Can the growth–differentiation balance hypothesis be tested rigorously?

Abstract

The growth Á /differentiation balance (GDB) hypothesis (as elaborated by Herms and Mattson) provides a framework for examining the impact of a resource gradient on the constant tradeoff between growth and differentiation in cells and tissues of plants, in particular with the consequences for plant defense. The GDB hypothesis, which is the most mature of the hypotheses of plant defensive levels, has not been tested directly. Examination of the requirements for a rigorous test indicates that, like the other hypotheses of plant defense, it cannot be tested directly. Furthermore, rigorously testing the primary derivative hypotheses, while possible, would require considerable methodological effort, on a scale not previously attempted for tests of plant defense, which is likely to discourage researchers, and understandably so, even though the GDB hypothesis warrants methodical investigation due to its potential explanatory power. Although farther removed from the abstract model (i.e. the GDB framework), other derivative hypotheses can be tested, but doing so will require thoughtful consideration and acknowledgement of that. Study of a few carefully chosen systems (i.e. plant species) may provide considerable insight and potentially useful refinement of the GDB framework.The growth Á/differentiation balance (GDB) hypothesis predicts how plants allocate between differentiationrelated processes and growth-related processes in different environmental conditions (Loomis 1932(Loomis , 1953. Growth is the production of roots, stems and leaves, or any process that requires substantial cell division and elongation. In contrast, differentiation is the enhancement of the structure or function of existing cells. Some examples of differentiation-related processes are secondary metabolism, trichome production and thickening of leaf cuticle, all of which can limit herbivory (Herms and Mattson 1992). Allocation to differentiation includes cost of enzymes, transport and storage structures involved in defense. Growth and secondary metabolism can compete for available photosynthate (Wadleigh et al. 1946, Veihmeyer and Hendrickson 1961, Mooney and Chu 1974, and so there is a trade-off for carbon allocation (Lorio 1986).The GDB hypothesis predicts that any factor that slows growth more than it slows photosynthesis can increase the internal resources available for allocation to differentiation (Loomis 1932(Loomis , 1953. For instance, growth is slowed by limitation of nutrients and water, whereas photosynthesis is less sensitive to such shortages (reviewed by Herms and Mattson 1992). Consequently, carbohydrates accumulate beyond growth demands and, thus, may be converted to secondary metabolites, with little additional cost to the plant, at least in terms of soil nutrients. Herms and Mattson's (1992) expansion of the GDB hypothesis provides an explanation for phenotypic variation in concentrations of secondary metabolites in plants and for predicting the consequences of that variation on plant Á/invertebrate herbivore interactions. Furtherm...

Methanol and isoprene emissions from the fast growing tropical pioneer species <i>Vismia guianensis</i> (Aubl.) Pers. (Hypericaceae) in the central Amazon forest

“…However, under stress conditions that diminish Pn but increase isoprene (Is) emissions such as high leaf temperatures, emissions of Is can account for over 50 % of Pn . While investments into Is production remain poorly understood among tropical plants (Harley et al, 2004), the pattern of the photosynthetic carbon allocation has been discussed through carbon-nutrient balance and growth-differentiation balance hypotheses (Stamp, 2004;Glynn et al, 2007;Massad et al, 2012). These hypotheses predict the existence of trade-off between investment in growth versus plant defense.…”

Ambrosia Beetle (Coleoptera: Scolytidae) Species, Flight, and Attack on Living Eastern Cottonwood Trees

“…Fertilization increased plant material available for weevil feeding, but it did not affect induced resistance capabilities. With only two irrigation and fertilization treatments, this study was not designed to test the GDBH (Wilkens 1997, Stamp 2004, nor was that its original purpose (Coleman et al 2004). Although growth losses to weevils were less than gains from fertilization, additional pest management tactics may be required if fertilization is used as a silvicultural treatment.…”

Consequences of light reduction for anti-herbivore defense and bioactivity against mussels in four seaweed species from northern-central Chile

“…Consequently, any environmental stress, as well as the limitation of resources, in a given habitat should reduce the potential of seaweeds to defend themselves against grazing and fouling. In this context, the widely accepted growth-differentiation balance hypothesis predicts that with decreasing light availability for photosynthetically active organisms, their chemically mediated defenses will decrease (Stamp 2004). In general, both hypotheses predict a decrease in the amounts of chemical defenses with decreasing light availability (Cronin 2001, Stamp 2003, 2004.…”

“…Light reduction strongly affects the energy budget of algae, as well as the amount of carbon available for life processes and for the production of defensive metabolites (Cronin & Hay 1996c, Pavia & Toth 2000, Stamp 2004. Assuming that defense is costly, limited energy and resources should result in lower growth rates and reduced defense capabilities.…”

“…Light limitation strongly affects carbon fixation (Stamp 2004 and references therein) and thus seems to lead to a reduction of the defense capabilities of the alga Lessonia nigrescens. This is in line with assumptions from the widely accepted growth-differentiation balance hypothesis, which predicts a decrease in defenses when energy is scarce, e.g.…”