• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.2 no.1
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• pp.37-48
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• 1998

Effect of plant hormones on the leaf senescence of mung bean (Phaseolus radiatus) was investigated by measuring the changes of reducing sugar contents and invertase isozyme activities in detached leaves treated with NAA, $GA_3$ or BA. During dark-induced senescence, reducing sugar contents in the detached leaves increased temporarily at 4 d, thereafter decreased rapidly and reached minimum values within 7-14 d. The pattern of soluble acid invertase activity in the senescing leaves kept in the dark was similar to that of reducing sugar accumulation, whereas the activities of alkaline and extracellular invertases were not significantly changed during leaf senescence. Therefore, these results suggest that soluble acid invertase, but not alkaline and extracellular invertases, induces the accumulation of reducing sugar during leaf senescence of mung bean plants. Exogenous NAA application had little or no effect in the increase of soluble acid invertase activity during dark-induced senescence compared to the control. However, exogenous applications of $GA_3$ and BA led to the increase of soluble acid invertase activity in the senescing leaves. Particularly, BA application was very effective in enhancing the activity of soluble acid invertase as well as in delaying chlorophyll breakdown during dark-induced senescence. These results suggest, therefore, that BA regulates the activity of soluble acid invertase, which leads to the accumulation of reducing sugar, and the stability of photosynthetic apparatus to delay leaf senescence.

• Journal of Environmental Science International
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• v.2 no.1
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• pp.37-48
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• 1993

Effect of plant hormones on the leaf senescence of mung bean (Phseoln radiatus) was investigated by measuring the changes of reducing sugar contents and invertase isozyme activities in detached leaves treated with NAA, $GA_3$ or BA. During dark-induced senescence, reducing sugar contents in the detached leaves increased temporarily at 4 6, thereafter decreased rapidly and reached minimum values within 7-14 6. The pattern of soluble acid invertase activity in the senescing leaves kept in the dark was similar to that of reducing sugar accumulation, whereas the activities of alkaline and extracellular invertases were not significantly changed during leaf senescence. Therefore, these results suggest that soluble acid invertase, but not alkaline and extracellular invertases, induces the accumulation of reducing sugar during leaf senescence of Rung bean plants. Exogenous NAA application had little or no effect In the increase of soluble acid invertase activity during dark-induced senescence compared to the control. However, exogenous applications of $GA_3$ and BA led to the increase of soluble acid invertase activity in the senescing leaves. Particularly, BA application was very effective In enhancing the activity of soluble acid invertase as well as in delaying chlorophyll breakdown during dark-induced senescence. These results suggest, therefore, that BA regulates the activity of soluble acid invertase, which leads to the accumulation of reducing sugar, and the stability of photosynthetic apparatus to delay leaf senescence.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.41 no.5
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• pp.563-568
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• 1996

This experiment was conducted to obtain basic information of biochemical changes in the process of senescence by measuring the total RNA, protein, protease activity and electrophoretic pattern of protein in tobacco plant. The content of soluble protein increased by 15 days after leaf emergence and its level was not changed from 15 to 35 days after leaf emergence. The content of total RNA showed a maximum value at 15 days after leaf emergence and then decreased rapidly until 30 days after leaf emergence. The activity of protease of neutral fraction was higher than that of acidic fraction and rapidly increased up to the end of senescence after 50 days after leaf emergence. According to the analysis of electrophoresis, polypeptide band of 61kd was developed after 35 days after leaf emergence and increased by the end of senescence.

• Journal of the Korean Society of Tobacco Science
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• v.17 no.1
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• pp.20-26
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• 1995

This study was carried out to obtain the basic data which include the change of the photosynthetic rate and protein content according to growth stage in the process of senescence of tobacco plant The photosynthetic rate was the maximum with 26.31$\mu$mol.CO2/m2.sec and stomatal resistance was the minimum with 0.2552cm/sec at 15th days after leaf emergence. However, after 50 days the photosynthesis was very little occurred. During leaf developments the number of chloroplast was increased and reached at the maximum at 25th days after emergence of leaf, thereafter, it was decreased gradually. The content of protein increased continuously and showed the highest value at 15th days after leaf emergence. The degradation rate of soluble protein was more rapid than that of insoluble protein at early stage of senescence. The range of decrement in the insoluble protein was low at late stage of senescence. The content of Rubisco, the key enzyme of photoamthesis, corresponded to about 50% of soluble protein and reached to the maximum at 150 days after leaf emergence. As the senescence progressed, the content of large subunit(UV) of Rubisco showed a tendency to decrease more rapidly than that of small subunit(SSU). The total amount of amino acids was the highest at 15th days after leaf emergence.

• Molecules and Cells
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• v.43 no.7
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• pp.645-661
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• 2020

Leaf senescence is a developmental process by which a plant actively remobilizes nutrients from aged and photosynthetically inefficient leaves to young growing ones by disassembling organelles and degrading macromolecules. Senescence is accelerated by age and environmental stresses such as prolonged darkness. Phytochrome B (phyB) inhibits leaf senescence by inhibiting phytochrome-interacting factor 4 (PIF4) and PIF5 in prolonged darkness. However, it remains unknown whether phyB mediates the temperature signal that regulates leaf senescence. We found the light-activated form of phyB (Pfr) remains active at least four days after a transfer to darkness at 20℃ but is inactivated more rapidly at 28℃. This faster inactivation of Pfr further increases PIF4 protein levels at the higher ambient temperature. In addition, PIF4 mRNA levels rise faster after the transfer to darkness at high ambient temperature via a mechanism that depends on ELF3 but not phyB. Increased PIF4 protein then binds to the ORE1 promoter and activates its expression together with ABA and ethylene signaling, accelerating leaf senescence at high ambient temperature. Our results support a role for the phy-PIF signaling module in integrating not only light signaling but also temperature signaling in the regulation of leaf senescence.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.36 no.2
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• pp.166-173
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• 1991

In order to determine the relationships between the rates of leaf senescence and photosynthate translocation during the grain filling periods in barley, field experiments were conducted through 1989/1990 crop year. Thirty barley varieties and lines having different leaf senescence were used for the experiments. Varieties differed significantly in the rate of leaf senescence and rate of grain filling. The rate of leaf senescence at early (10-20days after heading) and late period (20-30days after heading) during of grain filling were positively correlated with the rate of grain filling in same period, respectively. But the rate of leaf senescence at 10-20 days after heading negatively correlated with the rate of grain filling during the whole grain filling period (10-35 days after heading). Whereas, the rate of leaf senescence at late period was positively associated with the rate of grain filling during the whole grain filling period. Rates of grain filling at the late and whole periods have positively influence on grain weight(r=0.62**～-0.93**), but rate of leaf senescence at early period and duration of grain filling negatively correlated with the grain weight (r=-0.33～ -0.15). The patterns of leaf senescence index for the varieties tested were grouped by four. Among these patterns, the most ideal pattern was IV type.

• Journal of Plant Biology
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• v.31 no.2
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• pp.155-164
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• 1988

The rapid senescence of detached Chinese cabbage leaf discs in darkness is first manifested by a sharp rise in malondialdehyde content (indicated by distruption of membrane structure), then by a rise in peroxidase activity and a decrease in catalase activity, and ultimately by chlorophyll degradation. These changes in parameters besides the catalase activity during senescence were delayed by application of spermidine. Especially, 10-4M spermidine almost completely arrested chlorophyll degradation after incubaton over 5 days. Spermidine reduced the amount of ethylene produced by senescing leaf discs. Additionally, it also reduced IAA-induced ethylene production. Calcium ion (1mM, 10mM) supplied together with the spermidine diminished the spermidine action, indicating probable involvement of an initial ionic attachment mechanism. These results suggest that spermidine can be used as an anti-senescence agent for plants and that this agent may stabilize membrane structure through interaction with the negatively charged loci on the membrane and exert the influence during senescence.

