The Mechanism Of Roots Response To Salt Stress In Cotton Seedling

The aim of this research was to reveal the mechanism of cotton root response tosalinity, through investigating the growth, physiological indexes and root morphology, byusing J958as experiment material, grown in double layer MS medium mimicingnonuinform salt distribution in the vertical direction of soil. There were three treatments:CK/CK, both of the layers were1/2MS medium; CK/S, the above layer was1/2MSmedium and the below layer was1/2MS medium with NaCl (600mM); S/S, both of thelayers were1/2MS medium with171.4mM NaCl. The total salt content in CK/S was equalto S/S.The main results are as follows:1. The growth was significanly inhibited under salt stress: plant height, taproot length,root, stem and leaf fresh weight, and chlorophyll content were markedly reduced. However,cotton seedlings in CK/S, the inhibition effect of salinity on growth was significantlyreduced.2. Under salt stress, ROS of root and leaf, root tip cell apoptosis and MDA increased.However, when the root changed growth derection to avoid the salt layer in CK/S, O2-,root tip cell apoptosis, MDA content gradually reduced to the level of CK/CK, with theincrease of SOD, POD, GR, APX, and decrease of CAT.3. Salt treatment decreased concentrations of Na+and increased K+in leaf, root andstem. In root, Mg2+content was increased and Ca2+content was reduced. However bothMg2+and Ca2+content in stem and leaf were reduced. In CK/S, after avoiding salt layer, K+and Ca2+content in root, stem and leaf were increased slightly. The total K+and Ca2+content was between CK/CK and S/S. Futhermore, NMT(Noninvasive determination ofmicro measurement technology) results showed a increasing Na+and K+efflux anddecreasing H+efflux in root meristematic zone. Na+efflux in CK/S root side close to saltwas higher than far side. But K+and H+efflux showed a contrary trend. In gene exprentionlevel, Cotton seedlings under salt stress, SOS1and NHX1encoding the Na+/H+protonpump in the root, were complementarily expressed. SOS1expression were increased andearlier than NHX1gene expression. When the root growed to avoid salt layer, SOS1geneexpression decreased, and NHX1gene expression was increased significantly. Finally,SOS1and NHX1gene expression was reduced to normal levels. 4. After the cotton seedlings under salt stress, the hormones of root and leaf wereincreased. In CK/S, leaf hormone significantly reduced while the root remained in arelatively stable level. In root, IAA content was firstly increased then decreased, but thecontent of ABA and ZR were just the oppsite.