| Whether the calyx of Korla fragrant pear falls off or not determines the quality of its fruit.Although the fruit quality is improved to a certain extent in the short term,it is not conducive to the long-term healthy development of the Korla fragrant pear industry.To explore the mechanism of calyx shedding in Korla fragrant pear,this study measured the content of reactive oxygen species（ROS）,superoxide dismutase（SOD）activity and peroxidase（POD）activity treated with different inhibitors（DDC,SHAM,KI,PA,and PA+mono）in three periods according to previous studies on plant organ shedding and calyx shedding of Korla fragrant pear.The lignin content,phenylalanine ammonia lyase（PAL）activity,ferulic acid-5-hydroxylase（F5H）activity and caffeic acid-O-methyltransferase（COMT）activity of different inhibitors in three periods were determined.The lignification degree of calyx tissue was observed by paraffin section.The fluorescence intensity of calyx tissue cell wall was observed by laser confocal microscopy（CLSM）.The cell size and cell wall thickness of calyx tissue was observed and measured by transmission electron microscopy（TEM）.Scanning electron microscopy（SEM）was used to observe and measure the flatness of the tissue surface and the diameter of the surface particles.The main results are as follows:（1）After using DDC to inhibit the activity of SOD,the calyx removal rate increased significantly,while after using KI,SHAM,and PA to inhibit the content of H2O2,POD activity and lignin synthesis,the calyx removal rate decreased significantly.At 7 days after full bloom,H2O2 content and·OH scavenging ability were significantly positively correlated with calyx abscission rate,and SOD activity was significantly negatively correlated with calyx abscission rate,indicating that these three indicators were closely related to calyx abscission.At 14 days after full bloom,H2O2 content and O2·-content were significantly positively correlated with calyx abscission rate,and POD activity was significantly positively correlated with calyx abscission rate,indicating that these three indicators were closely related to calyx abscission of fragrant pear in this period.At 21 days after full bloom,the·OH scavenging ability was significantly positively correlated with the calyx shedding rate,indicating that this index was closely related to the calyx shedding of fragrant pear during this period.This study found that the level of H2O2 content was particularly closely related to the shedding of pear calyx,while SOD was closely related to the shedding of pear calyx at 7 days after full bloom,and POD was closely related to the shedding of pear calyx at 14 days after full bloom.（2）After DDC treatment inhibited the activity of SOD,the lignin content increased,and the activities of PAL,F5H and COMT also increased.After KI and SHAM treatment,the lignin and three enzyme activities decreased to varying degrees.At 7 days after full bloom,lignin content,COMT activity and PAL activity were significantly positively correlated with calyx removal rate.At 14 days after full bloom,COMT activity and PAL activity were significantly positively correlated with calyx abscission rate,and F5H activity was significantly positively correlated with calyx abscission rate,indicating that these three indexes were closely related to calyx abscission of fragrant pear in this period.At 21 days after full bloom,PAL activity was significantly positively correlated with calyx shedding rate.The accumulation of lignin had a significant effect on the calyx abscission of pear.PAL was closely related to the calyx abscission of pear at three stages.At 7 and 14 days after full bloom,F5H and COMT significantly affected the calyx abscission rate.（3）DDC treatment greatly increased the lignification degree of calyx cells of fragrant pear.The lignification degree of cells treated with KI,SHAM and PA decreased significantly,while PA+mono remained at normal level.The degree of cell wall lignification treated with different inhibitors was significantly lower than that of normal level.The calyx cell area and cell wall thickness of fragrant pear after PA treatment were significantly lower than those of other treatments.The cell wall thickness of DDC treatment was higher than normal level in three periods.PA+mono treatment was maintained at normal level,KI,SHAM,PA treatment was significantly lower than the normal level.Different inhibitor treatments have a significant effect on tissue smoothness and surface particle diameter.This study found that different inhibitors had significant effects on the microstructure and ultrastructure of the calyx of fragrant pear,and the cell wall thickness was closely related to the calyx removal rate. |
