Control of plant development by limiting factors: A nutritional perspective.

It is postulated that limiting nutritional factors play a major role in the regulation of some aspects of plant development, and can provide an alternative to mechanisms based on the concept of hormonal control. This hypothesis is consistent with experimental evidence of the role of water as a limiting factor in (1) seed maturation and viviparous germination, (2) the elongation and phototropism of hypocotyls and coleoptiles, (3) the NO3--induced germination of dormant seeds, and (4) the release of buds from correlative inhibition. Studies on the influence of nutrition on morphogenesis have shown that the relative amounts of nitrogen and carbohydrate can determine the path of bud development as a shoot or rhizome. There is also evidence that either NO3- or sugar can limit lateral root initiation, and it is postulated that they may influence this process by a combination of osmotic and nutritional effects. The close correlation between environmentally induced developmental responses and the associated changes in the water or nutritional status of the responsive tissues, together with increasing evidence of the role of water and nutrients as transmitted signals and as regulators of gene expression, are in good agreement with their postulated role as limiting factors in the regulation of plant development.