Studies Of Genome B On Tolerance Of Phosphorus Deprivation, Drought, And High Salinity In Wheat(triticum Aestivum L.)

The responses and tolerance in wheat to the abiotic stresses of deprivation Pi, drought,and high salinity are genetically regulated by chromosomes. In this study, using Chinesespring (CS) and a set of its derived ditelosomic line (DL) of B chromosome as materials,the plant phenotypes, characterizations of nutrient acquisition, photosynthetic parameters,chlorophyll fluorescence parameters, and cellular protection system behaviors have beensystematically investigated. In addition, the chromosomal localization of TaPHT2;1andTaPht1;4, two phosphate transporter genes in wheat, as well as their roles in mediating Piacquisition and utilization in plants have been studied. The main results are as follows.1. Compared with CS, the plant phenotypic features and dry weights of ditelosomicline (DL)4BS,6BS,3BL and7BL under sufficient-Pi condition as well as those of the DL4BS,6BS,7BS and7BL under low-Pi condition were not varied. Other DLs exceptaforementioned ones showed significant changes on the plant phenotypes and the dryweights under various Pi-supply conditions, showing a trend to have worse phenotypicfeatures and lower dry weights. The P accumulation amount per plant in the tested DLsdisplayed a dropped trend compared with CS under various Pi-supply conditions,suggesting that distinct wheat DLs regulate the plant phosphorus accumulation. Undersufficient-Pi condition, the total P contents of4BS and4BL were significantly higher thanCS, whereas5BS was significantly lower than CS. Under low-Pi condition, the total Pcontent of5BS was significantly higher than CS, whereas3BL and5BL were significantlylower than CS. Compared with CS, the tested DLs showed a relative higher variation rangeon plant P usage efficiencies under both sufficient-and low-Pi conditions, generally with areverse tendency of the plant P accumulation amount in each line. Therefore, this studyindicates that distinct wheat DLs play an important role in mediating plant responses toexternal Pi conditions and in genetically regulating plant usage efficiencies. Leaf area perplant can be used as one index for evaluation of plant P usage efficiency under bothsufficient-and low-Pi conditions.2. Under sufficient-Pi condition, the short arm of5B showed to carry the major genesin regulating photosynthetic pigment contents. The superoxide dismutase (SOD) activitiesin roots and leaves of1BS,2BS, and3BS were significant lower than those of CS, whereasthe peroxidase (POD) activities in roots and leaves of1BL were significant lower thanthose of CS. The superoxide production rates in leaves of1BS and in roots and leaves of2BS and4BL were faster than those of CS. Under deprivation-Pi condition, the long andshort arm of1B, long arm of3B and short arm of4B were shown to situate major genes inregulating photosynthetic rate (Pn). The long arm of3B and the short arm of1B exhibitedpositively regulation effects on Fv/Fm and qP, two chlorophyll fluorescence parameters. The long arms of1B,2B, and3B and the short arm of7B were shown to contain the majorgenes of SOD. The results indicate that the long arm of3B and the short arm of1B carrythe major genes in regulating the cellular lipid peroxidation degree under deprivation Pi,and the long arm of2B and the short arm of4B harbor the major genes in controlling thesuperoxide production rate. Thus, the long and short arms corresponding to the DLsaforementioned exert critical genetically regulation effects on the photosyntheticparameters and cellular protection system under low-Pi stress.3. For the CS and DLs of B genome, only1BS that a line lacking the long arm of1Bwas failed to detect the transcripts of TaPHT2;1, indicating that TaPHT2;1is located in thelong arm of1B. Under sufficient-Pi condition, the plant dry weight and total P content in1BS were significantly decreased in comparison with those in CS, but the P usageefficiency of1BS did not alter in comparison with that of CS. Under deprivation Pcondition, the plant dry weight of1BS was also significantly lower than that of CS, but1BS had higher total P content than CS and the accumulative P amount per plant wassimilar to that of CS. Therefore, the phosphate transporter gene TaPHT2;1that located onthe long arm of1B exerts dramatic effects on plant dry mass production under variousPi-supply conditions through its regulation of plant P acquisition and cellular Ptranslocation. In addition, the results of expression level of TaPHT2;1, plant dry weight,total P content, accumulative P amount per plant, and P usage efficiency in wheat cultivarsthat displayed varied P use utilization properties displayed similar patterns to thosementioned previously. Compared with wheat cultivars with low P utilization efficiency, thewheat cultivars with high P use efficiency showed high expression level of TaPHT;1together with more plant dry mass under conditions of Pi sufficience and Pi deprivation.4. The high-affinity phosphate transporter gene TaPht1;4in wheat was confirmed tolocate at the long-arm of3B because TaPht1;4as well as its expression could not bedetected in3BS, a ditelosimic line missing the long-arm of3B. Under sufficient Picondition, no variations were observed on plant dry weight, total P content, plantaccumulative P amount, and P usage efficiency between CS and3BS. Under Pi deprivation,the