Differential Responses of Growth and Nitrate Reductase Activity in Wild Type and NO 2-Tolerant Barley Mutants to Atmospheric NO 2 and Nutrient Nitrate

Abstract

Summary Strains of NO 2 -tolerant barley ( Hordeum vulgare L.) were selected from NaN 3 -mutated seeds using high levels of atmospheric 3 (5 μLL -1 ). Seedlings from NO 2 -tolerant mutant seeds (Types B1 and W3) were grown alongside wild type seedlings (cvs. Maris Mink and Zephyr) in glasshouses for 10 d with nutrient solution containing either no nitrogen or 5 mM nitrate and some of each were fumigated with 0.5 μLL -I NO 2 for 3d. Exposure of plants to NO 2 for 3d caused a substantial decline in root dry weight and an increase in the levels of nitrate reductase (NR) activity in the leaves of both mutants. Levels of root NR activities were also higher in NO 2 -fumigated plants but this increase could be explained by the decrease in root weights. The entire population of the wild type seedlings and about 5 % of the B 1 plants showed visible symptoms of NO 2 injury in the form of whitening of leaf tips or brown spots on the leaf blades but none was ever found on the W3 mutant. It would appear from these experiments that these NO 2 -tolerant mutants cope with the toxic symptoms of atmospheric NO 2 injury by reducing their root growth and enhancing the levels of their shoot NR activities.