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ABSTRACT: Kinetin maintains the protein content of detached leaves, but the reason is not clear. This work attempted to find out whether the effect arises from maintenance of protein synthesis or retardation of protein breakdown. Protein synthesis and degradation in detached Tropaeolum majus leaves were estimated by measuring the incorporation into amino acids and protein of photo-synthetically fixed 14C, and by determining the total amounts of amino acids and protein present in ageing leaves. Protein synthesis in kinetin-treated leaves kept in darkness was higher than in the control. Rough calculation showed, however, that enhancement of protein synthesis by kinetin cannot directly account for the higher protein level found after this treatment. It seems to result from decreased degradation rather than from the maintenance of protein synthesis.
New Phytologist 05/2006; 69(2):355 - 361. · 6.64 Impact Factor
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ABSTRACT: Exposure of cucumber seedlings (Cucumis sativus L.) to chilling temperature resulted in injuries such as increased leakage of cellular materials, loss of water and wilting. In addition, the development of the seedlings after the exposure to chilling was impaired. Abscisic acid applied to the seedlings prior to chilling significantly ameliorated these injuries.
Physiologia Plantarum 04/2006; 38(2):95 - 97. · 3.11 Impact Factor
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ABSTRACT: The possibility that c-phycocyanin serves as a nitrogen source in Spirulina platensis during nitrogen starvation was studied. The following evidence was obtained in support of this idea. 1. Under favourable conditions for growth, c-phycocyanin existed in large excess in the algal cells. 2. When the supply of nitrogen was low, about 30–50% of the c-phycocyanin disappeared without any effect on the maximal growth rate. 3. A culture which was deprived of nitrogen continued to grow unaffectedly for a period, the duration of which depended on the c-phycocyanin content in the cell before nitrogen starvation was initiated. 4. c-phycocyanin was the only nitrogenous compound that was depleted during the course of nitrogen starvation when growth was yet unaffected. 5. When protein synthesis was inhibited either by nitrogen starvation or by methionine sulfoximine (MSO), phycocyanin content began to decline immediately and growth continued at normal rates as long as c-phycocyanin did not decline below 50%. 6. The decrease in c-phycocyanin content during nitrogen starvation was accompanied by an increase in proteolytic activity.
Archives of Microbiology 01/1980; 125(1):143-147. · 1.43 Impact Factor
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ABSTRACT: Two main biliproteins c-phycocyanin and allophycocyanin were identified and characterized in the blue-green alga Spirulina platensis. The specific absorbance, fluorescence maxima, sub-unit make-up and amino acid composition of the biliproteins in Spirulina platensis resemble those reported for other blue-green algae. However, the minimum molecular weights (44,000 for c-phycocyanin and 38,000 for the allophycocyanin) and the specific extinction coefficients (73, and 58 for c-phycocyanin and allophycocyanin respectively) of these biliproteins were different from these values in other blue-green algae.
Archives of Microbiology 01/1979; 120(2):155-159. · 1.43 Impact Factor
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ABSTRACT: The interrelationship between water deficiency and hormonal makeup in plants was investigated in detached leaves of romaine lettuce (Lactuca sativa L. cv. ;Hazera Yellow'). Water stress was imposed by desiccating the leaves for several hours in light or darkness at different air temperatures and relative humidity. In the course of desiccation, a rise in abscisic acid content and a decline in gibberellin and cytokinin activity were observed by gas-liquid chromatography, by both the barley endosperm bioassay and radioimmunoassay and by the soybean callus bioassay. Gibberellin activity began to decline in the stressed leaves before the rise in abscisic acid, the rate of this decline being positively correlated with the rate of increase in leaf water saturation deficit. Recovery from water stress was effected by immersing the leaf petioles in water while exposing the blades to high relative humidity. This resulted in a decrease in leaf water saturation deficit, a reduction in abscisic acid content, and an increase in gibberellin and cytokinin activity.Application of abscisic acid to the leaves caused partial stomatal closure in turgid lettuce leaves, whereas treatment with gibberellic acid and kinetin of such leaves had no effect on the stomatal aperture. In desiccating leaves, however, gibberellic acid and kinetin treatment considerably retarded stomatal closure, thus enhancing the increase in leaf water saturation deficit. These results suggest that the effect of desiccation in changing leaf hormonal make-up, i.e. a rapid increase in abscisic acid and a decrease in both cytokinin and gibberellin activity, is related to a mechanism designed to curtail water loss under conditions inducing water deficiency.
