What is Growth? Increment in biomass Increase in volume Increase in length or area Cell division, expansion and differentiation Fig. 35.18 Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings 1
Both genes and environment affect plant structure 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. 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. Pinus radiata (Monterey pine) California ew Zealand Auxin Responses 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 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 H2 (ribose) Adenine (Adenosine) ATP DA RA AD(P) Cytokinin Responses Cell Division Apical Dominance High Auxin in Shoot Apex High Cytokinin in Root Apex -CH2-C=C-CH2-OH Zeatin (Riboside) CH3 (Ribose) Gradient Between: High Auxin:Cytokinin = Dormant Axillary Buds Low Auxin:Cytokinin = Branch Growth 2
Giberellin Responses Cell Division Fast growth Dwarfism Seed dormancy High ABA Reversed by GA application Synthesis of GA by embryo Abscissic Acid Responses Fruit Ripening Dormancy Maintenance high levels in dormant seed and buds Drought Resistance causes stomatal closure Leaf Abscission Allocation respiration 3
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) e.g. deserts, pastures Seed size compromise % annuals environmental predictability e.g. tropics large seeds shorter dispersal fewer produced, but more competitive small seeds longer dispersal more produced, but less competitive 4
How many versus how big? seedling weight seedling height seed mass How is the seed provisioned for establishment? large versus small reserve carbohydrates how is the seed dispersed? lipids greater caloric content per gram more rapid energy availability 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 how is the seed dispersed? how far is the seed dispersed? 5
How far is the seed dispersed? dispersed versus retained short-distance versus long-distance dispersal 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 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 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 Capsaicin 6
Atriplex California Pinus radiata (Monterey pine) ew 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? Common garden experiment by Clausen, Keck and Heisey A cross-section through California 7
Potentilla glandulosa 8
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. 9