chapter 9 lecture outline growth and development copyright © the mcgraw-hill companies, inc....

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


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 HormonesPlant 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.


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


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


• 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


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


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 G2 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


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


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 HormonesOther 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 oscillationso In bent hypocotyl of

bean - Facilitates progress of plant through soil Nutation

Plant MovementsGrowth 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


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


Movements resulting from external stimuli:

• Phototropism - Growth movement toward or away from light– Positive phototropism - Toward light

o Shoots

– Negative phototropism - Away from lighto 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.


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


Movements resulting from external stimuli:• Other Tropisms:

– Thigmotropism - Contact with solid objecto Twining

– Chemotropism - Chemicalso Germination of pollen grains

– Thermotropism - Temperatureo 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 leafo 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 MovementsTurgor 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 MovementsTurgor 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:

– Pr - Absorbs red light– Pfr - 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


Hormonal Interactions

Other Hormonal Interactions

Plant Movements

Photoperiodism

Cytochromes and Cryptochromes

A Flowering Hormone?

Temperature and Growth

Dormancy and Quiescence

chapter 9 lecture outline growth and development copyright © the mcgraw-hill companies, inc....

Documents

stem growth

growth regulators

normal growth

indeterminate growth

cell division

cell membranes

single cell

amino acid