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Senescent Leaves (senescent + leaf)
Selected AbstractsUptake and distribution of root-applied or foliar-applied 65Zn after flowering in aerobic riceANNALS OF APPLIED BIOLOGY, Issue 3 2007W. Jiang Abstract We investigated the uptake and distribution of zinc (Zn) either applied to the roots or to the leaves in rice during grain development. Plants of two aerobic rice cultivars were grown in a nutrient solution with either sufficient Zn or surplus Zn. Root treatment with 1 week,s supply of both 65Zn and unlabelled Zn was started at flowering or 15 days after flowering (DAF). Foliar treatment with 65Zn applied to the flag leaf or to senescent leaves was carried out at flowering. When 65Zn was applied to roots, plants continued to take up Zn after flowering, even beyond 15 DAF, irrespective of cultivar and Zn nutritional status of the plants. During the 1 week of supply of both 65Zn and unlabelled Zn, which either started at flowering or 15 DAF, the absorbed 65Zn was mainly distributed to roots, stem and grains. Little 65Zn was allocated to the leaves. Following a week of 65Zn supply directly after flowering, under sufficient Zn or surplus Zn, the proportions of total 65Zn uptake allocated to the grains continued to change during grain filling (9,33%). This Zn mainly came from the roots but under sufficient Zn supply also from the stem. With 65Zn applied to leaves (either the flag leaf or the lowest senescent leaf), both cultivars showed similar Zn distribution within the plants. About 45,50% of the 65Zn absorbed was transported out of the 65Zn-treated leaf. From that Zn, more than 90% was translocated to other vegetative organs; little was partitioned to the panicle parts and even less to the grains. These results suggest that in rice plants grown under sufficient or surplus Zn supply, most of the Zn accumulated in the grains originates from uptake by roots after flowering and not from Zn remobilisation from leaves. [source] Soil N dynamics in relation to leaf litter quality and soil fertility in north-western Patagonian forestsJOURNAL OF ECOLOGY, Issue 2 2003Patricia Satti Summary 1We examined the relationships among soil N dynamics, soil chemistry and leaf litter quality in 28 forest stands dominated by conifers, woody broad-leaf deciduous species or broad-leaf evergreens. Potential net N mineralization, net nitrification and microbial biomass N were used as indicators of soil N dynamics; pH, organic C, total N, exchangeable cations and extractable P as indicators of soil chemistry and N concentration, lignin concentration, C : N ratio and lignin : N ratio in senescent leaves as indicators of leaf litter quality. N dynamics were assessed in two consecutive years with contrasting precipitation. 2Net N mineralization was lower in stands of the three conifers and one of three broad-leaf evergreen species than in stands of the other six broad-leaf species (40,77 vs. 87,250 mg N kg,1 after 16-week incubations) and higher in the wetter year. 3The proportion of N nitrified was high beneath most species regardless of mineralization rates, soil N fertility and leaf litter quality, and was significantly higher for the wetter year. Ammonium was the predominant form of N in three sites affected by seasonal waterlogging and in two sites the predominant form changed from ammonium in the drier year to nitrate during the wetter year, probably due to differences in soil texture affecting soil moisture. 4Net N mineralization was linearly related to microbial biomass N, implying that the microbial activity per biomass unit was quite similar beneath all species. Constant microbial biomass during the wetter year suggested that as mineralization/nitrification increased, there was a higher potential risk of N losses. 5Although the litter lignin : N ratio allowed differentiation of soil N dynamics between broad-leaf species and conifers, its constant value (23,28) in all broad-leaf species made it a poor predictor of the differences found within this group. Across all sites and between broad-leaf species, soil N dynamics were best explained by a combination of leaf litter lignin and soil chemistry indicators, particularly soil total N for net N mineralization and net nitrification, and soil organic C for microbial biomass N. [source] Endopeptidase Isoenzyme Characteristics in Cucumis sativus Leaves During Dark-induced SenescenceJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 4 2007Peng Zhang Abstract The changes and characteristics of endopeptidase (EP) isoenzymes in cucumber (Cucumis sativus L.) leaves during dark-induced senescence were investigated by activity staining after gradient-polyacrylamide gel electrophoresis (G-PAGE) containing co-polymerized gelatin as substrate. The results showed that both the chlorophyll and the protein contents of leaves were decreased, and the protein degradation was correlated with the increase of proteolytic activity during the course of leaf senescence. Meanwhile, nine cucumber endopeptidases isoenzymes (CEP) with 140, 120, 106, 94, 76, 55, 46, 39 and 35 kDa molecular weights were detected. Four of these, CEP2, 3, 4 and CEP9 appeared all the time, but the changes of the activity were different during incubation. Another four CEPs (CEP5, 6, 7 and CEP8) whose activities increased with dark-induced time were only detected in senescent leaves. Furthermore, the biochemical properties of these nine CEP were also characterized. All the CEPs had high activities from 35 °C to 45 °C, and the optimum temperature was found to be 40 °C. However, the activities of CEPs were not detected below 25 °C or over 60 °C. The activity bands appeared at a wide range of pH from 5.0 to 9.0, but the optimum pH was found at 7.0. No CEPs were detected at pH 4 or pH 10. By inhibition analysis we concluded that CEP2, 3, 4 and CEP9 were serine endopeptidases and CEP6 was a kind of cysteine protease. It is suggested that serine endopeptidases might play a major role in cucumber leaf senescence, and for the first time, six senescence-related endopeptidases (CEP1, 5, 6, 7, 8 and 9) were found in cucumber leaves. [source] SAG2 and SAG12 protein expression in senescing Arabidopsis plantsPHYSIOLOGIA PLANTARUM, Issue 