The Expression Of Maize Calmodulin Genes Induced By Drought And Salt Stresses Is Associated With ABA And H₂O₂

Drought and salt stresses are two important environmental factors that affect plant growth and development.Abscisic acid(ABA) can regulate a variety of physiological and molecular responses for plant against stresses such as drought,chilling,salinity and so on. Drought and salt stresses can cause the accumulation of ABA.Recent work showed that ABA can cause the generation of H₂O₂,the increases in the content of CaM in leaves of maize and the expression of CaM1,and there is a cross talk between CaM and H₂O₂.The plants possess a large number of genes encoding CaMs families.Can all of the calmodulin genes be induced by stresses? The relationship between the expression of different calmodulin genes and the generation of H₂O₂,and the differences in either tissue expression or stimuli response need to be further determined.In this study the effects of the transcription of CaM1,CaM2 and CaM3 induced by drought and salt stresses,and the role of ABA,H₂O₂ in the regulation of the transcription of calmodulin genes were investigated.The results as follows:Treatments with PEG(25%) and ABA(100μM) led to an enhancement in the expression of three CaM genes in leaves of maize.Pretreatment with the ABA biosynthetic inhibitor fluridon(FLU) substantially blocked the enhancement in the expression of the CaM genes induced by drought stress,suggesting that the increased expression of CaM genes under drought stress is associated with the accumulation of ABA.There appeared two peaks in the expression of CaM genes in leaves of maize plants exposed to 10 mM H₂O₂ treatment.Pretreatments with H₂O₂ scavenger or NADPH oxidase inhibitor substantially reduced the ABA-induced increases in the expression of the CaM genes after the maximum values,but only had a very little effect on the expression before the maximum values.These results suggest that ABA and H₂O₂ are required for drought stress-induced expression of the CaM genes in leaves of maize plants,and there is a cross-talk between CaM and H₂O₂ under drought stress.Treatment with NaCl(250mM) led to the enhancement in the expression of three CaM genes in leaves of maize.The patterns of the expression of three genes were similar. Pretreatment with the ABA biosynthetic inhibitor fluridon(FLU) substantially blocked the increased expression of the CaM genes induced by salt stress,suggesting that the increased expression of CaM genes under salt stress is associated with the accumulation of ABA. Pretreatments with H₂O₂ scavenger or NADPH oxidase inhibitor obviously reduced the NaCl-induced increases in the expression of the CaM genes after the maximum values,but only had a very little effect on the expression before the maximum values.These results suggest that ABA and H₂O₂ are required for salt stress-induced expression of the CaM genes in leaves of maize plants,and there is a cross-talk between CaM and H₂O₂ under salt stress.Both drought and salt stresses could induce the expression of CaM1 in roots of maize. CaM2 hardly expressed in roots of maize under drought stress,whereas the CaM2 gene expressed very obviously in roots of maize under salt stress.Drought stress could strongly induce the expression of CaM3 in roots of maize,but salt stress could not induce the expression of CaM3 in roots a bit.Even under the same stimuli environment,the pattern of the calmodulin genes expression were dissimilar in different tissues of maize.The time when CaM1 and CaM3 expression reached the peak were different in roots and leaves under drought stress,and the expression of CaM3 in leaves were stronger than that in roots. The time when CaM1 and CaM2 expression reached the peak were different under salt stress,and the expression of CaM2 in leaves were stronger than that in roots.These results suggest that different calmodulin genes of maize show specificity in either tissue and stimuli response.