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Heirloom Fava bean Broad Windsor Seeds
Central roles for potassium and sucrose in guard-cell osmoregulation.
by Talbott L. D., Zeiger E. (1996)
L. D. Talbott
Osmoregulation in guard cells of intact, attached Vicia faba leaves grown under growth chamber and greenhouse conditions was studied over a daily light cycle of stomatal movements.
Under both growth conditions guard cells had two distinct osmoregulatory phases. In the first (morning) phase, opening was correlated with K+ uptake and, to a lesser extent, sucrose accumulation. In the second (afternoon) phase, in which apertures were maximal, K+ content declined and sucrose became the dominant osmoticum.
Reopening of the stomata after a CO2-induced closure was accompanied by accumulation of either K+ or sucrose, depending on the time of day, indicating that a single environmental signal may use multiple osmoregulatory pathways.
Malate accumulation, correlated with K+ uptake, was detected under growth chamber but not greenhouse conditions, whereas Cl- was the main K+ counterion in the greenhouse.
These results indicate that guard-cell osmoregulation in the intact leaf depends on at least two different osmoregulatory pathways, K+ transport and sucrose metabolism. Furthermore, the relative importance of the K+ counterions malate and Cl- appears to be environment-dependent.