ROLE OF PGR's IN SEED DORMANCY AND DEVELOPMENT

PLANT GROWTH REGULATORS

1. ROLE OF PLANT GROWTH REGULATORS IN SEED DORMANCY AND DEVELOPMENT Presenter: Tanveer abbas ansari College of agriculture BZU, LAYYAH TANVEER 1

2. Plant Growth Regulators PGR defined as small, simple chemicals produced naturally by plants to regulate their growth and development. Characteristics Plant Growth Regulators can be of a diverse chemical composition such as gases (ethylene), terpenes (gibberellic acid) or carotenoid derivates (abscisic acid). They are also referred to as plant growth substances, phytohormones or plant hormones.  TANVEER 2

3. PLANT GROWTH REGULATORS The effect on plant physiology is dependent on the amount of hormone present and tissue sensitivity to the plant growth regulator Substances produced in small quantities by a plant, and then transported elsewhere for use have capacity to stimulate and/or inhibit physiological processes TANVEER 3

4. What Are the Functions of Plant Hormones? Plants hormones help in regulation of the plant body by responding to the various signals from the plant and environment. The hormones are regulated in different tissues during the different development stages. There are five major hormones which are auxin, cytokinin, gibberellin, abscisic acid, and ethylene. Each hormone differs in its effects. TANVEER 4

5. Conti.. The auxins, gibberellins, and cytokinins act as growth stimulators, whereas, abscisic acid and ethylene act as growth inhibitors. Plant hormones are simple in their structure as compared to those of animals or humans. There are no specific or specialized glands that produce these hormones. In fact, they are synthesized anywhere in the plant and act on any part as their target. Besides the hormones, there are many plant growth factors that affect the function and growth of plants. TANVEER 5

6. Seed dormancy Seed dormancy allows seeds to overcome periods that are unfavourable for seedling established and is therefore important for plant ecology and agriculture. Several processes are known to be involved in the induction of dormancy and in the switch from the dormant to the germinating state TANVEER 6

7. PGR as a dormancy creator Abscisic acid inhibits germination of mature Arabidopsis seeds by limiting the availability of energy and nutrients. The addition of abscisic acid (ABA) to mature non-dormant seeds inhibits their germination. TANVEER 7

8. PGR’s and dormancy relatioin Gibberellins (GAs) break seed dormancy and promote germination Several other hormones, including  brassinosteroids , ethylene, and cytokinin, have also been shown to promote seed germination. However, abscisic acid (ABA) is the only hormone known to induce and maintain seed dormancy . TANVEER 8

9. Gibberellins Gibberellins are involved in the natural process of breaking dormancy and other aspects of germination. Gibberellins are produced in greater mass when the plant is exposed to cold temperatures. They stimulate cell elongation, breaking seed and budding dormancy , seedless fruits, and seed germination . TANVEER 9

10. Auxin as a plant development Auxin promotes activity of the vascular cambium and vascular tissues. plays key role in fruit development Cell Elongation: Acid growth hypothesis auxin works by causing responsive cells to actively transport hydrogen ions from the cytoplasm into the cell wall space TANVEER 10

11. Auxin Synthetic auxins widely used in agriculture and horticulture prevent leaf abscission prevent fruit drop promote flowering and fruiting control weeds Fruit development Apical dominance TANVEER 11

12. Apical Dominance Lateral branch growth are inhibited near the shoot apex, but less so farther from the tip. Apical dominance is disrupted in some plants by removing the shoot tip, causing the plant to become bushy. TANVEER 12

13. Gibberellin TANVEER 13

14. Gibberellins Gibberellins are named after the fungus Gibberella fujikuroi which causes rice plants to grow abnormally tall. synthesized in apical portions of stems and roots important effects on stem elongation in some cases, hastens seed germination TANVEER 14

15. Gibberellins and Fruit Size Fruit Formation - "Thompson Seedless" grapes grown in California are treated with GA to increase size.  TANVEER 15

16. Wild Radish TANVEER 16

17. Abscisic Acid Abscisic acid is produced chiefly in mature green leaves and in fruits. suppresses bud growth and promotes leaf senescence It also plays important role in controlling stomatal opening and closing General growth inhibitor. Causes stomatal closure. Produced in response to stress. TANVEER 17

18. Ethylene H H \ / C = C / \ H H TANVEER 18

19. Functions of ethylene Gaseous in form and rapidly diffusing. Gas produced by one plant will affect nearby plants. Fruit ripening. Epinasty – downward curvature of leaves. Encourages senescence and abscission. Initiation of stem elongation and bud development. Flowering - Ethylene inhibits flowering in most species, but promotes it in a few plants such as pineapple, bromeliads, and mango. TANVEER 19

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