[Effects of high temperature on grain filling and some physiological characteristic in flag leaves of hybrid rice].

The effects of high temperature on grain filling rate and some physiological indexes in flag leaves in hybrid rice Teyou 559 were studied. The results showed that chlorophyll content and superoxide dismutase (SOD) activity in flag leaves were lower significantly by high temperature stress (Figs.2A and 3A). The electrolyte leakage and malondialdehyde (MDA) content were higher significantly under high temperature stress (Figs.2B and 3B). The proline (Pro), ascorbic acid (AsA), glutathione (GSH), soluble protein and soluble sugar contents were lower significantly by high temperature stress than those of the control (Figs.4,5 and 6). Both the rate of grain filling and grain dry matter accumulation become lower significantly under high temperature stress (Figs.7 and 8). Therefore, it was suggested that high temperature accelerated the senescence of rice leaf and decreased the photosynthesis rate during grain filling period, and then which was the main reason in physiology which resulted the decrease of grain filling rate, seed setting rate, grain weight and yield.

Hybrid Rubisco of tomato large subunits and tobacco small subunits is functional in tobacco plants.

Biogenesis of functional ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in plants requires specific assembly in the chloroplast of the imported, cytosol-synthesized small subunits (SS) with the chloroplast-made large subunits (LS). Accumulating evidence indicates that chloroplasts (plastids) generally have a low tolerance for assembling foreign or modified Rubisco. To explore Rubisco engineering, we created two lines of transplastomic tobacco plants whose rbcL gene was replaced by tomato-derived rbcL: plant LLS2 with Rubisco composed of tobacco SS and Q437R LS and plant LLS4 with a hybrid Rubisco of tobacco SS and tomato LS (representing four substitutions of Y226F, A230T, S279T and Q437R from tobacco LS). Plant LLS2 exhibited similar phenotypes as the wild type. Plant LLS4 showed lower chlorophyll and Rubisco levels particularly in young emerging leaves, lower photosynthesis rates and biomass during early stages of development, but was able to reach reproductive maturity and somewhat wild type-like phenotype under ambient CO2 condition. In vitro assays detected similar carboxylase activity and RuBP affinity in LLS2 and LLS4 plants as in wild type. Our studies demonstrated that tomato LS was sufficiently assembled with tobacco SS into functional Rubisco. The hybrid Rubisco of tomato LS and tobacco SS can drive photosynthesis that supports photoautotrophic growth and reproduction of tobacco plants under ambient CO2 and light conditions. We discuss the effect of these residue substitutions on Rubisco activity and the possible attribution of chlorophyll deficiency to the in planta photosynthesis performance in the hybrid Rubisco plants.