Stomatal and Photosynthetic Limitations to Leaf Growth

Abstract

Leaf area derives from the product of cell number and cell size within lamina tissues. Cell division thus dictates potential size, while cell enlargement is responsible for expression of that potential. These two facets of leaf growth differ in their substrate requirements under well nourished conditions and also show dissimilar sensitivity to environmental stress. Meristematic activity in terminal apices and subsequent emergence of successive leaves seem relatively insensitive to drought and salinity, but do appear limited by photoassimilate supply because CO2 input and radiation level exert strong effects. By contrast, lamina expansion depends more heavily on adequate supplies of water and nutrients, and is especially sensitive to environmental stresses. Impact of adverse conditions on leaf growth can be alleviated by physiological adjustments such as alteration of viscoelastic properties of lamina tissues, regulation of ionic balance and accumulation of organic osmotica. Effective adjustment becomes manifest as turgor maintenance, continuity of leaf growth and sustained gas exchange. This necessitates finely tuned water relations and draws upon energy and substrate of recent photosynthetic origin. Alleviation of drought and salinity stress is thus subject to stomatal and photosynthetic limitations.