氮素形态及HCO_3^-对豌豆铁素营养的影响

EFFECT OF NITROGEN FORMS AND HCO_3^- ON IRON NUTRITION OF PEA

在水培条件下研究了NO3 N ,NH4 N及添加HCO- 3和HEPES对豌豆铁营养的影响。与NO3 N相比 ,供应NH4 N时豌豆根系铁还原力上升较早 ,铁还原酶活性显著较高 ,铁向地上部转移较多。供应NH4 N时培养Sparkle的营养液pH下降较快 ,而培养E10 7营养液 pH受氮源形态的影响较小。对根系质外体铁的利用 ,以NH4 N为氮源时 ,两种豌豆经过 15天后都全部利用 ;供应NO3 N的E10 7能全部利用 ,Sparkle也利用了约 3/ 4 ;以HCO- 3缓冲时E10 7利用了约 3/ 4 ,而Sparkle则几乎不能利用。但是生长在HCO- 3缓冲的营养液中的豌豆根系结构完好 ,转移到低pH环境中后铁还原力不仅没有降低 ,反而比对照有所提高。HCO- 3和HEPES对豌豆铁营养的影响相似。表明HCO- 3对豌豆铁营养的影响不是破坏了根系的结构和功能 ,而主要是通过提高根际 pH值 ,抑制了根系铁还原酶活性的作用 ,从而降低了对铁的吸收利用能力。氮素形态对豌豆铁营养的影响主要是通过影响质外体 pH起作用的。

The effects of nitrogen types, HCO - 3 and HEPES on iron nutrition of pea genotypes, Sparkle and E107, were studied by solution culture under controlled conditions. Compared with NO 3?N, NH 4?N application resulted in earlier and significantly higher iron reducing activities, stronger utilization of apoplastic iron in roots, and more iron transported to shoot for both genotypes. The pH of solutions of Sparkle plants decreased more quickly when supplied NH 4?N, however, there was no difference in solution pH in the two nitrogen types for E107. Apoplastic iron accumulated in roots was used up in low pH condition, but it could not be exploited by plants in 10mmol/L HCO - 3 buffering solution. However, plant roots in high pH condition were structurally and functionally undamaged, their iron reducing activities were higher than those grew in low pH solutions. The effect of HCO - 3 was similar with that of 5mmol/L HEPES. The results suggested that the effects of nitrogen types on iron nutrition were through changes of pH in rhizosphere and apoplast in plant, and the inhibition of iron nutrition of pea by HCO - 3 was not due to damage of root construction but the depression of iron reducing activity under high pH induced by HCO - 3.