Effects of high CO_2 atmosphere on growth and UVB resistance in rice.

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We previously found that elevated UVB suppresses the growth of rice. Tiller formation and biomass were most suppressed by UVB applied at the stages developing leaves from 2nd to 5th. More CPDs were produced by UVB applied at those stages. Ability to photoreapir CPDs in the 4th leaf increased from leaf emergence until full expansion. These results suggested that rice is more susceptible to CPD induction and UVB-caused growth retardation at the stage when the 2nd, 3rd, or 4th leaves are developing.We investigated the effects of CO2 (700ppm) on growth and yield of rice in an open-top chamber built in paddy field. Tiller formation, hulled grain weight, and the number of heavy-weight hulled grain increased, resulting in elevation of yield by ca.20 %. The period until ear emergence was shortened.Tiller number and biomass decreased in lower CO2 (200ppm) in a phytotron, whereas tiller number, biomass, and the contents of total N in a leaf, soluble protein, chlorophyll and Rubisco elevated more in higher CO2 (700ppm) than in ambient CO2. The degree of suppression of growth by UVB was higer in ambient CO2 than in higher CO2.Progenies having more resistance to UVB than sensitive perent were generated in F2 plants generated by crossing a cultivar resistant to UVB and a cultivars less resistant. We could not find any plants more resistant to UVB than parent in mutants of Kinmaze, but we found more sensitive plants to UVB,which would be useful for studying mechanism of UVB resistance in rice.