Analysis of spatial variation in CO ₂ uptake within the intact leaf and its significance in interpreting the effects of environmental stress on photosynthesis

Abstract

The responses of CO 2 uptake to environmental variables and to stress effects in vivo have been largely limited to measurements of whole leaves or ‘representative’ portions of the leaf. These responses therefore reflect an average for the photosynthetic cells within a leaf, which may differ in environmental pre-history, stage of development and ontogeny. These differences may also result in variation in responses to stress. Improvements in the resolution and accuracy with which gaseous exchanges can be measured in open and closed systems allow the use of small chambers that facilitate a separation of the contributions made by different parts of the leaf to total CO 2 uptake. In amphistomatous leaves with large internal resistances simultaneous measurements of CO 2 , N 2 O and H 2 O vapour allow separation of the contributions made by the upper and lower mesophyll. These techniques are applied to Zea mays leaves to examine (1) heterogeneity in the responses of CO 2 uptake to light and to internal air-space CO 2 pressure fraction, and (2) heterogeneity in the susceptibility to photoinhibition during chilling.

Changes in the photosynthetic light response curve during leaf development of field grown maize with implications for modelling canopy photosynthesis

“…However, the differential effects of photoinhibition on ~b and Asat, may be partly, or wholly offset by age-related variation in the susceptibility of leaves to photoinhibition (Long et al 1989). The tip region of the maize leaves is known to be most susceptible to photoinhibitory damage because of both its radiation microclimate (Long et al 1989) and age (Ireland et al 1985;Long et al 1989).…”

“…However, the differential effects of photoinhibition on ~b and Asat, may be partly, or wholly offset by age-related variation in the susceptibility of leaves to photoinhibition (Long et al 1989). The tip region of the maize leaves is known to be most susceptible to photoinhibitory damage because of both its radiation microclimate (Long et al 1989) and age (Ireland et al 1985;Long et al 1989). Therefore, while photoinhibition may cause a greater absolute reduction in the quantum yield than light-saturated rates as photosynthesis under natural conditions it is the older leaf tissue that will be predisposed to photoinhibition and for which the present model simulation predicts that photosynthesis will be more sensitive to reductions in Asat than ~, even under moderate light intensities (Fig.…”

“…Developmental stage has been shown to have a marked effect on the extent of chilling damage to photosynthesis, with mature leaves most sensitive to chill-induced photoinhibition (Ireland et al 1985;Long et al 1989), while immature leaves are susceptible to disruption in chloroplast development at low temperatures Stirling et al 1991;Robertson et al 1993). Surprisingly, in view of the known interactions between developmental stage and stress-induced damage to photosynthesis, few workers have quantified the underlying changes in photosynthesis with leaf development under field conditions.…”

Anatomy of non-uniform leaf photosynthesis

“…Since in amphistomatous leaves stomata on both surfaces usually function under natural conditions, the actual drop of Pi from the estimated Pi is much less than the above estimation (Parkhurst et al 1988). However, it is noteworthy that in some leaves such as Zea mays, there are structural barriers which obstruct the diffusion of CO 2 across the leaf (Farquhar and Raschke 1978, Long et al 1989a.…”

Stomatal patchiness in Mediterranean evergreen sclerophylls

“…While evidence of a coupling mechanism between stomatal and mesophyll behavior is lacking, much evidence exists on the inhomogeneous and frequently patchy distribution of stomatal aperture on the leaf surface of many plant species (Molisch 1912;Neger 1912Neger , 1918Ishihara et al 1971;Cruiziat et al 1979;Laisk et al 1980;Spence 1987;Downton et al 1988a, b;Robinson et al 1988;Terashima et al 1988;Ward and Drake 1988;Daley et al 1989;Loreto and Sharkey 1990;Mansfield et al 1990;Patzke 1990) and particularly within stressed leaves (Farquhar et al 1987;Long et al 1989;Sharkey and Seemann 1989). Although nonuniform stomatal closure cannot in general explain the midday depression in A, CE and E with constant Ci, a situation involving pneumatically isolated patches which consist of homogeneously wide-open or closed stomata would be consistent with these observations.…”