Rapid variations of mesophyll conductance in response to changes in CO₂ concentration around leaves

Abstract

The effects of short-term (minutes) variations of CO2 concentration on mesophyll conductance to CO2 (gm) were evaluated in six different C3 species by simultaneous measurements of gas exchange, chlorophyll fluorescence, online carbon isotope discrimination and a novel curve-fitting method. Depending on the species, gm varied from five-to ninefold, along the range of sub-stomatal CO2 concentrations typically used in photosynthesis CO2-response curves (AN-Ci curves; where AN is the net photosynthetic flux and Ci is the CO2 concentrations in the sub-stomatal cavity), that is, 50 to 1500 mmol CO2 mol -1 air. Although the pattern was species-dependent, gm strongly declined at high Ci, where photosynthesis was not limited by CO2, but by regeneration of ribulose-1,5-bisphosphate or triose phosphate utilization. Moreover, these changes on gm were found to be totally independent of the velocity and direction of the Ci changes. The response of gm to Ci resembled that of stomatal conductance (gs), but kinetic experiments suggested that the response of gm was actually faster than that of gs. Transgenic tobacco plants differing in the amounts of aquaporin NtAQP1 showed different slopes of the gm-Ci response, suggesting a possible role for aquaporins in mediating CO2 responsiveness of gm. The importance of these findings is discussed in terms of their effects on parameterization of AN-Ci curves.

Posttranscriptional Control of Photosynthetic mRNA Decay under Stress Conditions Requires 3′ and 5′ Untranslated Regions and Correlates with Differential Polysome Association in Rice

“…Photosynthesis is among the primary processes that are down-regulated under drought or salinity stress (Chaves, 1991;Munns et al, 2006;Chaves et al, 2009). Down-regulation has been attributed to consequences of decreased CO 2 availability caused by diffusion limitations through the stomata and mesophyll (Flexas et al, 2004(Flexas et al, , 2007, alterations in photosynthetic metabolism (Lawlor and Cornic, 2002), or they can arise as secondary consequences of oxidative stress (Ort, 2001). When the supply of CO 2 to Rubisco is impaired, the photosynthetic apparatus is predisposed to increased energy dissipation and down-regulates photosynthesis (Chaves et al, 2009).…”

Growth Characteristics, Physiological and Metabolic Responses of Teak (Tectona Grandis Linn. f.) Clones Differing in Rejuvenation Capacity Subjected to Drought Stress

“…There is now considerable consensus that reduced CO 2 diffusion from the atmosphere to the site of carboxylation in the leaf, as a result of both stomatal closure and reduced mesophyll conductance, is the main cause of decreased photosynthesis under most water stress conditions (GRASSI and MAGNANI, 2005;FLEXAS et al, 2006FLEXAS et al, , 2007. Stomatal closure leads to lowering of the influx of CO 2 resulting in inactivation of electron transport reactions in leaves (LAWLOR, 2002).…”

Salinity and Water Stress Effects on Biomass Production in Different Arundo donax L. Clones

“…Decreases in the photosynthetic rate under both stresses may be directly associated with a decrease in CO 2 availability related to stomatal closure [10] or due to alterations on photosynthetic metabolism 4 biomass in warm-temperate and semi-arid environments [17,19,25]. Giant reed is a C 3 perennial rhizomatous grass (PRG) belonging to the Poaceae family.…”