Aging induced changes in photosynthetic electron transport of detached barley leaves

Abstract

Primary leaf segments of 11-day-old seedlings of barley (Hordtum vulgare L. cv IB 65) were floated on distilled water in darkness at 25°C to induce senescence. This stress induced aging brings significant loss in the total content of pigments, proteins and nucleic acids (DNA, RNA) of the leaves and of chloroplasts isolated from the senescing leaves. Of the three macromolecular components, RNA content of theisolated chloroplasts was found most susceptible to stress-induced aging.Loss of DCPIP Hill activity of the isolated chloroplasts could be correlated, in a general way, with the loss of pigments, proteins and nucleic acids of the leaves and chloroplasts isolated from them. However, during the stress period, the ability of different exogenous electron donors like MnCl2 and diphenylcarbazide (DPC) to feed electrons to Photo System II (PS II) was found to be different. MnCl2 supported photoreduction of DCPIP only up to the fourth day, whereas DPC sustained its ability to donate electrons up to the seventh day of incubation of the leaves in darkness. These results suggest a sequential alteration of the sites in the electron-transport chain between H2O and PS II reaction centers of chloroplasts during dark-induced senescence. Kinetin not only prevented the loss of pigments and proteins during senescence, but also preserved the integrity of the electron-transport chain. © 1976 Oxford University Press.