Morphological, physiological and genetic analyses of an upward-curling leaf mutant in Brassica napus L.

Leaf rolling is a common phenotypic trait and has recently gained more attention due to its involvement in photosynthetic efficiency and crop yield. An upward-curling leaf mutant (Bnucl1) was obtained from the rapeseed cultivar Zhongshuang 9 population (Brassica napus L.) via ethyl methanesulfonate mutagenesis. In this study, morphological and histological features, physiological characters, and inheritance of the Bnucl1 were investigated. The results indicated that leaf structure such as midvein, epidermal cells, and palisade mesophyll cells displayed remarkable differences in the mutant compared to wild type (WT). Pronounced variations in the chloroplast size and shape, starch grana between the mutant and WT leaves were observed, and the chloroplasts might be largely undifferentiated in the mutant. Moreover, the net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, and transpiration rate were significantly decreased in the mutant. Likewise, chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid contents were also significantly decreased in the mutant compared to WT. Enzyme activity of SOD, POD, and CAT was reduced; however, the content of H2O2 and MDA was increased in the mutant. Among the tested agronomic traits and leaf area, all the traits except siliques on the terminal raceme decreased in the mutant plants. Hence, the mutation has imposed remarkable impacts on the structure and function of leaves and agronomic traits. Genetic study indicated that this trait was monogenic and the allele for curling leaf was dominant. These results provide inroads for further evaluation to understand the mechanism of leaf development in B. napus.