Effects of chilling tolerance induced by spermidine pretreatment on antioxidative activity,endogenous hormones and ultrastructure of indica-japonica hybrid rice seedlings

Spermidine（Spd） is known to be involved in the regulation of plant responses to chilling stress and counteract the adverse effect of stress conditions.Antioxidant activities,endogenous hormones and ultrastructure change under chilling stress were investigated in indica-japonica hybrid rice seedlings.12-d-old seedlings were subjected to exogenous Spd（1 mmol L^（-1）） and then a chilling stress（6℃,4 d） was induced,followed by a subsequent recovery（25℃,4 d）.Results showed that malondialdehyde（MDA） and proline content were enhanced significantly,whereas shoot fresh and dry weights decreased during chilling stress and after recovery;chlorophyll content of chilling-stressed seedlings increased slightly but declined after recovery;additionally,total soluble sugar,sucrose,fructose and starch contents increased significantly during chilling stress,and only soluble sugar and fructose contents were observed in increase after recovery;chilling stress-induced increases in superoxide dismutase（SOD）,peroxidase（POD） and catalase（CAT） activities,but declined after recovery,and the level of ascorbate peroxidase was lower during chilling stress and after recovery;however,endogenous indole-3-acetic acid（IAA）,zeatin riboside（ZR）,gibberellic acid（GA_3）,and abscisic acid（ABA） levels were induced decreased compared with Spd pretreatment.The microscopic analysis revealed that chilling stress-induced destruction of the chloroplast envelope during chilling stress and increased the number of plastoglobuli along with aberrations in thylakoid membranes after recovery.In contrast,exogenous Spd protected rice seedlings from chilling-induced injuries in terms of lower malondialdehyde,proline and carbohydrates accumulation coupled with increased endogenous hormones metabolism.After recovery,Spd pretreatment chilling-exposed seedlings showed higher activities of antioxidant enzymes and normal physiological function of chloroplasts.These results suggest that Spd could promote effectively chilling tolerance which might be largely attributable to the integrity of cell structure and normal metabolism of endogenous hormones in indica-japonica hybrid rice seedlings.

Effects of edible whole citrus fruits on endogenous antioxidant enzymes of HepG2 cells

The effects of eating fresh citrus fruits including two varieties of mandarins,one of sweet oranges,one of grapefruit,two of pomelo,and one of kumquat cultivated in China on endogenous antioxidant enzymes were investigated by in vitro digestion and HepG2 cells.The correlations between enzyme activity and cell uptake of phytochemicals and cellular antioxidant capacities were analyzed.The results showed that most fresh citrus fruits increased the endogenous antioxidant activity.Bairoumiyou,Hongroumiyou,Ponkan,and Jinju after digestion significantly increased the activity of catalase(P<0.05).Hongroumiyou,Bairoumiyou,Ponkan navel orange,and Jinju after digestion significantly increased glutathione peroxidases(GPxs)activity(P<0.05),while Huyou and satsuma could not increase the activity of GPxs after digestion.Thioredoxin oxidoreductase activity was improved significantly by most of the digested whole citrus fruits except Ponkan(P<0.05)and thioredoxin oxidoreductase added whole citrus fruits had a higher increase than added citrus fruits extracts.The results indicated that edible whole citrus fruits had similar effects as extracts on enzymes.