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Carbonic anhydrase (CA; EC 4.2.1.1) catalyzes the interconversion of CO2 and HCO3- and plays an important role in photosynthetic carbon assimilation. We report that the effect of manipulating AtβCA6 expression on the growth and biomass accumulation of Arabidopsis thaliana shows that AtβCA6 was expressed in mitochondria. Overexpression of AtβCA6 increased the fresh weight, dry weight and rosette leaf area and it was also linked to a slight decrease in the rate of respiration. By contrast, when the respiration rate in the AtβCA6 knock-out mutant SALK_065611 increased, the fresh weight, dry weight and rosette leaf area decreased. The expression level of AtβCA6 mainly affected the expression of the genes that were related to metabolism, photosynthesis and respiration. We discuss these data with respect to a potential role of AtβCA6 in refixation of CO2 released from respiration and its potential as an option to increase biomass production.

Soil salinity is a major abiotic stress that lowers agricultural production around the world. Mainly caused by elevated levels of NaCl, it induces a wide range of responses in plants. In addition to ion toxicity, high salt levels can induce oxidative stress with the formation and accumulation of reactive oxygen species (ROS). We introduced the transcription factor YAP1, originally from yeast (Saccharomyces cerevisiae), into Arabidopsis thaliana (ecotype Columbia). When treated with various NaCl concentrations, transgenic plants showed increased activities of antioxidant enzymes catalase, superoxide dismutase, ascorbate peroxidase, peroxidase, glutathione S-transferase, and glutathione reductase compared with the wild-type Arabidopsis. This demonstrated that an active oxygen scavenging system was enhanced to protect plants from salt stress by equilibrating ROS metabolism. Transgenic Arabidopsis maintained higher photosynthesis levels and lower amounts of H2O2, suggesting that ROS production was reduced. Physiological analysis implied that transgenic Arabidopsis might employ multiple mechanisms to improve its salt tolerance.

In yeast, the plasma membrane Na+/H+ antiporter and Na+-ATPase are key enzymes for salt tolerance.Saccharomyces cerevisiae Na+-ATPase (Enalp ATPase) is encoded by theENA1/PMR2A gene; expression ofENA1 is tightly regulated by Na+ and depends on ambient pH. Although Enalp is active mainly at alkaline pH values inS. cerevisiae, no Na+-ATPase has been found in flowering plants. To test whether this yeast enzyme would improve salt tolerance in plants, we introducedENA1 intoArabidopsis (cv. Columbia) under the control of the cauliflower mosaic virus 35S promoter. Transformants were selected for their ability to grow on a medium containing kanamyin. Southern blot analyses confirmed thatENA1 was transferred into theArabidopsis genome and northern blot analyses showed thatENA1 was expressed in the transformants. Several transgenic homozygous lines and wild-type (WT) plants were evaluated for salt tolerance. No obvious morphological or developmental differences existed between the transgenic and WT plants in the absence of stress. However, overexpression ofENA1 inArabidopsis improved seed germination rates and salt tolerance in seedlings. Under saline conditions, transgenic plants accumulated a lower amount of Na+ than did the wild type, and fresh and dry weights of the former were higher. Other experiments revealed that expression ofENA1 promoted salt tolerance in transgenicArabidopsis under both acidic and alkaline conditions.