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What is Growth? •  Increment in biomass •  Increase in volume •  Increase in length or area •  Cell division, expansion

and differentiation

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 35.18

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A plant’s structure reflects interactions with the environment of two time scales.

– Over the long term, entire plant species have, by natural selection, accumulated morphological adaptations that enhance survival and reproductive success.

– Over the short term, individual plants, even more than individual animals, exhibit structural and physiological responses to their specific environments.

Both genes and environment affect plant structure

The architecture of a plant is a dynamic process, continuously shaped by plant’s genetically directed growth pattern along with fine-tuning to the environment.

California

New Zealand →

Pinus radiata (Monterey pine)

Mechanism of Action a. Bind Receptor Protein Plasma membrane b. Transport into cell c. Activate ATPase in Plasma membrane d. H+ ion extrusion e. Acidify cell wall f. Break hemicellulose-pectin bonds g. Cellulose microfibrils slide apart h. Cell enlarges

Auxin Responses Cell Enlargement •  Shoot Growth

–  Internodes –  Tubers –  Bulbs

•  Root Growth –  Storage Roots –  Adventitious Roots

•  Fruit Growth –  Strawberry - Receptacle enlargement

Apical Dominance •  Auxin:Cytokinin Ratio

–  High - Dormant Axillary Buds –  Low - Axillary Bud Growth

N

N N

N NH2

Adenine

ATP DNA RNA NAD(P)

N

N N

N N-CH2-C=C-CH2-OH

CH3

(Ribose)

(ribose)

Zeatin (Riboside)

(Adenosine)

Cytokinin Responses Cell Division •  Apical Dominance

High Auxin in Shoot Apex High Cytokinin in Root Apex

Gradient Between:

High Auxin:Cytokinin = Dormant Axillary Buds Low Auxin:Cytokinin = Branch Growth

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Giberellin Responses Cell Division •  Fast growth •  Dwarfism Seed dormancy

High ABA Reversed by GA application Synthesis of GA by embryo

Fruit Ripening

Dormancy Maintenance high levels in dormant seed and buds

Drought Resistance causes stomatal closure

Leaf Abscission

Abscissic Acid Responses

Allocation

respiration

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Variations in life history patterns

• annuals • biennials • perennials

• sexual versus asexual reproduction (clones) • frequency of reproduction

iteroparous - reproducing more than once semilparous - reproduce once and die - “big bang”

Age to first reproduction often involves a tradeoff between rapid growth successful establishment

Fecundity schedules in annuals often reflect predictability of the end of the growing season predictable - reproductive delayed until end of season (main meristem transformed into reproductive tissue) unpredictable - reproduction begins as soon as plants have

attained some minimal size (often axillary)

environmental predictability

% annuals

e.g. deserts, pastures

e.g. tropics

large seeds shorter dispersal fewer produced,

but more competitive

small seeds longer dispersal more produced,

but less competitive

Carbon and nutrient allocation patterns in seed production

• how many versus how big ? Seed size compromise

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How many versus how big ?

seedling weight

seedling height

seed mass

Carbon and nutrient allocation patterns in seed production

• how many versus how big ? • how is the seed provisioned for establishment ?

How is the seed provisioned for establishment?

large versus small reserve • carbohydrates • lipids

greater caloric content per gram

more rapid energy availability

Carbon and nutrient allocation patterns in seed production

• how many versus how big ? • how is the seed provisioned for establishment ? • how is the seed dispersed ?

How is the seed dispersed?

• physical dispersal structures such as wings and barbs • attractants such as odors and colors • fleshy fruit attractants • protection from ingestion injury

Carbon and nutrient allocation patterns in seed production

• how many versus how big ? • how is the seed provisioned for establishment ? • how is the seed dispersed ? • how far is the seed dispersed ?

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How far is the seed dispersed?

• dispersed versus retained • short-distance versus long-distance dispersal

Carbon and nutrient allocation patterns in seed production

• how many versus how big ? • how is the seed provisioned for establishment ? • how is the seed dispersed ? • how far is the seed dispersed ? • how is germination delayed following maturation ?

How is germination delayed following germination ?

• mechanical features such as thick seed coats • chemical features such as photoperiod cues

Carbon and nutrient allocation patterns in seed production

• how many versus how big ? • how is the seed provisioned for establishment ? • how is the seed dispersed ? • how far is the seed dispersed ? • how is germination delayed following maturation ? • how is the seed protected from predators and microbes?

How is the seed protected from predation ?

• mechanical features such as barbs and thick seed coat • chemical features such as alkaloids

Morning glory

Capsaicin

Seed dimorphism permits multiple life-history adaptations

Seed polymorphisms occur in a variety of characters and are often produced by different flowers on the same plant

• dispersal structure • adhesive mechanism • elaiosomes • size and shape • seed coat thickness • germination behavior • storage compound provisioning

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Atriplex

California↑ Pinus radiata (Monterey pine)

New Zealand →

How does genetic and environmental variation affect plant growth and physiology?

How does genetic and environmental variation affect plant growth and physiology?

Common garden experiment by Clausen, Keck and Heisey

How does genetic and environmental variation affect plant growth and physiology?

A cross-section through California

Common garden experiment by Clausen, Keck and Heisey

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Potentilla glandulosa

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Common garden experiment by Clausen, Keck and Heisey If developmental plasticity alone: All populations at same site should look identical. If genetic differences alone: All plants from a population should look the same at all locations.