Changes in Diffusive Conductance and Water Potential of Wheat Plants Before and After Anthesis

Abstract

The relationships between stomatal conductance and leaf water potential, Ψ_L, of wheat plants during drying under controlled conditions showed three phases: (1) no apparent effect until Ψ_L reached about - 1.8 J g^-1; (2) increasing closure as Ψ_L decreased to about - 3 J g^-1; and (3) complete failure to open at lower Ψ_L values. At any given water potential in the first two phases, the stomata were always more open during the post-anthesis stage than during the pre-anthesis stage. Although the relationship between leaf water potential and relative water content differed with growth stage, this was not important in the overall plant response to a water deficit. Over a wide range of Ψ_L, the conductance of the adaxial surface was less variable and more sensitive than that of the abaxial surface. The ratio of these conductances was very variable and followed no discernible pattern. The water potential of spikelets was appreciably higher than that of flag leaves, especially at low values of the latter. Both organs died at about the same water potential (about -4 J g^-1); hence, spikelets survived longer periods of water deficit than leaves. These responses are discussed in respect of sensitivity of grain yield to the stage of growth at which a water deficit is experienced and to the phenomenon of spikelet death. Differences between three cultivars examined were small.