Interaction of Growth Regulators in the Senescence of Nasturtium Leaf Disks

Beevers, Leonard; Guernsey, Frances S.

doi:10.1038/214941a0

Cited by 35 publications

(10 citation statements)

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“…In the present study kinetin and especially 6-benzylaminopurine markedly retarded senescence in Rume.r leaf discs. It thus appears that the senescence of leaf discs which respond to gibberellin can in most cases also be retarded by cytokinins ' (2,5,10).…”

Section: Resultsmentioning

confidence: 99%

Control of Senescence in Rumex Leaf Discs by Gibberellic Acid

Goldthwaite

Laetsch

1968

Plant Physiol.

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Abstract. The kinetics of chlorophyll and protein decomposition and the effect of gibberellic acid (GA) were examined in senescing leaf discs of Rumex crispus and R. obtusifolius. Loss of Rumex total chlorophyll proceeds at ia s9low rate for about 2 days followed by a period of rapid logarithmic decline. Chlorophyll b is lost at a slightly faster rate than chlorophyll a during senescence in discs as well as in situ. GA causes a complete cessation of net chlorophyll and protein degradation for several days in Rumex, in contrast to the incomplete senescence inhibition generally observed with cytokinins. GA is fully effective even when added at the middle of the logarithmic phase of chlorophyll loss. Senescence inhibition by GA is apparen,tly gradually reversed upon GA removal. The cytokinins, kinetin and 6.benzylaminopurine, were also effective in Rumex leaf discs, indicating that 'the senescence retarding effect was not restricted to the gibberellins. ResultsThe time course of chlorophyll and protein loss is illustrated in figure 1. The loss of chlorophyll alwa-s shows a distinct lag phase during whllicl total chlorophyll decreases at a rate of less thin 5 % per day. After this time chlorophyll loss proceeds at a rapid pace until more than 80 % of the initial amount is degraded. Chlorophyll loss durlin this period follows a logarithmic decline. The decay of chlorophyll a and b follows a similar patterln except for the following: a more rapid drop in chlorophyll b during the lag phase; and a less rapid decrease in b toward the end of the period of chlorophyll loss.. The slightly greater rate of chlorophyll b loss during the log phase leads to an increase in the chlorophyll a :b ratio during senescence (from 32-4.6 in this case). A relativelv faster chlorophyll b decline was also measured in R. crispus leaves yellowing on the plant. 1S55www.plantphysiol.org on May 12, 2018 -Published by Downloaded from

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Section: Resultsmentioning

confidence: 99%

Control of Senescence in Rumex Leaf Discs by Gibberellic Acid

Goldthwaite

Laetsch

1968

Plant Physiol.

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“…Application of the cytokinin kinetin has little effect on the senescence of Taraxacum leaves but the process is strongly inhibited by gibberellins (GAs; Fletcher & Osborne, 1966). In Tropaeolum and Rumex leaves, GAs and cytokinins are both effective in retarding senescence (Beevers & Guernsey, 1967;Manos & Goldthwaite, 1975). As Tropaeolum leaves senesce, their GA content decreases steadily (Chin & Beevers, 1970).…”

Section: Plant Grozcth Regulators (A) Cytokininsmentioning

confidence: 99%

Gene expression during leaf senescence

1994

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SUMMARY Leaf senescence is a hiphly‐controlled sequence of events comprising the final stage of development. Cells remain viable during the process and new gene expression is required. There is some similarity between senescence in plants and programmed cell death in animals. In this review, different classes of senescence‐related genes are defined and progress towards isolating such genes is reported. A range of internal and external factors which appear to cause leaf senescence is considered and various models for the mechanism of senescence‐ initiation are described. The current understanding of senescence at the wrganelle and molecular levels is presented. Finally, same ideas are mooted as to why senescence occurs and why it should be studied further.

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“…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.…”

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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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Interaction of Growth Regulators in the Senescence of Nasturtium Leaf Disks

Cited by 35 publications

References 17 publications

Control of Senescence in Rumex Leaf Discs by Gibberellic Acid

Control of Senescence in Rumex Leaf Discs by Gibberellic Acid

Gene expression during leaf senescence

The Metabolism of Oat Leaves during Senescence

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