Effect of nitrogen and/or sulfur deprivation on the uptake and assimilation steps of nitrate and sulfate in maize seedlings

Abstract

Seedlings of two maize genotypes, differing in grain yield, were deprived for five days of either nitrogen or sulfur, or both. At the end of each shortage period, prior to the development of any deficiency symptom, uptake rates and internal pools of sulfate and nitrate, extractable activities of ATPS, OASS, NR, GDH, GS were evaluated. The comparison with seedlings supplied with complete solution showed that after S + N deprivation the rate of sulfate uptake was enhanced 46 and 30% in the higher and lower yield genotype respectively, while that of nitrate was the same of control. In both genotypes GS activity did not change, sulfate and nitrate internal pools were reduced and significant changes in activity concerned NR, which was strongly depressed, GDH, which increased 35%. OASS increased 60 and 30% in the higher and lower yield genotype respectively. In the case of deprivation of only one of the two elements, each of the metabolic parameters tested, except GS activity, was differently affected by N and S deprivation. SO^2‐ ₄ uptake rate, OASS activity and SO^2‐ ₄ pools were affected mainly by S; NR and GDH activities by N deprivation, the responses being similar to those given to S + N deprivation. Interactions between S and N metabolism were demonstrated by NO⁻ ₃ pool in roots, which was enhanced mainly by S deficiency, and by ATPS activity, which was depressed mainly by N deficiency. Sulfur metabolism appears better adapted than N metabolism to withstand nutrient shortage. A key‐role in productivity could be assumed for the SO^2‐ ₄ transport system and OASS activity which were the only parameters showing a better efficiency in the higher yield genotype.

Key words:

• Nitrogen
• sulfur deprivation
• Zea mays