Patro Lichita, Mohapatra Pranab Kishor, Biswal Udaya Chand, Biswal Basanti
Laboratory of Biophysics, Biochemistry and Molecular Biology, School of Life Sciences, Sambalpur University, Jyoti Vihar, Burla 768019, Odisha, India.
Laboratory of Biophysics, Biochemistry and Molecular Biology, School of Life Sciences, Sambalpur University, Jyoti Vihar, Burla 768019, Odisha, India; Department of Chemistry, CV Raman College of Engineering, Bidyanagar, Mahura, Janla, Bhubaneswar 752054, Odisha, India.
J Photochem Photobiol B. 2014 Aug;137:49-54. doi: 10.1016/j.jphotobiol.2014.03.018. Epub 2014 Apr 2.
The physiology of loss of photosynthetic production of sugar and the consequent cellular sugar reprogramming during senescence of leaves experiencing environmental stress largely remains unclear. We have shown that leaf senescence in Arabidopsis thaliana causes a significant reduction in the rate of oxygen evolution and net photosynthetic rate (Pn). The decline in photosynthesis is further aggravated by dehydration. During dehydration, primary photochemical reaction of thylakoids and net photosynthesis decrease in parallel with the increase in water deficit. Senescence induced loss in photosynthesis is accompanied by a significant increase in the activity of cell wall hydrolyzing enzyme such as β-glucosidase associated with cell wall catabolism. The activity of this enzyme is further enhanced when the senescing leaves experience dehydration stress. It is possible that both senescence and stress separately or in combination result in the loss in photosynthesis which could be a signal for an enhancement in the activity of β-glucosidase that breaks down cell wall polysaccharides to sugar to sustain respiration for metabolic activities of plants experiencing stress. Thus dehydration response of cell wall hydrolases of senescing leaves is considered as plants' strategy to have cell wall polysaccharides as an alternative energy source for completion of energy requiring senescence process, stress survival and maintenance of recovery potential of energy deficit cells in the background of loss in photosynthesis. Withdrawal of stress (rehydration) distinctly exhibits recovery of photosynthesis and suppression of enzyme activity. Retention of the signaling for sugar reprogramming through breakdown of cell wall polysaccharides in the senescing leaves exposed to severe drought stress suggests that senescing leaves like mature ones possess potential for stress recovery. The precise mechanism of stress adaptation of senescing leaves is yet to be known. A significant accumulation of anthocyanin and flavonoids may be an indicator of stress adaptation of senescing leaves. In addition, stress induced enhancement of nonphotochemical quenching (NPQ), a stress protection provision in green plants, also suggests the potential of the leaves to develop adaptational mechanism to counter the dehydration stress.
在经历环境胁迫的叶片衰老过程中，光合产糖量损失的生理机制以及随之而来的细胞糖重编程在很大程度上仍不清楚。我们已经表明，拟南芥叶片衰老会导致氧气释放速率和净光合速率（Pn）显著降低。脱水会进一步加剧光合作用的下降。在脱水过程中，类囊体的初级光化学反应和净光合作用随着水分亏缺的增加而平行下降。衰老诱导的光合作用损失伴随着细胞壁水解酶（如与细胞壁分解代谢相关的β-葡萄糖苷酶）活性的显著增加。当衰老叶片遭受脱水胁迫时，这种酶的活性会进一步增强。衰老和胁迫单独或共同作用都可能导致光合作用的损失，这可能是一种信号，促使β-葡萄糖苷酶活性增强，该酶将细胞壁多糖分解为糖，以维持经历胁迫的植物代谢活动的呼吸作用。因此，衰老叶片细胞壁水解酶的脱水反应被认为是植物的一种策略，即在光合作用损失的背景下，将细胞壁多糖作为替代能源，以完成需要能量的衰老过程、应对胁迫存活以及维持能量亏缺细胞的恢复潜力。去除胁迫（复水）明显表现出光合作用的恢复和酶活性的抑制。在遭受严重干旱胁迫的衰老叶片中，通过细胞壁多糖分解进行糖重编程的信号保留表明，衰老叶片与成熟叶片一样具有胁迫恢复的潜力。衰老叶片胁迫适应的确切机制尚不清楚。花青素和类黄酮的显著积累可能是衰老叶片胁迫适应的一个指标。此外，胁迫诱导的非光化学猝灭（NPQ）增强，这是绿色植物的一种胁迫保护机制，也表明叶片具有发展适应机制以应对脱水胁迫的潜力。
