BOTANY: Lecture Course for Bachelor Degree Students Specializing in Agronomy - 2016

LECTURE 5. Vegetative Plant Organs. Root. Shoot. Leaf

Concept of Vegetative plant Organs. FORMATION AND Structure. Morphology of plant seedlings. GENERAL PATTERNS OF organ arrangement: metamerism, Symmetry, polarity, geotropism, heliotropism. ANALOGOUS AND HOMOLOGOUS organs. ROOT formation in ontogeny and evolution. Root Functions. Root morphology. Root types. Root system. Microscopic structure. Origin and development of primary root Tissues. Root zones. Primary root structure. Water/144.html">Origin of the cambium and The Role of the pericycle in secondary root thickening. Structural Features of root crops. Root Metamorphoses. Symbiosis of roots with nitrogen-fixing Bacteria. Mycorrhiza, its types, and significance in agricultural and forestry practices. Concept of the SHOOT and its functions. Macroscopic structure. Types of shoots by structure, arrangement, and purpose. Shoot growth. Shoot branching. Buds, their structure, types, and significance. Tillering of cereals. Patterns of leaf arrangement. Biological types of shoots. Shoot metamorphoses. Stem. Definition and Functions of the stem. Macroscopic structure. Microscopic structure. Primary stem structure of dicotyledonous plants. Secondary stem structure. Structural types of stems in dicotyledons. Structural features of gymnosperm stems. Stem structure of monocotyledonous plants. Utilization of phloem and wood. Definition and function of the leaf. Origin and Development of the leaf. Macroscopic structure. Leaf Morphology and its parts. Leaf types. Cereal leaves. Leaf formations. Size and lifespan of leaves. Venation. Mosaic arrangement. Heterophily. Leaf fall and its biological significance. Proportion of leaves and leaf surface area in phytomass structure and crop yield formation of leading agricultural crops. Microscopic structure. Leaf structure. Structural features of cereal leaves. Structure of needles. Dependence of the Anatomical and morphological leaf structure on environmental factors. Leaf metamorphoses. Leaf succulence.

Plant organs are divided into vegetative and generative. The plant body consists of vegetative organs that perform vital metabolic functions (root, stem, and leaf). A stem with leaves (buds) forms a shoot.

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Generative (reproductive) organs are organs of Selection/8.html">Asexual and sexual reproduction (flower, inflorescence, fruit, seed).

The organs are characterized by the following patterns:

- polarity;

- geotropism and heliotropism;

- symmetry;

- metamerism;

- correlation.

Modified (metamorphosed) organs are organs that have undergone a heritably fixed drastic change in shape under the Influence of the environment or in connection with the performance of a specific function.

Metamorphosed organs are homologous and analogous.

ROOT is an axial subterranean vegetative organ of the vascular plant sporophyte, characterized by unlimited apical growth, radial symmetry, positive geotropism, and the capacity for metamerism.

Functions:

1. Anchorage of plants in the soil;

2. Absorption of water and dissolved mineral nutrients from the soil;

3. Initial transformation of certain absorbed substances and synthesis of Organic compounds;

4. Storage site for reserve organic substances (e.g., carrot root crop);

5. Organ of vegetative propagation.

Diversity of roots:

By origin – primary (taproot or embryonic), lateral, and adventitious roots. All root metamorphoses are adventitious.

Types of Root systems:

Taproot system – consisting of the main root and lateral roots (sunflower, parsley).

Fibrous root system - formed by adventitious roots (wheat, corn).

Mixed root system - composed of primary, lateral, and adventitious roots (tomatoes, peppers, cabbage, cucumbers, pumpkins).

Root forms.

By growth direction: horizontal, vertical, universal.

