Temperature dependence of guard cell respiration and stomatal conductance co-segregate in an F2 population of Pima cotton

In Pima cotton (Gossypium barbadense L.), stomatal conductance shows a strong response to temperature. At high temperature (40˚C), the stomatal conductance of greenhouse- and growth chamber-grown leaves is three and four times higher than that measured at lower temperature (25ºC), respectively. The segregation of stom-atal conductance observed in an F2 population obtained from a cross between a primitive cotton (B368) and a modern Pima line (Pima S-6) increased substantially with temperature in both light and darkness. Furthermore, F2 segregants with high stomatal conductance at high temperature were more sensitive to temperature, showing larger changes in conductance in response to an increase in temperature when compared to F2 segregants having low stomatal conductance. Rates of guard cell respiration measured in enzymatically-cleaned epidermal peels, mechanically isolated from the same F2 plants, showed the same temperature dependence. The temperature-induced respiration enhancement was higher in guard cells with high respiration rates. There were positive correlations between stomatal conductance and guard cell respiration rates, and between stomatal conductance and the sensitivity of respiration to changes in temperature. These results imply that guard cell respiration and stomatal conductance co-segregate in Pima cotton plants, suggesting that guard cell respiration is a component of the sensory transduction pathway controlling stomatal responses to temperature.