Salt-Tolerant Sorghum Screening And The Machanisms Of Toterances

Salt stress is one of the major abiotic stresses that depress plant growth and drasticallylimit plant production. Because of the increasing salinization in soils, it has been a greatthreat to crop production. Sorghum is one of the main food crops, forage and potential energycrops. The understanding of the mechanism for its response to salt stress is important inagriculture application and plant improvement. Researches were conducted with hydroponicculture in incubator in the laboratory of Shenyang Agriculture University in2009-2012.Forty-two sorghum cultivars were screened for salinity tolerance and classified. Salt tolerantcultivar （Liaoza15） and salt sensitive cultivar （Longza11） were used, and the influence ofsalt stress to photosynthesis and cholorophyll fluorescence, the contents of osmotic regulationsubstances and ions, antioxidization system of the two sorghum cultivars wer analyzed. Wealso examined the response of ABA to the germination and growth and the expression ofABA-regulated genes under salt stress of the two sorghum cultivars. The salt tolerancemechanism and molecular basis of sorghum were clarified. The major results of the studieswere as below:1. The concentration of NaCl,150mmol L^-1, could be suitable for salt toleranceidentification of sorghum cultivars. Principal component analysis results showed that rootlength, leaf weight and germination rate were were the most significant factors and arerecommended as the main indexes to identify salinity tolerance of sorghum at germination.The analysis showed five of the42cultivars were highly salt tolerant eg Liaoza15, fourteencultivars were salt tolerant eg Shenshi104, twelve cultivars were medium salt sensitive egAoza1, eight cultivars were salt sensitive, eg Tieza17, and three were highly salt sensitive egLongza10.2. The low NaCl concentration (50mmol L^-1) increased the chlorophyll content, and thehigh NaCl concentration (100-200mmol L^-1) reduced content substantially. Salt stressreduced Pn, Gs, Tr, Fm, Fv/Fo, Fv/Fm, Fv’/Fm’ and qP, and increase Fo and NPQ. The lowNaCl concentration (50mmol L^-1) reduced Ci, and the high NaCl concentration (100-200 mmol L^-1) increased it. The adverse impact of salt stress on Liaoza15was less than onLongza11. The small reduction in net photosynthesis rate caused by50mmol L^-1NaCl stresswas considered to be a result of non-stomatal restriction; but increased stomatal restrictionwith increased NaCl concentration resulted in more severe reductions in photosynthesis.Under salt stress, salt tolerant cultivar could protect the photosynthetic organs moreeffectively than salt sentitive cultivar and thus improve the production of sorghum in saltaffected areas.3. Under salt stress, the contents of proline, soluble sugar, reducing sugar, solubleprotein, amino acid and membrane permeability of leaves of the two sorghum cultivarsincreased, and the root activity of the two orghum cultivars decreased. The increases ofpraline, soluble sugar, reducing sugar, soluble protein and amino acid of leaves of Liaoza15were more than those of Longza11. The increases of membrane permeability and thereduction of root activity were less than those of Longza11. The osmotic adjustment abilityof Liaoza15was stronger than that of Longza11. Under salt stress, Na⁺content of the twocultivars increased, and the Na⁺content of roots was higher than that of leaves. These showedthat roots did well in storing sodium, and could reduce the transportation of sodium to leaves.Under salt stress, the increases of roots Na⁺content of Liaoza15were more than those ofLongza11, and the increase of leaves Na⁺content of Liaoza15were less than those ofLongza11. The contents of K⁺, Ca²⁺, and K⁺/Na⁺, Ca²⁺/Na⁺of leaves and roots of the twosorghum cultivars reduced under salt stress, and the reduction of Liaoza15were less thanthose of Longza11. These showed that the ability of selective absorption of Liaoza15wasbetter than that of Longza11.4. Under salt stress, the contents of O-2and MDA increased, and the increase extents gothigher along with the increase of NaCl concentration. The contents of O-2and MDA of thesalt tolerant cultivar Liaoza15were less than those of salt sensitive cultivar Longza11. Theseshowed that the O-2scavenging ability Liaoza15was stronger than that of Longza11. Theactivity of SOD, POD, CAT, APX of sorghum seedlings improved under salt stress, and theincreases of activity of Liaoza15were more than those of Longza11.5. Under the exogenous ABA treatments, the germination rate, leaf length, root length, leaf dry weight and root dry weight of the two sorghum cultivars reduced, and the reductionwent up with the increase of ABA concentration. The reduction of all traits of Liaoza15wasless than that of Longza11, and it showed that the tolerance to ABA and salt of sorghumcultivars were the same.Under salt stress, the ABA content of the two cultivars increased with the increase ofstress time. The content of ABA of the two cultivars went up at3h of stress, and the peaks ofboth cultivars were at6h of stress. The ABA content of Liaoza15were less than that ofLongza11, and influence of Liaoza15was smaller than that of Longza15.The expression of ABA-regulated genes （SbABI1、SbABI3、SbABI4、SbABI5andSbRAB28） of the two sorghum cultivars were analyzed under salt stress, and the resultsshowed that the expression of SbABI1went up obviously, the expression of SbABI3andSbABI4went down sharply, the SbABI5and SbRAB28of leaves had no obvious change, butthose of roots had obvious change. The SbABI5and SbRAB28of roots of Liaoza15increasedsharply, but we could not see obvious change in Longza11, suggesting that ABI5was themost likely key gene in SbABIs for salt tolerance in sorghum. Data for Arabidopsis indicatedthat expression of ABI5was a key step in the ABA signaling pathways to improve salttolerance in sorghum.The expression of SbABIs in the roots of the two cultivars was determined underABAtreatments. The results showed that the low concentrations of ABA treatments stronglyinduced the expression of the SbABI5gene in the roots in two cultivars. While in the highconcentrations of ABA treatments, the obvious accumulation of SbABI5transcript was notobserved at any times. The results proved that the induced increasing expression of SbABI5was inhibited by higher ABA contents.