Chapter 39 ~Chapter 39 ~ Plant Responses to Internal Plant Responses to Internal and External Signalsand External Signals

Background - Plant Organization Cell Cell e.g. Parenchyma-metabolic functionse.g. Parenchyma-metabolic functionsCollenchyma - supportCollenchyma - supportSclerenchyma – supportSclerenchyma – supportGuard cells Guard cells

Tissue Tissue parts of each organ e.g. leaf tissuesparts of each organ e.g. leaf tissuesDermalDermal – – protectionprotection

GroundGround – pith – pith and cortex (photosynthesis, and cortex (photosynthesis, storage, support)storage, support)

VascularVascular – xylem, phloem– xylem, phloem

Plant Organizationcon’t OrganOrganRoots – fibrous, taprootRoots – fibrous, taprootStems – nodes, internodes, axillary bud, Stems – nodes, internodes, axillary bud,

terminal budterminal budLeaves – blade, petiole Leaves – blade, petiole

SystemSystemROOT system - rootsROOT system - rootsSHOOT system – stems, leaves and flowers SHOOT system – stems, leaves and flowers

( combo of stem and leaf)( combo of stem and leaf)

OrganismOrganismAngiosperms (monocots, dicots)Angiosperms (monocots, dicots)GymnospermsGymnosperms

Plant Hormones

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

Hormone vs. vending Machine Exposing a plant tissue Exposing a plant tissue

to a hormone compares to a hormone compares to putting money in a to putting money in a vending machine. vending machine.

The coin (hormone) is The coin (hormone) is the same but…….the same but…….

What you get depends What you get depends largely on: largely on: the target the target tissues tissues AND AND the the chemical environment chemical environment these tissues are in these tissues are in

Plant Sensitivity –

Plant hormonesResponseResponsemainly of growth, mainly of growth,

differentiation, development, differentiation, development, stomatal movement, stomatal movement,

Tropism Tropism movement toward or movement toward or

away from a stimulusaway from a stimulus Phototropism –Phototropism – Photoperiodism – Photoperiodism – gravitropism - gravitropism - Thigmotropism Thigmotropism - -

Location:Location: tips (meristems) tips (meristems) of shootsof shoots

Function:Function: stem elongationstem elongationroot growth root growth differentiation differentiation (phloem and xylem)(phloem and xylem), , branching branching fruit development fruit development apical dominance apical dominance tropisms (bending)tropisms (bending)

Auxin

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

Cytokinins – stimulate cytokinesis Location:Location: actively growing roots, embryos, fruits actively growing roots, embryos, fruits Function:Function: cell division and growthcell division and growthroot growthroot growthdifferentiation differentiation germination germination delay leaf senescence (aging)delay leaf senescence (aging)apical dominance (w/ auxin)apical dominance (w/ auxin)Chloroplast developmentChloroplast developmentLeaf expansionLeaf expansion

Cytokinins Commercial uses: Commercial uses: Delay senescence andDelay senescence andMaintain greenness. Maintain greenness. E.g. The treatment of holly E.g. The treatment of holly for festive decorations for festive decorations enables its harvest many enables its harvest many weeks prior to use. weeks prior to use. E.g. Post-harvest sprays or dips prolong the storage life of E.g. Post-harvest sprays or dips prolong the storage life of

green vegetables such as asparagus, broccoli, and celery.green vegetables such as asparagus, broccoli, and celery.

Gibberellins GAGA33 Location:Location: meristems of apical buds and roots, meristems of apical buds and roots,

young leaves, embryoyoung leaves, embryo Function:Function: germination of seed and bud; stem germination of seed and bud; stem

elongation; leaf growth; flowering (bolting); elongation; leaf growth; flowering (bolting); fruit development; root growth and differentiationfruit development; root growth and differentiation

Gibberellic Acid (GA) Uses Enhanced production of seedless grapes. Bigger, Enhanced production of seedless grapes. Bigger,

more uniformmore uniform bunches with larger fruit bunches with larger fruit Prevent orange rind senescence, longerPrevent orange rind senescence, longer storage on storage on

the tree, extending the marketing period.the tree, extending the marketing period. Enhancement of flower bud formation ad Enhancement of flower bud formation ad

improvement of fruitimprovement of fruit quality e.g.cherries.quality e.g.cherries. To substitute for a chilling requirementTo substitute for a chilling requirement1. flower induction for seed production (radish).1. flower induction for seed production (radish). 2. increased elongation (celery, rhubarb).2. increased elongation (celery, rhubarb). 3. earlier flower production (artichokes).3. earlier flower production (artichokes). Increased malt production - a greater production of Increased malt production - a greater production of

beer beer Increased sugarcane yield: elongation of sugarcaneIncreased sugarcane yield: elongation of sugarcane

stalks with no change in the sugar concentrationstalks with no change in the sugar concentration

