| Pecan and hickory are the deciduous tree,belonging to the genus Carya(Juglandaceae).The fruit has been widely welcomed by consumers because of its high nutritional value and unique taste.Salt stress is one of the most harmful abiotic stresses that restrict the growth and yield of plants,causing physiological water deficiency and a series of ion specific toxicity caused by changes in Na+/K+.Spermidine(Spd),also known as three spermidine hydrochloride,is widely distributed in organisms.It is a highly bioactive aliphatic compound.Studies have shown that exogenous Spd can directly participate in many physiological activities of plants,and play an important role in enhancing stress tolerance in plant growth and development.In this experiment,the grafted plantlets of pecan and hickory were used as the research materials.The salt stress environment was simulated by pot planting with Nacl(0(control,no Nacl),4g·L-1(moderate stress)and 4g·L-1(severe stress))were used to study 3 salt gradients,and the exogenous 1 m M Spd spraying was thinner under 4g·L-1 and 8g·L-1 salt concentration.The leaf phenotypes,relative water content(RWC),chlorophyll(Chl)content,malondialdehyde(MDA)content,antioxidant enzyme activities(superoxide dismutase SOD,peroxidase POD,catalase CAT),Na+/K+,photosynthetic parameters(photosynthesis rate Pn,intercellular carbon dioxide concentration Ci,pore conductivity Gs and transpiration rate Tr)were found in the grafted plantlets of pecan and hickory.The chlorophyll fluorescence parameters(actual optoelectronic production Y(II),maximum photochemical rate Fv/Fm,photochemical quenching coefficient q P,electron transfer rate ETR),endogenous hormones(abscisic acid ABA and ethylene ETH)and chloroplast ultrastructure and other physiological and biochemical characteristicsThe results show that:1.Under salt stress,as processing time extends,the leaf phenotype of grafted plantlets pecan and hickory lost gradually green,and the RWC of leaves,the Chl content,photosynthetic parameters and chlorophyll fluorescence parameters showed a decreasing trend,which caused the increase of Na+/K+,three kinds of antioxidant enzyme activities(SOD,POD and CAT)to increase continuously.The chloroplast ultrastructure of the leaves of grafted plantlets of pecan and hickory were also subjected to different degrees of destory.In addition,the contents of ABA and ETH were accumulated continuously under salt stress,especially under severe salt stress.2.With the extension of treatment time,the effect of salt stress was alleviated in a certain time.The results showed that the grafted plantlets of pecan and hickory in exogenous Spd treatment group had the phenotype of leaves between the blank control group and the self-blank salt control group,and within a certain period of time.Exogenous Spd treatment could slow down the decrease of relative water content,chlorophyll content,photosynthesis parameters and chlorophyll fluorescence parameters,and slow down the increase of MDA content and Na+/K+ ration.The activity of SOD,POD and CAT was increased to some extent,and the accumulation of endogenous hormones was promoted.In addition,the ultrastructure of chloroplast was protected to some extent,especially under severe salt stress.3.During the whole experiment,with the extension of treatment time,compared with the physiological and biochemical indexes of the grafted plantlets of hickory under salt stress,the physiological and biochemical indexes of the grafted plantlets of the pecan were smaller,the response time was late,and the index content(or activity)under the same conditions was larger.These results indicated that exogenous Spd treatment might alleviate salt stress in the grafted plantlets of pecan and hickory by reducing peroxidation,increasing antioxidant capacity and regulating the content of endogenous hormones in plants. |
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