Research Of Nitric Oxide Fumigation On Lignification Of Postharvest Loquat Fruits And The Mechanisms Dring Cold Storage

In this paper,loquat fruits（Eriobotrya japonica Lindl.cv.Jiefangzhong）were investigated in term of their quality,lignin metabolism,energy metabolism,sugar metabolism and analysed the relationship of energy metabolism and sugar metabolism to the lignification of loquat fruits after nitric oxide treatments during cold storage,of which the effects on lignification of postharvest loquat fruits and the possible mechanisms were discussed.The results were as follows:1.In this research,loquat fruits were fumigated with 0（control group）、5、15、25、35、45μl/L nitric oxide（NO）gas.Fruits firmness,juice percentage,total soluble solid,total acid,lignin content and the related enzymes of lignin metabolism were analysed during cold storage（5.℃）The results showed that the juice percentage and total acid gradually decreased and the firmness increased.Total soluble solid（TSS）increased at early storage,then declined until the end of the storage.Lignin content increased rapidly 10 days later.The activity of PAL rase gradually and finally maintained at a high level.PPO activity was higer from 10 to 20 days during the storage,then fell rapidly.CAD activity was on the rise overall.The activity of 4-CL increased rapidly in the first 10 days,then dropped and maintained a stable level.As compared with control group,NO treatments delayed the increase of fruits’firmness and the decrease of juice percentage,inhibited the reduce of total soluble solid and total acid.Ligin content was significantly lower than control by NO treatments after 10 days later.NO treatments significantly inhibited the activities of PAL and CAD,inhibited 4-CL activity at the early storage stage and PPO activity at the later storage of loquat fruits.However,the research showed that 4-CL and PPO played a small role in the process of lignification of loquat fruits.We proposed that NO treatments delayed loquat fruits’lignification process mainly by inhibiting the activities of PAL and CAD,thus reducing the generation of lignin,and the treatment with nitric oxide at 15μl/L and 25μl/L were beneficial.2.Loquat fruits were fumigated with 15μl/L and 25μl/L NO gas to determine the influences of membrane permeability,lignin content,adenosine contents and related enzymes of mitochondria metabolism.Results showed that the membrane permeability increased during cold storage.The activities of succinia dehydrogenase,cytochrome C oxidase,H⁺-ATPase,Ca²⁺-ATPase dropped sharply at the later storage.The results indicated that mitochondrial function was impaired.Meanwhile,adenosine triphosphate（ATP）content,adenosine diphosphate（ADP）content and energy charge showed a decline trend which lead to energy metabolism disorder and the chilling injury sympotoms of fruits was obvious.NO treatments delayed the increase of membrane permeability and maintained the integrity of the cell membrane,thus postponed the onset of chilling injury symptoms of loquat fruits.NO trentments significantly inhibited the decrease of ATP content,and ADP content was higer in the first 15days during the storage.NO treatments were highly significant inhibited the decrease of the activities of succinia dehydrogenase（SDH）,cytochrome C（CCO）,H⁺-ATPase,Ca²⁺-ATPase,which maintained higher energy level and prolonged the shelf life of fruits.In addition,correlation analysis showed that energy charge was very significantly negatively correlated with lignin content after NO treatments.The results showed that energy deficit had a closely relationship with lignification of loquat fruits.All the results showed that NO treatments could maintain higher energy level by inhibiting the decline of the activities of mitochondria metabolism related enzymes,thereby delayed the development of lignification of loquat fruits.The treatment with 25μl/L was better.3.Loquat fruits were fumigated with 15μl/L and 25μl/L NO gas to determine the influences of total sugar content,soluble sugars and the related enzymes of sugar metabolism.The results showed that the total sugar content was on the rise during the first 10 days of the storage,then decreased until the end of the storage.During cold storage,sucrose gradually decomposed and fructose content increased gradually.Glucose content rapidly increased at the early stage of storage and then declined gradually.The activities of invertase and sucrose synthetase（decomposition direction）increased gradually.Sucrose phosphate synthase and sucrose synthase（synthetic direction）declined,of which promoted the sucrose decomposition.NO treatments significantly inhibited the rising of sucrose decomposition enzymes and the falling of sucrose synthesis,which delayed the reduce of total soluble sugar content and sucrose content.Correlation analysis showed that total soluble sugar content was negatively correlated with lignin content.And further analysis showed that sucrose content was very significantly negatively correlated with lignin content.These results indicated that the decomposition of sucrose promoted the synthesis of lignin.We proposed that sugar metabolism have certain relevance with the lignification of loquat fruits.Soluble sugars may be involved in thesynthesis of lignin.NO treatments delayed the reduce of soluble sugars,therefore reduced the process of lignification of loquat fruits during cold storage and 25μl/L NO treatment was better.