Root metamorphoses

Root crop (carrot, parsley)

Root tubers or tuberous roots (lesser celandine, dahlias)

Climbing roots (ivy)

Parasitic roots (haustoria) (dodder, mistletoe)

Prop (stilt) roots (corn)

Contractile roots (tulip, daffodils)

Aerial roots (orchids)

Respiratory roots (pneumatophores in mangroves)

Photosynthetic roots (water chestnut)

Symbiosis with legume roots (nitrogen-fixing bacteria), symbiosis with Fungi (mycorrhiza). In many flowering plants (about 90%), roots form symbioses with fungi to create mycorrhiza or with bacteria to create bacteriorhiza. Symbiotic microorganisms are part of the rhizosphere, a 2–3 mm soil layer adjacent to plant roots. The accumulation of numerous fungi and bacteria in the rhizosphere is due to root exudates that serve as nutrients for these microorganisms.

Anatomical Structure of the root tip: the root cap, which protects the root from damage and does not belong to any root zone; apical meristem (apex or growing cone);

zone of division at a distance of

zone of growth and elongation

zone of absorption

zone of lateral roots or branching zone

Anatomical STRUCTURE OF THE root

Primary root structure - consists of the epiblema, primary cortex (exodermis, mesodermis, endodermis), and central cylinder.

Secondary root structure.

In most dicotyledonous plants, the Primary Structure is replaced by the secondary one.

Stages of transition from primary to Secondary structure:

1) fascicular cambium, whose Cells undergo tangential division → secondary phloem is laid down outwards, and secondary xylem (in greater amounts) inwards. Thus, open collateral vascular bundles are formed.

2) interfascicular cambium, which gives rise to radially arranged medullary rays (parenchyma cells).

3) cambial ring.

4) secondary meristematic tissue, the phellogen (cork cambium).

5) cork (phellem). The primary cortex becomes suberized and dies off → The root ceases to absorb water and minerals from the soil, shedding its outer layers ("root molting"). The root now serves solely to anchor the plant.

6) Fascicular cambium cells located between the secondary phloem and xylem form 4 collateral bundles separated by radial parenchymatous rays.

Tertiary root structure is typical of plants with modified roots. It begins with the appearance of an additional cambial ring formed from a parenchymatous layer derived through the division of primary phloem and pericycle cells. This tertiary cambium produces tertiary collateral vascular bundles. Beets are characterized by a polycamibial structural type, carrots by a phloem type, and radishes by a xylem type of root structure.

THE SHOOT is a complex axial organ of higher plants responsible for aerial Nutrition, substance transport, secondary synthesis, and starch storage. It consists of a stem, leaves and buds, nodes, and internodes.

The stem is an above-ground axial organ exhibiting negative geotropism, positive heliotropism, radial symmetry, and indeterminate apical growth.

- hypocotyl – the portion of the shoot between the root and the cotyledons;

- cotyledons – embryonic leaves that often function as foliage until true leaves appear;

- epicotyl – the portion of the shoot between the cotyledons and the true leaves;

- primordial leaves – the first true leaves;

- apical bud.

Functions – a site for nutrient storage and an organ of vegetative propagation.

Node – the region of the stem where leaves are attached.

Internode.

Leaf axil containing axillary buds.

Classification of buds:

- By function – vegetative, generative (floral), or mixed.

- By position – terminal (apical) and lateral (axillary);

- By arrangement – solitary, serial, collateral;

- By state – active or overwintering, dormant, epicormic, adventitious;

- By internode length – shortened (brachyblasts, rosettes), normal (plum, hazel, pea), elongated (water sprouts or epicormic shoots).

- By spatial orientation – erect, ascending (knotweed, heather, common speedwell), twining (lianas – hops, beans, hardy kiwi up to 300 m), climbing/tendril-bearing (wild grapes, ivy), prostrate (pumpkins), decumbent (melon), runners and stolons (strawberries).

- A leafless stem that bears a flower or inflorescence is a scape (onion, primrose); a stem portion with shortened internodes is a basal rosette.

- By shape: round, cylindrical; solid and hollow (culm);

- By cross-section: quadrangular (Lamiaceae), triangular (sedges), polygonal (Apiaceae), flat (opuntia), flattened (plun), winged (Lathyrus sylvestris), cistern-like (Cavanillesia).

