Chapter 9 Lecture Outline Growth and Development Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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 a single cell into tissues and organs

Nutrients, Vitamins, and Hormones  Nutrients - Furnish elements and energy for plant growth and maintenance Obtained from air and soil  Vitamins - Organic molecules that participate in catalyzed reactions, mostly by functioning as electron acceptors or donor Synthesized in cell membranes and cytoplasm Required in small amounts for normal growth and development

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  Plant growth response results form signal transduction pathway. Signaling molecule binds to receptor releasing messenger molecule Eventually enzyme is produced, catalyzing reaction and responding to environmental cue

Nutrients, Vitamins, and Hormones  Hormones can have multiple effects.  Hormones act by chemically binding 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

Nutrients, Vitamins, and Hormones Plant Hormones  Auxins Auxin production occurs 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.

Nutrients, Vitamins, and Hormones Plant Hormones  Auxins 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 – 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

Nutrients, Vitamins, and Hormones Plant Hormones  Auxins Movement of auxins from cells where they originate requires energy expenditure. – Movement is polar - Away from source – Move through parenchyma cells surrounding vascular bundles

Nutrients, Vitamins, and Hormones Plant Hormones Natural occurring growth regulators include: o Indoleacetic acid (IAA) o Phenylacetic acid (PAA) o 4-chloroindoleacetic acid (4-chloroIAA) o Indolebutyric acid (IBA) Synthetic growth regulators include: o Naphthalene acetic acid (NAA) o 2,4-dichlorophenoxy acetic acid (2,4-D)  Auxins

Nutrients, Vitamins, and Hormones Plant Hormones  Gibberellins(GA) Named after a fungus that produces it (Gibberella fujikuroi) 110 currently known gibberellins Movement is nonpolar. Most dicots and a 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

Nutrients, Vitamins, and Hormones Plant 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 G 2 phase to mitosis phase. Also play role in: – Cell enlargement – Differentiation of tissues – Development of chloroplasts – Stimulation of cotyledon growth – Delay of aging in leaves

Nutrients, Vitamins, and Hormones Plant Hormones  Abscisic acid (ABA) Has 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 water loss – Interferes with transport or retention of potassium ions in guard cells, causing stomata to close

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

Nutrients, Vitamins, and Hormones Other 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 are highly specific and responses are same in all species.  Brassinosteroids Bind to receptors on cell surfaces Affect apical dominance, gravitropism, seed germination

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 axillary buds, they will begin to grow, even in presence of terminal bud.

Hormonal Interactions  Senescence - Breakdown of cell components and membranes, eventually leading to death of cell Some studies have 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 gibberellins and ABA.

Plant Movements  Growth movements - Result from varying growth rates in different parts of an organ Movements resulting primarily from internal stimuli: – Nutations - Spiraling movements not visible to eye – Nodding movements - Side-to-side oscillations o In bent hypocotyl of bean - Facilitates progress of plant through soil Nutation

Plant Movements Growth Movements  Movements resulting primarily from internal stimuli: 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 Tendril of manroot plant

Plant Movements Growth Movements  Movements resulting from external stimuli: Tropisms - Permanent movements resulting from external stimuli – Growth of a plant toward or away from a stimulus – Can be divided into three phases: o Initial perception - Organ receives greater stimulus on one side. o Transduction - One or more hormones become(s) unevenly distributed across organ. o Asymmetric growth - Result of greater cell elongation on one side

Plant Movements Growth Movements  Movements resulting from external stimuli: Phototropism - Growth movement toward or away from light – Positive phototropism - Toward light o Shoots – Negative phototropism - Away from light o Roots either insensitive or negatively phototrophic. – Auxin migrates away from light, and accumulates in greater amounts on opposite side, promoting greater elongation of cells on dark side.

Plant Movements Growth Movements  Movements resulting from external stimuli: Gravitropism - Growth responses to stimulus of gravity – Primary roots - Positively gravitropic – Shoots - Negatively gravitropic – Gravity may be perceived by amyloplasts in root cap, by proteins on outside of plasma membrane, or by whole protoplast. o Auxin causes cell elongation that produces curvature of root. Negative gravitropism

Plant Movements Growth Movements  Movements resulting from external stimuli: Other Tropisms: – Thigmotropism - Contact with solid object o Twining – Chemotropism - Chemicals o Germination of pollen grains – Thermotropism - Temperature o Horizontal stems when cold in some weeds – Traumotropism - Wounding – Electrotropism - Electricity – Skototropism - Dark – Aerotropism - Oxygen

Plant Movements  Turgor movements - Result from changes in internal water pressures and often initiated by contact with objects outside of plant Leaf movement by pulvini – Pulvini - Special swellings at base of leaf o Sensitive plant, redwood sorrel – Turgor contact movements are not confined to leaves. o Many flowers exhibit movements of stamens and other parts, facilitating pollination. Sensitive plant

Plant Movements Turgor movements  “Sleep” movements - Circadian rhythms Regular daily cycles – Leaves or petals fold in regular daily cycles. o Members of the legume family, prayer plants Turgor movements, and stimuli of light and temperature involved. Controlled by a biological “clock” on approximately 24 hours cycles – Appear to be controlled internally Circadian rhythm in prayer plant

Plant Movements Turgor movements  Solar tracking – Heliotropism-Leaves often twist on their petioles in response to illumination and become perpendicularly oriented to light source. Blades oriented at right angles to sun.  Water 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 water

Plant Movements  Taxes (taxic movement) - Movement that involves 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 o Sperm in ferns swim toward chemical produced by female reproductive structures. – Phototaxic - Light – Aerotaxic - Oxygen concentrations

Photoperiodism  Photoperiodism - Length of day (night) directly related to onset of flowering. Short-day plants - Will not flower unless day length is shorter than a critical period – Asters, poinsettias, ragweed, sorghums, strawberries Long-day plants - Will not flower unless periods of light are longer than a critical period – Beets, larkspur, lettuce, potatoes, spinach, wheat

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 there is 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

Phytochromes and Cryptochromes  Phytochromes - Pigments that control photoperiodism Pale blue proteinaceous pigments that absorb light Mostly in meristematic tissues Two stable forms: – P r - Absorbs red light – P fr - Absorbs far-red light – When either form absorbs light - Converted to other form

Phytochromes and Cryptochromes  Phytochromes Play role in other plant responses: – Plant development, changes in plastids, production of anthocyanins, and detection of shading  Cryptochromes - Blue, light-sensitive pigments that play a role in circadian rhythms and interact with phytochromes to control reactions to light

A Flowering Hormone?  Flowering Locus T (FT)-gene produced by Arabidopsis thaliana associated with flowering When phytochrome senses a short photoperiod, it represses CONSTANS gene When phytochrome senses a long photoperiod, it activates FT FT is transported from leaves, to shoot apical meristem, where it stimulates flowering.

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 is roughly proportional to prevailing temperatures.

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 are present  After-ripening - Factors that control change from dormancy to germination in seeds  Stratification - Artificially breaking dormancy

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