The Dilemma of Plants: To Grow or Defend

Abstract

Physiological and ecological constraints play key roles in the evolution of plant growth patterns, especially in relation to defenses against herbivores. Phenotypic and life history theories are unified within the growth-differentiation balance (GDB) framework, forming an integrated system of theories explaining and predicting patterns of plant defense and competitive interactions in ecological and evolutionary time. Plant activity at the cellular level can be classified as growth (cell division and enlargement) of differentiation (chemical and morphological changes leading to cell maturation and specialization). The GDB hypothesis of plant defense is premised upon a physiological trade-off between growth and differentiation processes. The trade-off between growth and defense exists because secondary metabolism and structural reinforcement are physiologically constrained in dividing and enlarging cells, and because they divert resources from the production of new leaf area. Hence the dilemma of plants: They must grow fast enough to compete, yet maintain the defenses necessary to survive in the presence of pathogens and herbivores. The physiological trade-off between growth and differentiation processes interacts with herbivory and plant-plant competition to manifest itself as a genetic trade-off between growth and defense in the evolution of plant life history strategies. Evolutionary theories of plant defense are reviewed. We also extend a standard growth rate model by separating its ecological and evolutionary components, andformalizing the role of competition in the evolution of plant defense. We conclude with a conceptual model of the evolution of plant defense in which plant physiological trade-offs interact with the abiotic environment, competition and herbivory. theory ofplant defense has not kept pace. The complexity of the subject has hindered the development of a synthetic framework, because any comprehensive treatment of plant defense theory must transcend both the disciplines and the levels of biological organiza

CONTENTS OF SOLUBLE, CELL-WALL-BOUND AND EXUDED PHLOROTANNINS IN THE BROWN ALGA Fucus vesiculosus, WITH IMPLICATIONS ON THEIR ECOLOGICAL FUNCTIONS

“…The amount of exudation was not affected by nutrient shortage. Since a shortage of nutrients may slow the growth rate and increase the amount of secondary metabolites (Herms and Mattson, 1992) our result suggests that a diminished need of phlorotannins for cell-wall construction would not lead to an increase in their exudation. The amount of exudation may be relatively independent of the growth rate, for instance if exudation also takes place in the old, nongrowing thallus that comprises a major part of the algal biomass.…”

“…Resource-based hypotheses assume that under conditions of good nutrient availability, the allocation of carbon will shift from the production of secondary metabolites to growth (e.g., Bryant et al, 1983;Herms and Mattson, 1992). Often, negative correlations have been found between the contents of available nutrients and the production of soluble phenolic compounds, both in terrestrial plants (reviewed by Herms and Mattson, 1992) and brown algae, although much spatial and temporal variation in this relationship exists (e.g., Yates and Peckol, 1993;Steinberg, 1995;Peckol et al, 1996;Pavia and Toth, 2000b). Variation in the contents of soluble phlorotannins has also been found among different parts of algae.…”

Do Elevated Temperature and CO2 Generally Have Counteracting Effects on Phenolic Phytochemistry of Boreal Trees?

“…Although the effects of elevated atmospheric CO 2 on plant physiological processes has long been studied, the combined effects of elevated temperature and CO 2 are only poorly known. The growth-differentiation balance model of plant development suggests elevated CO 2 may generally increase carbon partitioning to secondary metabolites like phenyl propanoids because it typically increases plant source strength (rates of photosynthate accumulation) more than sink strength (Herms and Mattson, 1992;Mattson et al, 2005). However, the effects of elevated temperature are much less predictable because it is not fully obvious how that will simultaneously influence both source and sink processes and thus the crucial source-sink carbon balance over plant development.…”

“…If plant sink (growth) processes are more sensitive to ameliorative changes in temperature than is photosynthesis (Mattson and Haack, 1987a,b;Herms and Mattson, 1992), then the plant's source-sink balance may generally decline with rising temperatures because sink demands will outpace source supplies. This could lead to reduced carbon partitioning to facultative secondary metabolism.…”

A comparison of plants and animals in their responses to risk of consumption

“…Plants simultaneously acquire different resources, mate, and also defend. While they certainly encounter tradeoffs among these various activities [58,59], their redundant construction allows them to accomplish more tasks simultaneously than animals.…”