Differing substomatal and chloroplastic CO2 concentrations in water-stressed wheat

Abstract

Gas exchanges of wheat (Triticum aestivum L. cv. Courtot) shoots were measured before and during a water stress. While photosynthesis, transpiration and dark respiration decreased because of the stress, photorespiration increased initially, up to a maximum of 50% above its initial value. The CO2 concentration in the intercellular space was calculated from gas-diffusion resistances, and remained approximately constant before and during the stress. On the other hand, the CO2 concentration in the chloroplast, in the vicinity of Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco), was evaluated from the ratio of CO2 to O2 uptake, using the known kinetic constants of the oxygenation and carboxylation reactions which compete for Rubisco. In the well-watered plants, the calculated chloroplastic concentration was slightly smaller than the substomatal concentration. During water stress, this concentration decreased while the substomatal CO2 concentration remained constant. Hypotheses to explain this difference between substomatal and chloroplastic CO2 concentrations are discussed.

Limitation of photosynthetic activity by CO2 availability in the chloroplasts of oak leaves from different species and during drought

“…In the absence of water stress, the c c /c a ratio was around 0. 35-0.45 (Renou et al, 1990;Tourneux and Peltier, 1994). Similar results have been obtained by Ridolfi and Dreyer (1995) (1996) showed that a calcium deficiency in oak leaves induced a parallel decrease of A and c c .…”

“…Moreover, it has been hypothesized that a high mesophyll resistance may be a discriminating factor between highly productive crops (with low resistances) and less productive species (as, for instance, tree species). It has also been observed that the concentration of CO 2 in the chloroplasts (c c ) decreased during drought stress (Renou et al, 1990;Cornic and Briantais, 1991;Tourneux and Peltier, 1994 where A 1% = net CO 2 assimilation under nonphotorespiratory conditions; R d = nonphotorespiratory respiration; and PFD = incident photosynthetic photon flux density (Genty et al, 1989;Epron et al, 1994;Valentini et al, 1995).…”

“…ii) An analysis of the relative rates of carboxylation and oxygenation of RuBP in the chloroplasts yielded indirect estimates of c c . Rates of oxygenation were computed using either 18 O 2 -enriched air (Renou et al, 1990;Tourneux and Peltier, 1994), or with simultaneous measurements of gas exchange and chlorophyll a fluorescence (Peterson, 1989;Di Marco et al, 1990;Comic and Briantais, 1991).…”

Responses to water stress in an ABA‐unresponsive hybrid poplar (Populus koreana×trichocarpa cv. Peace) III. Consequences for photosynthetic carbon assimilation

“…Recent developments, based on the use of chlorophyll a fluorescence signals to monitor light-dri\en electron fluxes (Genty, Briantais & Baker, 1989), yielded a useful tool to quantify carboxylation and photorespiration rates in situ (Peterson, 1989;Di Marco et al, 1990;Cornic & Briantais, 1991, Valentini et aL, 1995 and to compute COj availability in the chloroplasts (Roupsard, Gross & Dreyer, 1996). Thus a drought-induced decrease in chloroplastic CO, concentration (C(,) was recently reported with apparently constant CO.2 mole fractions in the substomatal spaces (c,) (Renou et al, 1990;Tourneux & Peltier, 1994;Roupsard et al, 1996). These techniques, together with on-line measurements of carhon isotope discrimination in gas exchange systems (Evans et al, 1986;Lloyd et al, 1992) also underlined that CO.â vailabihty in the chloroplasts of well watered plants was much lower than that computed for the substomata!…”

A D1 protein mutáció hatása a kettes fotokémiai rendszer energiahasznosítására eltérő vízellátású növényekben

“…Ezek a mechanizmusok a többletenergiának egy biztonságos módon történő disszipációját teszik lehetővé (Osmond & Grace, 1995). A fotorespiráció (glikolát-ciklus) (Cornic et al, 1989;Renou et al, 1990;Tourneux & Peltier, 1995;Flexas & Medrano, 2002), mely folyamat a C 3 típusú növényekre jellemző, a fotoszintézis egy lehetséges alternatív útjaként jelentős lineáris elektrontranszportot képes fenntartani, így nagymértékben biztosíthatja a többlet gerjesztési energia elvezetését. Az oxigén egyes fotokémiai rendszer (PSI) általi fotoredukciója (Mehler-reakció, Asada, 1999) úgy tűnik, csak elenyésző mértékben járul hozzá az energia-disszipáció folyamatához.…”