Plant Water Status, Leaf Temperature, and the Calculated Mesophyll Resistance to Carbon Dioxide of Cotton Leaves

Abstract

SummaryThe influence of plant water status and leaf temperature on the mesophyll resistance to C02 transfer for Deltapine cotton leaves was determined under conditions when the C02 supply was limiting photosynthesis. The mesophyll resistance was calculated from C02 response curves in normal air and oxygen-free air, under conditions when air was forced from the abaxial to adaxial side of the leaf to obtain a direct estimate of the CO 2 concentration at the mesophyll cell wall.The mesophyll resistance was about 25 % higher in normal air (rm ~ 4 sec em-I) than oxygen-free air (rm ~ 3 sec em-I), but neither variation in the relative leaf water content from 56 to 92% nor leaf temperature from 22·5 to 38°C affected the calculated mesophyll resistance in the oxygen-free air treatment.Photorespiration was substantially inhibited by the oxygen-free air and was approximately linearly related to leaf temperature in both oxygen-free and normal air treatments. The temperature dependence of the C02 compensation point was explained by the influence of temperature on photorespiration.

Response of Carbon Dioxide Fixation to Water Stress

“…A 2-fold increase in liquid phase resistance was found in tobacco leaves when their relative water content fell from 96 to 86% (24). In cotton leaves, no effect on liquid phase diffusion of CO2 was found even when relative water loss was much greater (29). While this discrepancy may be due to structural differences of the mesophyll of the different species, it is more difficult to account for the discrepancies found in the literature concerning the degree of stress required to inhibit chloroplast activity.…”

“…This was also indicated by other investigators on the basis of indirect evidence (15,29). It should be taken into account that exposure of chloroplasts to water stress within the cytoplasm may not be identical to exposure of isolated chloroplasts to osmotic potential of a solution ( Figs.…”

“…The boundary layer resistance (ra), the stomatal resistance (r,), and the mesophyll resistance (rm) (13,14). The mesophyll resistance includes, besides a resistance to CO2 diffusion in the liquid phase, the photochemical and biochemical resistances which take place inside the chloroplast.It is known that increased plant water stress is followed by a decrease in the rate of photosynthesis (5, analyzing leaf temperature and CO2 and H20 exchange rates, that the decline in photosynthesis at reduced leaf water potentials was due primarily to an increase in stomatal diffusion resistance (2,5,13,29). In some circumstances an increase in mesophyll resistance to CO, diffusion in the liquid phase was implied as a factor controlling photosynthesis under stress conditions (15,24,28).…”

Relation between Mesophyll Surface Area, Photosynthetic Rate, and Illumination Level during Development for Leaves of Plectranthus parviflorus Henckel

“…Ignoring respiration and photorespiration, the net rate of photosynthesis per unit leaf area (JC02) is Jco2 = co2/Rco2 = cco2/(1.56 R,, + Rc02) (1) where cCO2 is the CO2 concentration outside the leaf, and RCO2 is a total resistance for CO2 fixation expressed per unit leaf area (3,4,8,13,15,16,20). As equation 1 indicates, RCO2 has a gaseous phase component in common with the water vapor pathway, the factor 1.56 accounting for the ratio of the diffusion coefficient of water vapor to that of CO2 in air at 20 C (16).…”

Effects of Intercellular Resistances on Estimates of the Intracellular Resistance to Co2 Uptake by Plant Leaves

“…It is in fact a complex term including limitations to photosynthesis caused by the various diffusion and enzymic processes involved in CO 2 assimilation. The intracellular resistance used in this paper is equivalent to the "mesophyll resistance" of Troughton and Slatyer (1969), and is defined by the following equation r't = (cs-f)/P, (1) where r't is the intracellular resistance, Cs is the CO 2 concentration at the cell surface, f is the C02 compensation point, and P is the net photosynthetic rate. This relation only applies under conditions where CO2 alone is limiting photosynthesis.…”