Effects Of Drought Stress On Photosynthetic Characteristics Of Wheat Near-isogenic Lines With Different Wax Contents

Wheat is one of the most widely grown crops in the world and accounts for 30%of cereal planting area.Wheat is the staple food for 35%to 40%population in the world.However,wheat is also a crop requiring much water.Precipitation in the growing season of winter wheat is scarce.Drought disasters occur frequently and have a great impact on wheat yield.Studies suggest that there is a remarkable positive relationship between plant epidermis wax and drought resistance.In order to investigate the effect of wax content on drought resistance of wheat,two pairs of near-isogenic lines,multi waxy strain?JM205,JM208?and less waxy?JM204,JM206?were used as experimental materials.Dry huts method in field was used to explore changes of waxy structure and the relationship of waxy with water loss and photosynthetic characterizations in wheat.In order to explore the range of drought resistance in waxy wheat,we carried out a gradual drought treatment in artificial climate chamber to simulate the process of soil moisture changes in field,and measured water potential,photosynthetic gas exchange and chlorophyll fluorescence parameters in wheat flag leaf.The results of field experiment showed that under normal watering conditions,the waxy content of JM205 was significantly higher than that of JM204.After drought stress,wax content of both multi waxy and less waxy wheat increased.The structure of front and back of flag leaf was different.The front of the flag leaf mainly has a linear structure and scattered around the stomata,whereas the back is mainly vertical lamellar and also scattered around the stomata.More wax is in the back of leaf than the front in the same line.Under normal watering conditions,water potential and photosynthetic rate in the flag leaf were not significantly different between multi-wax lines and less-wax lines.After drought treatment,water potential and photosynthetic rate in flag leaf were less decreased in multi-wax line than less-wax line,but the wax content in the less-wax lines decreased more significantly.The results of pot experiments suggested that under normal watering conditions,flag leaf water potential in JM205 and JM204 wax lines was not significantly different.With prolongation of drought stress,flag leaf water potential of multi-waxy lines and less-waxy lines gradually decreased,but the less-wax line declined greater.Especially,from the 3rd to the 5th days of treatment,soil moisture content was decreased from 49%to 32%,and flag leaf water potential in the multi-wax strain JM205 and the less waxy strain JM204 was significantly decreased,but the decrease was obviously different.After 5 days of drought treatment,water potential of multi-waxy strain JM205 and less-wax strain JM204 was respectively decreased by 12.7%and 33%.When soil water content was higher than 49%,there was no significant difference in the photosynthetic rate?Pn?between the flag leaf of multi waxy JM205 and less waxy line JM204.During drought treatment,photosynthetic rate in multi waxy and less waxy strains gradually decreased,but the decrease was greater in less waxy strain JM204.Changes in transpiration rate?E?and intercellular CO₂ concentration?Ci?were similar to the photosynthetic rate.When soil water content was higher than 49%,the stomatal conductance of less waxy line JM204 was higher than that of the multi-waxy line.With drought becoming severe,the decrease of gas exchange parameters was greater inless wax lines.When the soil moisture content was 32%,the difference of gas exchange parameters was significant between multi and less waxy lines.As drought become severe,the photosynthetic parameters decreased sharply,and there was no significant difference between the different strains.Under moderate drought stress,the PSII actual photochemical efficiency??PSII?and maximum photochemical efficiency?Fv/Fm?decreased more rapidly in the low-wax line,indicating that PSII electron transfer inhibition and light inhibition were more serious.JIP-test analysis indicated that PSII electron transport from Q_A to Q_B was blocked.In contrast,high-wax line maintained relatively higher photosynthetic capacity under drought conditions,with a higher electron transfer and less excess light energy dissipation,resulting in lessphotoinhibition.When relative soil water content decreased below 32%,the water potential and photosynthetic capacity in both high and low waxy lines decreased significantly,and the decresase was not significant.This study improved the understanding of physiological mechanism of drought tolerance in plants with different wax content.The high-wax line JM205 has significant drought resistance in the soil moisture range of 49%³2%,providing theoretical guidance for breeding drought-tolerant wheat varieties and field cultivation.