VEGETATIVE GROWTH RESPONSE TO LIGHT AND TEMPERATURE, INTERPRETED BY CARBOHYDRATE-POOL DYNAMICS

Abstract

The growth of plants may be divided into two stages: (1) the supply of carbohydrate from photosynthesis, and (2) the demand of carbohydrate for biosynthesis, leading to structural growth. Normally supply exceeds demand in cool temperatures, while the opposite is true at warm temperatures. To match supply and demand, photosynthesis is inhibited in the cool temperature range and synthesis (growth) is inhibited in the warm temperature range. The signal for the supplydemand imbalance is presumably obtained from the state of the carbohydrate pool (temporary storage), which fluctuates between a maximum level around sunset and a minimum level around dawn. A simple model, that incorporates this presumed mechanism, is presented and used to estimate the response of structural growth and of carbohydrate content to light and temperature in the cool and warm temperature ranges. The model predicts maximum growth rate at an intermediate temperature, which is positively correlated with light level. It also predicts an increase of nonstructural carbohydrate at cool temperatures. Both predictions are in qualitative agreement with observations. The model may be considered as an attempt at a mechanistic explanation of the observed phenomena, but experimental and modelling deficiencies currently restrict its predictions to the general features of the process only.