Stomatal Responses to High Temperature in Darkness

Abstract

The effect of a temperature increase from 25 to 35°C on stomatal opening in darkness (‘night opening’) on excised, turgid leaves of Stachytarpheta indica was investigated by microscopic examination of a baxial epidermis fixed in absolute ethanol. An appreciable degree of opening occurred towards the end of a 14-h night at 25°C, and this was substantially enhanced by the temperature increase to 35°C in the dark, which also promoted a marked increase in starch hydrolysis and accumulation of potassium in the guard cells. The degree of temperature-induced night opening was somewhat smaller than that of light-induced opening, and was higher in CO₂-free air than in normal air. 2,4-dinitrophenol (DNP) was effective in arresting stomatal opening and suppressing starch hydrolysis and increase in stomatal potassium. The temperature-induced night opening is related, to a great extent, to the enhancement by high temperature of starch hydrolysis and potassium accumulation in the guard cells, and the inhibitory effect of DNP on stomatal opening is attributed largely to its suppression of these two metabolic processes. The importance of oxidative phosphorylation as a possible source of energy for stomatal opening is briefly discussed.