- By vegetation period: annuals (cereal crops, peas, flax, etc.), biennials (cabbage, carrots, beets, parsley), perennials (tau-saghyz, irises, plantain, trees).

By shoot branching type: dichotomous (clubmosses, Algae); false-dichotomous (lilac, chickweed), monopodial (spruce, fir), sympodial (apple, plum, tomato).

Tillering of grasses:

Shoot metamorphoses

Tuber (potato)

Rhizome (couch grass, irises)

Stolon (potato)

Bulb (onion, garlic)

Corm (gladiolus)

Runner (strawberry)

Thorn (pear)

Cladode (asparagus).

Phylloclade (Ruscus).

Phyllotaxis: alternate (spiral); opposite; whorled.

Anatomical structure of the stem

From the Tissues of the apical meristem—the primary dermal tissue epidermis, primary cortex. Inner Cells of the corpus—the central cylinder. Three tissue blocks originate from two blocks—the tunica and corpus.

The Introduction/19.html">Primary structure of the stem is characteristic of monocotyledonous plants throughout their lives, and of dicotyledonous and gymnosperm plants during the early Stages of development.

Schmidt's tunica-corpus theory

Structure: epidermis

primary cortex

central cylinder

Conclusion: the stem exhibits an increased amount of mechanical tissues, collateral vascular bundles, and a high degree of parenchymatization.

Structure of the monocot stem

Corn: epidermis, a layer of chlorophyll-bearing parenchyma forming the primary cortex parenchyma, and a central cylinder (pericyclic bast fibers, ground parenchyma) with closed collateral vascular bundles arranged haphazardly and surrounded by a sclerenchymatous ring.

In many cereals (wheat, oats, barley), the stem is hollow, known as a straw. The sclerenchyma appears gear-like, with the chlorophyll-bearing parenchyma interspersed between its Teeth, featuring a substomatal cavity and a stoma in the epidermis.

The vascular bundles are arranged in two concentric circles and are collateral and closed.

Structure of the dicotyledonous stem

Primary stem structure persists only in the early developmental stage, during The Emergence of the first pair of embryonic leaves:

Epidermis

Primary cortex (collenchyma, multilayered primary cortical parenchyma, endodermis [starch sheath]).

Central cylinder (pericycle, a layer of parenchyma, vascular bundles arranged in a ring).

Vascular bundles are of the open collateral type.

Pith.

Secondary stem structure:

epidermis with a cuticle,

primary cortex consisting of collenchyma, cortical parenchyma, and endodermis; central cylinder, in the peripheral part of which open collateral vascular bundles are embedded in the parenchyma.

Fascicular stem structure (Aristolochia)

Fascicular type: procambium originates in the shoot apex as procambial strands arranged in a regular circle along the periphery of the central cylinder → primary xylem, primary phloem, and cambium between them, which gives rise to secondary phloem and secondary xylem.

Transitional stem structure

Interfascicular cambium cuts off phloem outwards and xylem inwards rather than pith ray parenchyma → incomplete xylem bundles. As they develop, they merge with adjacent ones, forming continuous cylinders of phloem, cambium, and xylem, or cambium and secondary xylem.

Non-fascicular stem structure

characteristic of trees, shrubs, and certain herbaceous plants (such as flax and hemp). The procambium initiates as a continuous cylinder, giving rise to three continuous layers: primary xylem, cambium, and primary phloem.

Epidermis with numerous Stomata

Primary cortex with chlorophyll-bearing parenchyma. The innermost layer is the endodermis (starch sheath).

Central cylinder, along the periphery of which lie primary bast fibers of pericyclic and phloem origin.

THE LEAF is a lateral plagiotropic vegetative organ with determinate growth, whose primary functions are Photosynthesis, Transpiration, and Respiration. It evolved through two distinct pathways:

- as an outpocketing of the surface tissues of the stem apex (microphylls in clubmosses);

- As a result of the flattening and fusion of axes (telomes not yet differentiated into vegetative organs, characteristic of large fern fronds).

