Partial Restoration of the High Rate of Plastid Pigment Development and the Ultrastructure of Plastids in Detached Water-stressed Wheat Leaves

Abstract

Detached etiolated wheat (Triticumn aestivum L. cv. Chris) leaves accumulated plastid pigments at a high rate, developed chloroplasts with stacked thylakoids, and stored plastid starch when wetted on filter paper in light. A moderate water deficit of -10 bars markedly reduced the accumulation of chlorophyll and carotenoids in the 8-day-old detached leaves during greening. 6-Aminolevulinic acid treatment of stressed leaf segments resulted in slightly increased pigment accumulations but benzyladenine application restored plastid pigment formation in stressed tissue to within 15% of the pigment content of the nonstressed detached leaves. The addition of 6-aminolevulinic acid to benzyladenine-treated stressed leaf segments improved both chlorophyll and carotenoid formation to nearly the amounts found in nonstressed leaf tissue. Stressed leaf sections developed plastids that were small, lacked starch, contained few thylakoids per granum, and possessed dilated thylakoids.Benzyladenine application to the stressed leaf segments did not restore normal plastid stacking but benzyladenine induced the formation of extended intergranal lamellae and stimulated pigment accumulations in both stressed and nonstressed detached leaves. Starch was absent in plastids of benzyladeninetreated leaf sections.Mild water deficits have been shown to impair the formation of plastid pigments (6, 9, 33) and modify chloroplast development (7, 13) in intact leaves of seedlings during greening. An imposed stress of -10 bars reduced Chl and carotenoid accumulations early in the development of chloroplasts (9). Plastids of wheat leaves subjected to a moderate stress were small and contained fewer grana per plastid, fewer thylakoids per granum, and more dilated thylakoids (13) than when there was little or no stress.

PEG-induced osmotic stress in Mentha x piperita L.: Structural features and metabolic responses

“…Studies have reported changes in plastid format (Lechno et al, 1997;Li et al, 2012), destruction of the plastid envelope (Yamane et al, 2003) and altered thylakoid membranes (Paakknonen et al, 1998;Lima et al, 2013) in plants under different stresses. Moreover, Duysen and Freeman (1975) reported that structural changes in plastids caused by osmotic stress led to decreases in the production of chlorophyll, which may influence photosynthetic activity, similar to the results we observed in plants subjected to 100 g L À1 of PEG. The abundance of plastoglobules may be associated with increased oxidative stress (Paakknonen et al, 1998;Austin et al, 2006) and they may act to protect against free radicals (Austin et al, 2006); their number increases when plants are exposed to low water availability (Paakknonen et al, 1998).…”