Growth

1. Growth Chapter 11

2. Outline • Introduction • Nutrients, Vitamins, and Hormones • Hormonal Interactions • Other Hormonal Interactions • Plant Movements • Photoperiodism • Cytochromes and Cryptochromes • A Flowering Hormone? • Temperature and Growth • Dormancy and Quiescence

3. Introduction • Growth -irreversible increase in mass due to division and enlargement of cells • Determinate Growth -plant grows, stops growing and dies in one season • Indeterminate Growth -plant or parts of plant grow and continue to be active for several to many years • Differentiation -cells develop different forms adapted to specific functions • Development -coordination of growth and differentiation of single cell into tissues and organs

4. Nutrients, Vitamins, and Hormones • Nutrients -substances that furnish elements and energy to produce organic molecules • Obtained from air and soil • Vitamins -organic molecules of varied structure that participate in catalyzed reactions, mostly as electron acceptor or donor • Synthesized in cell membranes and cytoplasm • Required in small amounts for normal growth and development

5. Nutrients, Vitamins, and Hormones • Hormones -production dictated by genes • Mostly produced in actively growing regions • Produced and active in smaller amounts than vitamins and enzymes • Some effects of vitamins similar to those of hormones -> can be difficult to distinguish • Growth Regulators -compounds that affect plant development similar to those of naturally produced hormones and vitamins

6. Nutrients, Vitamins, and Hormones • Hormones can have multiple effects • Hormones chemically bind to specific receptors • Hormone-receptor association initiates effect • Triggers series of biochemical events, including turning genes on and off • Biochemical events = Signal Transduction • Major types of hormones: auxins, gibberellins, cytokinins, abscisic acid, ethylene

7. Nutrients, Vitamins, and HormonesPlant Hormones • Auxins • Produced mainly in apical meristems, buds, young leaves and actively growing parts of plants • Similar structure to amino acid, tryptophan • Plant responses vary according to concentration, location, and other factors • Generally, monocots less sensitive than dicots and shoots less sensitive than roots

8. Nutrients, Vitamins, and HormonesPlant Hormones • Auxins cont’d. • Some effects include: • Stimulate enlargement of cells by increasing cell wall plasticity • Trigger production of other hormones • Cause dictyosomes to increase rate of secretion • Control some phases of respiration

9. Nutrients, Vitamins, and HormonesPlant Hormones • Auxins cont’d. • Effects cont’d.: • Influence growth • Promote cell enlargement and stem growth, cell division in cambium, initiation of roots and differentiation of cell • Delay development processes such as fruit and leaf abscission, and fruit ripening • Inhibit lateral branching

10. Nutrients, Vitamins, and HormonesPlant Hormones • Auxins cont’d. • Movement of auxins from cells where they originate requires energy expenditure • Movement is polar - away from source • Move through parenchyma cells surrounding vascular bundles • Several Forms: • Indoleacetic acid (IAA) • Phenylacetic acid (PAA) • 4-chloroindoleacetic acid (4-chloroIAA) • Indolebutyric acid (IBA)

11. Nutrients, Vitamins, and HormonesPlant Hormones • Gibberellins (GA) • Named after fungus that produces it (Gibberellafujikuroi) • 110 currently known gibberellins • Movement is nonpolar • Most dicots and few monocots grow faster with an application of GA • Dramatically increases stem growth • Involved in same regulatory processes as auxins Effect of gibberellins on cabbage

12. Nutrients, Vitamins, and HormonesPlant Hormones • Cytokinins • Regulate cell division • Synthesized in root tips and in germinating seeds • Movement is nonpolar • If auxin present during cell cycle, cytokinins promote cell division by speeding up progression from G2 phase to mitosis phase

13. Nutrients, Vitamins, and HormonesPlant Hormones • Cytokinins cont’d. • Also play role in: • Cell enlargement • Differentiation of tissues • Development of chloroplasts • Stimulation of cotyledon growth • Delay of aging in leaves

