The retention of photosynthetic activity by senescing chloroplasts of oat leaves

Choe, Hyung T.; Thimann, Kenneth V.

doi:10.1007/bf00387157

Cited by 25 publications

(11 citation statements)

References 19 publications

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“…These experiments were repeated with young, expanding leaves and similar results were obtained. The intact chloroplasts contained no hemoglobin- (6,7), indicating that they contained proteolytic enzymes. It has also been shown that the processing of the precursor of the small subunit of RuBPCase involves a proteolytic cleavage carried out by an intrachloroplastic proteinase (8).…”

Section: -70mentioning

confidence: 98%

Autodigestion in Crude Extracts of Soybean Leaves and Isolated Chloroplasts as a Measure of Proteolytic Activity

Ragster¹,

Chrispeels²

1981

Plant Physiol.

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Two methods of measuring protein breakdown resultiag from self-digeston during incubation in extracts of soybean leaves were examined. The release of free a-amino-nitrogen was measured with ninhydrin, and the disappearance of the large subunit of ribulose bisphosphate carboxylase (RuBPcase) was foDlowed with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Rates of protein breakdown were measured as a function of temperature, pH, and leaf developmental stage and in the presence of various proteinase inhibitors. These treatments had differential effects on apparent proteolysis, depending on the method used. Determination of the ratio of a-amino-nitrogen plus peptide bond-nitrogen to a-amino-nitrogen indicated that the ninhydrin method detected the activity of exopeptidases preferentiaDy. The disappearance of the large subunit of RuBPCase as shown on gels was due primarily to the activity of endopeptidases. The sensitivity of the two types of proteolytic degradation to proteinase inhibitors differed.Determination of temporal changes in proteolytic activity during leaf development showed that total proteolytic activity, measured by either method, increased during leaf expansion and maturation and decreased during senescence. Incubation of intact isolated chloroplasts at 37 C resulted in the breakdown of the large subunit of RuBPcase, although the chloroplasts contained no measurable proteinase activity as determined by the release of a-amino-nitrogen during the incubation. No acid proteinase (pH 4.5) activity was detected in the chloroplasts when hemoglobin was used as a substrate. These results indicate that the proteinases which break down RuBPCase in isolated chloroplasts may not be detectable by conventional assay procedures.Leaf senescence in many plants, and especially in monocarpic crop plants, is accompanied by breakdown of leaf protein and reutilization of the hydrolysis products by the developing seeds (9-11, 21, 26). It has been suggested that the amount of protein which accumulates in the seeds is related to the extent of leaf protein breakdown (1 1, 19). Attempts have been made to correlate leaf protein breakdown with the levels of various proteinases in the leaves and, in some cases, a correlation was found (9,11,26,37), whereas, in others, there appeared to be no relation between proteinase levels and protein breakdown (1,28, 32 (10)(11)(12)23), by the loss of immunochemical determinants (35-37), or by the breakdown of polypeptides as ascertained by SDS-acrylamide gel electrophoresis (33).As part of our study on the role of proteinases in protein breakdown during leaf senescence, we have examined the hydrolysis of the LS of RuBPCase during the autodigestion of crude leaf extracts. Proteolysis was measured by the release of ninhydrinreactive material and the disappearance of the LS of RuBPCase on SDS-polyacrylamide gels. Our results show that the two methods probably measure different complements of proteinases. The discrepancy between the two methods was most obvious in isolated ch...

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Section: -70mentioning

confidence: 98%

Autodigestion in Crude Extracts of Soybean Leaves and Isolated Chloroplasts as a Measure of Proteolytic Activity

Ragster¹,

Chrispeels²

1981

Plant Physiol.

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“…Leaf senescence also results in alterations in the absorption and fluorescence properties of photosynthetic pigments [3,6,19]. Recently a number of studies have been made on the changes of these photosynthetic parameters during senescence of chloroplasts in vitro [11,18]. But few attempts have been made to compare the kinetics of the degradation of chloroplasts during ageing of the organelles in vivo and in vitro.…”

Section: Introductionmentioning

confidence: 99%

Ageing of chloroplasts in vitro ? III. Comparison of the effects of ageing in vitro and senescence on the red absorption band and primary photochemical reactions of sunflower chloroplasts

Panigrahi

Biswal

1983

Photosynth Res

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A comparison of changes in absorption properties and electron transport activities of chloroplasts ageing in vivo and in vitro is made. Chloroplasts from sunflower leaves senescing in vivo during 7 days in dark do not show a blue shift of the red absorption band; in contrast, the shift becomes apparent within 24 h of in vitro ageing of isolated organelles. Photosynthetic activity by chloroplasts is lost much faster during in vitro than in vivo ageing. During in vitro ageing, the rate of degradation of thylakoid membranes as characterised by the shift in the red absorption band and loss in Hill reaction is further accelerated in chloroplasts isolated from dark-induced senescing leaves, suggesting the influence of the in vivo status of the chloroplasts on their in vitro stability.

