TOPICAL PRESENTATIONS TOPICAL PRESENTATIONS ON GROWTH AND ON GROWTH AND DEVELOPMENTDEVELOPMENTFeb 01, 2017.Feb 01, 2017.@ UNIK BIOLOGY LAB

TOPIC ONE: Primary and secondary growth in plants using Arabidopsis thaliana as a model plant.By Mr. Orache Francis 15BSCED1154

Arabidopsis thaliana plantArabidopsis thaliana plant

Arabidopsis thalianaArabidopsis thaliana

Overview Overview

Definations of the terms, growth, development, primary growth, and finally growth.

Meristems ( apical and lateral meristems)

Primary growth in details. Secondary growth in details Annual rings

Defination of terms..Defination of terms.. Growth simply refers to the permanent

increase in size of an organism. Development is the increase in

complexity of an organism. Primary growth is the increase in length

of a plant. Secondary growth is the increase in

girth of a plant.

Meristems Meristems Meristematic tissues are clumps of

small cells with dense cytoplasm and proportionately large nuclei.

Meristem is a type of plant tissue consisting of undifferentiated cells that can continue to divide and differentiate.

Meristems Meristems Apical meristems located at tip of stems and roots Plant tissues that result from primary

growth are called primary tissues. make up primary plant body root apical meristem protected by root

cap

Meristems Meristems

Lateral meristemsLateral meristems Most trees, shrubs, and some herbs

have active lateral meristems. increases girth in nonwoody plants -

secondary growth Woody stemscork cambium produces cork cells vascular cambium produces secondary vascular tissue

Meristems Meristems

Primary and secondary growthPrimary and secondary growth

Primary growth results from cell division at the apical meristem at the plant tip.

Secondary growth results from cell division at the lateral meristem, increasing the shoot’s girth.

Primary growth in plantsPrimary growth in plants Primary growth is the upward growth of

the stem and the downward growth of the roots. It is the type of growth that makes a plant longer.

Primary growthPrimary growth Most primary growth occurs at the

apices, or tips, of stems and roots. Primary growth is a result of rapidly-dividing cells in the apical meristems at the shoot tip and root tip.

Primary growthPrimary growth

Subsequent cell elongation also contributes to primary growth. The growth of shoots and roots during primary growth enables plants to continuously seek water (roots) or sunlight (shoots).

Primary growthPrimary growth Zone of cell division cells divide every 12 to 36 hours toward

the edges of the concave dome Apical meristem daughter cells divide

into protoderm, procambium, and ground meristem tissues.

Zone of elongation roots lengthen because cells produced

by primary meristems grow longer than wide

Primary growthPrimary growth Zone of maturation cells differentiate into specific cell types root surface cells mature into epidermal

hairs, each with root hair cortex produced by parenchyma cells inner boundary differentiates into

endodermis surrounded by Casparian strips

composed of suberin

Primary growthPrimary growth

Secondary growthSecondary growth The increase in stem thickness that

results from secondary growth is due to the activity of the lateral meristems, which are lacking in herbaceous plants. Lateral meristems include the vascular cambium and, in woody plants, the cork cambium .

Secondary growthSecondary growth The vascular cambium is located just

outside the primary xylem and to the interior of the primary phloem.

Secondary growthSecondary growthThe cells of the vascular cambium divide and form secondary xylem (tracheids and vessel elements) to the inside and secondary phloem (sieve elements and companion cells) to the outside

Secondary growthSecondary growth The thickening of the stem that occurs

in secondary growth is due to the formation of secondary phloem and secondary xylem by the vascular cambium, plus the action of cork cambium, which forms the tough outermost layer of the stem. The cells of the secondary xylem contain lignin, which provides hardiness and strength.

Secondary growthSecondary growth In woody plants, cork cambium is the

outermost lateral meristem. It produces cork cells (bark) containing a waxy substance known as suberin that can repel water. The bark protects the plant against physical damage and helps reduce water loss.

Secondary growthSecondary growth The cork cambium also produces a

layer of cells known as phelloderm, which grows inward from the cambium. The cork cambium, cork cells, and phelloderm are collectively termed the periderm.

Secondary growthSecondary growth The periderm substitutes for the

epidermis in mature plants. In some plants, the periderm has many openings, known as lenticels, which allow the interior cells to exchange gases with the outside atmosphere . This supplies oxygen to the living- and metabolically-active cells of the cortex, xylem, and phloem.

Secondary growthSecondary growth After a long period of secondary

growth, two types of woods appear in the stem such as, sapwood, heartwood. Sapwood is recently formed wood and heartwood is earlier formed wood.

Secondary growthSecondary growth In woody stems the stomata are

blocked by the presence of cork cells The epidermis of woody stems breaks

up to form tiny pores called lenticels which allow gaseous exchange.

Annual ringsAnnual rings The activity of the vascular cambium

gives rise to annual growth rings. During the spring growing season, cells of the secondary xylem have a large internal diameter; their primary cell walls are not extensively thickened.

This is known as early wood, or spring wood.

Annual ringsAnnual rings During the fall season, the secondary

xylem develops thickened cell walls, forming late wood, or autumn wood, which is denser than early wood.

Annual ringsAnnual rings This alternation of early and late wood

is due largely to a seasonal decrease in the number of vessel elements and a seasonal increase in the number of tracheids. It results in the formation of an annual ring, which can be seen as a circular ring in the cross section of the stem .

Annual ringsAnnual rings An examination of the number of

annual rings and their nature (such as their size and cell wall thickness) can reveal the age of the tree and the prevailing climatic conditions during each season.

Topic one summaryTopic one summary So my fellow students we’ve looked at:

What growth and development mean Meristems Primary growth Secondary growth, and finally Annuall rings

Thank you for your kind attentionThank you for your kind attention

Your classmateYour classmate, , ~ ~ Orache Francis~Orache Francis~

+256 773165393 / +256 750089250 francyorache@gmail.com FACEBOOK: Orache Francis Twitter: @Francis Orache

Before a bye-bye…….Before a bye-bye…….