the rhizome and bottom (stem in the bulb), and young above-ground shoots develop from the apical or axillary bud in the spring.

6. What above-ground modifications of shoots do you know?

Aboveground modifications of the shoot are the spines of wild apple, pear, and hawthorn, which protect plants from being eaten by animals. The tendrils of grapes, cucumbers, pumpkins, melons, and strawberry tendrils are also modified shoots. Another example of an above-ground modified shoot is the thickening of the internodes of the kohlrabi cabbage stem.

Think

By what signs can you distinguish tubers from root crops, rhizomes from roots?

The tuber and rhizome will have buds, as well as modified leaves.

Tasks

1. Place the onion bulb in a jar with a narrow neck so that it does not fall through, but only touches the bottom of the water poured into the jar. Observe the development of adventitious roots and green leaves on the bulb. Why does it grow even though it is not in the soil?

The bulb is a collection of nutrients necessary for leaves and roots. In the presence of heat and moisture, growth begins. That is, the bulb provides the plant with everything it needs even without soil.

2. With the onset of warm spring weather, watch the flowering of bulbous and rhizomatous plants. Determine the names of these plants. Note the beginning and end of flowering, and also indicate what is typical for these plants at this time of year.

Bulbous:

1. Simple early tulips bloom in early May for 15–30 days. The change of generations of bulbs, unlike daffodils, occurs annually. During the short spring growing season, the tulip blooms, bears fruit and lays young bulbs underground, and the faded bulb dies.

2. Daffodils bloom in April-May. The narcissus bulb is perennial. After the end of flowering, the leaves of faded daffodils are not cut off, but wait until they dry out. During this period, nutrients are stored in the bulbs.

Rhizomes:

1. Lilies of the valley bloom from mid to late May. After the end of the flowering period, lily of the valley fruits appear - small red berries.

2. Irises bloom profusely from late May to mid-July. In the summer, irises develop a flower bud, so irises overwinter with already formed buds, from which new flowers will appear in the new season.

The shoot is one of the main vegetative organs of higher plants. It consists of a stem on which buds and leaves are located. The shoot is the most variable structural element of the plant in appearance.

The above-ground part of the plant is a shoot or shoot system.

The shoot consists of a stem (axis) and leaves and buds located on it. The place where a leaf is attached to the stem is called a node, and the area between two adjacent nodes is called an internode. The angle between the stem and the leaf is called the leaf axil. The shoot develops from the bud.

A bud is a rudimentary shoot with very shortened internodes. The central part of the bud is occupied by a rudimentary stem, at the top of which there is a growth cone, which is educational tissue. The stem contains rudimentary leaves. The outside of the bud is covered with bud scales, which can protect the rudimentary leaves and growth cone from unfavorable environmental conditions. To perform a protective function, the bud scales form thick pubescence, secrete resinous substances, etc. A modified shoot is a plant organ in which the shape and function of the stem, buds and leaves are irreversibly changed in the process of evolutionary adaptations to certain conditions of existence of the organism. In cultivated plants, shoot modification is caused by human intervention.

Metamorphoses of the shoot can be either minor or significant - up to greatly changed plant forms. Both main and lateral shoots, as well as buds and leaves, undergo metamorphosis.

The main types of shoots of green plants are aboveground and underground. Aboveground (aerial) shoots are assimilative, along the axis of which the leaves are located. Assimilating shoots are very diverse in appearance. In many cases, in addition to the main function of photosynthesis, such shoots perform the role of a storage and supporting organ of the plant, as well as the function of vegetative propagation.

Modifications of aboveground shoots

Modified shoots are those that perform some additional functions: protection, climbing, storing nutrients, etc. Modified shoots include spines, tendrils, tubers, succulent shoots, stolons, and shoots of insectivorous plants. Spines are needle-like structures that protect the plant from being eaten by animals. Spines can be formed from leaves (barberry), stipules (yellow acacia), shoots (sea buckthorn, hawthorn). Tendrils are thread-like axillary shoots (grapes, cucumbers) that perform a supporting function. In peas, part of the leaf turns into tendrils. A tuber is a thickened shoot that serves as a reserve of nutrients (kohlrabi cabbage - approx. biofile.ru). Stolons (common name “mustache”) are horizontal creeping shoots that promote plant reproduction. On each stolon there are rosettes with adventitious roots. After the rosette takes root, the horizontal shoot dies (strawberry, creeping tenacious).

Succulent shoots are an adaptation of plants to hot and dry climates. Their function is to store moisture. Water can accumulate in the leaves (sedum, sedum, aloe) or in the stem (euphorbia, cactus). Mexican cacti have fleshy stems of a wide variety of shapes: ribbed balls, columns, cylinders, even candelabra and cakes. Cacti have no green leaves: they have turned into bunches of thorns. The function of photosynthesis is performed by the stems.

