Effect Of γ-Ray Irradiation On Suppressing Germination Of Fresh Walnuts

In recent years,the consumption and price of fresh walnuts are increasing due to their rich nutrition and unique flavor,but it is easy to germinate during storage,which significantly affects its commodity value and market supply period.Previous studies showed that ⁶⁰Coγrays inhibited the germination of some fruits,vegetables and fresh walnut after harvest.However,it is still unclear how irradiation affects the germination of fresh walnut by affecting the contents of endogenous hormones especially ABA related substances and enzyme activities.In this study,"Liaohe No.2"fresh walnuts treated by 0,50 and 300 Gy ⁶⁰Coγray were stored at（25±1）℃,and then the endogenous hormones contents,cell ultrastructure and the indexes related to ABA metabolism were measured,which will provide the theoretical basis and technical support for the storage of.The main results are as follows:（1）γray irradiation destroyed the cell structure of fresh walnut embryo and had significant effect on the postharvest germination fresh walnut.The germination rate of fresh walnut was 86.33%and 29.33%in control and 50 Gy treatment at 24 d,and the average bud length was 65.2 mm and 15.47 mm,respectively.The germination of fresh walnut was completely inhibited by 300 Gy treatment.（2）Irradiation significantly affected the contents of endogenous hormones ABA,GA₁₊₃,IAA and ZR in fresh walnut,increased the content of ABA in embryos,and decreased the contents of GA₁₊₃,IAA and ZR and the ratio of the above three hormones to ABA content,therefore resulting in the hormone imbalance.（3）Irradiation improved the zeaxanthin content in seed kernel and embryo,and improved the NCED activity in seed kernel,inhibited the decline of NCED activity in embryo,and further promoted ABA biosynthesis,inhibited ABA metabolism by inhibitingβ-glucosidase activity and the synergistic effect of synthesis and metabolism pathways reduced the decline rate of ABA content.（4）Irradiation regulated ABA synthesis by promoting the expression of ABA biosynthesis related genes SDR,IPI1,ZEP,especially NCED6 in fresh walnut embryos.With the increase of irradiation dose,the expression level of NCED6 decreased more slowly after 12 days,and the ABA biosynthesis increased.Meanwhile,irradiation reduced ABA metabolism by inhibiting the expression of CYP707A1 gene in seed kernel and embryo.The results showed that irradiation could cooperatively inhibit the postharvest germination of fresh walnut by affecting several key genes.（5）Irradiation changed the correlation among different hormones contents in kernel and embryo,the same hormone in kernel and embryo,as well as different hormones in different parts of fresh walnut,which affected the balance of the original hormones,and finally inhibited the postharvest germination of fresh walnut.