With untransformed rice cv. Kitaake as control, the characteristics of carbon assimilation and photoprotection of a transgenic rice line over-expressing maize phosphoenolpyruvate carboxylase (PEPC) were investigated. The PEPC activity in untransformed rice was low, but the activity was stimulated under high irradiance or photoinhibitory condition. PEPC in untransformed rice contributed by about 5-10 % to photosynthesis, as shown by the application of the specific inhibitor 3,3-dichloro-2-(dihydroxyphosphinoylmethyl)propenoate (DCDP). When maize PEPC gene was introduced into rice, transgenic rice expressed high amount of maize PEPC protein and had high PEPC activity. Simultaneously, the activity of carbonic anhydrase (CA) transporting CO 2 increased significantly. Thus the photosynthetic capacity increased greatly (50 %) under high CO 2 supply. In CO 2 -free air, CO 2 release in the leaf was less. In addition, PEPC transgenic rice was more tolerant to photoinhibition. Treating by NaF, an inhibitor of phosphatase, showed that in transgenic rice more phosphorylated light-harvesting chlorophyll a/b-binding complexes (LHC) moved to photosystem 1 (PS1) protecting thus PS2 from photo-damage. Simultaneously, the introduction of maize PEPC gene could activate or induce activities of the key enzymes scavenging active oxygen, such as superoxide dismutase (SOD) and peroxidase (POD). Hence higher PS2 photochemical efficiency and lower superoxygen anion (O 2˙-) generation and malonyldiadehyde (MDA) content under photoinhibition could improve protection from photo-oxidation.

In this study, water solutions with different concentrations of abscisic acid (ABA) (10, 20, and 40 μmol L-1) were sprayed on leaves of drought-stressed tobacco seedlings. The results showed that under drought stress, both water content and photosynthetic carbon assimilation ability were reduced, PSII activity was also inhibited. Drought stress also led to the outbreak of reactive oxygen species in tobacco leaves and increased the degree of membrane peroxidation. However, spraying exogenous ABA significantly alleviated the damage caused by drought stress on the leaves. The potential mechanisms by which drought resistance in tobacco is improved by spraying exogenous ABA include: (1) regulation of the stomatal limitation of leaves, which is beneficial to water retention ability and can enhance photosynthetic function; (2) reduction of the energy pressure of the PSII reaction center by increasing nonphotochemical quenching (NPQ); and (3) effective reduction of the production of reactive oxygen species in the leaves and reducing the degree of membrane peroxidation.