A protein competition model of phenolic allocation

We present a Protein Competition Model (PCM) for predicting total phenolic allocation and concentration in leaves of terrestrial higher plants. In contrast to predictions based on the carbon composition of end products, the PCM is based on metabolic origins of pathway constituents, alternative fates of pathway precursors, and biochemical regulatory mechanisms. Protein and phenolic synthesis compete for the common, limiting resource phenylalanine, so protein and phenolic allocation are inversely correlated. Phenolic allocation can be predicted from the effects of development, inherent growth rate and environment on leaf functions that create competing demands for proteins or phenolics. We present the model general principles. We predict phenolic concentrations as leaves develop; in inherently fast versus slow growing species; and in response to the environment (nitrogen, light, phosphorus, heat shock, herbivore and pathogen injury, and carbon dioxide). Because predictions generally fit observed patterns, we argue that, for phenylalanine-derived phenolics, the mechanistically distinctive PCM complements the Growth Differentiation and Resource Availability Hypotheses, and is a viable, testable alternative to the Carbon Nutrient Balance Hypothesis.