• BMB Reports
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• v.52 no.11
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• pp.653-658
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• 2019

MYB-type transcription factors (TFs) play important roles in plant growth and development, and in the rapid responses to unfavorable environmental conditions. We recently reported the isolation and characterization of a rice (Oryza sativa) MYB TF, OsMYB102, which is involved in the regulation of leaf senescence by downregulating abscisic acid (ABA) biosynthesis and the downstream signaling response. Based on the similarities of their sequences and expression patterns, OsMYB102 appears to be a homolog of the Arabidopsis thaliana AtMYB44 TF. Since AtMYB44 is a key regulator of leaf senescence and abiotic stress responses, it is important to examine whether AtMYB44 homologs in other plants also act similarly. Here, we generated transgenic Arabidopsis plants expressing OsMYB102 (OsMYB102-OX). The OsMYB102-OX plants showed a delayed senescence phenotype during dark incubation and were more susceptible to salt and drought stresses, considerably similar to Arabidopsis plants overexpressing AtMYB44. Real-time quantitative PCR (RT-qPCR) revealed that, in addition to known senescence-associated genes, genes encoding the ABA catabolic enzymes AtCYP707A3 and AtCYP707A4 were also significantly upregulated in OsMYB102-OX, leading to a significant decrease in ABA accumulation. Furthermore, protoplast transient expression and chromatin immunoprecipitation assays revealed that OsMYB102 directly activated AtCYP707A3 expression. Based on our findings, it is probable that the regulatory functions of AtMYB44 homologs in plants are highly conserved and they have vital roles in leaf senescence and the abiotic stress responses.

• Plant Biotechnology Reports
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• v.3 no.4
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• pp.285-292
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• 2009

Zoysiagrass (Zoysia japonica) is one of the important turfgrass species. Extending green period of zoysiagrass via delaying leaf senescence will make this species have more potential in the turfgrass industry. In this study, we found that zoysiagrass seedlings treated with $GA_3$ could delay the leaf senescence induced by darkness. To study expression of genes responsive to staying green in zoysiagrass, suppression subtractive hybridization (SSH) was used to identify differentially expressed genes between non-$non-GA_3-treated$ and $GA_3-treated$ seedlings subjected to darkness. A total of 307 ESTs were generated, of which 226 ESTs clustered into 54 contigs and 81 were singlets. Differentially expressed genes selected by subtractions were classified into six categories according to their putative functions generated by BLAST analysis. Expression of five selected genes, Met, SAM, V-ATPase, Cry (Cryptochrome gene), and An (diphthine synthase gene) were examined by RT-PCR and Real-time PCR. Both RT-PCR and Real-time PCR results demonstrated that the differential expressions of these genes were attributable to delaying senescence by exogenously applied gibberellic acid. This is the first genome-wide study of senescence in a species of turfgrass.

• Journal of Plant Biology
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• v.31 no.3
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• pp.197-203
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• 1988

The rates of photorespiration and total CO2 fixation depending on leaf ages of spinach (Spinacia oleracea L.) were investigated. Metabolic rates of glycolate and glyoxylate in isolated peroxisomes were also measured. The rate of photorespiration and total CO2 fixation ability increased with the maturing of leaf, but decreased with senescence. Activities of enzymes involved in the peroxisomal photorespiratory pathway such as catalase, glycolate oxidase, NADH-glyoxylate reductase and glutamate-glyoxylate transaminase were highest in the mature leaf, but also decreased with aging of leaf. Glutamate-glyxolate transaminase activity significantly decreased with senescence, especially. the metabolic rate of glycolate was observed to be lower than that of glyoxylate in isolated peroxisomes. Glycolate seemed to be metabolized mainly to glycine, however, it also oxidized to CO2 when glycolate was supplied as a substrate for glycine synthesis instead of glyoxylate. The conversion rates of glycolate and glyxylate into CO2 increased with the senescence of leaves.