Melatonin delays leaf senescence in pak choi(Brassica rapa subsp.chinensis)by regulating biosynthesis of the second messenger cGMP

Melatonin(MT)is a low molecular weight compound with multiple biological functions in plants.It is known to delay leaf senescence in various species.However,no data are available on the MT signaling pathway in postharvest vegetables.This study demonstrates that MT increases cGMP concentration and the expression of the cGMP synthesis gene BcGC1 in pak choi.The c GMP inhibitor LY83583 destroys effect of MT delaying the leaf senescence.LY83583 also prevents MT treatment from reducing the expression of chlorophyll metabolism-related genes(BcNYC1,BcNOL,BcPPH1/2,BcSGR1/2,and BcPAO)and senescence genes(BcSAG12 and BcSAG21).It also inhibits MT from reducing the activity of the key chlorophyll catabolism enzymes Mg-dechelatase,pheophytinase,and pheide a oxygenase.Thus,the ability of MT to maintain high levels of chlorophyll metabolites is also destroyed.The Arabidopsis c GMP synthetic gene mutant atgc1 was used to confirm that delayed leaf senescence caused by MT is mediated,at least in part,by the second messenger c GMP.

Green LED irradiation promotes the quality of cabbage through delaying senescence and regulating glucosinolate metabolism

Light-emitting diode(LED)irradiation can affect postharvest vegetable and fruit shelf life and nutritional quality.In this study,11 kinds of glucosinolates(GLS)and 6 types of GLS breakdown products were identified in cabbage leaves.To investigate the effects of LED irradiation on quality and GLS metabolism,postharvest cabbage was irradiated with 25μmol/(m2·s)green LED(GL)light at room temperature for 12 d.The dark condition and natural light were used as controls.GL irradiation inhibited the respiration rate and the accumulation of malondialdehyde,and maintained higher cabbage sensory score,chlorophyll content,and antioxidant enzyme activities,thus extending its postharvest shelf life.Additionally,GL irradiation promoted GLS profile accumulation,including glucoraphanin,glucoiberin,gluconapin,gluconasturtiin,glucobrassicin,and sinigrin,which could have resulted from upregulated expression of the transcription factors MYB28 and MYB51,and the key genes involved in GLS biosynthesis(CYP83A1,CYP83B1,ST5b,and UGT74B1).Furthermore,GLS degradation was promoted by this treatment during the late stage of shelf life,as higher myrosinase activity and relative MYR and ESM expression levels were found in treated cabbage leaves,resulting in higher isothiocyanate(ITC)and indole-3-carbinol contents after day 6.Therefore,GL irradiation was beneficial for cabbage preservation.