The Wheat Spikelet—Growth Response to Light and Temperature—Experiment and Hypothesis

Abstract

Effects of temperature and light treatment, applied to whole wheat plants, on the growth rates of individual kernels of central spikelets of the intact ear are examined. The treatments applied are the factorial combinations of 10, 15, 20 and 25 °C, and 100, 50 and 25 per cent light over a 2-week period beginning about 2 weeks after anthesis. The growth-rate ratios, which provide information about possible mechanisms responsible for the dry matter partitioning between kernels within a spikelet, are examined in conjunction with a model. An anatomically-based model of the spikelet is constructed and analysed, and the predicted results are compared with the experimental data. It is suggested that the more distal kernels are increasingly handicapped by pathway resistances, but this effect is partly nullified by the fact that the proximal kernels, which are exposed to higher substrate levels, may be operating on the flatter part of a Michaelis-Menten-like response. Further, it is found necessary to assume that the biochemical rate constants (not the Michaelis-Menten constants) of the kernels fall off towards the more distal kernels.