Abstracts Photoinhibition is the inhibition of photosynthesis by excessive light resulting in the reduction of plant growth. Exposure to additional stress factors during exposure to light increases the potential for photoinhibitory effects. Reversible photoinhibition is indicative of a protective mechanism aimed at dissipating excess light energy, while irreversible photoinhibition indicates damage to the photosynthetic systems. The present review summarizes the physiological mechanisms of photoinhibition and discusses the interaction between light and other stress factors. In addition, some of the features and strategies that help plants avoid or restrict the occurrence of photoinhibition are analyzed. Most of these defense mechanisms are associated with the dissipation of excessive energy such as heat. Therefore, these mechanisms would regulate the carbon available to the plant by the output ratio of ATP/NADPH to the stressful environmental conditions. Understanding these mechanisms can help avoid plant cell death and increase plant productivity.
Duckweeds are small, floating aquatic plants with a number of useful characteristics, including edibility, fastgrowing, and a clonal proliferation. Duckweed is also fed to animals as a diet complement because of its high nutritional value. Porcine epidemic diarrhea virus (PEDV) is a major causative agent of fatal diarrhea in piglets and is a serious problem in the hog-raising industry. In this study, we assessed the feasibility of producing a protective antigen for the PEDV spike protein 1 using duckweed, Lemna minor. Stably transformed Lemna were obtained by co-cultivation with A. tumefaciens EHA105 harboring the PEDV spike protein gene. Transgene integration and expression of the PEDV spike protein 1 gene were confirmed by genomic PCR and RT-PCR and western blot analysis of transgenic Lemna, respectively. This is the first report of the expression of a vaccine antigen against an animal infectious disease in duckweed.Additional key words: aquatic plant, porcine diarrhea, spike protein, transformation, vaccine Hort. Environ. Biotechnol. 52(5):511-515. 2011.
The rice CHLH gene encodes the Mg 2? -chelatase H subunit, which is involved in chlorophyll biosynthesis. Growth of the chlorophyll-deficient oschlh mutant is supported by mitochondrial activity. In this study, we investigated the activity of mitochondrial respiration in the illuminated leaves during oschlh seedling development. Growth of mutant plants was enhanced in the presence of 3% sucrose, which may be used by mitochondria to meet cellular energy requirements. ATP content in these mutants was, however, significantly lowered in light conditions. Low cytosolic levels of NADH in illuminated oschlh mutant leaves further indicated the inhibition of mitochondrial metabolism. This down-regulation was particularly evident for oxidative stressresponsive genes in the mutant under light conditions. Hydrogen peroxide levels were higher in oschlh mutant leaves than in wild-type leaves; this increase was largely caused by the impairment of the expression of the antioxidant genes, such as OsAPX1, OsRAC1, and OsAOXc in knockout plants. Moreover, treatment of mesophyll protoplasts with ascorbic acid or catalase recovered ATP content in the mutants. Taken together, these results suggest that the light-mediated inhibition of mitochondrial activity leads to stunted growth of CHLH rice seedlings.
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