Phenotypic Identification Of Etiolated Mutant Ylm In Tomato

【Objective】Leaf color mutants are important materials for studying plant photosynthesis,chloroplast structure and related gene functions.A trait with a genetically stable yellowing mutant ylm was obtained in the early stage of this experiment,and the material was found to be temperature-sensitive during cultivation.This study aimed to identify the phenotypic differences between tomato flavation mutant ylm and wild type M82.To explore the sensitivity of ylm to temperature,hoping to lay the foundation for tomato breeding and analyzing the formation mechanism of the leaf color mutation.【Methods】The leaf color,growth index,leaf pigment content,photosynthetic and fluorescence characteristics were identified and analyzed,including ylm and M82,the background material.The size,color,pigment content and nutritional quality indexes of the fruits in the result period were determined.According to the leaf color that is sensitive to temperature,three different temperature levels were set:16℃,25℃,30℃,respectively for 48 h.The chlorophyll content,photosynthetic content and chlorophyll fluorescence characteristics of the mutant ylm were determined and analyzed.【Results】1.The study found that the heart leaves of ylm were significantly yellow,the true leaves were fully expanded yellow-green,the lower leaves of the plant gradually turned green,and its growth was significantly inhibited,showing that the plant height,stem thick and above-ground dry fresh weight,leaf area and root volume were significantly lower than that of the wild type M82.2.The content of chlorophyll a,chlorophyll b and total chlorophyll in the leaves of ylm was significantly lower than that of wild-type M82,while the content of carotenoid was significantly higher than that of the cultivar M82,indicating that the reduction of pigment content led to the leaf color yellowing of the mutant.Moreover,the chloroplast number was significantly small in the mesophyll cells of the mutant ylm,and the lamelayer structure of the chloroplast basa was blurred.It contains a large number of osmium-tropic particles,dense distribution,but a small number of starch particles,and small size.Tomato etiked leaf mutant ylm chloroplast is dysplastic and severely damaged in structure.3.The net photosynthetic rate（Pn）and transpiration rate（Tr）of etized leaf mutant ylm were significantly or significantly lower than M82,stomatal conductivity（Gs）was significantly lower than M82,while intercellular CO₂concentration（Ci）was significantly higher than M82.It is speculated that the abnormal chloroplast structure and the decrease of chlorophyll content reduce the ability of chloroplast to capture,transform and transmit light energy,and reduce the efficiency of light energy utilization.The Fv/Fm,Y（II）,q P,q N and ETR of the mutant ylm were all significantly lower than the wild type M82,indicating that the mutant has reduced photosynthetic capacity,sensitive to photoinhibition and reduced electron transport rate.4.After mutant ylm for 48 h,the upper leaves showed distinct yellow.As the temperature increased,after 48 h of 25℃,the leaves were less yellow and the yellow leaves gradually turned green,while after 48h of 30℃,the leaves were green,basically the leaf color of the wild type.The variability in leaf chlorophyll content of mutant ylm and wild type M82 is consistent with the visually observed leaf color phenotype.5.The mutants had higher SOD and POD activities at 16℃and 30℃.These results indicate that the mutants also have improved antioxidant enzyme activity and enhanced reactive oxygen species in response to temperature changes.6.The mutant ylm fruit is orange-red,slightly lighter compared to M82,with single fruit weight,flesh thickness,and transverse longitude less than M82.The carotenoids and lycopene of ylm were significantly lower than the wild type M82.The results showed that the content of vitamin C and soluble total sugar in ylm was significantly higher than that in M82.【Conclusion】The change of leaf color of the mutant ylm at seedling stage was closely related to chlorophyll content,and the chloroplast structure of the mutant was seriously damaged,which resulted in the decrease of photosynthetic capacity and photosynthetic electron transfer ability,and inhibited the growth of the plant;The mutant ylm,at low temperature,The yellowing was even more pronounced,The color difference was not obvious from M82 at high temperature;The change in pigment content is consistent with the phenotype observed by the naked eye;Preliminary identification of the fruits of the etiizing mutant ylm in the outcome phase,The mutants were found to be of orange-yellow fruit;In contrast to the wild type,There were significant differences in fruit size and peel thickness,The contents of vitamin C and sugar in ylm were significantly increased compared with M82.Mutant ylm contains lower carotenoids and lycopene than M82 at different mature stages,consistent with the phenotype of fruit color.