Changes in K+, Cl− and P contents in stomata of Zea mays leaves exposed to different light and CO2 levels

Abstract

Maize plants (Zea mays L. hybrid INRA 508) were placed under controlled conditions of light and CO2 partial pressure. The K+, Cl− and P contents were then determined by X‐ray microanalysis in the bulbous end of guard cells and in the center of subsidiary cells. The results were interpreted in connection with the stomatal conductance at the time of sampling.In normal air, the K+ and Cl− contents in guard cells only rose from a light threshold of about 300 μmol m−2 s−1 at which stomata were already largely open. At 600 μmol m−2 s−1, the K+ and Cl− levels in guard cells attained values that were 3‐ and 8‐fold greater, respectively, than the values observed in darkness. The K+ and Cl− contents in the subsidiary cells remained quite constant irrespective of the light conditions. CO2‐free air in darkness induced a significant K+ influx towards guard and subsidiary cells. Under light and in CO2‐free air, the K+ and Cl− contents dramatically increased in the guard cells, but slightly decreased in the subsidiary cells. Thus, when subjected to strong light in CO2‐free air, the K+ and Cl− contents in the subsidiary cells were approximately equal to those measured in normal air conditions. In the guard cells, stomatal opening was associated with a marked shift of the Cl−/K+ ratio – from 0.3 for closed stomata to ca 1 for fully open stomata. This could imply a slow change in the nature of the principal counterion accompanying K+ during stomatal opening. The content of P in guard cells appeared, in contrast to that of K+ and Cl−, to be practically independent of stomatal aperture.