Abdolzadeh Ahmad, Shima Kazuto, Lambers Hans, Chiba Kyozo
Gorgan University of Agricultural Sciences and Natural Resources, POB 49175-386, Gorgan, Iran.
Ann Bot. 2008 Nov;102(5):735-46. doi: 10.1093/aob/mcn156. Epub 2008 Sep 4.
The source of nitrogen plays an important role in salt tolerance of plants. In this study, the effects of NaCl on net uptake, accumulation and transport of ions were investigated in Nerium oleander with ammonium or nitrate as the nitrogen source in order to analyse differences in uptake and cycling of ions within plants.
Plants were grown in a greenhouse in hydroponics under different salt treatments (control vs. 100 mm NaCl) with ammonium or nitrate as the nitrogen source, and changes in ion concentration in plants, xylem sap exuded from roots and stems, and phloem sap were determined.
Plant weight, leaf area and photosynthetic rate showed a higher salt tolerance of nitrate-fed plants compared with that of ammonium-fed plants. The total amount of Na+ transported in the xylem in roots, accumulated in the shoot and retranslocated in the phloem of ammonium-fed plants under salt treatment was 1.8, 1.9 and 2.7 times more, respectively, than that of nitrate-treated plants. However, the amount of Na+ accumulated in roots in nitrate-fed plants was about 1.5 times higher than that in ammonium-fed plants. Similarly, Cl- transport via the xylem to the shoot and its retranslocation via the phloem (Cl- cycling) were far greater with ammonium treatment than with nitrate treatment under conditions of salinity. The uptake and accumulation of K+ in shoots decreased more due to salinity in ammonium-fed plants compared with nitrate-fed plants. In contrast, K+ cycling in shoots increased due to salinity, with higher rates in the ammonium-treated plants.
The faster growth of nitrate-fed plants under conditions of salinity was associated with a lower transport and accumulation of Na+ and Cl- in the shoot, whereas in ammonium-fed plants accumulation and cycling of Na+ and Cl- in shoots probably caused harmful effects and reduced growth of plants.
氮源在植物耐盐性中起着重要作用。本研究以铵态氮或硝态氮为氮源，研究了NaCl对夹竹桃离子净吸收、积累和运输的影响，以分析植物体内离子吸收和循环的差异。
以铵态氮或硝态氮为氮源，将植物种植在温室水培条件下，进行不同盐处理（对照与100 mM NaCl），测定植物、根系和茎部渗出的木质部汁液以及韧皮部汁液中离子浓度的变化。
与铵态氮供氮植物相比，硝态氮供氮植物的植株重量、叶面积和光合速率表现出更高的耐盐性。盐处理下，铵态氮供氮植物根系木质部运输、地上部积累和韧皮部再转运的Na+总量分别比硝态氮处理植物多1.8倍、1.9倍和2.7倍。然而，硝态氮供氮植物根系积累的Na+量比铵态氮供氮植物高约1.5倍。同样，在盐胁迫条件下，铵处理时通过木质部运输到地上部的Cl-及其通过韧皮部的再转运（Cl-循环）远大于硝态氮处理。与硝态氮供氮植物相比，铵态氮供氮植物地上部K+的吸收和积累因盐胁迫而下降更多。相反，地上部K+循环因盐胁迫而增加，铵处理植物的速率更高。
在盐胁迫条件下，硝态氮供氮植物生长较快与地上部较低的Na+和Cl-运输及积累有关，而铵态氮供氮植物地上部Na+和Cl-的积累及循环可能会产生有害影响并降低植物生长。
