短期夜间低温胁迫对秋茄幼苗碳氮代谢及其相关酶活性的影响

Abstract

The frequency,duration and intensity of extreme cold events have been hypothesized to explain the current latitudinal limits of mangrove distribution. At present,Kandelia obovata is the major mangrove species for forestation on the southeast coast of China,whose northern distribution boundary transplanted is in Yueqing county( 28°25'N). Therefore, the incidence of extreme cold events is likely to be a factor limiting mangrove survival ratio. Kandelia obovata seedling grown in a controlled-environment chamber equipped were exposed to two different night temperature regimes:( low temperature treatment)-2℃ and( control) 20℃ for 12 h. During the day,temperature were maintained in both treatments at a minimum of 5 ℃ and a maximum of 25 ℃ for 4 h. Our objective was to investigate the possible physiological mechanisms of Kandelia obovata in responses to the short-term chilling 16 hours. Kandelia obovata seedling were cultivated in the illuminating incubator to study the effects of short-term dark chilling on photosynthetic characteristic,photosynthetic pigment contents,antioxidation system,cell membrane permeability and involved activities of enzymes in carbon and nitrogen metabolism. The results obtained are as follows:( 1) The leaf net photosynthetic rate( Pn),stomatal conductance( Gs) and stomatatal limitation( Ls) of Kandelia obovata were significantly decreased at low temperature 16 h,while leaf intercellular CO 2 concentration was increased.( 2) The contents of chlorophyll,carotenoids,and Chl a / Chl b ratio in leaf had no significantly changes at low temperature less than 8 h,whereas leaf Car / Chl ratio was significantly improved. In addition,photosynthetic pigment contents were decreased at low temperature between 12 h and 16 h.( 3) The leaf total soluble sugars was increased during low temperature 16 h,while sucrose content,sucrose synthase( SS) and sucrose phosphate synthase( SPS) activities were decreased after low temperature 12 h.( 4) The contents of soluble protein and free amino acid and carboxypeptidase activity in leaf were increased during low temperature 16 h,while endopeptidase activity in leaf begun to drop at low temperature 8 h.( 5) During low temperature 16 h,the relative conductivity and malondialdehyde( MDA) content in leaf were increased,while activity of POD was decreased,especially in dark. Also, low temperature both 4 h and 16 h treatments suppressed leaf superoxide dismutase( SOD) activity. These results demonstrate that non-stomatal restriction was cause for reduced Kandelia obovata photosynthesis at low temperature 16 h, which was mainly associated with reduced photosynthetic pigment and depressed antioxidant enzyme activity. Moreover, short-term low night temperature restrained leaf carbon and nitrogen metabolic self-regulation in Kandelia obovata by affecting activities of SS,SPS,endopeptidase and carboxypeptidase.