Photosynthesis, cellulose contents and ultrastructure changes of mutant rice leading to screw flag leaf

Leaf rolling is one of the most commonly observed phenotypes in plants and recently more concentration has been paid by researchers on the rolling leaf mutants because of the abundance of rolling leaf phenotypes in rice. The photosynthesis efficiency, chlorophyll contents, cellulose contents, chlorophyll fluorescence and ultrastructure changes between screw flag leaf 1 (sfl1) mutant found in Zhenong 34 (Oryza sativa L. ssp. indica) and wild type (WT) were investigated in the present study. The results indicated that the net photosynthesis rate, stomata conductance, intercellular CO2 concentration and transpiration rate in sfl1 were significantly lower than those in WT. Compared with the WT plant, the chlorophyll a, chlorophyll a + b, Chl a/b and carotenoid contents in sfl1 were significantly decreased, however, the chlorophyll b was lower in WT. The results of chlorophyll fluorescence showed that the variations in maximal quantum yield of PSII (Fv/Fm), effective quantum yield of PSII (I broken vertical bar PSII) and electron transfer rate (ETR) in sfl1 mutant flag leaves were visibly decreased but photochemical quenching coefficient (qP) and non photochemical quenching coefficient (NPQ) were increased compared with those in the WT. We demonstrated that the cellulose and hemicelluloses contents in sfl1 were significantly lower than those in the WT, while the lignin content was significantly increased in sfl1. Transmission electron micrographs (TEM) revealed that there were distinguishing differences in the chloroplast, mitochondria and starch grana between sfl1 and WT at vegetative stage. However, there was no observable thylakoid in sfl1 chloroplasts at the reproductive stage, indicating that the chloroplasts could be largely undifferentiated in this mutant. These results might provide the significant basis for further understanding the screw leaf development mechanism in rice.