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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]

The denser leaf vasculature of C4 plants than of C3 plants may suit rapid export of assimilates associated with their higher photosynthetic rate. However, some C4 grasses have partially reduced leaf vasculature with vascular bundle (VB)-free bundle-sheath cells called distinctive cells (DCs). The shade-tolerant C4 grass Paspalum conjugatum has such a reduced leaf vascular system with DCs. We examined whether irradiance during growth affects vascular formation in leaves of P. conjugatum grown under 100%, 30%, or 14% sunlight for 1 month alongside the C4 grass maize. Under all conditions, P. conjugatum leaves had partially reduced vasculature: DCs and incomplete small VBs without phloem occurred between VBs with a normal structure consisting of both xylem and phloem. Shaded plants had less phloem in the small VBs than the full-sunlit plants. In maize, however, all VBs always had both xylem and phloem under all light conditions. The net photosynthetic rate of both grasses was reduced under shade; that of P. conjugatum was always lower than that of maize under all light conditions, but was reduced less by shade than that of maize. The light compensation point was lower in P. conjugatum than in maize, indicating that P. conjugatum acclimatizes better to low light. The reduction of phloem in VBs of P. conjugatum may be an acclimatization to shade, because dense vasculature may be expensive for C4 plants growing in environments where the higher photosynthetic rate is not realized. [ABSTRACT FROM AUTHOR]

Higher plants are divided into three major photosynthetic groups known as C3, C4, and crassulacean acid metabolism (CAM) plants. It is considered that cell wall thickness (TCW) affects diffusion and leakiness of CO2 within leaves, but it is unclear whether TCW of photosynthetic cells differs among these groups. This study investigated TCW of photosynthetic cells in herbaceous C3, C4, and CAM species under an electron microscope. Among 75 species of monocots and eudicots grown in a growth chamber in the same environment, the TCW of mesophyll cells (MCs) was much higher in CAM species than in C3 and C4 species. However, when TCW was compared between C3 and C4 species of grasses and eudicots, TCW of MCs tended to be lower in C4 species than in C3 species; the opposite trend was observed for TCW of bundle sheath cells (BSCs). TCW of MCs and BSCs almost did not differ among the C4 decarboxylation types (NADP-ME, NAD-ME, and PCK). In plants grown outdoors (51 species), similar trends of TCW were also found among photosynthetic groups, but their TCW was generally higher than that of growth-chamber plants. This study provides the TCW spectrum of photosynthetic cells in herbaceous C3, C4, and CAM species. The results obtained would be valuable for our understanding of the diffusion and leakage of CO2 in the leaves of different photosynthetic groups. [ABSTRACT FROM AUTHOR]

Eleocharis vivipara Link is a unique amphibious leafless plant of the Cyperaceae. The terrestrial form develops culms with Kranz anatomy and C4-like traits, while the submerged form does culms with non-Kranz anatomy and C3 traits. The submerged form develops new culms with C4-like mode when exposed to air or exogenous abscisic acid. In this study, we investigated whether salt stress (0.05–0.3 M NaCl) has a similar effect. When the submerged form was grown for one month in solutions of 0.1 M NaCl and more, culm growth was strongly suppressed. However, these plants slowly developed new culms that had Kranz anatomy with chloroplast-abundant Kranz bundle sheath cells. Although the culms of the submerged form had only few stomata, culms grown in the NaCl solution had many stomata. The NaCl-grown culms also accumulated large amounts of C4 photosynthetic enzymes (phosphoenolpyruvate carboxylase and pyruvate Pi dikinase), and the cellular localization patterns of these enzymes and ribulose 1,5-bisphosphate carboxylase/oxygenase were similar to those in terrestrial culms. Accumulation of C4 enzymes increased in mature culms of the submerged form (with non-Kranz anatomy) when exposed to 0.2 M NaCl solution for one week. These results suggest that salt stress induces development of Kranz anatomy and expression of C4 photosynthetic enzymes in the submerged C3 form of E. vivipara, whereas the anatomical and biochemical traits of C4 photosynthesis appear to be regulated independently. [ABSTRACT FROM AUTHOR]