Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh Edition Solomon Berg Martin Chapter 36 Plant Growth and Development

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Plant growth and development are controlled by Internal factors like location of cell in plant body –Causes some genes in cell to be turned off and others to be turned on, thus affecting gene expression during development Environmental factors like changing day length

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Germination and seedling growth

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Germination is the process of seed sprouting Internal factors affecting germination –Maturity of the embryo –Presence or absence of chemical inhibitors –Presence or absence of hard, thick seed coats

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Germination, cont. External environmental factors affecting germination include requirements for –Oxygen –Water –Temperature –Light

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Photoperiodism is any response of plants to the duration and timing of light and dark In many plants, flowering is a photoperiodic response –Short-day plants –Long-day plants –Intermediate-day plants

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Light treatment Short-day plant Long-day plant Photo- periodic responses of short- day and long-day plants

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Photoperiodism, cont. Day neutral plants –Flowering is not affected by photoperiod

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Phytochrome is The photoreceptor in photoperiodism A family of ca. 5 blue-green pigments Each type has two forms named by the wavelength of light they absorb –Pr –Pfr

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Phytochrome, cont. Pfr is the active form, triggering or inhibiting physiological responses such as –Flowering –Shade avoidance –A light requirement for germination

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development This pigment occurs in two forms, Pr and Pfr, and readily converts from one to the other. Red light (660 nm) converts Pr to Pfr, and far-red light (730 nm) converts Pfr to Pr Phytochrome

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Phytochrome, cont. Each type of phytochrome may have physiological functions both –Unique and –Overlapping PhyB seems to exert its influence at all stages of the plant life cycle

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Phytochrome-induced responses Some are rapid and short-term –E.g., changes in membrane properties Others are slower and long term –E.g., regulation of gene transcription

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Absorption of light by phytochrome Triggers one or more signal transduction pathways –In signal transduction, a receptor converts an extracellular signal into an intracellular signal that causes some change in the cell

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Phytochrome signal transduction

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Circadian rhythm A regular period in the growth or activities of a plant or organism –That approximates the 24-hour day –Is reset by the rising and setting of the sun

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Circadian rhythm, cont. Examples are –The opening and closing of stomata –Sleep movements

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Phytochrome and cryptochrome Photoreceptors that sometimes interact to regulate similar responses –Phytochrome strongly absorbs red light –Cryptochrome absorbs blue light

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Plant movements occurring in response to external stimuli Nastic movements –Temporary and reversible –Direction of movement is independent of the direction of the stimulus

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Nastic movements Mimosa pudica: Leaves photographed before being touched (above) and several seconds after being touched (below)

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Nastic movements Pulvini are located in three areas —at the base of each leaflet, at the base of each cluster of leaflets, and at the base of each leaf; Only changes in the pulvini at the base of leaflets are shown

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Plant movements occurring in response to external stimuli, cont. Tropisms –Directional growth responses (i.e., the direction of growth is dependent on the direction of the stimulus)

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Phototropism Response to the direction of light Gravitropism Response to gravity Thigmotropism Response to contact with a solid object Heliotropism Ability of leaves or flowers to track the sun across the sky

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Gravitropism

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Heliotropism

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Plants produce and respond to hormones that Act as highly specific chemical signals Elicit a variety of responses that regulate –Growth –Development

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Hormones Are effective in very small concentrations Functions of some overlap Many physiological activities are regulated by interactions of several at once

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development I General mechanism of action of plant hormones

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Plant hormones bind to specific receptor proteins in or on target cells Binding may trigger production of a second messenger (e.g., Ca 2+ ) –Second messenger may bind to and activate or inactivate certain enzymes

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Plant hormone binding, cont. Activation or inactivation of enzymes may lead to either or both –Altered membrane permeability –Altered gene expression

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Hormones affecting plant growth and development Auxin is involved in –Cell elongation –Tropisms –Apical dominance –Inhibition of axillary buds by the apical meristem

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Isolating auxin from coleoptiles

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Hormones, cont. Auxin, cont. –Fruit development –Stimulating root development on stem cuttings Some synthetic auxins (2,4-D and 2,4,5-T) are selective herbicides

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Phototropism and the unequal distribution of auxin

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Hormones, cont. Gibberellins are involved in –Stem elongation –Flowering –Germination

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Gibberellin and stem elongation

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Hormones, cont. Cytokinins –Promote cell division and differentiation –Delay senescence –Interact with auxin and ethylene in apical dominance –Induce cell division in tissue culture

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Auxin- cytokinin interactions in tissue culture

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Hormones, cont. Ethylene plays a role in –Ripening fruits –Apical dominance –Leaf abscission –Wound response –Thigmomorphogenesis –Senescence

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Hormones, cont. Abscisic acid is an environmental stress hormone involved in stomatal closure caused both –By water stress –In seed dormancy

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Abscisic acid and seed germination Arrows show where some of the kernels have germinated while still on the ear, producing roots

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Brassinolides are Plant steroids Probably involved in aspects of plant growth and development such as –Cell division –Cell elongation

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Salicylic acid Helps defend plants against –Pathogens –Insect pests May bind to a cell receptor to switch on genes to –Fight infection –Promote wound healing

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Salicylic acid, cont. A volatile form of it may serve as an airborne chemical signal from virus-infected plants to healthy ones

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Systemin Is a plant polypeptide with hormonal properties Stimulates a natural defense mechanism in which –Plant produces protease inhibitors to disrupt insect digestion

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Oligosaccharins Are short, branched chains of sugar molecules Have various functions –Inhibit flowering –Stimulate vegetative growth Bind to membrane receptors and alter gene expression

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Jasmonates Affect several plant processes like –Pollen development –Root growth –Fruit ripening –Senescence

Copyright © 2005 Brooks/Cole — Thomson Learning Biology, Seventh EditionCHAPTER 36 Plant Growth and Development Jasmonates, cont. Are produced in response to the presence of –Insect pests –Disease-causing organisms