Comparison Of Postharvest Tissue Structure And Physiological Changes Of Apple Cultivars With Different Texture

Different apple cultivars vary considerably in texture and storage properties,and the speed of fruit softening after harvest is the key to fruit quality and shelf life.In order to reveal the main physiological factors of fruit texture variation of apple cultivars with different softening speed,and lay a foundation for us to explore the internal regulation mechanism of fruit texture change of different cultivars in the later stage.And further provide a reference for breeding good cultivars with good storage tolerance.In this study,fruits of the two cultivars(‘Qinguan' and ‘Cripps Pink')with obvious differences in softening speed were used as test materials,we measured the changes of physiological indicators during the softening period of fruit texture,and regularly observed and compared the changes of tissue structure and subcellular structure during fruit softening.The research results are as follows:1.On the day of harvest,there were significant differences in fruit firmness between ‘Qinguan' and ‘Cripps Pink'.During storage at room temperature,fruit firmness of the two cultivars showed a downward trend,but the degree of the decline was significantly different.The fruit firmness of ‘Qinguan' decreased significantly faster than that of ‘Cripps Pink'.When stored to 49 d,the firmness of ‘Qinguan' decreased by 34 %,while that of ‘Cripps Pink' decreased by only 18 %.In addition,when stored to 84 d,the weight loss rate of ‘Qinguan' fruit was significantly higher than that of ‘Cripps Pink'.2.There was a layer of cuticle covering the outermost cell wall of epidermal cells on the surface of fruit peel of the two cultivars,on which there were non-crystalline waxes of different thickness.On the day of harvest,there were no obvious micro-cracks on the surface of fruit peel of the two cultivars.Compared with ‘Cripps Pink',the number of micro-cracks on the surface of fruit peel of ‘Qinguan' was obvious during storage,and became wider and deeper.3.On the day of harvest,compared with ‘Qinguan',the epidermal cells of ‘Cripps Pink' fruit arranged more closely than that of ‘Qinguan'.During storage,the epidermal cells,hypodermal cell and intercellular space of ‘Qinguan' fruit increased significantly.With the prolongation of storage time,the change range of ‘Cripps Pink' cells was relatively small,and the epidermal cells and hypodermal cells were still closely arranged.Moreover,with the extension of storage time,the majority of the parenchyma cells of ‘Qinguan' separated from each other and the intercellular space was obviously increased,while the intercellular space of ‘Cripps Pink' was relatively small.4.On the day of harvest,the ultrastructure of parenchyma cells of the two cultivars was similar.By the middle stage of storage,the cell walls of ‘Qinguan' parenchyma cells were relax,the middle lamella was almost all degraded,intercellular cracks appeared,and the microfilament structure was loosely arranged,while the cell walls of ‘Cripps Pink' parenchyma remained unchanged.At the end of storage,the microfilament structure of the cell wall of the former was disordered,while that of the latter was still intact.5.The respiration rate of the two cultivars showed typical climacteric fruit characteristics during the whole storage period,but there was no significant difference between the two cultivars.With the prolongation of storage time,the ethylene production of both cultivars reached a peak at 21 d of storage,but the ethylene production of ‘Qinguan' was significantly higher than that of ‘Cripps Pink',and the ethylene peak of the former was about 5 times higher than that of the latter.6.At the initial stage of storage,the starch content and AM activity of ‘Qinguan' were significantly higher than that of ‘Cripps Pink'.At 14 d after harvest,the AM activity of fruits reached a peak and the starch was rapidly hydrolyzed.With the extension of storage time,the SSC content of the two cultivars increased first and then decreased.On the day of harvest,the TA content of ‘Cripps Pink' was about twice as much as that of ‘Qinguan',and the decrease of the former was significantly greater than that of the latter during storage,but the TA content of the former was still significantly higher than that of the latter at the end of storage.7.During the middle and late storage period,the increase of pectinase(PG,PE,?-Gal)and cellulase(CEL)activities promoted the degradation of protopectin and cellulose,the content of protopectin and cellulose decreased and the content of soluble pectin increased.And the change rate of ‘Qinguan' was faster than that of ‘Cripps Pink'.In summary,the softening of apple fruits during storage is mainly manifested as the decrease of firmness.At the beginning of storage,namely before the climacteric stage,the decrease of fruit firmness was mainly due to the rapid hydrolysis of starch,which was related to the increase of respiration rate and ethylene production,the rapid increase of AM activity and the hydrolysis of starch into soluble sugar.The subsequent softening is closely related to the increase of hydrolytic enzymes activities related to pectin,cellulose and hemicellulose increased,and the corresponding macromolecular substances degraded,resulting in cell tissue separation,structural relaxation and disintegration.And the softening speed of ‘Qinguan' is faster than that of ‘Cripps Pink',which is closely related to these factors.