14. Nutrients, Vitamins, and HormonesPlant Hormones • Abscisic Acid (ABA) • Inhibitory effect on stimulatory effects of other hormones • Synthesized in plastids from carotenoid pigments • Movement is nonpolar • Common in fleshy fruits - prevents seeds from germinating while still on plant • Helps leaves respond to excessive H2O loss • Interferes with transport or retention of K+in guard cells, causing stomata to close

15. Nutrients, Vitamins, and HormonesPlant Hormones • Ethylene • Produced by fruits, flowers, seeds, leaves and roots • Produced from amino acid methionine • Can trigger own production • Used to ripen green fruits • Production almost ceases in absence of O2 • Causes leaf abscission Ethylene from apple caused abscission of holly leaves

16. Nutrients, Vitamins, and HormonesOther Hormones or Related Compounds • Oligosaccharins • Released from cell walls by enzymes - influence cell differentiation, reproduction, and growth in plants • Produce effects at concentrations 1000x less than auxins • Effects highly specific and responses same in all species • Brassinosteroids • Have GA-like effects on plant stem elongation • Known from legumes and few other plants

17. Hormonal Interactions • Apical Dominance -suppression of growth of lateral (axillary) buds • Believed to be brought about by auxin-like inhibitor in terminal bud • Strong in trees with conical shapes • Pines, spruces, firs • Weak in trees that branch more often • Elms, ashes, willows • If cytokinins applied in appropriate concentration to axillarybuds -> begin to grow, even in presence of terminal bud

18. Hormonal Interactions • Senescence -breakdown of cell components and membranes, eventually leading to death of cell • Suggested certain plants produce a senescence “factor” • Not certain of precise mechanisms involved • Other hormonal interactions • Root and shoot development in tissue culture regulated by auxins and cytokinins • Seed germination regulated by GA and ABA

19. Plant Movements • Growth Movements -result from varying growth rates in different parts of organ • Movements resulting primarily from internal stimuli: • Nutations - spiraling movements not visible to eye • Nodding Movements - side-to-side oscillations • In bent hypocotyl of bean - facilitates progress of plant through soil

20. Plant MovementsGrowth Movements • Movementscont.’d • Twining Movements - visible spiraling in growth • Stems of flowering plants - Morning glory • Tendrils • Contraction Movements • Contractile roots that pull roots deeper • Nastic Movements - non-directional • Epinasty - permanent downward bending

21. Plant Movements Tendril of manroot plant Nutation

22. Plant MovementsGrowth Movements • Movements cont’d. • Tropisms -permanent movements resulting from external stimuli • Growth of plant toward or away from stimulus • Can be divided into 3 phases: • Initial Perception -organ receives greater stimulus on one side • Transduction -one or more hormones become(s) unevenly distributed across organ • Asymmetric Growth -result of greater cell elongation on one side

23. Plant MovementsGrowth Movements • Movements cont’d. • Phototropism -growth movement toward or away from light • Positive phototropism -toward light (Ex. shoots) • Negative Phototropism -away from light (Ex. roots) • Auxinmigrates away from light, and accumulates in greater amounts on opposite side, promoting greater elongation of cells on dark side Positive phototropism

24. Plant MovementsGrowth Movements • Movements cont’d. • Gravitropism -growth responses to stimulus of gravity • 1° roots -positively gravitropic • Shoots -negatively gravitropic • Gravity perceived by amyloplasts in root cap, by proteins on outside of plasma membrane, by whole protoplast, or by mitochondria and dictyosomes • Auxin causes cell elongation producing curvature of root Negative gravitropism

25. Plant MovementsGrowth Movements • Movements cont’d. • Other Tropisms: • Thigmotropism -contact with solid object • Twining • Chemotropism -chemicals • Germination of pollen grains • Thermotropism -temperature • Horizontal stems when cold in some weeds

26. Plant MovementsGrowth Movements • Movements cont’d. • Other Tropisms cont’d.: • Traumotropism - wounding • Electrotropism - electricity • Skototropism - dark • Aerotropism - O2