Lifespan ranges from a single vegetative period (annuals and deciduous woody plants) to an extended duration (more than 2 years).

Functions:

- Photosynthesis;

- Transpiration;

- Gas exchange;

- Vegetative propagation;

- Storage of nutrients, water, mineral salts, Alkaloids, Glycosides, Tannins, and Essential Oils;

- Capturing insects (drosera, venus flytrap, Nepenthes);

- Climbing (tendrils in peas);

- Protection (spines in cacti);

- Excretion of toxic substances.

Ontogenetic development

PARTS OF THE leaf: Petiole, blade (lamina), stipules.

Leaf formations:

scale leaves (cataphylls);

foliage leaves (mesophylls);

bracts (hypsophylls).

Leaves can be classified as simple or compound.

Simple leaves are classified:

- by The Nature of attachment to the stem (petiolate, sessile, amplexicaul, perfoliate, decurrent)

- by the shape of the leaf blade (ratio of length to width and THE POSITION OF the widest part of the blade): broadly ovate (black poplar), orbicular (aspen), obovate (hazel), ovate (lilac), oval (bird cherry), lanceolate (willow), oblong (white willow), oblanceolate (ox-eye daisy), linear (couch grass), acicular (pine).

- by the shape of the base: rounded (hornbeam), cordate (linden), cuneate (birch), hastate (field bindweed), sagittate (arrowhead);

- by the shape of the apex: obtuse (asarabacca), acute (willow), acuminate (black poplar), mucronate with a spine (creeping thistle), emarginate (ginkgo biloba);

- by the margin of the leaf blade: entire (lilac), dentate (nettle, mulberry), serrate (pear, willow), doubly serrate (violet), sinuate (dandelion), wavy, etc.

- According to the degree of leaf blade incision: lobed (indentations along the margin reach a quarter of the blade width, but no more than a third), cleft (indentations exceed half the width), divided (indentations reach the midrib).

- according to venation: dichotomous (forked) — ginkgo; parallel venation — grasses, sedges; arcuate venation — lily of the valley; palmate venation — Norway maple; pinnate venation — pear, plum.

Phyllotaxy: alternate or spiral (apple trees, birch), opposite (lilac, carnation), whorled (bedstraw). Leaf mosaic — the mutual arrangement of leaves on a plant that ensures the most efficient absorption of sunlight.

Compound leaves (several individual simple leaflets, possessing their own sometimes inconspicuous petioles, are attached to a common petiole, the rachis).

Heterophilly — the presence of morphologically different leaves on a single shoot (arrowhead). Anisophilly — The phenomenon of difference in shape and size of leaves belonging to the same shoot node (spikemosses, maples).

Leaf formations:

- lower leaves are underdeveloped and modified, accumulating nutrients or serving a protective function;

- middle leaves are typical for a given plant species and carry out photosynthesis;

- upper leaves are located at the apex of the shoot and differ from middle leaves by their smaller size and simpler shape.

Anatomical structure of leaves

1. Dorsiventral (heterofacial) type (dicotyledonous plants).

It consists of assimilatory, dermal, vascular, and mechanical tissues. Secretory Tissues are also present in some species.

The leaf is differentiated into the epidermis, mesophyll, and vascular bundles.

2. Isobilateral (homeofacial) type (monocots).

The leaf is illuminated evenly, therefore the mesophyll is homogeneous, —

palisade tissue. The leaf is isolateral.

3. Plicate type (gymnosperms).

Needles — the acicular leaves of conifers — have a long lifespan.

Xeromorphic structure of gymnosperm leaves: thick-walled epidermis, hypodermis, deeply sunken stomata, plicate mesophyll, resin canals, a single layer of starch-storing endodermal cells, beneath which lies transfusion parenchyma enclosing two vascular bundles.

Leaf modifications

Spines, bracts, bud scales, dry and fleshy bulb scales; succulents, tendrils, phyllodes; cotyledons, leaves of carnivorous plants