Underground modified shoots.

Stolons and tubers can be either aboveground or underground. In addition to them, underground shoots include rhizomes and bulbs. Underground stolons perform the same functions as aboveground stolons - plant dispersal and reproduction. This explains the similarity in their structure. Tuber. This shoot has a short and thick stem. The scaly leaves quickly die off and scars remain in their place (in potatoes they are popularly called “edges”). In their sinuses there are buds called “eyes”. The tuber performs the function of storing nutrients (for example, starch), surviving unfavorable seasons and reproduction. Not only potatoes have tubers, but also Jerusalem artichoke and corydalis. They appear on underground stolons. The rhizome often looks like a root in appearance, but the rhizome also has scaly leaves, and in their axils there are lateral buds, and at the top there are apical buds. Adventitious roots are formed on the rhizome. Unlike the stolon, the rhizome is a perennial shoot that allows the plant to survive unfavorable conditions. This underground shoot is common to many plants and can perform a variety of functions. Nutrients are stored in the thick short rhizomes of iris, kupena. Creeping wheatgrass, mouse pea, and lily of the valley have long and thin rhizomes. They are able not only to store nutrients, but also to capture new territories. The rhizome not only grows quickly in length (for butterbur it is 1.5 meters long, for coltsfoot it is 1 meter - note biofile.ru), but it also branches. As a result, the mother plant may split into several daughter plants. Rural residents know how difficult it is to fight long-rhizome weeds: wheatgrass, cowgrass, coltsfoot. Sea buckthorn, rose hips, and raspberries grow quickly. The bulb is a greatly shortened, modified shoot with a flat stem – “bottom”, with leaves in the form of scales. The scales can be succulent (storing) or dry covering), can be narrow and only slightly cover each other (lily) or embrace each other almost completely (hyacinth, tulip, onion). The bulb allows the plant to survive unfavorable periods of the year. Axillary buds can turn into bulbs - babies. Consequently, the bulb is also a propagation shoot. In the colchicum and gladiolus, the underground shoot is called a corm. Externally, the corm resembles an onion, but differs from it in its highly overgrown bottom, to which small scale-like leaves are attached, and serves as an organ for storing reserve nutrients. The corm has well-developed apical and axillary buds, giving rise to flowering shoots and daughter corms.

VEGETATIVE REPRODUCTION, the formation of a new organism from a part of the maternal one; one of the methods of asexual reproduction of multicellular organisms. In lower plants (for example, in algae) it is often carried out by division, in fungi - by budding (for example, in yeast, some basidiomycetes) or parts of the mycelium (for example, in cap mushrooms), in higher plants - by parts of vegetative organs ( root, stem, leaf), but more often in their modified forms - rhizomes (wheatgrass, pigweed, etc.), tubers (potatoes, dahlias, etc.), bulbs (onion, tulip, etc.), root suckers (raspberries, cherries, plum, etc.), tendrils (strawberries, wild strawberries), etc. Characteristic of almost all perennial plants (based on their ability to regenerate). The vegetative offspring of one individual is called a clone. Artificial methods of vegetative propagation include all natural ones, as well as reproduction cuttings(currants, sea buckthorn, grapes, aloe, begonias, etc.), vaccination cuttings and buds (pear, apple, rose, lilac, etc.), layering(currants, hazelnuts, etc.). Vegetative propagation of cultivated plants has been used for many centuries. Modern practice uses effective tissue culture methods (micropropagation). Clonal micropropagation is based on obtaining planting material from cells of the apical meristem (shoot tips). This method makes it possible to obtain from one plant within a year, by the required date, several thousand plants that have maternal characteristics and are free from viral and other infections. In this way, planting material for vegetable, fruit and ornamental plants is obtained. In animals, vegetative reproduction is carried out either by fragmentation - separation of body parts from the mother's body, which then complete themselves into a whole organism, or by budding. During budding, an outgrowth (bud) is formed on the mother’s body, from which a new individual develops. Vegetative reproduction is characteristic of some worms, sponges, coelenterates, and tunicates.

The escape is one of the main vegetative organs of higher plants. It consists of a stem on which buds and leaves are located. The shoot is the most variable structural element of the plant in appearance. Modified escape is a plant organ in which the shape and function of the stem, buds and leaves are irreversibly changed in the process of evolutionary adaptations to certain conditions of existence of the organism. In cultivated plants, shoot modification is caused by human intervention.

Metamorphoses of the shoot can be either minor or significant - up to greatly changed plant forms. Both main and lateral shoots, as well as buds and leaves, undergo metamorphosis.

