Genotypic Differences In Rice Leaf Structure And Its Response To Different Light Conditions

With the continuous development of rice breeding process,the high-yield rice varieties bred in modern times have the characteristics of large panicle,proper canopy structure,and high utilization rate of light.Our previous research on rice varieties that are cultivated in different periods of time in China shows that variety improvement also indirectly changes the structure of rice leaves.However,few studies look at the differences in the leaf structure of rice varieties from different regions and how the leaf structure of rice is influenced by the photosynthetic characteristics and growth rate of rice under different lighting conditions.This study is based on 272 rice varieties from3,000 Rice Genomes Project（3K RGP）and 533 rice populations（including Southeast Asian indica rice,improved indica rice varieties of diverse origins,temperate japonica rice,tropical japonica rice,aus-type group,rice of mixed types,etc.）,and analyzes how the leaf structure of rice varieties from the different subgroups differs from each other,as well as how each trait of the rice’s leaf structure influences each other.The study compares a near-isogenic line of rice with low stomatal density and the variety 9311 to explore the photosynthetic characteristics of rice varieties with different stomatal densities.At the same time,this study selects 20 rice varieties from 6 different subgroups to see how the gas exchange coefficients of rice leaves and the growth rate of rice are influenced by the leaf structure under different light conditions.The main results are as follow:There are significant genotypic differences in stomatal anatomical traits and leaf vein structure among the 272 rice varieties.The stomatal density（Daba）varies from300 mm^-2 to 410 mm^-2,the distance between major veins（IVDmajor）varies from 1251μm to 1564μm,and the distance between minor veins（IVDminor）varies from 204μm to 219μm.The stomatal density of indica varieties is significantly higher than that of japonica varieties,while the distance between veins is significantly smaller than that of japonica varieties.The modern improved indica subgroup features higher stomatal density,but the vein structure of rice in this subgroup does not show great difference from that of other subgroups.There is a significant correlation between the inter-vein distances and the stomatal density and the size of cross-sectional anatomy of rice veins.The distance between leaf veins is positively correlated with the size of single xylem conduits in veins,and the distance between veins is negatively correlated with the stomatal density.There are significant differences in stomatal anatomical traits and stomatal conductance and photosynthesis between 9311 and Zhenshan 97×9311 near-isogenic No.95 rice material.The stomatal density of variety 9311 is significantly higher than that of No.95,but these two varieties have no significant differences in stomatal size.Stomatal anatomical traits are not related to stomatal conductance and the plant’s response rate of photosynthesis to changes in light intensity.The density of veins of the variety 9311 is higher than that of the No.95 and thus higher hydraulic conductance,but the water use efficiency is slightly lower than that of No.95.Lighting conditions have great effects on the leaf structure,stomatal conductance,photosynthesis and growth rate of the 20 rice varieties.A fluctuating light condition significantly reduces the stomatal width,but has little effects on the stomatal density.In addition,the fluctuating light condition significantly increases the distance between major veins and the width of single xylem conduits in major veins.The effects of different lighting conditions on leaf gas exchange coefficients vary across rice varieties,and stomatal anatomical traits are not related to gas exchange coefficients and might be related to the low-light environment in which the plants are grown.The fluctuating light significantly reduces the growth rate of plants,but there is no obvious correlation between the gas exchange coefficients and the growth rate of rice plants.Future research should focus more on the relationship between leaf structure and leaf carbon assimilation efficiency and plant growth rate by studying the rice population in natural environment.