27. Plant Movements • Turgor Movements -result from changes in internal H2O pressures and often initiated by contact with objects outside of plant • Pulvini -special swellings at base of leaf • Sensitive plant, redwood sorrel • Turgor contact movements not confined to leaves • Stamens of flowers Sensitive plant

28. Plant Movements Stigmas folding in bush monkey flower Stamens folding

29. Plant MovementsTurgor movements • “Sleep” movements - Circadian rhythms • Regular daily cycles • Leaves or petals fold in regular daily cycles • Members of legume family, prayer plants • Turgor movements, and stimuli of light and temperature involved • Controlled bybiological “clock” on approx. 24 hours cycles • Controlled internally Circadian rhythm in prayer plant

30. Plant MovementsTurgor movements • Solar Tracking -leaves often twist on their petioles in response to illumination and become perpendicularly oriented to light source • Blades oriented at right angles to sun • H2O Conservation Movements • Bulliform Cells -special thin-walled cells in leaves of many grasses that lose turgor and cause leaves to roll up or fold during periods of insufficient H2O

31. Plant Movements Leaf of grass folding due to bulliform cells Bulliform cells in rolled leaf

32. Plant Movements • Taxes (Taxic Movement) -movement involving entire plant or reproductive cells • In several groups of plants and fungi, but not in flowering plants • Cell or organism, moves by flagella or cilia toward or away from stimulus • Chemotaxic -chemicals • Sperm in ferns swim toward chemical produced by female reproductive structures • Phototaxic -light • Aerotaxic - O2concentrations

33. Photoperiodism • Photoperiodism -length of day (night) directly related to onset of flowering • Short-day Plants -will not flower unless day length shorter than critical period • Asters, poinsettias, ragweed, sorghums, strawberries • Long-day Plants -will not flower unless periods of light longer than critical period • Beets, larkspur, lettuce, potatoes, spinach, wheat

34. Photoperiodism • Intermediate-day Plants -will not flower if days too short, or too long • Several grasses • Day-neutral Plants -will flower under any day-length, provided minimum amount of light necessary for normal growth • Tropical plants, beans, carnations, cotton, roses, tomatoes • Vegetative activities affected by phototropisms: • Dormancy of buds • Germination of seeds • Prepares plants for seasons

35. Phytochromes and Cryptochromes • Phytochromes -pigments controlling photoperiodism • Pale blue proteinaceous pigments that absorb light • Mostly in meristematic tissues • Two stable forms: • Pr -absorbs red light • Pfr -absorbs far-red light • When either form absorbs light -> converted to other form

36. Phytochromes and Cryptochromes • Phytochromes cont’d. • Play role in other plant responses: • Plant development, changes in plastids, production of anthocyanins, and detection of shading • Cryptochromes -blue, light-sensitive pigments playing role in circadian rhythms and interact with phytochromes to control reactions to light

37. A Flowering Hormone? • Florigen -floral stimulus transported from leaf to apical meristems where flower buds initiated • mRNA of gene, Flowering Locus T (FT), transported from leaves, where photoperiod is perceived, to shoot apical meristem, where transition from vegetative to flowering state occurs

38. Temperature and Growth • Each plant species has optimum temperature for growth and minimum temperature below which growth will not occur • Thermoperiod - optimum night and day temperatures • Optimum temperatures may change with growth stage of plant • Lower night temperatures often result in higher sugar content and in greater root growth • Growth of many field crops roughly proportional to prevailing temperatures

39. Dormancy and Quiescence • Dormancy -period of growth inactivity in seeds, buds, bulbs, and other plant organs even when temperature, water, or day length would typically cause growth • Quiescence -state in which seed cannot germinate unless environmental conditions normally required for growth present • After-ripening – factors control change from dormancy to germination in seeds • Stratification -artificially breaking dormancy

40. Review • Introduction • Nutrients, Vitamins, and Hormones • Hormonal Interactions • Other Hormonal Interactions • Plant Movements • Photoperiodism • Cytochromes and Cryptochromes • A Flowering Hormone? • Temperature and Growth • Dormancy and Quiescence