The senescence of isolated chloroplasts

Choe, Hyung T.; Thimann, Kenneth V.

doi:10.1007/bf00388760

Cited by 31 publications

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“…However, isolated chloroplasts from the algae Vaucheria litorea in symbiotic association with the sea slug Elysia chlorotica remarkably remain functional for at least 9 months 3,4 . Land plant chloroplast photosystem activity declines within a day after extraction 5,6 , and ex vivo sugar output has been reported for only a few hours 1,7 . Although chloroplasts have mechanisms in place to self-repair photodamaged proteins 8 , as well as a double-stranded circular DNA with a subset of protein-encoding genes involved in photosynthesis 9 , and ribosomal units for protein synthesis and assembly 10 , little is known about engineering these plant organelles for long-term, stable photosynthesis ex vivo.…”

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confidence: 99%

Plant nanobionics approach to augment photosynthesis and biochemical sensing

et al. 2014

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The interface between plant organelles and non-biological nanostructures has the potential to impart organelles with new and enhanced functions. Here, we show that single-walled carbon nanotubes (SWNTs) passively transport and irreversibly localize within the lipid envelope of extracted plant chloroplasts, promote over three times higher photosynthetic activity than that of controls, and enhance maximum electron transport rates. The SWNT-chloroplast assemblies also enable higher rates of leaf electron transport in vivo through a mechanism consistent with augmented photoabsorption. Concentrations of reactive oxygen species inside extracted chloroplasts are significantly suppressed by delivering poly(acrylic acid)-nanoceria or SWNT-nanoceria complexes. Moreover, we show that SWNTs enable near-infrared fluorescence monitoring of nitric oxide both ex vivo and in vivo, thus demonstrating that a plant can be augmented to function as a photonic chemical sensor. Nanobionics engineering of plant function may contribute to the development of biomimetic materials for light-harvesting and biochemical detection with regenerative properties and enhanced e ciency.

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confidence: 99%

Plant nanobionics approach to augment photosynthesis and biochemical sensing

et al. 2014

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“…A brief preliminary account of some of the findings was presented earlier (8), and a note on the photosynthesis of senescing chloroplasts was published elsewhere (9). sec, thoroughly washed with distilled H20, and soaked in distilled H20 for 12 hr with air bubbling through.…”

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The Metabolism of Oat Leaves during Senescence

Choe¹,

Thimann²

1975

Plant Physiol.

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The changes in chlorophyll and protein in senescing chloroplasts isolated from the first leaves of 7-day-old oat (Avena sativa) seedlings have been investigated. In darkness the chlorophyll in these plastids is highly stable, losing only 5 to 10% of its content after 7 days at 26 C. This result contrasts with the behavior of chlorophyll in intact leaves, in which about 80% of the pigment would have disappeared in that time. The protein is less stable than the chlorophyll, though more stable than in the leaf; probably a small amount of protease is present in the plastids. Some protein is also being synthesized in the chloroplasts along with its breakdown; gains of up to 38% in protein and 13% in chlorophyll were observed under different conditions. L-Serine, which actively promotes senescence in the leaf, has only a very slight effect on the chloroplasts, and kinetin antagonizes it. Kinetin also has a small but significant effect in preserving the protein from breakdown. Acid pH somewhat promotes the breakdown, both of chlorophyll and protein. A loss of chlorophyll and protein comparable to that occurring in the senescence of the leaf could not be induced in the chloroplasts by suspending them in malate, in cytoplasmic extract, or in any of a number of enzymes tested alone. Incubation with a mixture of four enzymes was the only treatment which approximated the senescent process in the leaf, causing 34% loss of chlorophyll at pH 5 and 40% loss of protein at pH 7.4, both in 72 hours.In white light, the chlorophyll and the carotenoids, but not the protein, disappear rapidly. This disappearance was shown to be prevented in an atmosphere of nitrogen or in air by a number of reducing agents, of which ascorbic acid was the most effective. It is, therefore, ascribed to photooxidation rather than to normal senescence.The senescence of leaves, which has been studied in a number of laboratories over the years (3, 7, 10, 11, 18, 19, 21-23, 25, 26, 29, 31, 33-39), involves loss of Chl, decrease in carotenoids, enhanced proteolysis, hydrolysis of starch and other polysaccharides, and, in some cases, increase in respiration. In detached leaves, the hydrolyzed products accumulate and may be partly converted to organic acids (21, 23, 37), whereas if the leaves remain on the plant the amino acids, and perhaps 'This work was supported in part by National Science Foundation Grant GB35238 to K. V. T. other products, are re-exported to the stem or base (34). Both proteolysis and Chl loss can be effectively prevented by cytokinins and, in a few cases, also by gibberellins (e.g. 4, 13). The mechanism of this interference with hydrolytic reactions is under active study.In our own laboratory, detailed studies of the senescent process in the detached first leaves of 7-day-old oat seedlings have shown that senescence is largely prevented not only by cytokinins but also by anaerobiosis and by certain inhibitors of protein synthesis, i.e. it is dependent on some synthetic processes, probably formation of enzymes, at the start. There ...