Plant physiology 07/1977; 59(6):1169-73. · 6.53 Impact Factor
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ABSTRACT: This work supports further the thesis that under conditions of water stress, cell water content may supersede hormonal regulation in effecting enzyme activity, thus becoming a regulatory factor in cellular metabolism. Addition of NaCl to the root medium of barley plants (Hordeum vulgare L.) markedly increased leaf RNase activity parallel to an increase of leaf water saturation deficit (WSD). Kinetin and abscisic acid, applied to the salinated plants, also modified RNase activity, as well as leaf-WSD. The familiar pattern of effects of these hormones on leaf RNase as well as leaf chlorophyll content was inverted, kinetin effected a relative increase in RNase activity and a decrease in leaf chlorophyll, whereas abscisic acid effected a relative decrease in RNase activity and maintained chlorophyll content. A close relationship between enzyme activity and leaf WSD became evident when leaf RNase and protease activities in the salinated plants were plotted against leaf WSD. This close relationship was maintained irrespective of the hormonal treatments, which in themselves markedly modified leaf WSD. As predicted, high relative humidity which relived the leaves from salt-induced water stress prevented the salt-induced rise in RNase activity.
Plant physiology 05/1976; 57(4):656-8. · 6.53 Impact Factor
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ABSTRACT: Tobacco plants (Nicotiana rustica L.) were exposed to a period of stress of either mineral deprivation or salination of the root medium. Thereafter the plants were transferred back to the pre-stress growth medium, for study of the pattern of recovery. Abscisic acid (ABA) content and the extent of stomatal opening in leaves of tobacco plants were found to be inversely related. The results support the possibility that the phenomenon know as after-effect of stress may not be exclusive to recovery from water stress, but may be typical of the pattern of plant recovery from the effects of several growth restricting environments. It is suggested that the after-affect results from the delay in resumption of the pre-stress hormonal balance in the plant, particularly with regard to ABA, after termination of the stress.
Planta 12/1975; 129(3):217-219. · 3.00 Impact Factor
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ABSTRACT: Tobacco plants (Nicotiana rustica L.) pre-exposed to leaf dehydration, mineral deprivation, salination, or BO(3) (3-) toxicity exhibited increased resistance to subzero temperature and to reduced oxygen in the root medium. The stressed plants all showed an elevated content of leaf abscisic acid. Upon transfer of mineral deprived and salinated plants to prestress conditions, a decline in leaf abscisic acid content to prestress levels took place together with a loss of the increased resistance to subzero temperature and to deprivation of root oxygen. Treatment with abscisic acid by direct application to the leaves or by addition to the root medium improved leaf resistance to subzero temperature and to deprivation of root oxygen. A common hormone-regulation mechanism involving abscisic acid is suggested for this phenomenon of "cross-adaptation" by which a given stress confers increased resistance to other, apparently unrelated stresses.
Plant physiology 09/1975; 56(2):337-9. · 6.53 Impact Factor
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ABSTRACT: A marked loss of leucine (14)C 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 re-illumination 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.
Plant physiology 05/1975; 55(4):786-90. · 6.53 Impact Factor
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Plant physiology 08/1970; 46(1):169-71. · 6.53 Impact Factor
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ABSTRACT: Thirty six different 3-methyl-5-aryl-2,4-pentadienoic acids and esters were synthesized using the Reformatsky and Wittig reactions. The different geometrical isomers were conveniently separated by the dry column technique. Assignment of configuration of the pentadienoic side chain was based on NMR and UV properties. The biological activities of the aromatic analogs of ABA were determined in four bioassays. Most of the analogs were less active than the natural hormone. Only 3-methyl-5-p-chlorophenyl Δ2-trans, Δ4-trans-pentadienoic acid exhibited high ABA-like activity in all four bioassays.
Phytochemistry 16(8):1143-1151. · 3.35 Impact Factor
