Identification and expression analysis of twelve members of the nucleobase-ascorbate transporter (NAT) gene family in Arabidopsis thaliana.

By screening genome databases, 12 genes encoding membrane proteins homologous to nucleobase-ascorbate transporters (NATs) were identified in Arabidopsis thaliana. A similar number of genes was found in the rice genome. The plant NAT proteins split into five clades (I-V) based on protein multisequence alignments.

Do mature shade leaves of tropical tree seedlings acclimate to high sunlight and UV radiation?

Seedlings of neotropical forest trees grown in low light were exposed to 0.5-9 h d direct sunlight, for up to 3 months, to test the capability of mature shade leaves to acclimate to full solar visible and UV radiation. Photosynthetic pigments and the antioxidant, ascorbate, were analysed in leaves of two pioneer and two late-succession species.

Sudden exposure to solar UV-B radiation reduces net CO(2) uptake and photosystem I efficiency in shade-acclimated tropical tree seedlings.

Tree seedlings developing in the understory of the tropical forest have to endure short periods of high-light stress when tree-fall gaps are formed, and direct solar radiation, including substantial UV light, reaches the leaves. In experiments simulating the opening of a tree-fall gap, the response of photosynthesis in leaves of shade-acclimated seedlings (Anacardium excelsum, Virola surinamensis, and Calophyllum longifolium) to exposure to direct sunlight (for 20-50 min) was investigated in Panama (9 degrees N). To assess the effects of solar UV-B radiation (280-320 nm), the sunlight was filtered through plastic films that selectively absorbed UV-B or transmitted the complete spectrum.