Drought-induced changes in free amino acid and ureide concentrations of nitrogen-fixing chickpea

Abstract

The metabolic products of nitrogen (N) fixation in a legume can be amides or ureides. Chickpea (Cicer arientinum L.) is a cool-season legume which transports both ureides and amides from N fixation. Ureides are purine derivatives which are synthesized solely in the nodules. Drought-sensitive legumes accumulate ureides, but the regulation of these N fixation products during drought in chickpea is not yet known. The objectives of this study were (1) to measure the metabolic products of N fixation during drought and (2) to quantify the differences in N fixation among chickpea cultivars during drought by acetylene reduction activity under controlled environment conditions. Five chickpea cultivars were exposed to drought by soil dehydration. Plants were harvested at 1, 5, 10 and 15 d after drought and were analyzed for leaf and stem ureide concentrations and total N. In separate growth chamber experiments, N fixation was quantified daily. Leaf ureide and free amino acid concentrations were analyzed at 1, 5, and 15 d after drought. Drought increased ureide accumulation in drought-sensitive cultivars and decreased total N, alanine and asparagine concentrations over time. Drought-tolerant chickpea cultivars maintained ureide and amide concentrations during drought. Of the chickpea cultivars examined, Myles was the most drought tolerant and CDC Chico was the least. Further research on leaf ureides, alanine and asparagine concentrations would be valuable to determine if these metabolic products could serve as measures for screening chickpea germplasm for drought-tolerant N fixation. Key words: Ureides, N fixation, Asparagine, Acetylene reduction