Correlation Analysis Of Sugarcane Leaf Structure,Function And Cold Resistance

Warm climate origin C₄ sugarcane（Saccharum officinarum）has been the subject of decades of hybridization and breeding.However,its cold resistance did not substantially evolved and cold adaptation mechanism is still less understood.This study experienced on 60 sugarcane varieties from the global germplasm collection at the Guangxi Academy of Agricultural Science.During the winter coldest period（2°C）,fast measurements of the chlorophyll fluorescence of intact leaves were undergone on intact leaves.The maximum photochemical efficiency Fv/Fm of the photosystem Ⅱ was used to quantify the leaf cold resistance.Simultaneously,we measured the specific leaf area,the thickness of the leaf and the mesophyll tissues,the stomatal index,the leaf vein density and structure as well as the leaf resistance to punch and turgor loss point among other functional traits.Then,trait correlations were analyzed.Besides,the most largely cultivated Xintaitang 22（ROC22）was used to compare the proteome of the mesophyll（M）,the bundle sheath（BS）chloroplast before and after cold stress.The objective was to analyze the effect of the chilling on the leaf structure and functions at micro-molecular level.The results showed that:1)During the coldest winter period,the early morning Fv/Fm of the 60studied varieties ranged from 0.415-0.796.55 varieties were significantly affected by cold stress（Fv/Fm<0.7）,35 of them were severely affected（<0.6）.Correlative analysis revealed that the winter coldest early morning Fv/Fm negatively correlated the minimum temperature of the coldest month and the winter mean temperature at the origins of the studied varieties.It indicated that most sugarcane populations were cold sensitive but cold resistance among varieties showed significant differences.The variety’s cold sensitivity and the climate at their origins were strongly related.Long term exposure to the climatic conditions at the cultivation site less affected the cold resistance of the sugarcane varieties.2)The winter coldest early morning Fv/Fm negatively correlated with the leaf specific leaf area(which ranged from 99.87 cm²×g^-1-180.03 cm²×g^-1)and positively correlated with the leaf thickness（which ranged from 344.62μm-523.39μm）,the mesophyll thickness（which ranged from 294.07μm-470.68μm）and the leaf resistance to punch(which ranged from 0.77 k N×m^-1-1.53 k N×m^-1).This indicates that the cold tolerance of sugarcane leaves needs a solid structural foundation.3)M and BS chloroplast proteomics analysis of the revealed significant difference between the protein structure of the two types of the chloroplast prior to cold stress.Before low temperature,compared with M chloroplast,the expression of stress response proteins（osmotin-like protein,zeaxanthin epoxidase,et.）in BS chloroplast was higher,while the expression of antioxidant proteins（glutathione transferase,et.）and chlorophyll synthesis related proteins（Mg-protoporphyrin IX chelatase）in BS chloroplast was lower.BS chloroplast responded to cold stress mainly by reducing light capture and assimilation,and emphasizing the photoprotection of the chloroplast.M chloroplast responded by photosynthetic carbon metabolism regulation,photoreaction,electron transfer and antioxidant protection.These results showed that The specific chloroplast structure of C₄ plants performed different photosynthetic functions in response to low temperature.In conclusion,the cold resistance of sugarcane is affected by the climatic conditions in the source area,which is closely related to the leaf structure.At the same time,the protein expression changes of M and BS chloroplasts under low temperature can reduce the damage of low temperature.These results constitute theoretical knowledge on C₄ plant cold resistance and can be used for the breeding of cold tolerance sugarcane and variety selection.