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“…Lubben andKceg-stra 1986). The fact that the chloroplasts senesee very much more rapidly when in the leaf than when isolated (Choe and Thimann 1974) supports this interpretation. However, in the cbloroplasts of barley leaves, the proteases seem to be more aetive than in oats, the acidrange protease of barley being directly active on both the envelope and the thylakoids (Tang and Huffaker 1985).…”

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confidence: 68%

“…Seeondly, Barber and Thompson (I9K0) have shown that liposomes from 7-day-old bean cotyledons allow the outflow of glucose, while similar liposomes from 2-day-oId cotyledons do not. Thirdly, as noted above, the chlo- roplasts of Avcnu contain only traces of active protease and, when isolated from the leaf, their protein is stable for at least 7 days in the dark (Choe and Thimann 1974), so that for proteolysis to take plaee in them would require activation of a proenzyme or. more simply, entry of protease through the chloroplast tiiembrane.…”

Section: The Delay Of Proteolysis In Lightmentioning

confidence: 95%

The control of protein breakdown and synthesis in the senescence of oat leaves

Veierskov¹,

Thimann

1988

Physiologia Plantarum

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During the senescence of detached first leaves of oat (Avena sativa L. cv. Victory) seedlings (grown in continuous light) the protein is hydrolyzed and the proteases increase, but the expected simple relation between these two factors is not always realized. The present experiments examine the timing, the influence of light and darkness and the action of the protein synthesis inhibitors cycloheximide (CHI) and cordycepin. Transfer from dark to light delays the breakdown of both chlorophyll (Chl) and protein, but some residual proteolysis is ascribed to the enzyme initially present. Transfer to CHI resembles transfer to light, while the action of cordyceptin is similar but much weaker. Repeated determinations of the acid protease, which is the most active one and the first to appear, show that this enzyme is formed in the light about as rapidly as in the dark, though with different kinetics. In spite of this there is little proteolysis in light in the first 5 days. One possible explanation of that could be that protein is rapidly resynthesized in light, but treatment with [14C]‐leucine shows that such resynthesis is no faster in light than in darkness. It is therefore concluded that the protease initially does not have access to its substrates and, as a corollary, that the senescence process must be controlled by the gradual impairment of the vacuolar membrane, allowing protease to enter the cytosol and attack the proteins there and in the organelles. This concept is supported by many observations on the timing and on the known changes in membrane permeability during senescence.

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The senescence of isolated chloroplasts

Cited by 31 publications

References 3 publications

Plant nanobionics approach to augment photosynthesis and biochemical sensing

Plant nanobionics approach to augment photosynthesis and biochemical sensing

The Metabolism of Oat Leaves during Senescence

The control of protein breakdown and synthesis in the senescence of oat leaves

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