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Effects of water deficit on the activity of nitrate reductase and content of sugars, nitrate and free amino acids in the leaves and roots of sunflower and white lupin plants growing under two nutrient supply regimes
Author(s) -
Correia Maria João,
Fonseca Filomena,
AzedoSilva João,
Dias Celeste,
David Maria Manuela,
Barrote Isabel,
Osório Maria Leonor,
Osório Júlio
Publication year - 2005
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.2005.00486.x
Subject(s) - lupinus , nitrate reductase , helianthus annuus , sunflower , nitrate , helianthus , nutrient , chemistry , botany , biology , horticulture , organic chemistry
The effects of soil drying on the activity of nitrate reductase (NR; EC 1.6.6.6) were studied in Helianthus annuus L. and non‐nodulated Lupinus albus L. plants growing under two nutrient supply regimes. NR activity was assessed in leaf and root extracts by measuring the activity of the unphosphorylated active form (NR act ), the maximal extractable activity (NR max ) and the activation state. To obtain an insight into potential signalling compounds, nitrate, free amino acids and soluble sugars were also quantified. In both species, foliar NR act and NR max were negatively affected by soil drying and a decreased supply of nutrients, the observed changes in NR activity being linearly correlated with the depletion of nitrate. Similar results were obtained in the roots of sunflower. Conversely, in white lupin roots, NR max was found to be independent of tissue nitrate concentration. Regardless of the species and organ, the activation state of the enzyme was unaffected by the nutrient supply regime. In well‐watered sunflower roots, only about 50% of the existing NR was unphosphorylated, but the activation state increased significantly in response to drought. In contrast, lupin roots always exhibited NR activation state values close to 80%, or even higher. At the leaf level, the NR activation state was hardly changed in response to soil drying. The observed changes in the concentrations of soluble sugars and free amino acids are discussed in terms of their possible contribution to the variations in NR activity.