Chapter 39 ~ Plant Responses to Internal and External Signals

1. Chapter 39 ~ Plant Responses to Internal and External Signals

2. Background - Plant Organization • Tissue • parts of each organ e.g. leaf tissues • Dermal – protection • Ground – pith and cortex (photosynthesis, storage, support) • Vascular– xylem, phloem • Cell e.g. Parenchyma-metabolic functions Collenchyma - support Sclerenchyma – support Guard cells

3. Plant Organizationcon’t • Organ Roots – fibrous, taproot Stems – nodes, internodes, axillary bud, terminal bud Leaves – blade, petiole • System ROOT system - roots SHOOT system – stems, leaves and flowers ( combo of stem and leaf) • Organism Angiosperms (monocots, dicots) Gymnosperms

4. Plant Hormones • Plant hormones are a group of naturally occurring, organic substances which influence physiological processes at low concentrations.

5. Hormone vs. vending Machine • Exposing a plant tissue to a hormone compares to putting money in a vending machine. • The coin (hormone) is the same but……. • What you get depends largely on: the target tissues AND the chemical environment these tissues are in

6. Plant Sensitivity –

7. Plant hormones Response mainly of growth, differentiation, development, stomatal movement, Tropism movement toward or away from a stimulus • Phototropism – • Photoperiodism – • gravitropism - • Thigmotropism -

8. Location: tips (meristems) of shoots • Function: stem elongation root growth differentiation (phloem and xylem), branching fruit development apical dominance tropisms (bending)

9. Auxin Horticultural uses: promotion of rooting of cuttings, induces flowering, prevention of preharvest fruit drop, herbicide

10. Cytokinins – stimulate cytokinesis • Location: actively growing roots, embryos, fruits • Function: cell division and growth root growth differentiation germination delay leaf senescence (aging) apical dominance (w/ auxin) Chloroplast development Leaf expansion

11. Cytokinins • Commercial uses: Delay senescence and Maintain greenness. E.g. The treatment of holly for festive decorations enables its harvest many weeks prior to use. E.g. Post-harvest sprays or dips prolong the storage life of green vegetables such as asparagus, broccoli, and celery.

12. Gibberellins • GA3 • Location: meristems of apical buds and roots, young leaves, embryo • Function: germination of seed and bud; stem elongation; leaf growth; flowering (bolting); fruit development; root growth and differentiation

13. Gibberellic Acid (GA) Uses • Enhanced production of seedless grapes. Bigger, more uniformbunches with larger fruit • Prevent orange rind senescence, longerstorage on the tree, extending the marketing period. • Enhancement of flower bud formation ad improvement of fruitquality e.g.cherries. • To substitute for a chilling requirement 1. flower induction for seed production (radish). 2. increased elongation (celery, rhubarb). 3. earlier flower production (artichokes). • Increased malt production - a greater production of beer • Increased sugarcane yield: elongation of sugarcanestalks with no change in the sugar concentration

14. Plant Growth Hormones

15. Ethylene • Gaseous hormone (C2H4) – moves by diffusion • Location: Ethylene is synthesized by most tissues in response to stress. i.e. tissues undergoing senescence or ripening e.g. fruit tissue; stem nodes; aging leaves and flowers • Function: fruit ripening; oppositional to auxin (leaf abscission); promotes/inhibits: growth/development of roots, leaves, and flowers; senescence

16. Ethylene – commercial use • Acceleration and enhancement of uniform fruit ripening and coloration. E.g. field tomatoes picked at a single time by machine, ripening green transported bananas • Promotion of female flower production in e.g. cucumber, squash, melon, so as to increase the number of fruits produced per plant.

17. Abscisic acid • ABA • Location: mature leaves, stems, roots, green fruit, seeds, • Function: inhibits shoot growth; closes stomata during stress; induces storage of protein synthesis in seeds, induces and maintains some aspects of dormancy in seeds. NOTE: ABA does not, however, appear to be the controlling factor in "true dormancy" or "rest," which is dormancy of low temperature or light.

18. Hormones working together • Auxin + Cytokinins = cell division • Auxin + Ethylene = inhibits or promotes leaf and fruit abscission

19. Plant Hormones – Rappin’ • Auxin in the tip • Gibberellins in the seed • Cytokinins cell division and branching in a tree • Ethylene, a gas, for the ripening of fruits • ABA abscisic acid makes your plants go for a “snoose” O.K. I tried!

20. Photoperiodism • Photoperiodism (phytochromes) timing growth and reproduction to the seasons

21. Daily and Seasonal Responses • Circadian rhythm (24 hour periodicity) • Critical night length controls flowering Short-day plant: light period shorter than a critical length to flower (flower in late summer, fall, or winter; poinsettias, chrysanthemums) Long-day plant: light period longer than a critical length to flower (flower in late spring or early summer; spinach, radish, lettuce, iris) Day-neutral plant: unaffected by photoperiod (tomatoes, rice, dandelions)

22. Photoperiodism

24. photoperiodism • During the day In the leaves of a plant-light changes the phytochrome B shape from the Pr form to an alternative Pfr form • At night (more Pr) The phytochrome changes shape back to the old form. The length of night and day are different the concentrations of these forms will be different • Little Pfr – leaf drop dormancy • More Pfr – flowering and growth

25. Phytochromes • Plant protein pigment that measures length of darkness in a photoperiod (red light) • Change form when they absorb light • Pr (red absorbing) 660nm • Pfr (far-red absorbing) 730nm