The Role And The Relationship Of Nitric Oxide And Ethylene In Aluminum-reduced Root Elongation In Phaseolus Radiatus L.

Aluminum toxicity is one of the most important factors that limit the growth and development of the plants in acidic soils.Nitric oxide(NO) and ethylene are the important signalling molecules and hormones in plants.In recent years,studies have shown that NO and ethylene involved in responding to a wide range of stresses in plants,but the role and the relationship of NO and ethylene in aluminum-reduced root elongation are unclear.By means of hydroponic culture,the role and the relationship of NO and ethylene in aluminum-reduced root elongation of Phaseolus radiatus L.were investigated in the present study.Main results were as follows:1.Experiments showed that different concentrations of AlCl₃ had different effects on root elongation in Phaseolus radiatus L.,25μmol/L AlCl₃ had no significant effects(P＞0.05),50. 75μmol/L AlCl₃ significantly inhibited the root elongation(P＜0.05),and 100 and 150μmol/L AlCl₃ had extremely significant inhibition on root elongation(P＜0.01),which showed obvious concentration-dependent effect.In addition,the root elongation was inhibited significantly if treated with 150μmol/L AlCl₃ for 4,8,12 and 24h(P＜0.05),and the degree of inhibition enhanced with the extension of the treatment-time,which showed obvious time-dependent effect.2.Experiments showed that all of the NO scavenger(methylene blue,MB)(10μmol/L),nitric oxide synthase inhibitor(N^G-nitro-L-arginine methyl ester,L-NAME)(1mmol/L) and nitrate reductase inhibitor(tungstate,Na₂WO₄)(100μmol/L) had similar inhibition on root elongation with AlCl₃(100μmol/L),NO donor(SNP)(100μmol/L) could reverse AlCl₃(100μmol/L)-reduced root elongation,AlCl₃(100μmol/L) inhibited the root elongation and also reduced the level of endogenous NO of root apices,which proved that AlCl₃(100μmol/L) inhibited the root elongation by reducing the level of endogenous NO of root apices.3.Experiments showed that both ethephon(1μmol/L) and the ethylene precursor (1-aminocyclopropane-1-carboxylic acid,ACC)(1μmol/L) had similar inhibition on root elongation with AlCl₃(100μmol/L),the inhibitor of ethylene synthesis both CoCl₂(50μmol/L) and aminooxyacetic acid(AOA)(5μmol/L) could reverse AlCl₃(100μmol/L)-reduced root elongation, AlCl₃(100μmol/L) inhibited the root elongation and also increased the level of endogenous ethylene of root apices,which proved that AlCl₃(100μmol/L) inhibited the root elongation by increasing the level of endogenous ethylene.4.Experiments showed that ethephon(1μmol/L) and the ethylene precursor ACC(1μmol/L) lowered NO donor(SNP)(100μmol/L)-treated root growth,ethephon(1μmol/L) and the ethylene precursor ACC(1μmol/L) inhibited the root elongation and also reduced the level of endogenous NO of root apices,all of NO scavenger(methylene blue,MB)(10μmol/L),nitric oxide synthase inhibitor(N^G-nitro-L-arginine methyl ester,L-NAME)(1mmol/L) and nitrate reductase inhibitor (tungstate,Na₂WO₄)(100μmol/L) could reduce the increase of NO and root elongation induced by the inhibitor of ethylene synthesis both CoCl₂(50μmol/L) and AOA(5μmol/L),all of which showed that ethylene could reduce the level of endogenous NO of root apices in the root elongation. Experiments also showed that NO donor(SNP)(100μmol/L) reversed ethephon(1μmol/L) and the ethylene precursor ACC(1μmol/L)-reduced root elongation,also reduced the level of endogenous ethylene of root apices,the inhibitor of ethylene synthesis both CoCl₂(50μmol/L) and AOA (5μmol/L) could reverse the increase of ethylene and root elongation induced by NO scavenger (methylene blue,MB)(10μmol/L),nitric oxide synthase inhibitor(N^G-nitro-L-arginine methyl ester, L-NAME)(1mmol/L) and nitrate reductase inhibitor(tungstate,Na₂WO₄)(100μmol/L),all of which showed that ethylene could reduce the level of endogenous NO of root apices in the root elongation.In summary,the results of this paper prove that AlCl₃-reduced root elongation is related to the decrease of NO and the increase of ethylene root apices.Moreover,it promotes the increase of ethylene by reducing NO and the decrease of NO by increasing ethylene,thus inhibits the root elongation in Phaseolus radiatus L.