The main types of green plant shoots are: aboveground and underground. Aboveground (aerial) shoots are assimilative, along the axis of which the leaves are located. Assimilating shoots are very diverse in appearance. In many cases, in addition to the main function of photosynthesis, such shoots perform the role of a storage and supporting organ of the plant, as well as the function of vegetative propagation.

To modifications of aboveground shoots include spines, antennae, cladodes, phyllocladies. In some cases, not the entire shoot of a plant changes, but only its leaves, and the metamorphoses are externally similar to those of the shoot as a whole (antennae, spines).

The thorn is a lignified shortened shoot without leaves with a sharp tip. The role of spines originating from the shoot is mainly protective. The wild apple tree, laxative buckthorn, and wild pear have such spines. In honey locust, thick branched spines appear on the trunks from dormant buds. Hawthorn spines are also formed from the axillary buds of the leaves and are located where the side shoots of other plants are located.

A tendril is a shoot of a metameric structure without leaves, having a rope-like shape with or without branches. Thanks to the presence of stem tendrils, the plant receives additional support. The straightened section of the tendril without branches is the first internode of the axillary shoot, and the twisted, thinner section is a modified leaf. Tendrils develop in plants that are not able to stand upright on their own. Blue passionflower, grapes, and many members of the Cucurbitaceae family (pumpkin, watermelon, melon, cucumber) have tendrils.

Cladodium is a lateral shoot that has undergone modification, which is capable of continuous growth and has green, flattened long stems that take on the functions of leaves. Cladodium performs the function of photosynthesis, since well-developed chlorophyll-bearing cells are located under the epidermis. The group of plants with cladodes includes the Decembrist cactus, prickly pear, Mühlenbeckia planiflora, and southern carmichelia.

Phyllocladium is a modified flat leaf-shaped side shoot that has limited growth and serves as a leaf in the life of the plant. The lateral buds of the shoot give rise to phyllocladia, and therefore, phyllocladia are always located in the axils of small scale-like or membranous leaves. Such modified shoots perform the function of photosynthesis, so they look like leaves in appearance. Their growth is limited, and there is no metameric structure. Phyllocladies are characteristic of plants such as phyllanthus, mossy, butcher's broom, and some representatives of the Asparagus genus.

Modified underground shoots- these are the rhizome, caudex, bulb, corm, underground tuber and stolon. The conditions for the existence of shoots located underground are very different from the terrestrial environment. Therefore, they acquired other important functions, such as the ability to endure unfavorable periods of life, the deposition of nutrients into reserves, and the possibility of vegetative reproduction.

Rhizome (rhizome) is an underground shoot with scale-like leaves, adventitious roots and buds. Wheatgrass has thick and branched rhizomes. Kupena and iris have shortened and fleshy rhizomes, while water lilies and water lilies have the thickest rhizomes of all plants.

Caudex is a perennial structure derived from a shoot, characteristic of perennial grasses and subshrubs with a taproot system. The caudex, along with the root, is a place of accumulation of reserve nutrients and has many buds. Plants that have a caudex are lupins and alfalfas from the Legumes, femoris and ferula from the Apiaceae, dandelion, and wormwood from the Asteraceae.

Bulb is a specialized underground shortened shoot. In it, organic substances are stored in scales of leaf origin, the stem in the bulb is transformed into the bottom. Vegetative propagation is carried out using bulbs. Bulbs are formed in monocots of the Amaryllidaceae family (hyacinth, narcissus), the Liliaceae family (onion, tulip, lily), and less often in dicotyledonous plants.

Corm- also a modified underground shoot that has a thickened stem, where nutrients are stored, adventitious roots growing on the lower surface of the corm, and a protective cover of dried leaf bases. Corms are characteristic of saffron, gladiolus, ixia, and colchicum.

underground stolon is an annual long underground shoot. This thin shoot with underdeveloped scale-like leaves has a tuber or bulb at the thickened end with a reserve of organic substances. Underground stolons are formed in potatoes, adoxa, and sedmichnik.

underground tuber- a modified underground shoot, in which the storage function comes to the fore. This shoot has scale-like leaves that quickly fall off, and buds located in the axils of the leaves.

In our article we will get acquainted with such a modification of the root as the growth of the rhizome. This is an underground shoot that can easily be confused with a root. Let's look at the structural features and differences of these systems.

Escape modifications

A shoot is the above-ground part of a plant, which consists of an axial part - the stem, and a lateral part - the leaves. It also contains rudimentary organs called kidneys. The shoot plays an important role in the life of the plant: it ensures growth, vegetative propagation and photosynthesis.

But to carry out additional functions, various organs are modified. The growth of rhizomes is one of the proofs of such metamorphoses. Modifications of the shoot include stem tubers of kohlrabi, bulbs of leeks, lilies and tulips, thorns of thorns and wild pears, tendrils of melon and grapes, tendrils of strawberries and strawberries.

