胞外ATP、H_2O_2、Ca^(2+)与NO调控木榄根系离子平衡机理研究

Extracellular ATP,hydrogen peroxide,calcium and nitric oxide mediate root ion fluxes in Bruguiera gymnorrhiza subjected to salt stress

运用非损伤微测技术(NMT),研究了短期盐胁迫下胞外ATP(eATP)、H2O2、Ca2+与NO对非泌盐红树木榄根系K+Na+平衡的调控作用。NaCl(100 mmolL,24 h)与等渗甘露醇处理的实验表明,木榄根尖对盐胁迫的响应具有高度的离子特异性。盐胁迫增强了木榄根尖的Na+外流,但Na+外流被Na+H+逆向转运蛋白抑制剂Amiloride和质膜H+-ATPase抑制剂Vanadate抑制,表明Na+外流源于根尖表皮细胞质膜Na+H+逆向转运系统驱动的Na+外排。短期盐胁迫处理能诱导木榄根尖K+外流,但被氯化四乙胺(TEA,外向K+通道抑制剂)明显抑制,证明K+外流是由激活的去极化外向型离子通道KORCs介导。胞外ATP(300μmolL)、H2O2(10 mmolL)、Ca2+(10 mmolL)与SNP(NO供体,100μmolL)均能增加短期盐胁迫下的Na+外流,同时抑制K+外流。其中,促进Na+外流效果较强的是H2O2和Ca2+,而Ca2+和NO抑制K+外流的效果突出。这些实验结果表明,胞外ATP、H2O2、Ca2+与NO这4种盐胁迫信使是通过上调木榄根系细胞质膜Na+H+逆向转运体系(Na+H+逆向转运体和H+泵)活性,在促进Na+和H+逆向跨膜转运的同时,抑制去极化激活的K+离子通道来减少盐诱导的K+外流。

Using the noninvasive microtest technique （NMT） , the effects of extracellular ATP （eATP） , hydrogen peroxide （H2O2） , calcium （Ca^2＋ ） and nitric oxide （NO） on root K^＋/Na^＋ homeostasis were investigated in a nonsecretor mangrove species Bruguiera gymnorrhiza under short-term （ST, 24 hours） salt stress （ 100 mmol/L NaCl）. The experiments of NaCl and Mannitol in B. gymnorrhiza roots indicated that there were mainly high ionspecific effects on NaCl-induced ion fluxes in roots. Salt stress resulted in an increased Na^＋ efflux along the root axis of B. gymnorrhiza. However, the salt-enhanced Na^＋ efflux was inhibited by amiloride, a Na ^＋/H ^＋ antiporter inhibitor or sodium orthovanadate, a plasma membrane （PM） H^＋-ATPase inhibitor obviously, suggesting that the Na^＋ efflux was resulted from active Na^＋ exclusion. NaCl treatment caused an evident K^＋ efflux in B. gymnorrhiza, but it was significantly restricted by the K ^＋ channel blocker, TEA, suggesting that the K ^＋ efflux was mediated by K^＋ permeable channels. Exogenously applied eATP （300 μmol/L） , H2O2 （10 mmol/L）, Ca^2＋（10 mmol/L） , or SNP （NO donor, 100 μmol/L） enhanced the salt-elicited Na^＋ efflux but reduced K^＋ efflux under ST treatment. Under salt stress, H202 and Ca^2＋ showed of K^＋ efflux was more pronounced by Ca^2＋ or NO a capacity to exclude Na^＋ , while the inhibition application. In conclusion, our data revealed that eATP, H202, Ca^2＋ , and NO upward regulated Na^＋/H^＋ antiporter and H ^＋ pump, an activity of Na^＋/ H ^＋ antiport system, which compelled the Na^＋/H ^＋ exchange across the plasma membrane and restricted the K ^＋ loss via depolarization-activated K ^＋ channels simultaneously.