2 2003Vojislava Grbi During leaf senescence, nutrients are remobilized from the senescing tissues to the growing parts of the plant. Many senescence-associated genes (SAGs) were identified based on the induction of their transcripts. However, little is known about the protein expression of the corresponding genes. We have raised antibodies against two Arabidopsis SAGs, SAG2 and SAG12, which encode putative cysteine proteases. The SAG2 antibodies recognized a 29-kDa protein that was abundant in senescing leaves, but was also present at low levels in green tissues. SAG12 antibodies labelled a 38-kDa protein present only in senescent leaves. The protein expression of these SAGs parallels their mRNA expression patterns, indicating that control of SAG2 and SAG12 is at the level of transcription or transcript stability. In addition, we found that SAGs are induced during stem senescence with delayed kinetics of their expression relative to leaf expression, suggesting that age-dependent factor(s) regulating the onset of senescence in Arabidopsis may act in tissue-dependent manner. [source] Photoinhibition and loss of photosystem II reaction centre proteins during senescence of soybean leaves.PHYSIOLOGIA PLANTARUM, Issue 3 2002Enhancement of photoinhibition by the, stay-green' mutation cytG The ,stay-green' mutation cytG in soybean (Glycine max) partially inhibits the degradation of the light-harvesting complex II (LHCII) and the associated chlorophyll during monocarpic senescence. cytG did not alter the breakdown of the cytochrome b6/f complex, thylakoid ATP synthase or components of Photosystem I. In contrast, cytG accelerated the loss of oxygen evolution activity and PSII reaction-centre proteins. These data suggest that LHCII and other thylakoid components are degraded by separate pathways. In leaves induced to senesce by darkness, cytG inhibited the breakdown of LHCII and chlorophyll, but it did not enhance the loss of PSII-core components, indicating that the accelerated degradation of PSII reaction centre proteins in cytG was light dependent. Illumination of mature and senescent leaves of wild-type soybean in the presence of an inhibitor (lincomycin) of chloroplast protein synthesis revealed that senescence per se did not affect the rate of photoinhibition in leaves. Likewise, mature leaves of the cytG mutant did not show more photoinhibition than wild-type leaves. However, in senescent cytG leaves, photoinhibition proceeded more rapidly than in the wild-type. We conclude that the cytG mutation enhances photoinhibition in senescing leaves, and photoinhibition causes the rapid loss of PSII reaction-centre proteins during senescence in cytG. [source] Uptake and distribution of root-applied or foliar-applied 65Zn after flowering in aerobic riceANNALS OF APPLIED BIOLOGY, Issue 3 2007W. Jiang Abstract We investigated the uptake and distribution of zinc (Zn) either applied to the roots or to the leaves in rice during grain development. Plants of two aerobic rice cultivars were grown in a nutrient solution with either sufficient Zn or surplus Zn. Root treatment with 1 week,s supply of both 65Zn and unlabelled Zn was started at flowering or 15 days after flowering (DAF). Foliar treatment with 65Zn applied to the flag leaf or to senescent leaves was carried out at flowering. When 65Zn was applied to roots, plants continued to take up Zn after flowering, even beyond 15 DAF, irrespective of cultivar and Zn nutritional status of the plants. During the 1 week of supply of both 65Zn and unlabelled Zn, which either started at flowering or 15 DAF, the absorbed 65Zn was mainly distributed to roots, stem and grains. Little 65Zn was allocated to the leaves. Following a week of 65Zn supply directly after flowering, under sufficient Zn or surplus Zn, the proportions of total 65Zn uptake allocated to the grains continued to change during grain filling (9,33%). This Zn mainly came from the roots but under sufficient Zn supply also from the stem. With 65Zn applied to leaves (either the flag leaf or the lowest senescent leaf), both cultivars showed similar Zn distribution within the plants. About 45,50% of the 65Zn absorbed was transported out of the 65Zn-treated leaf. From that Zn, more than 90% was translocated to other vegetative organs; little was partitioned to the panicle parts and even less to the grains. These results suggest that in rice plants grown under sufficient or surplus Zn supply, most of the Zn accumulated in the grains originates from uptake by roots after flowering and not from Zn remobilisation from leaves. [source] The effect of plant cytokinin hormones on the production of ethylene, nitric oxide, and protein nitrotyrosine in ageing tobacco leavesBIOFACTORS, Issue 1-4 2006N. Wilhelmová Abstract Transgenic plants with genetically increased or decreased levels of cytokinins were used to investigate the effect of cytokinin level on the production of ethylene, a plant hormone with suggested role in senescence, and the production of nitric oxide, potentially important signalling and regulatory molecule. The production of these gases was followed during the course of leaf development and senescence. The production of ethylene and nitric oxide is under genetic control of genes other than those involved in regulation of senescence. The difference in basic ethylene and NO levels in different tobacco cultivars was higher than their changes in senescence. The results of this study did not indicate a direct link between ethylene production and cytokinin levels. However, there was a decreased production of NO in senescent leaves. Low cytokinins level was associated with increased NO production during leaf development. Protein nitrotyrosine proved to be a better indicator of the reactive nitrogen species than measuring of the NO production. Higher nitrotyrosine concentrations were found in insoluble proteins than in the soluble ones, pointing to membrane proteins as the primary targets of the reactive nitrogen species. In plants with elevated cytokinin levels the content of nitrated proteins decreased both in soluble and insoluble fractions. This finding indicates an antioxidative function of cytokinins against reactive nitrogen species. [source] | ||||||||||