Degeneration of leaf cells resulting from starvation after excision. I. Electron microscopic observations

Ragetli, H. W. J.; Weintraub, M.; Lo, Esther

doi:10.1139/b70-281

Cited by 35 publications

(16 citation statements)

References 15 publications

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“…Various studies suggest that chloroplasts 74 and nonchlorophyllcontaining plastids engulf portions of the cytoplasm. [75][76][77][78] According to the interpretion of Ragetli et al 74 their data showed chloroplasts sending out a protrusion that swirls around a portion of the cytoplasm, then encloses this cytoplasmic portion as it merges with the main plastid body again.…”

Section: Macroautophagymentioning

confidence: 99%

“…[75][76][77][78] According to the interpretion of Ragetli et al 74 their data showed chloroplasts sending out a protrusion that swirls around a portion of the cytoplasm, then encloses this cytoplasmic portion as it merges with the main plastid body again. An alternative interpretation suggested that the two outer membranes of the plastids invaginate (move inwards), thereby forming a space inside the plastid that is contiguous with the cytoplasm.…”

Section: Macroautophagymentioning

confidence: 99%

“…78 Whatever the correct interpretation, structures in the sequestered portion of the cytoplasm included at least ribosomes, membranes, and vesicles 74,78 and possibly also mitochondria. 74 In Dendrobium petal cells the opening of the plastid interior to the cytoplasm is approximately circular and less than 0.2 μm in diameter, which is small compared with the size of the plastid. 78 It is not yet known whether this opening closes.…”

Section: Macroautophagymentioning

confidence: 99%

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Ultrastructure of autophagy in plant cells

2013

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Section: Macroautophagymentioning

confidence: 99%

Section: Macroautophagymentioning

confidence: 99%

Section: Macroautophagymentioning

confidence: 99%

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Ultrastructure of autophagy in plant cells

2013

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Section: Introductionmentioning

confidence: 99%

“…Several observations suggest, however, that the two situations are different. These include the apparent inability of the detached leaf to synthesize particular species of RNA (15) as well as differences in patterns of nuclease accumulation (33) and ultrastructural breakdown (25).In spite of the likely requirement for respiratory energy by the integrated process of leaf senescence, data are lacking on the respiratory metabolism of both attached and detached yellowing leaves. The present paper examines the esterification of '2P, into respiratory metabolites by discs from such leaves, using as a point of reference discs from nonsenescent green leaves.…”

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Metabolic Regulation in the Senescing Tobacco Leaf

Macnicol

Young²,

Biale³

1973

Plant Physiol.

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Changes in phosphate metabolism were explored in discs from tobacco (Nicotiana tabacum) leaves of three contrasting types: green leaves which were fully expanded and attached to the plant, leaves which had yellowed following excision and dark starvation, and leaves which had yellowed while attached to the plant. 2,4-Dinitrophenol at 10-5M stimulated the respiration rate of discs from green and yellow-detached leaves only slightly, but markedly stimulated that of discs from yellow-attached leaves. Following a 10-minute uptake period the incorporation of 'P-orthophosphate into phosphate esters and lipids of discs from yellow-detached leaves was resistant to 2,,4-dinitrophenol, whereas in discs from green and yellowattached leaves it was inhibited by 2, 4-dinitrophenol. (16,20) but is also subject to "triggering" by external and internal signals such as shading (12), photoperiodic regime (14), and changed sink-source relationships (27).Although the over-all process of leaf yellowing is catabolic, as witnessed by the loss of chlorophyll, protein, and RNA (e.g., 11, 13, 32), there is evidence for synthesis of amides (34), pigments and lipids (10), and enzymes (7,19). Any remobilization of leaf components will require a supply of ATP. It is, in fact, well established that the dark respiration rate usually rises during yellowing (1,6,13). These considerations suggest an important interaction between the orderly events of senescence and the control of energy generation.The more rapid and pronounced nature of the changes in the detached leaf, coupled with their broad similarity to those in the attached leaf, has led to the widespread assumption (e.g., 19, 32) that the detached leaf can serve as an experimental model for senescence in the attached leaf. Several observations suggest, however, that the two situations are different. These include the apparent inability of the detached leaf to synthesize particular species of RNA (15) as well as differences in patterns of nuclease accumulation (33) and ultrastructural breakdown (25).In spite of the likely requirement for respiratory energy by the integrated process of leaf senescence, data are lacking on the respiratory metabolism of both attached and detached yellowing leaves. The present paper examines the esterification of '2P, into respiratory metabolites by discs from such leaves, using as a point of reference discs from nonsenescent green leaves. The uncoupler DNP is employed to gauge to what extent ATP formation is coupled to respiratory electron transport. The results reveal marked differences between yellow and green leaves, on the one hand, and between attached and detached yellow leaves, on the other, which are indicative of altered metabolic control. A companion paper (18) reports changes in endogenous metabolite levels in the yellowing detached leaf during its "climacteric rise" in respiration and their interpretation in terms of control points.MATERIALS AND METHODS Plant Materials. Tobacco plants (Nicotiana tabacumn L., cv. Virginia Gold) were grown in ...

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

Hurkman

1979

American J of Botany

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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.

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Degeneration of leaf cells resulting from starvation after excision. I. Electron microscopic observations

Cited by 35 publications

References 15 publications

Ultrastructure of autophagy in plant cells

Ultrastructure of autophagy in plant cells

Metabolic Regulation in the Senescing Tobacco Leaf

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

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