Effect of postharvest nitric oxide treatment on the activities of disease-resistant related enzymes in chestnuts during cold-storage

Abstract: 【Objective】Chestnut (Castanea mollissima BL.) is well known for its nutritional value andpleasant flavor. Chestnut fruits usually ripe in late summer when temperatures are still higher, so thatthe processes of water loss, microbial attack and decay are accelerated after harvest. As a result, thefresh nut has a short shelf life, losing marketability within a few days at ambient temperatures. Coldstorage could delay ripening and improve the resistance of nuts to pathogens effectively, but the nutqualities decline obviously after storage. Nitro oxide (NO) is a signaling molecule in plant and animaltissues, and has an important function of regulating postharvest physiology of fruits. It has been report-ed that NO treatment could reduce decay and extend storage life of various fruits. According to the cur-rent results, sodium nitroprusside (SNP, NO donor) treatment could reduce the decay of chestnut. Thestudy aimed to investigate the effects of postharvest NO treatment on the activities of disease-resistantrelated enzymes of chestnut during low temperature storage.【Methods】'Jinyou 2'nuts at mature stagewere used as the material. The fruits were harvested from an orchard in Luotian county of Hubei prov-ince and immediately transferred to laboratory on the same day. Nuts with uniform size, free of visibleinjuries and defects, were selected and treated with 0.4 mmol·L^-1 SNP solution for 5 minutes, while wa-ter treatment was used as the control. After air-dried and pre-cooling, all the nuts were packed andstored at cold temperatures (0-3 ℃) with 80%-85% relative humidity for 180 days. The rot rate of nutswas investigated every 20 d, and meanwhile pulp samples were stored in a ultra-low temperature freez-er after liquid nitrogen freezing. The physiological indexes were measured during storage. The indexesincluded malondialdehyde (MDA) content and the activities of peroxidase (POD) , superoxide dis-mutase (SOD) , catalase (CAT) , polyphenol oxidase (PPO) , polygalacturonase (PG) , chitinase (CHT) and β-1, 3-glucanase (GLU) . Microsoft Excel 2007 software was used to calculate the mean and stan-dard deviation. The SAS 8.0 software was used to analyse the significance of difference.【Results】Thedecay rate of nuts increased significantly during the long period storage. Compared with the control, SNP treatment effectively inhibited the rot of nuts. After 180 days of storage, the rot rate of SNP treat-ment was 18.89%, which was just 43.6% of the control. During the whole storage period, the activitiesof POD and CAT increased slightly at the beginning and then decreased, but SOD activity kept increas-ing until the 100 th day and then decreased. Compared with the control, SNP treatment kept a higherPOD activity remarkably during the storage, and the POD activity was 12.32% higher than the controlat 120 th day. SNP treatment also kept a higher SOD activity significantly, which was 9.17% higher thanthe control at 160 th day. The CAT activity of SNP treatment was 40.19% higher than the control after180 days of storage. The PPO activities kept increasing until the 120 th day and then decreased, SNPtreatment inhibited the PPO activity, and the activity was lower than the control significantly from day60 to 120. The PPO activity of SNP treatment was 75.43% of the control at day 60, and 73.33% at day120. The PG activity kept increasing during the storage, SNP treatment kept a lower PG activity signifi-cantly, which was 74.71% of the control at day 60, and 84.54% at day 140. The CHT activities in-creased to the maximum at 80 th day, and then decreased. SNP treatment enhanced the CHT activity ob-viously, the maximum value was 16.10% higher than the control at 80 th day, and the activity was46.85% higher than the control at 120 th day. The GLU activity was also enhanced by SNP treatment, es-pecially from day 60 to 120. The GLU activity of SNP treatment was 27.14% higher than the control atday 60, and 16.34% at day 180. The MDA content in nuts increased during the storage, and SNP treat-ment decreased the MDA content significantly. After 180 days of storage, the MDA content with theSNP treatment was 84.26% of the control.【Conclusion】Postharvest NO treatment might enhance the ac-tivities of disease-resistant related enzymes in chestnut. Under low temperature conditions, postharvestSNP treatment increased the activities of SOD, CAT, POD, CHT and GLU, reduced MDA content andthe activities of PG and PPO, and then effectively inhibited the rot of nuts.