n Chapter 39 ~ Plant Responses to Internal and External Signals

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

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

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

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

Plant Sensitivity –

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

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

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

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

Cytokinins n 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.

Gibberellins n GA 3 n Location: meristems of apical buds and roots, young leaves, embryo n Function:germination of seed and bud; stem elongation; leaf growth; flowering (bolting); fruit development; root growth and differentiation

Gibberellic Acid (GA) Uses Enhanced production of seedless grapes. Bigger, more uniform bunches with larger fruit Enhanced production of seedless grapes. Bigger, more uniform bunches with larger fruit Prevent orange rind senescence, longer storage on the tree, extending the marketing period. Prevent orange rind senescence, longer storage on the tree, extending the marketing period. Enhancement of flower bud formation ad improvement of fruit quality e.g.cherries. Enhancement of flower bud formation ad improvement of fruit quality e.g.cherries. To substitute for a chilling requirement 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 malt production - a greater production of beer Increased sugarcane yield: elongation of sugarcane stalks with no change in the sugar concentration Increased sugarcane yield: elongation of sugarcane stalks with no change in the sugar concentration

Plant Growth Hormones

Ethylene n Gaseous hormone (C 2 H 4 ) – moves by diffusion n 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 n Function:fruit ripening; oppositional to auxin (leaf abscission); promotes/inhibits: growth/development of roots, leaves, and flowers; senescence

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

Abscisic acid n ABA n Location: mature leaves, stems, roots, green fruit, seeds, n 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.

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

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

Photoperiodism n Photoperiodism (phytochromes) timing growth and reproduction to the seasons

Daily and Seasonal Responses n Circadian rhythm (24 hour periodicity) n 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)

Photoperiodism

photoperiodism n During the day In the leaves of a plant-light changes the phytochrome B shape from the Pr form to an alternative Pfr form n 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 n Little Pfr – leaf drop dormancy n More Pfr – flowering and growth

Phytochromes n Plant protein pigment that measures length of darkness in a photoperiod (red light) n Change form when they absorb light n P r (red absorbing) 660nm n P fr (far-red absorbing) 730nm