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Plant Morphology & Physiology 2011

Plant Morphology & Physiology

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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 - PowerPoint PPT Presentation

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Plant Morphology & Physiology

Plant Morphology & Physiology2011

RootsRoots MorphologyOutline Definition characteristics of a rootWhy are roots important?Contributors to Root GrowthParts of a RootRegions of RootAnatomy of the rootDifferences between dicot and monocot rootsTypes of rootsModifications of rootFunctions of rootsTask

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 plantsIs not normally greenDoes not commonly bear buds except in Batatas.Ends in and protected by root cap.Bears unicellular hairsLateral 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 significantParts of a RootRoots supports the plant and absorb, transport, and store nutrients. Like other plant parts, root contain all three tissue systemVascularGround and Dermal

stemleafroot

Dermal tissueGround tissueVascular tissue

Dermal Tissue System

Plants dont 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 plants 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 roots growth occurs. Groups of cells that are the source of new cells form tissue called meristem. Meristem cells arent specialized, but when they divide, some of the new cells specialize into tissues.

Regions of Root

Regions of the Root

Regions of the rootRoot cap:protects the tender apex of rootouter parts of the root cap wears awaynewer cells formed by underlying tissue are added to it.Absent is aquatic plants2.Region of Cell Division:lie within and little beyond the root capfew mm in length cells very small, thin walled & contain dense mass of protoplasmcells under go repeated division- meristematic region

Region of elongation:above meristematic regions, 1-5 mm in lengthrapid elongation and enlargementgrowth in the length of root

4.Region of maturation:few mm to few cm in lengthregion produce cluster of very fine thread like str.- Root hairsabsorb water & minerals salt from the soilInternally the cells in this region undergo maturations and differentiation various kinds of primary tissues.

Root HairsMeristematic 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 rootEpiblemaExodermis CortexEndodermisPericycleConjuctive tissueProtoxylemMetaxylemPhloemPith

Dicot RootMonocot root

Structure

cross section of a root in a region where only primarygrowth has occurred

Dicot Mature Root Structure - AnatomyEpidermisCortexVascular CylinderRanunculus acris - buttercup27

Monocot Root in Cross Section

Dicot and monocot rootsMonocotDocotNumerous vascular bundlesVary fron 2-4 rarely 6Cambium is absentCambium appears as secondary meristem at the times of secondary growthXylem vessels are large, more or less circularSmaller and polygonal in shapeSecondary growth is absentDevelops after the cambium develops/appearspith is well developedSmall or absentPericycle gives rise roots onlyGives rise to lateral root and cambiumThe inner walls of the endodermis are considerably thickened to give U-shaper appearanceThickening is not prominent and is due to the presence of casparian stripsCasparian Strip Special thickened band present on radial and tangential walls of the endodermal cells.

lignin and suberin

Types of RootsIn 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 RootTap 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 RootsRoots 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 treeStilt 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 RootsPlant attaches itself to tree branchRoots hang down in mid-air and absorb water from rainfall

ExamplesSome Orchids

PROP ROOTSe.g. Corn

STILT ROOTSe.g. MangroveAdventitious RootsGrow from unusual places on plants such as - Stems.

Functions of RootsThe 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 plantTaskExplain 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 END