BIO1PS 2012 Plant Science Lecture 4 Hormones Pt. I

Transcription

1 BIO1PS 2012 Plant Science Lecture 4 Hormones Pt. I Dr. Michael Emmerling Department of Botany Room 410 m.emmerling@latrobe.edu.au

2 Hormones and Ghost gum Eucalyptus papuana Coordination ~3 Lectures Leaves ~4 Lectures Stems ~2 Lectures ~3 Lectures Ladiges et al. (2010), 4 th ed., Fig Soil and Roots

3 Recommended Reading Ladiges et al. (2010), "Biology", 4 th Edition Ch. 18, Plant hormones and growth responses, pp Knox et al. (2005), "Biology", 3 rd Edition Ch. 17, Plant hormones and growth responses, pp Useful website:

4 Plant Hormones Introduction General principles Discovery of plant hormones: auxin Major groups of plant hormones

5 Learning Objectives Part 1 Define a plant hormone Describe how Went s curvature test lead to the discovery of auxin Describe the major roles of the plant hormone auxin Describe the role of conjugation in regulating plant hormone levels

6 Classes of Plant Hormones Auxin (IAA) Cytokinins Ethylene Gibberellins (GAs) Abscisic acid (ABA) Other hormones: Brassinosteroids Jasmonates

7 Plant Development and Physiology plants can t move (!!!!) external environment can change dramatically plants are very adaptable

8 growth and flowering leaf drop and abscission dormancy and germination light and shade heat and drought cold and frost Plant hormones influence almost every aspect of plant development and physiology

9 Plant Development Influenced by many factors internal genetics evolution, adaptation external light amount, quality, direction nutrients soil, CO 2 temperature water humidity, rainfall

10 Plant Hormones are small molecules are effective at very low concentrations regulate the development of plants through changes in the production changes in the sensitivity of the plant/tissue to the hormone

11 Plant Hormones are synthesised in a discrete organ or tissue are transported to a (specific) target tissue control a physiological response in a concentration-dependent manner regulate gene expression

12 The Study of Plant Hormones Traditional approach: purified from plants (or other organisms) and applied to an intact plant, or plant segment Modern approach: use of genetics and mutants has clarified many aspects of hormone action

13 Phototropism Canary grass seedlings Ladiges et al. (2010), 4 th ed., Fig Shoot apex perceives light, and induces bending below the tip, towards the light

14 Went's Avena Curvature Test Hypothesis/Idea: Frits Warmolt Went, 1956 The shoot apex is producing a diffusible factor that promotes growth Ladiges et al. (2010), 4 th ed., Fig J. R. Eyerman, Time/Life

15 Went's Avena Curvature Test Coleoptile and agron5.jpg

16 Went's Avena Curvature Test 1926 Ladiges et al. (2010), 4 th ed., Fig. 18.3

17 Auxin The substance inducing the curving of the coleoptile is auxin or indole-3-acetic acid (IAA) Indole acetic acid tryptophan Ladiges et al. (2010), 4 th ed., Fig Ladiges et al. (2010), 4 th ed., Fig. 18.3

18 Auxin-Induced Growth Cell elongation cell wall is acidified acidified cell wall is more "stretchable" turgor pressure expands cells Taiz and Zeiger (2010), 5 th ed., Fig. 19.2

19 IAA Conjugation IAA is often bound to sugars or amino acids within the plant 50-90% of auxin in maize is conjugated the level of active IAA within the plant is dependent on the formation and breakdown of these IAA conjugates the level of free IAA is tightly controlled

20 Auxin - Amino Acid Conjugates indole-3 acetic acid (IAA) IAA-aspartate Want to know more? Ludwig-Müller, J. (2011) Auxin conjugates: their role for plant development and in the evolution of land plants. J. Exp. Bot. 62(2), IAA-glycine Bakllamaja, V. (2003), J Young Investigators 8 (1)

21 Plant Hormones Auxin GA Cytokinin Abscisic Acid Ethylene Dormancy Juvenility Extension Growth Root Development Flowering Fruit Development Senescence

22 Auxin Transport Shoot Transported in the phloem to the rest of the plant Roots Transported to the tip in the stele, then laterally in the epidermal/cortical cells

23 Gravitropism Tendency for shoots to grow away from gravity roots to grow towards gravity mediated by auxins

24 Gravitropism + auxin promoter GFP Confocal microscopy of live roots Green Fluorescent Protein (GFP): auxinresponsive gene expression Correlates with auxin concentration Auxin in the root? Transported via the Ottenschläger et al. (2003), Proc Nat Acad Sci USA 100, 2987 phloem

25 Redistribution of Auxin 1.5 hours + auxin gravitropism 3 hours promoter GFP Ottenschläger et al. (2003), Proc Nat Acad Sci USA 100, 2987 high auxin levels in root tissue reduce cell expansion

26 Apical Dominance The shoot apical meristem produces an "inhibitory substance" which prevents the outgrowth of other dormant buds (axillary meristems) low dominance ME ME high dominance

27 Apical Dominance regulates plant architecture ME ME

28 Ladiges et al. (2010), 4 th ed., Fig Trimming

29 Differential Responses to Auxin Observations: auxin in shoot inhibits expansion of lateral buds auxin in shoot promotes cell elongation (phototropism) auxin in root promotes growth of lateral roots auxin in roots reduces cell elongation (gravitropism) Different sensitivities to auxin Elongation, division, differentiation

30 Sensitivity to Auxin stimulates roots, no effect on shoots shoots Stimulation stimulates shoots inhibits roots auxin concentration Inhibition roots

31 Sensitivies to Hormones different tissues have different responses to hormones this is due (in part) to different sensitivities to hormone levels, and also due (in part) to interactions with other hormones

32 IAA and Auxins Involved in the regulation of many aspects of plant development: cell elongation (and division) tropisms differentiation apical dominance senescence abscission flowering

33 Synthetic Auxins similar in structure to IAA more "stable" than IAA transported less slowly than IAA 2,4-dichlorophenoxyacetic acid 2,4,5-trichlorophenoxyacetic acid results in excessive cell expansion Ladiges et al. (2010), 4 th ed., Fig. 18.4

34 "Rainbow Herbicides" Agent Pink Agent Green Agent Purple Agent Blue Agent White Agent Orange Deployed (1960s and 70s) in Korea and Vietnam

35 Agent Orange Mix of 2,4-D and 2,4,5-T Contaminated with the dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) Dioxins are fat-soluble and very stable carcinogenic lead to serious impairment of development, reproduction, immune function