| Abstract: | Epidermal strips were taken from plants of Commelina communisat opposite phases of an entrained circadian rhythm, at timeswhich corresponded to the middle of the day phase and the middleof the night phase. Earlier observations of much reduced openingin response to external stimuli in the night phase were confirmed. Evidence is now presented that uptake or retention of specificions by the guard cells is affected by the phase of the rhythm.The overt expression of the rhythm was reduced if the epidermiswas presented with potassium iminodiacetate instead of potassiumchloride. Iminodiacetate is a non-absorbable anion, and thisresult suggested that chloride uptake is important for the fullexpression of the rhythm. The use of an anion channel inhibitor(DIDS) gave strong support for this conclusion. Reduced uptakeof chloride would explain an earlier observation that formationof malate is greater during the night phase. When the guard cells were presented with sodium chloride insteadof potassium chloride there was still an overt expression ofthe rhythm, but this was of reduced magnitude. This suggeststhat potassium movements might contribute to the rhythm, andstudies of ionic fluxes using 86Rb as a tracer showed greatereffluxes during the night phase. It is concluded that the circadian rhythm in stomatal openingmay be the result of a varying ability of the guard cells toaccumulate or retain both chloride and potassium ions. Key words: Circadian rhythm, stomatal opening, Commelina communis, potassium and chloride fluxes |
