Oryza coarctata, is a triploid plant with initial events of C4 photo synthesis evolution

Abstract Oryza coarctata is an obligate halophyte of wild species of rice which thrives well under high saline as well as submerged conditions. We report here for the first time that O. coarctata is triploid (2n = 3x = 36), though it was previously known as tetraploid (2n = 4x = 48). The chromosome number of O. coarctata was determined from mitotic plates of root tips and flow cytometer, where it was found to be triploid (2n = 3x = 36). In addition, this species was found to possess several unique anatomical features in leaves such as presence of Kranz-anatomy, increased number of vein density and higher ratio of bundle sheath to mesophyll cell area with compared to rice variety (IR-29). Ultra-structure of leaf showed the presence of bundle sheath cells with significant number of chloroplasts and mitochondria which were arranged centripetally. Chloroplasts lack grana whereas, mesophyll cell contain well-developed grana. These anatomical and ultra structural characteristics indicate that this plant is in initial stage of evolving towards C4 photosynthesis due to high selection pressure which might help it to survive in wide range of ecological conditions i.e. from submerged saline aquatic to non-saline terrestrial condition.