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Background and aims The introduction of crassulacean acid metabolism (CAM) into C3 crops has been considered as a means of improving water-use efficiency. In this study, we investigated photosynthetic and leaf structural traits in F 1 hybrids between Cymbidium ensifolium (female C3 parent) and C. bicolor subsp. pubescens (male CAM parent) of the Orchidaceae. Methods Seven F 1 hybrids produced through artificial pollination and in vitro culture were grown in a greenhouse with the parent plants. Structural, biochemical and physiological traits involved in CAM in their leaves were investigated. Key results Cymbidium ensifolium accumulated very low levels of malate without diel fluctuation, whereas C. bicolor subsp. pubescens showed nocturnal accumulation and diurnal consumption of malate. The F 1s also accumulated malate at night, but much less than C. bicolor subsp. pubescens. This feature was consistent with low nocturnal fixation of atmospheric CO2 in the F 1s. The δ13C values of the F 1s were intermediate between those of the parents. Leaf thickness was thicker in C. bicolor subsp. pubescens than in C. ensifolium , and those of the F 1s were more similar to that of C. ensifolium. This was due to the difference in mesophyll cell size. The chloroplast coverage of mesophyll cell perimeter adjacent to intercellular air spaces of C. bicolor subsp. pubescens was lower than that of C. ensifolium , and that of the F 1s was intermediate between them. Interestingly, one F 1 had structural and physiological traits more similar to those of C. bicolor subsp. pubescens than the other F 1s. Nevertheless, all F 1s contained intermediate levels of phosphoenolpyruvate carboxylase but as much pyruvate, Pi dikinase as C. bicolor subsp. pubescens. Conclusions CAM traits were intricately inherited in the F 1 hybrids, the level of CAM expression varied widely among F 1 plants, and the CAM traits examined were not necessarily co-ordinately transmitted to the F 1s. [ABSTRACT FROM AUTHOR]

C4 plants have higher photosynthetic nitrogen- and water-use efficiencies (PNUE and PWUE) than C3 plants. Some studies on C4 grasses have reported that NADP-malic enzyme (NADP-ME) grasses have higher PNUE than NAD-malic enzyme (NAD-ME) grasses, whereas other studies have suggested that this difference is caused by the traits of phylogenetic lineage. Further extensive studies are required to properly understand the PNUE and PWUE of C4 grasses. We investigated the PNUE and PWUE for 22 grass species of four photosynthetic types [4 NADP-ME, 6 NAD-ME, 6 phosphoenolpyruvate carboxykinase (PCK), and 6 C3 species] grown under two N supply levels. Under the same N level, the three C4 types showed higher photosynthetic rate and lower stomatal conductance and transpiration rate than the C3 type, but these parameters were similar in the C4 types. Although there were no significant differences in leaf mass per area and N content per leaf area among the four types, these traits tended to be somewhat lower in the NADP-ME type than in other types. As a result, PNUE was highest in the NADP-ME type, lowest in the C3 type, and intermediate in the NAD-ME and PCK types. PWUE was much higher in the C4 types than in the C3 type but similar in the C4 types. The N supply level did not greatly affect the trends of PNUE and PWUE. This study suggests that the NAD-ME and PCK grasses have the N-related physiological traits similar to each other but differing from the NADP-ME grasses. [ABSTRACT FROM AUTHOR]

Plants contain chloroplasts in various organs exposed to sunlight. The C4 crop, sorghum (Sorghum bicolor), develops prop roots on stems above the soil level with the progression of growth. These roots penetrate in the soil and form green above-ground (AG) and non-green below-ground (BG) portions. We investigated the structure and photosynthetic metabolism in the AG portion of prop roots in comparison with leaf blades and the BG portion. The AG portion lacked stomata on the epidermis and showed typical root structure as in the BG portion. However, they contained granal chloroplasts in the cortex and stele parenchyma. The chlorophyll content was much lower in the AG portion than in leaf blades. Western blot analysis showed that the AG portion accumulates ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) but lacked substantially phosphoenolpyruvate carboxylase and pyruvate, Pi dikinase. An immunolocalization study confirmed that Rubisco is accumulated in the chloroplasts of AG portion. The AG portion accumulated only small amount of malate without diurnal change as in other organs, indicating that crassulacean acid metabolism (CAM) is inactive. The δ13C values of all organs including the AG portion were within the C4 range, suggesting that their tissue carbon is derived from C4 photosynthesis of leaves. These data suggest that the AG portion of prop roots could re-fix internally respired CO2 via C3 cycle, whereas this photosynthetic function may provide O2 to heterotrophic tissues of prop roots. This study also demonstrates that different photosynthetic types can function in different organs of a single plant. [ABSTRACT FROM AUTHOR]