Effects Of Shading On Photosynthetic Physiological Characteristics Of Yellow Leaf Mutant Cmygl-1 In Hami Melon

[Objective]Leaf color mutants are important materials for studying plant photosynthesis,chloroplast structure and development.This study aims to explore the adaptability of the yellow-green leaf mutant Cmyg1-1 of cantaloupe to different light intensities,and lay the foundation for further analysis of the mechanism of leaf color mutation.[Method]In this experiment,the seedlings of the yellow-green leaf mutant of Hami melon were used as the test material.Through shading treatment,4 different light intensity levels were set:（no shading,A）,（light shading,B）,（medium shading,C）,（Deep shading,D）.Determine and analyze the effects of different light intensity on the growth traits,chlorophyll content,antioxidant capacity,photosynthesis and chlorophyll fluorescence characteristics of the mutants.[results]1.The growth of the mutant under B treatment was the best,showing that the plant height,stem thickness,dry weight per plant,fresh weight,chlorophyll a and chlorophyll b content were significantly higher than the other three treatments,while the mutants under A and D treatments had the best growth.Obviously inhibited growth.The wild type grows best under the A treatment,and with the weakening of the light intensity,it shows a significant downward trend.2.Under B treatment,the mutants had the strongest antioxidant capacity,the accumulation of active oxygen and the lowest degree of membrane lipid peroxidation,which showed that the content of malondialdehyde（MDA）and H₂O₂ and the production rate of O₂.^-were significantly lower than those of other treatments,POD（peroxidase）,SOD（superoxide dismutase）,CAT（catalase）and APX（ascorbate peroxidase）activities are significantly higher than other treatments.The mutant has the weakest antioxidant capacity under treatment A,and the accumulation of reactive oxygen species and the highest degree of membrane lipid peroxidation.3.The mutants had the highest photosynthesis and photosynthetic product transport ability under B treatment,showing that the net photosynthetic rate（Pn）,transpiration rate（Tr）,stomatal conductance（Gs）and leaf starch content were significantly higher than that of C and D treatments,and light saturation Point（LSP）and apparent quantum efficiency（AQY）are significantly higher than the other 3 treatments.The mutant has the lowest LSP under the D treatment,indicating that the mutant has low light energy utilization efficiency and significant light inhibition under deep shading;the wild-type light compensation point（LCP）and dark respiration rate（Rd）values are the lowest under the A treatment.It shows that the wild type has the highest light utilization efficiency and the lowest consumption capacity of organic substances without shading.4.From the analysis of chlorophyll fluorescence characteristics,Under treatment B,the non-regulated energy dissipation quantum yield Y（NO）of the mutant,the quantum yield used for electron transfer（φEo）,and the performance index（PIabs）based on the absorption of light energy of the PSII reaction center are all significant higher than the other 3 treatments.However,The energy dissipated in the PSII reaction center in the mutant（DIo/RC）,the energy used for electron transfer in the PSII reaction center（ETO/RC）,the light absorbed per unit area（ABS/CSo）and the light energy captured Per unit area（TRo/CSo）,the value of the quantum yield（ETo/CSo）of electron transfer per unit area,there is no significant difference between the C and D treatments.The results showed that the mutant could optimize the energy distribution of PSII reaction sites and improve the activity and electron transfer ability of PSII reaction sites under mild shading.[Conclusion]The mutant has higher chlorophyll content,less accumulation of active oxygen,less membrane lipid peroxidation and plasma membrane damage under light shading（B treatment）,and high PSII reaction center activity and electron transfer ability,so it has Facilitate the growth of mutant plants.However,under no shading（treatment A）,the PSII receptor side of the mutant is damaged and electron transfer is blocked,resulting in the excessive light energy captured under strong light cannot be effectively used,and the accumulation of reactive oxygen species is induced.Oxidative damage,growth is inhibited.