total P content and P use efficiency of3BS were similar to those of CS, but the plantdry weight and accumulative P amount of3BS were significantly lower than those of CS.These results suggest that missing TaPht1;4due to lacking the long arm of3B can notaffect the plant growth and Pi acquisition under Pi sufficience, but can modify the Piacquisition capacity under Pi deprivation. The results on relationship between theexpression level and plant dry weight, total P content, accumulative P amount, and P useefficiency obtained in wheat cultivars with different low-Pi use efficiencies were similarwith those in CS and3BS. Compared with the cultivars with low P use efficiency, thecultivars with high P use efficiency exhibited increased TaPht1;4expression level and more accumulated dry mass and P amount under low-Pi stress.5. Under drought stress condition, the long arm of1B, the short arms of4B and5Bshow positive effects on plant growth traits, plant dry weight, and plant leaf area. Similarly,the long arm of1B and6B exhibited positive effects in regulating plant height. The shortarm of1B has negative effects on ratio of root dry weight to aboveground dry weight. Thelong arm of1B and the short arm of5B carry the major genes for plant nitrogenaccumulative amount. In addition, the short arm of5B also situates the major genes forplant accumulative amount of phosphorus and potassium. Moreover, it was also observedthat the long arm of1B and the short arm of4B exhibit positive effects on contents ofproline and soluble carbohydrate under drought stress in addition that the short arm of5Balso shows significant positive effect on the soluble carbohydrate content. The results inthis study revealed that the genetic effects of the long arm of1B and the short arms of4Band5B on plant leaf area, accumulative amount of plant nitrogen, phosphorus, andpotassium, and the contents of proline and soluble carbohydrate are similar to the geneticeffect of aforementioned chromosomes on plant dry weight under the condition of droughtstress. Furthermore, the plant growth traits, the nutrient accumulative amount, and thecontents of osmotic regulators mentioned above exhibited significant or most significantpositive correlations with the plant dry weight under drought stress.6. Under drought stress condition, the photosynthetic parameters such asphotosynthetic rate (Pn), transpiration rate (Tr), chlorophyll content (Chl), and carotioniodcontent (Car) of1BS were significant lower that those of CS. These results indicate that thelong arm of1B corresponding to the aforementioned DLs exert dramatic effects onphotosynthetic and chlorophyll fluorescence parameters under conditions of drought stress.In addition, the long arm of2D contains the major genes of SOD and the short arms of1Band5B harbors the major genes of POD, as well as the long arm of3B and the short arm of4B situate the major genes of soluble protein content and the short arms of1B and4B havethe negative effects on MDA content, and the short arm of1B and the long arm of2B exertnegative effects in regulating superoxide production rate, and the short arm of2B haspositive effect in controlling the superoxide production rate.7. Under salt stress condition, the long-and short-arm of1B, as well as the short armsof2B and3B show significant positive effects on plant dry weight and leaf area. The shortarms of2B and4B exhibit positive effects on plant total P content. The long arms of1Band7B show positive effects on plant K2O content. The long arm of1B and5B and theshort arms1B to3B carry the major genes on regulating the contents of proline and solublecarbohydrate. It was observed that the long arms of1B and3B and the short arms of1Band2B exert significantly negative effects on plant Na+content. It is suggested that some distinct arms of B chromosome displayed similar regulation effects on plant dry weight,leaf area, plant accumulative amount of nitrogen, phosphorus, and potassium, and contentsof proline and soluble carbohydrate, indicating that the strongly positive regulation effectsof distinct long-and short-arms of wheat chromosome (such as the long-and short-arm of1B and the short arms of2B and3B) on resisting the salt stress are closely associated withtheir positive regulation effects on plant photosynthetic organ area, nutrient acquisitioncapacity, and osmotic regulation function, as well as their negative regulation effects onplant Na+content.8. Under salt stress condition, the Parameters of photosynthetic and chlorophyllyfluorescence of2BS,1BL,2BLand5BL were all lower than those of CS. Furthermore, theSOD activities in roots and leaves of1BS,2BS,3BS, and5BL, the POD activities inleaves of1BS,7BS,1BL,4BL, and5BL and in roots of1BL and5BL were alsosignificant lower than those of CS. The soluble protein contents in roots and leaves of4BLand in roots of1BL were significant lower than those of CS. Furthermore, the superoxideproduction rates in roots and leaves of1BS,2BS, and1BL and in roots of4BL weresignificantly decreased in comparison with those of CS. The MDA contents in roots andleaves of1BS and1BL, in leaves of5BS, and in3BL of roots were significant higher thanthose of CS. Taken together, the results in this study confirm that distinct long and shortarms deleted in aforementioned DLs play important roles in regulating photosyntheticparameters and cellular protection system under conditions of salt stress.