采后中上部烟叶衰老过程中呼吸代谢特征研究OA

[Objective]The present paper aimed to explore the relationship between senescence characteristics and respiratory metabolic path-ways of postharvest tobacco leaves.[Method]The middle and upper tobacco leaves of K326 were used as test materials to carry out the camer-a obscura test.The color changes of tobacco leaves during senescence were observed,and the production rate of superoxide anion radical(O2-·),the contents of hydrogen peroxide(H2O2)and malondialdehyde(MDA)were determined.Additionally,the activities of key en-zymes involved in glycolysis(EMP),the tricarboxylic acid cycle(TCA),and the pentose phosphate pathway(PPP),as well as the contents of pyridine nucleotides such as NAD(H)and NADP(H),were measured.[Result](ⅰ)The overall senescence rate of the upper leaves was faster than that of the middle leaves.As evidenced by more rapid browning,a higher O2-·production rate,and faster accumulation of H2O2 and MDA.(ⅱ)Compared with the middle leaves,the activities of hexokinase(HK),phosphofructokinase(PFK),pyruvate kinase(PK),citrate synthase(CS),α-ketoglutarate dehydrogenase(α-KGDH),succinate dehydrogenase(SDH)and NAD(H)contents in the upper leaves EMP-TCA were up-regulated at most postharvest time points.(ⅲ)During the postharvest senescence process,especially at the brown-ing stage(4-8 days after harvest),the activities of glucose-6-phosphate dehydrogenase(G6PDH)and 6-phosphogluconate dehydrogenase(6PGDH)in the PPP,as well as the NADPH content,were significantly higher in the middle leaves than in the upper leaves.[Conclusion]EMP-TCA metabolism is more vigorous in the upper leaves after harvest,which increases the consumption of respiratory substrates,making se-nescence browning more likely to occur.In contrast,the overall EMP-TCA activity in the middle leaves is lower,and respiratory metabolic re-sources preferentially allocated to the PPP,resulting in a higher PPP metabolic flux,and thus showing a stronger anti-senescence ability.