Plant Morphology & Physiology 2011

Roots Roots Morphology

Outline Definition characteristics of a root Why are roots important? Contributors to Root Growth Parts of a Root Regions of Root Anatomy of the root Differences between dicot and monocot roots Types of roots Modifications of root Functions of roots Task

Definition Plant morphology: The study of the forms and structures, especially their external form. The study of forms and features of different plant organs such as roots, leaves, flowers, seeds and fruits Physiology: the branch of biology concerned with the vital functions of plants such as nutrition, respiration, reproduction, etc.

What are the characteristics of a root? The descending portion of the axis of the plants Is not normally green Does not commonly bear buds except in Batatas. Ends in and protected by root cap. Bears unicellular hairs Lateral roots always develop from an inner layer pericycle - Endogenous

Why are roots important? Roots may make up over half of the body of a plant. They anchor the plant to the ground From the soil they absorb water and minerals the plant needs

Contributors to Root Growth Roots grow in length only at the tips. they grow where moisture occurs, moisture is not only requirement for their growth. Sugar produced in the leaves by photosynthesis is also necessary, hormones necessary, which are also produced in the leaves. Hormones must be transported from the leaves to the roots in order to influence root growth.

Temperature the presence of minerals acidity or alkalinity are other important factors in both root and plant growth. In addition to moisture, air in the soil is also significant

Parts of a Root Roots supports the plant and absorb, transport, and store nutrients. Like other plant parts, root contain all three tissue system Vascular Ground and Dermal

stem leaf root Dermal tissue Ground tissue Vascular tissue

Dermal Tissue System Plants don’t have skin, have a system of dermal tissue and protects it in a variety of ways. Dermal tissue called epidermis is made up of live parenchyma cells in the non-woody parts of plants. On leaves and some stems, epidermal cells may secrete a wax-coated substance that becomes the cuticle. Dermal tissue made of dead parenchyma cells makes up the outer bark of woody plants.

Ground Tissue System Dermal tissue surrounds the system of ground tissue, which makes up much of the inside of a plant. Ground tissue provides support and stores materials in roots and stems. In leaves, ground tissue is packed with chloroplasts, where photosynthesis makes food for the plant.

The ground tissue system consists of all three of the simple tissues— parenchyma tissue 2. collenchyma tissue 3. and sclerenchyma tissue Parenchyma is by far the most common of the ground tissues.

Vascular Tissue System Surrounded by ground tissue, the system of vascular tissue transports water, mineral nutrients, and organic compounds to all parts of the plant. Plants can transport necessary fluids and nutrients throughout their systems. A plant’s vascular system is made up of two networks of hollow tubes somewhat like our veins and arteries.

Each network consists of a different type of vascular tissue that works to move different resources throughout the plant. Xylem (ZY-luhm) is the vascular tissue that carries water and dissolved mineral nutrients up from the roots to the rest of the plant. Phloem (FLOH-EHM) is the vascular tissue that carries the products of photosynthesis through the plant.

In the center of the root is the vascular cylinder, which is made of xylem and phloem tissues. The vascular cylinder is surrounded by ground tissue, covered by dermal tissue. A plant absorbs most of its water in the dermal tissue just above the root tips. These cells have tiny projections called root hairs, Root hairs find their way through the spaces between soil particles, greatly adding to the surface area available to take up water.

Covering the tip of the root is the root cap, a small cone of cells that protects the growing part of the root as it pushes through the soil. Just behind the root cap is where most of the root’s growth occurs. Groups of cells that are the source of new cells form tissue called meristem. Meristem cells aren’t specialized, but when they divide, some of the new cells specialize into tissues.

Regions of Root

Regions of the Root

Regions of the root Root cap: protects the tender apex of root outer parts of the root cap wears away newer cells formed by underlying tissue are added to it. Absent is aquatic plants 2. Region of Cell Division: lie within and little beyond the root cap few mm in length cells very small, thin walled & contain dense mass of protoplasm cells under go repeated division- meristematic region

Region of elongation: above meristematic regions, 1-5 mm in length rapid elongation and enlargement growth in the length of root 4. Region of maturation: few mm to few cm in length region produce cluster of very fine thread like str.- Root hairs absorb water & minerals salt from the soil Internally the cells in this region undergo maturations and differentiation various kinds of primary tissues.

Root Hairs Meristematic activity, which increases the length of the root, occurs only at the tip. When the cells here divide, they produce the new root cells and root cap cells. The root cap cells are sloughed off as the root grows through the soil. The epidermal cells produce root hairs a short distance above the tip. Root hairs are part of epidermal cells.

Root hairs

Anatomy of the root Epiblema Exodermis Cortex Endodermis Pericycle Conjuctive tissue Protoxylem Metaxylem Phloem Pith

Dicot Root Monocot root

Structure cross section of a root in a region where only primary growth has occurred

Dicot Mature Root Structure - Anatomy Ranunculus acris - buttercup Epidermis Cortex Vascular Cylinder

Monocot Root in Cross Section

Dicot and monocot roots Docot Numerous vascular bundles Vary fron 2-4 rarely 6 Cambium is absent Cambium appears as secondary meristem at the times of secondary growth Xylem vessels are large, more or less circular Smaller and polygonal in shape Secondary growth is absent Develops after the cambium develops/appears pith is well developed Small or absent Pericycle gives rise roots only Gives rise to lateral root and cambium The inner walls of the endodermis are considerably thickened to give U-shaper appearance Thickening is not prominent and is due to the presence of casparian strips

Casparian Strip Special thickened band present on radial and tangential walls of the endodermal cells. lignin and suberin

Types of Roots In majority of the dicotyledonous plants, the direct elongation of the radicle leads to the formation of primary root which grows inside the soil. It bears lateral roots of several orders that are referred to as secondary, tertiary roots. The primary roots and its branches constitute the tap root system, as seen in the mustard plant

Types of Root Tap root Root Systems: Arise from radicle Adventitious Roots: arise from anything other than the radicle

In monocotyledonous plants, the primary root is short lived and is replaced by a large number of roots. These roots originate from the base of the stem and constitute the fibrous root system, as seen in the wheat plant. In some plants, like grass, Monstera and the banyan tree, roots arise from parts of the plant other than the radicle - adventitious roots .

Modifications of Root Tap Roots Roots in some plants change their shape and structure become modified to perform functions other than absorption and conduction of water and minerals. They are modified for support storage of food and respiration . Tap roots of carrot, turnips and adventitious roots of sweet potato, get swollen and store food.

Prop roots- Provide additional supports to plant. Eg. banyan tree Stilt roots the stems of maize and sugarcane have supporting roots coming out of the lower nodes of the stem. Pneumatophores Rhizophora growing in swampy areas, many roots come out of the ground and grow vertically upwards. help to get oxygen for respiration.

Prop root. E.g Banyan

Aerial Roots Plant attaches itself to tree branch Roots hang down in mid-air and absorb water from rainfall Examples Some Orchids

PROP ROOTS e.g. Corn

STILT ROOTS e.g. Mangrove

Adventitious Roots Grow from unusual places on plants such as - Stems.

Functions of Roots The main functions of the root system are absorption of water and minerals from the soil, providing a proper anchorage to the plant parts, storing reserve food material and synthesis of plant growth regulators of some plants can be used to grow a new plant

Task Explain the following modifications of root and state their functions: 1. Tap root: Fusiform, napiform, conical and tuberous. 2.Branched root: Pneumatophores. 3. Adventitious root: a. tuberous, fasciculated, nodulose, moniliform and annulated root. b. prop root, climbing root, Buttress root, haustoria, respiratory root and epiphytic root

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