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“…reported to be pH sensitive (6). We then examined thylakoidal and stromal performance both individually and combined in a reconstituted system fortified with adenine and pyridine nucleotides, Fd, and Pi in order to determine pretreatment-sensitive reactions.…”

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confidence: 99%

Effects of Temperature Pretreatment in the Dark on Photosynthesis of the Intact Spinach Chloroplast

Gibbs²

1988

Plant Physiol.

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Isolated, intact spinach (Spinacia okracea L. var. 'Long Standing Bloomsdale") chloroplasts were heated in the dark and the effect of this treatment on photosynthetic activities was determined at 25°C. Dark incubation of the chloroplasts for 10 minutes at 35°C and pH 8.1 resulted in a 50% decline in CO2 photoassimilation. This decline in photosynthetic performance was dependent upon time, temperature, and medium pH with the optimum effect at acidic pH values. Photosynthetic decline was not observed if MgATP, MgADP, or a mixture of fructose 1,6-bisphosphate, aldolase, and oxaloacetate or ribose 5-phosphate and oxaloacetate was added prior to but not after the temperature pretreatment. A chloroplast preparation reconstituted with thylakoids and stroma from pretreated (35°C, 10 minutes, pH 8.1) intact chloroplasts and supplemented with ferredoxin, ADP, and NADP was photosynthetically competent, indicating that ATP-coupled electron flow and the enzymes comprising the Benson-Calvin cycle remained stable during the dark treatment. In contrast, exposure of isolated thylakoids to 35°C for 10 minutes uncoupled photophosphorylation from NADP and ferricyanide reduction. We propose that the decline of intact chloroplast photosynthesis is the result of a decrease in the content of or a change in the ratios of the adenine nucleotides. Maintenance of an adequate supply of adenine nucleotide is the effect of the externally added MgATP or of chloroplastic respiration of a sugar phosphate.Many studies have been reported on the effect of temperature pretreatment on photosynthetic electron transport and phosphorylation in isolated thylakoidal preparations (13,16, 25, 27), but less attention has been paid to relate these findings to CO2 photoassimilation in the parent chloroplast (7,(28)(29)(30). Of the thylakoidal reactions measured, there appears to be a collective agreement that phosphorylation is the most susceptible to thermal inactivation, followed by PSII and with PSI the most stable. The isolated stromal enzymes that comprise the Benson-Calvin cycle when assayed individually were found to be comparatively stable to high temperature (18, 28, 29). This approach makes evaluation of the temperature-sensitive steps of photosynthesis within the intact chloroplast difficult inasmuch as there is evidence that soluble stromal compounds (sugar, proteins) are able to protect cell structures against heat inactivation (18, 26, 27).We show here a quantitative study on the effects of preheating up to 40°C in the dark on the photosynthesis ofthe intact spinach chloroplast at 25C. The pH of the medium during the pretreatment was varied since the stability of the thylakoidal reactions is 'Supported by National Science Foundation PCM 83-04147. 2Present address: Roche Institute of Molecular Biology, Nutley, NJ 07110.reported to be pH sensitive (6). We then examined thylakoidal and stromal performance both individually and combined in a reconstituted system fortified with adenine and pyridine nucleotides, Fd, and Pi in order to determine...

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The retention of photosynthetic activity by senescing chloroplasts of oat leaves

Cited by 25 publications

References 19 publications

Autodigestion in Crude Extracts of Soybean Leaves and Isolated Chloroplasts as a Measure of Proteolytic Activity

Autodigestion in Crude Extracts of Soybean Leaves and Isolated Chloroplasts as a Measure of Proteolytic Activity

Ageing of chloroplasts in vitro ? III. Comparison of the effects of ageing in vitro and senescence on the red absorption band and primary photochemical reactions of sunflower chloroplasts

Effects of Temperature Pretreatment in the Dark on Photosynthesis of the Intact Spinach Chloroplast

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