The inhibition of kohlrabi chloroplast degeneration by kinetin

Section: Resultsmentioning

confidence: 76%

mentioning

confidence: 99%

The Role of Cytokinins in Chloroplast Lamellar Development

Alberte¹,

Naylor²

1975

“…The synthesis of a protein associated with ALA formation has been suggested as a control mechanism of greening beyond the lag phase in plastid development (22). Remy (24) found that proteins associated with photosystem I, photosystem II, and "primary thylakoids" were present in etioplasts but that new proteins involved in the development of the numerous granal formations were synthesized later.…”

Section: Discussionmentioning

confidence: 99%

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

Duysen¹,

Freeman²

1975

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.

“…We have described the course of leucine and UTP incorporation activity in chloroplasts isolated from detached, darkened leaves-a system commonly used by many workers studying leaf senescence (3,(5)(6)(7)(8)(9). Initially, after a 24-hr exposure, the sharp decline in chloroplast protein synthesis potential may be fully restored upon reillumination of the leaves.…”

Section: Resultsmentioning

confidence: 99%

“…These include structural alterations in the volume and shape of the chloroplast (5,6,9) as well as changes in several metabolic activities. The latter are reflected in the well known decline in the contents of RNA, protein, and Chl of leaf cells (3,8).…”

mentioning

confidence: 99%

Initial Stages in the Onset of Senescence in Tobacco Leaves

Vonshak¹,

Richmond²

1975

A marked loss of leucine "4C incorporation occurred in chloroplasts isolated from Nicotiana rustica L. leaves exposed to 24 hours of darkness. This loss is not due to an initial decline in RNA-synthesis potential of the chloroplasts, as was inferred from the extent of UTP incorporation by the isolated chloroplasts. Upon reillumination of the leaves, leucine incorporation by the isolated chloroplasts reverted to its original level within 3 to 4 hours, hence it is doubtful whether the period of 24 hours after detachment should be regarded as the initial phase of leaf senescence.After 48 and 72 hours of darkness, however, complete recovery of the incorporation activity was not achieved by reillumination of the leaves, representing the apparent onset of an irreversible process. Treatment with kinetin, which markedly delayed the symptoms of senescence in these tobacco leaves, did not prevent the dark-induced decline in chloroplast protein synthesis activity. Nor, up to 24 hours of darkness, did it have any effect on the light-induced complete recovery of this synthesis. Nevertheless, after reilluminating kinetin-treated leaves that had been exposed to darkness for 48 and 72 hours, leucine incorporation in the isolated chloroplasts was resumed at a faster rate and reached a higher level than did the untreated controls.Detached leaves maintained in darkness provide a standard system for the study of leaf senescence. Various senescenceinduced modifications in such leaves have been documented.These include structural alterations in the volume and shape of the chloroplast (5, 6, 9) as well as changes in several metabolic activities. The latter are reflected in the well known decline in the contents of RNA, protein, and Chl of leaf cells (3,8). These senescence symptoms become clearly observable usually some 48 hr after leaf detachment. However, Richmond et al. (8) reported that in detached tobacco leaves kept in darkness, a marked change in the protein synthesis potential of the chloroplasts isolated from these leaves takes place within 24 hr.This study aims at a more detailed characterization of the decline in the protein synthesis activity of chloroplast isolated from senescing leaves. MATERIALS AND METHODSLeaves of Nicotiana rustica L. grown in a greenhouse in half-strength Hoagland solution were washed thoroughly under a stream of running tap water and sterilized in a 70% ethanol solution for 10 sec. They were then dipped in 1% calcium hypochlorite for 60 sec and finally washed in sterile H20. The major veins were removed, and the pieces of the blade were placed in a plastic bag, weighed, and cooled in ice for 5 min. The leaf pieces were scissors-cut into an ice-cooled mortar and the chloroplasts were extracted according to Spencer and Wildman (10). Two ml Honda solution (containing 25 mg of Ficoll, 50 mg of Dextran T-40, 250 ,tmoles of sucrose, 100 ,ug of BSA, 42 ,umoles mercaptoethanol fatty-acid poor [Cal-biochem] 100 ,moles of magnesium acetate, 100 ,umoles of manganese acetate) were added for each g of l...