Nitrate reductase activity in a submersed marine angiosperm: Controlling influences of environmental and physiological factors
2001
Touchette, B.W. ((North Carolina State University, Raleigh (Etats Unis). Department of Botany)) | Burkholder, J.M.
In plants, nitrate reductase (NREC 1.6.6.1) is considered to be a key enzyme in nitrate assimilation. Therefore, the activity of NR as influenced by major environmental factors may affect the survival of many aquatic nitrogen-limited plant species. In this study, the in vivo activity of NR following exposure to increased water-column nitrate was examined in a submersed marine angiosperm (eelgrass, Zostera marina L.). NR activity was primarily localized in new leaf tissue, and was related to light and/or soluble carbohydrate availability. Under extended periods of darkness (18 h), enzyme activity decreased by more than 60 /. Nevertheless, in vivo NR activity was induced during dark periods provided that water-column nitrate (/= 8 micro M N03-) was available. Enzyme activities were lower in plants that were exposed to hypoxic conditions ( 3.5 mg o2/L for 14 h), and/or elevated growth temperatures (3 to 4 degrees C above mean weekly temperatures). In contrast, exposure to the atmosphere for 90 min promoted a significant increase in in vivo NR activity. A temporal investigation (14 weeks in autumn) revealed that the intensity of in vivo NR response to water-column nitrate was directly correlated with the quantity of soluble carbohydrates within the leaf tissue. Many of the observed in vivo NR responses were likely related to carbohydrate availability. During periods where soluble carbohydrate availability was expected to be low, in vivo NR response to increased water-column nitrate was substantially compromised
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