Leaf Growth Under Water-Limited Conditions
François Tardieu
Abstract
Leaf growth is one of the most sensitive processes in plants affected by water deficit, because a reduction in leaf expansion rate usually occurs before any reduction in photosynthesis (Boyer, 1970; Saab and Sharp, 1989) or in growth of other plant organs (Westgate and Boyer, 1985; Saab et al., 1995). Reduction in leaf growth rate occurs in response to both air- and soilwater deficits (Frensch, 1997; Ben Haj Salah and Tardieu, 1997; Serpe and Matthews, 2000). It is an adaptive process that contributes to the avoidance of cell-water stress by mechanisms operating on two timescales, On short timescales, reduction in leaf area has a similar role to stomatal closure, which is to reduce the water flow through the plant, thereby flattening the gradient of water potential between the soil and the leaves. This avoids deleterious leaf water potential in leaves. On longer timescales a reduced leaf area saves soil water for later stages of plant development via a reduction in transpiration. Several genetic manipulations are based on this strategy, and they increase plant survival under water deficit. For instance, Arcibidopsis plants that overexpress a gene involved in the synthesis of abscisic acid (ABA) stay green longer and die after control plants (Iuchi et al., 2001). This is probably linked to an overproduction of ABA, which has a reducing effect on leaf area and stomatal conductance and therefore on transpiration. The same sequence of events allows tomato plants, which overexpress the transcriptional activator C-repeat binding factor 1 (CBF1), to stay green longer than wild-type plants (Hsieh et al., 2002).