The relationship between resistance to tobacco brown spot and nitrogen metabolism in mature tobacco (Nicotiana tabacum) plants

Abstract

Differences in nitrogen metabolism were analyzed in mature leaves of three tobacco cultivars with different levels of resistance to brown spot disease (Alternaria alternata) including one resistant (JYH) and two susceptible cultivars (NC89 and CBH). The results were as follows: All three cultivars had low levels of both total nitrogen and leaf tissue NH4 +; the activity of glutamine synthetase (GS) declined sharply in all cultivars, but that of JYH was significantly higher than that of NC89 and CBH; levels of NAD(H)-glutamate dehydrogenase (NAD(H)-GDH) activity in JYH increased until 75 days after germination, and then decreased. In contrast, NAD(H)-GDH activities in NC89 and CBH increased gradually at maturity; apoplastic NH4 + concentrations in the three cultivars gradually increased, but their apoplastic pHs and NH3 compensation points decreased, and these apoplastic parameters were significantly higher in NC89 and CBH than in JYH. These results indicated that the nitrogen metabolism in mature leaves differed remarkably among tobacco cultivars with different levels of resistance to brown spot disease. The resistant cultivar has a greater capacity to re-use nitrogen, while the susceptible cultivar loses more nitrogen via ammonia volatilization, which plays an important role in the initiation of tobacco brown spot. Our data suggest that the characteristics of leaf nitrogen metabolism of tobacco cultivars affect the level of resistance to tobacco brown spot.