Ultrastructural Changes of Chloroplasts in Attached and Detached, Aging Primary Wheat Leaves

Abstract

Degradation of chloroplasts is shown in mesophyll cells of primary leaves of wheat. The sequence of ultrastructural changes in chloroplasts of naturally senescing leaves is compared with that of detached, aging leaves. In chloroplasts of naturally senescing leaves, the first indications of aging are the appearance of osmiophilic globuli and reorientation of the thylakoidal system. The membranes of the grana and intergrana lamellae then become distended and later dissociate into distinct vesicles. Concurrent with these membrane changes, osmiophilic globuli increase in size and number, and the stroma breaks down. Finally, the chloroplast envelope ruptures and plastid contents disperse throughout the cell's interior. In chloroplasts of mesophyll cells in detached, aging leaves, initial changes also include appearance of osmiophilic globuli, but later stages of chloroplast degradation are different. The chloroplast envelope ruptures before the lamellae break down. Swelling of grana and intergrana lamellae is not pronounced and, additionally, the thylakoidal system degenerates without forming vesicles or numerous osmiophilic globuli. These differences in the sequence of chloroplast degradation indicate that naturally senescing leaves rather than detached, aging leaves should be used in studies of chloroplast senescence.

Dismantling of Arabidopsis thaliana mesophyll cell chloroplasts during natural leaf senescence

“…3D. Similar loose folds were observed in dark-induced artificial senescence in detached wheat leaves (Hurkman 1979). TEM micrographs of Zone 1 tissue are shown in Fig.…”

“…There have been some reports suggesting that chloroplasts are brought into the vacuole, where they are degraded (Wittenbach et al 1982; Minamikawa et al 2001), but other studies indicate that chloroplasts are dismantled internally, with a progressive loss in electron transport and Rubisco activity (Woolhouse 1984). Ultrastructural studies show persisting chloroplasts near the periphery of the cell, but the tonoplast is often ruptured, and it is not possible to determine if the chloroplast is outside of the vacuole (Hurkman 1979; Thomson & Platt-Aloia 1987). …”

“…Accumulation of plastoglobuli in chloroplasts of senescent leaves is observed in transmission electron micrographs (Barton 1966; Freeman et al 1978; Hurkman 1979). Tomographic analysis indicates that plastoglobuli remain attached to thylakoid membranes, where they function in lipid biosynthesis and storage (Austin et al 2006).…”

Leaf senescence and nutrient remobilisation in barley and wheat

“…1995). When ultrastructural changes in chloroplasts were compared between attached and detached ageing primary foliage leaves of wheat, distinct differences in the sequence of events were observed (Hurkman 1979). While in attached leaves the envelope ruptures after degradation of thylakoids, in detached leaves the envelope was observed to rupture before thylakoids were degraded.…”

Electron Microscopic Studies of Spruce Needles in Connection with the Occurrence of Novel Forest Decline

“…There is strong evidence that swelling of the thylakoids in general and specifically in our case are a basic stress response. This symptom was observed after treatment with ozone (ATHANASIOUS 1980, MIYAKE et al 1984, NOx (WELLBURN et al 1972), and SO2 (WELLBURN et al 1972, MALHOTRA 1976, in senescent plants (HURKMAN 1979, HUDAK 1981, TAGEEVA et al 1981, and under water stress conditions (FELLOWS and BOYER 1976).…”