Effects of UV-B radiation on growth, photosynthesis, UV-B-absorbing compounds and NADP-malic enzyme in bean (Phaseolus vulgaris L.) grown under different nitrogen conditions.
The effects of UV-B radiation on growth, photosynthesis, UV-B-absorbing compounds and NADP-malic enzyme have been examined in different cultivars of Phaseolous vulgaris L. grown under 1 and 12 mM nitrogen. Low nitrogen nutrition reduces chlorophyll and soluble protein contents in the leaves and thus the photosynthesis rate and dry-matter accumulation. Chlorophyll, soluble protein and Rubisco contents and photosynthesis rate are not significantly altered by ambient levels of UV-B radiation (17 microW m-2, 290-320 nm, 4 h/day for one week). Comparative studies show that under high nitrogen, UV-B radiation slightly enhances leaf expansion and dry-matter accumulation in cultivar Pinto, but inhibits these parameters in Vilmorin. These results suggest that the UV-B effect on growth is mediated through leaf expansion, which is particularly sensitive to UV-B, and that Pinto is more tolerant than Vilmorin. The effect of UV-B radiation on UV-B-absorbing compounds and on NADP-malic enzyme (NADP-ME) activity is also examined. Both UV-B radiation and low-nitrogen nutrition enhance the content of UV-B-absorbing compounds, and among the three cultivars used, Pinto exhibits the highest increases and Arroz the lowest. The same trend is observed for the specific activity and content of NADP-ME. On a leaf-area basis, the amount of UV-B-absorbing compounds is highly correlated with the enzyme activity (r2 = 0.83), suggesting that NADP-ME plays a key role in biosynthesis of these compounds. Furthermore, the higher sensitivity of Vilmorin than Pinto to UV-B radiation appears to be related to the activity of NADP-ME and the capacity of the plants to accumulate UV-B-absorbing compounds.
Pinto
M E
ME
Facultad de Ciencias Agrarias y Forestales, Universidad de Chile, Santiago, Chile. manpinto@abello.dic.uchile.cl
Casati
P
P
Hsu
T P
TP
Ku
M S
MS
Edwards
G E
GE
D002245:Carbon Dioxide; D002734:Chlorophyll; D007887:Fabaceae / Q000201:enzymology / Q000254:growth & development / Q000502:physiology / Q000528:radiation effects*; D008291:Malate Dehydrogenase / Q000378:metabolism / Q000528:radiation effects; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis / Q000528:radiation effects; D018515:Plant Leaves / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D010946:Plants, Medicinal; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D014466:Ultraviolet Rays
D010940:Plant Proteins; D002734:Chlorophyll; D002245:Carbon Dioxide; D008291:Malate Dehydrogenase; C031917:malate dehydrogenase (oxaloacetate-decarboxylating) (NADP+); D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen