Drought Resistance Of Wheat NILs With Different Cuticular Wax Content In Flag Leaf

The relationship between flag leaf cuticular wax content and leaf water potential, excised-leaf water loss, leaf photosynthesis characteristics and wheat yield under drought stress were analyzed in this study using two pairs of nearly isogenetic lines(NILs) of wheat with high(JM205 and JM208) and low(JM204 and JM206) cuticular wax content in flag leaf. The paper conduct a comprehensive system of research from wax content and composition, morphological structure, drought-resistant physiology, yield formation and gene expression controlling wax biosynthesis.The results indicated that wax morphology was different in NILs with high(JM205 and JM208) and low(JM204 and JM206) cuticular wax content in wheat flag leaf adaxial side and the abaxial surfaces under both normal irrigation and drought stress condition. The flag leaf adaxial side and the abaxial surfaces in high(JM205 and JM208) cuticular wax content were covered with a large number of wax crystal and larger wax block, while there was less wax crystal on low(JM204 and JM206) cuticular wax content. Meanwhile, SEM showed that the wax layer was thicker in wheat flag leaves with high(JM205 and JM208) cuticular wax content. The layer thickness was about 1.04?m and 1.24?m in wheat flag leaves with low and high(JM205 and JM208) cuticular wax content under drought stress condition, respectively. The results showed that the drought-resistance was related to the flag leaf cuticular wax content and was morphology.The results also indicated that the average cuticular wax content in flag leaf of wheat NILs, JM205 and JM208(15.15mg/g) was higher than that in JM204 and JM206 with the average of 8.43mg/g. The flag leaf water potential of wheat NILs, JM205, JM208, JM204 and JM206 was 0.19 MPa, 0.22 MPa, 0.32 MPa and 0.25 MPa, respectively, which indicated that the water potential of wheat lines with high cuticular wax content in flag leaf was higher than that of lines with low cuticular wax content under drought stress. And the average excised-leaf water loss rate of JM205 and JM208 was lower than the average of JM204 and JM206, indicating that lines with high cuticular wax content in flag leaf was more resistant to drought tolerance than lines with low cuticular wax content.Compared with normal irrigation condition, WUE decreased by 16.3% in JM206 flag leaf and decreased 32.2% in JM204 flag leaf under the drought stress, and WUE had no difference with normal conditions of JM205 and JM208 flag leaf under drought stress, while that was higher than lines with low cuticular wax content(JM204 and JM206). RWC increased 5.1% and 9.8% on low and high lines. No matter normal irrigation or drought stress condition, WUE and RWC were significantly higher in JM205 and JM208 than JM204 and JM206, which indicated that drought resistance and water-saving on high lines flag leaf is higher than low lines.In addition, wheat lines with high cuticular wax content in flag leaf had higher Pn, lower Ci, lower E, and lower decrease of Fv/Fm than lines with high cuticular wax content under drought stress, which indicated that wheat flag leaf cuticular wax content can alleviate the decreasing of Fv/Fm caused by drought stress, and maintain high photosynthetic rate.Relative gene expression in lines with cuticular wax content(JM204 and JM206) were significantly lower on JM205 and JM208 at heading stage, to flowering period, which reduced on the different cuticular wax content wheat lines, and which increased at filling stage under normal irrigation condition. Under drought stress condition, relative gene expression increased continuously on low lines, and increased first and then falled over time on high lines. It indicated that trying to improve relative gene expression improve the wax content in flag leaf of low lines, to resist drought stress, while, under drought stress, the relative expression of four genes reduced on high lines flag leaf, with the extension of drought time, expression quantity increased in order to improve the wax content to resist drought stress.Furthermore, the average yield of JM205 and JM208 was higher(3.73%) than that of JM204 and JM206, and the drought tolerance index TOL and drought susceptible index SSI in JM205, JM208, JM204 and JM206 was 825.86, 351.33, 1120.64 and 1267.85. 0.92, 0.41, 1.21 and 1.42, respectively, which indicated that wheat NILs with high cuticular wax content in flag leaf was more resistant to drought tolerance than NILs with low cuticular wax content. All in all, the wheat cuticular wax content in flag leaf were closely related to plant drought tolerance and the cuticular wax content, as a supplementary physiological trait, can be used to improve the drought resistance of wheat.