Plant rhizome

The rhizome is a thickening of the shoot located underground. A similar transformation is typical for wheatgrass, lily of the valley, crow's eye, gravilat, hellebore, valerian, and iris.

How to prove that the rhizome is really a shoot? Very simple. Rhizomes are structures that consist of a thickened stem. In them one can distinguish elongated internodes with axillary and apical buds. There are no leaves, they are replaced by scales. Mineral nutrition, water supply and fixation in the soil are provided by bundles of adventitious roots.

Since the shoot develops underground, its color is not green, although its cells contain the green pigment chlorophyll. Its growth is carried out due to the apical buds. From these, ground shoots appear on the surface in spring. Remember what a lily of the valley looks like: the shoot is located underground, and on the surface we see only leaves and fragrant inflorescences.

How to distinguish a rhizome from a root

The root also develops underground, but has a number of distinctive features. Firstly, it provides the plant with minerals, absorbing their aqueous solution from the soil. Rhizomes are shoots, so they cannot perform this function. They only accumulate nutrients, ensuring the viability and development of plants during unfavorable periods.

Another difference is the absence of chloroplasts in the root cells. Therefore, it is not capable of photosynthesis. In addition, buds and leaves do not develop on the root.

Functions of the rhizome

Elongated and thickened internodes serve to adapt plants to conditions of drought and cold. Most often they develop in perennial species. During the period of intensive growth and development, they accumulate a significant supply of water and inorganic substances. This is a necessary condition for the normal functioning and development of the aerial part. With the onset of autumn, the leaves die off, and the plant continues to live underground.

Rhizomes are often used for vegetative propagation of some cultivated species. They allow you to create a large amount of planting material. Because many of the rhizomes are quite long, they provide anchorage in sandy soil.

But any modifications also have a negative side. The fact is that developed rhizomes are characteristic of many weeds, so it is difficult to fight them. Examples of these are wheatgrass and thistle. By tearing out their leaves or individual internodes, you leave most of the shoot in the soil, so after a certain time the above-ground part begins to develop again.

So, the rhizome is a modification of the shoot that develops underground. Its main functions are the supply of water with a solution of minerals and vegetative propagation of plants.

Common modifications of angiosperm shoots are rhizomes, bulbs and tubers. They are usually formed in perennial herbaceous plants as organs in which reserve nutrients are deposited. In such plants, the green above-ground parts die off during the winter, but modified shoots remain in the soil. In the spring, due to the nutrients they contain, the plants again develop ordinary above-ground shoots.

In addition to storing nutrients, modified shoots also perform another function. With their help, plants can reproduce vegetatively.

Rhizome

Modified escape rhizome found in many perennial plants (nettle, lily of the valley, wheatgrass, etc.). The rhizome is located in the upper layers of the soil, resembles a root, but spreads horizontally.

The rhizome is a shoot, since it has apical and axillary buds, as well as leaves that are modified into scales. The resemblance to a root is given to the rhizome by adventitious roots that grow from it along its entire length.

During the growing season, the plant deposits reserve nutrients in the rhizome. Due to them, new young shoots grow from the buds of the rhizome next year.

With the help of parts of the rhizome containing buds and roots, vegetative propagation of plants is possible.

Bulb

Modified escape bulb characteristic of onions, tulips, lilies and other plants. At the bottom of the bulb there is a flattened stem called bottom. Two types of leaves, modified into scales, grow from the bottom. The outer leaves are changed into dry scales, which perform a protective function. The inner thick and juicy scales contain reserve nutrients (the bulbs contain many different sugars, among other substances) and water. The bulbs also grow buds from the bottom.

In favorable conditions, adventitious roots grow from below the bottom of the bulb, resulting in the formation of a fibrous root system. Shoots can grow from the buds, but they can also develop into so-called baby bulbs. Each such bulb can give rise to a separate new plant. Thus, vegetative propagation is carried out using bulbs.

Tuber

Modified escape tuber can be observed in plants such as potatoes and Jerusalem artichokes, as well as some others.

The tuber is formed at the top of another modified shoot - stolon. Stolons grow from the lower parts of above-ground shoots and go into the soil. Organic substances synthesized by the green parts of the plant during photosynthesis move along the stolons to their tops, and thus tubers are formed here. A lot of starch accumulates in the tubers.

A tuber is, although modified, a shoot. It has short, but thick internodes and many buds, which are called eyes. The leaves of the tubers are reduced. The eyes are located in the recesses of the tuber, and in each such recess there may be several eye-buds.

The part of the tuber that is connected to the stolon is called the base of the tuber. On the opposite side of the base is the top of the tuber. There are more eyes closer to the top. Most often, the apical eye-bud develops into a young green shoot.