Plant Growth Hormones

Ethylene

Gaseous hormone (CGaseous hormone (C22HH44) – moves by diffusion) – moves by diffusion Location:Location: Ethylene is synthesized by most tissues Ethylene is synthesized by most tissues

in response to stress. i.e. tissues undergoing in response to stress. i.e. tissues undergoing senescence or ripening e.g. fruit tissue; stem nodes; senescence or ripening e.g. fruit tissue; stem nodes; aging leaves and flowersaging leaves and flowers

Function:Function: fruit ripening; oppositional to auxin (leaf fruit ripening; oppositional to auxin (leaf abscission); promotes/inhibits: growth/development abscission); promotes/inhibits: growth/development of roots, leaves, and flowers; senescence of roots, leaves, and flowers; senescence

Ethylene – commercial use Acceleration and enhancement of uniform Acceleration and enhancement of uniform

fruit ripening and coloration. E.g. field fruit ripening and coloration. E.g. field tomatoes picked at a single time by tomatoes picked at a single time by machine, ripening green transported machine, ripening green transported bananasbananas

Promotion of female flower production in e.g. Promotion of female flower production in e.g. cucumber, squash, melon, so as to increase the cucumber, squash, melon, so as to increase the number of fruits produced per plant. number of fruits produced per plant.

Abscisic acid

ABA ABA Location:Location: mature leaves, stems, roots, green fruit, seeds, mature leaves, stems, roots, green fruit, seeds, Function:Function: inhibits shoot growth; closes stomata during inhibits shoot growth; closes stomata during

stress; induces storage of protein synthesis in seeds, stress; induces storage of protein synthesis in seeds, induces and maintains some aspects of dormancy in seeds. induces and maintains some aspects of dormancy in seeds.

NOTE: ABA does NOTE: ABA does not, not, however, appear to be the however, appear to be the controlling factor in "true dormancy" or "rest," which is controlling factor in "true dormancy" or "rest," which is dormancy of low temperature or light. dormancy of low temperature or light.

Hormones working together

Auxin + Cytokinins = cell divisionAuxin + Cytokinins = cell division Auxin + Ethylene = inhibits or promotes Auxin + Ethylene = inhibits or promotes

leaf and fruit abscissionleaf and fruit abscission

Plant Hormones – Rappin’

Auxin in the tipAuxin in the tip Gibberellins in the seedGibberellins in the seed Cytokinins cell division and branching in a Cytokinins cell division and branching in a

treetree Ethylene, a gas, for the ripening of fruitsEthylene, a gas, for the ripening of fruits ABA abscisic acid makes your plants go for ABA abscisic acid makes your plants go for

a “snoose”a “snoose”

O.K. I tried!

Photoperiodism PhotoperiodismPhotoperiodism (phytochromes) timing (phytochromes) timing

growth and reproduction to the seasonsgrowth and reproduction to the seasons

Daily and Seasonal Responses Circadian rhythmCircadian rhythm (24 hour periodicity) (24 hour periodicity) Critical night lengthCritical night length controls flowering controls floweringShort-day plantShort-day plant: light period shorter than a critical length to flower (flower : light period shorter than a critical length to flower (flower

in late summer, fall, or winter; poinsettias, chrysanthemums)in late summer, fall, or winter; poinsettias, chrysanthemums)Long-day plantLong-day plant: light period longer than a critical length to flower (flower : light period longer than a critical length to flower (flower

in late spring or early summer; spinach, radish, lettuce, iris)in late spring or early summer; spinach, radish, lettuce, iris)Day-neutral plantDay-neutral plant: unaffected by photoperiod (tomatoes, rice, dandelions): unaffected by photoperiod (tomatoes, rice, dandelions)

Photoperiodism

photoperiodism During the dayDuring the dayIn the leaves of a plant-light changes the phytochrome B In the leaves of a plant-light changes the phytochrome B

shape from the Pr form to an alternative Pfr formshape from the Pr form to an alternative Pfr form At night (more Pr)At night (more Pr)The phytochrome changes shape back to the old form. The The phytochrome changes shape back to the old form. The

length of night and day are different the concentrations of length of night and day are different the concentrations of these forms will be differentthese forms will be different

Little Pfr – leaf drop dormancyLittle Pfr – leaf drop dormancy More Pfr – flowering and growthMore Pfr – flowering and growth

Phytochromes

Plant protein pigment Plant protein pigment that measures length of that measures length of darkness in a darkness in a photoperiod (red light)photoperiod (red light)

Change form when they Change form when they absorb lightabsorb light

PPrr (red absorbing) 660nm (red absorbing) 660nm PPfrfr (far-red absorbing) (far-red absorbing)

730nm730nm