Effects Of Drought On Cuticular Wax And Photosynthetic Characteristics In Glaucousness Flag Leaves And Mining Of Wax Synthetic Genes In Bread Wheat

Wheat?Triticum aestivum L.?,as one of the three major crops in the world,is mainly distributed in arid and semi-arid regions.The glaucous trait refers to the performance of blue-green or bright green of wheat leaves,sheaths,stalks and ears,that is divided into glaucous and non-glaucous type,which can be quickly identified and recorded in the field.The glaucous trait is one of the main manifestations of drought adaptation,and it has been widely used in wheat varieties'breeding with drought resistance.With global warming and frequent occurrence of drought events,drought stress affects the safety of wheat production seriously and give a greater challenge to wheat breeding with drought-resistance.More and more studies have considered that glaucous wheat does not always show drought resistance,and many non-glaucous wheat varieties are also widely adapted to drought condition.The glaucous trait is caused by epidermal waxy deposits.The leaf waxy affects the non-stomata transpiration of plants,and together with the stomata pathway regulates the gas-exchange between plant and environment.Under drought stress,the stomata are closed,and the role of wax in reducing leaf water loss and CO₂ exchange is important.Therefore,figure out the effect of drought stress on the waxy and photosynthetic characteristics of flag leaves form different glaucous wheats is important to clarify the relationship between glaucous phenotype and wheat drought resistance,and lay the foundation for the use of glaucous wheat in drought resistance scientifically.In addition,this study provides important clues for wheat drought resistance of molecular breeding by digging more kinds of genes involved in wheat wax synthesis.The main results are as follows:1. The difference between glaucous and non-glaucous wheat varieties on waxy composition and crystal structure in the field were evaluated to figure out the regulatory mechanism of wax in flag leaves.The glaucous phenotype of wheat is not related to total wax content but related to the content and ratio of diketone under normal water condition.The glaucous type of wax crystals on the abaxial side of flag leaves was tube-shaped,and the non-glaucous type of wax crystals on the same part was more thin-shaped.In the meantime,the photosynthetic characteristics of flag leaves at the heading stage were determined.Different glaucous phenotypes did not affect net photosynthetic rate,intercellular CO₂ concentration,and electron transfer efficiency in wheat.Glaucous wheat showed higher intrinsic water use efficiency compared with non-glaucous wheat.The total content of wax is positively related to intercellular CO₂ concentration?r=0.66?.The content of diketone is significantly related to intrinsic water use efficiency?r=0.56?.The properties of wax might play an important role in the exchange of gas-water of wheat photosynthesis.2. The glaucous and non-glaucous wheat varieties were subjected to drought treatment using pot experiment in the greenhouse,the response of waxy and photosynthetic characteristics of flag leaves at heading stage was evaluated.Drought-resistant variety HY2912 with glaucous phenotype maintained the supplement of intercellular CO₂ through increasing the ratio of diketone maintaining lower stomata conductance and improving leaf mass per area?LMA?.Drought-resistant variety Jinmai 47 with non-glaucous phenotype balance water loss and CO₂ absorption through decreasing stomata conductance,increasing the ratio of alkane,and decreasing LMA.Correlation analysis showed that there was a significant positive correlation between intercellular CO₂,the concentration ratio of diketone?r=0.81?and LMA?r=0.62?under drought stress.Therefore,wax compositions had a certain effect on limiting CO₂ diffusion during photosynthesis under drought stress.Therefore,waxy content,composition,and the regulation of mesophyll and stomata should be considered in drought-resistant and glaucous wheat selection.3. In the field experiment,the relationship between drought resistance of glaucous and non-glaucous lines of two populations,waxy composition,and photosynthetic characteristics of flag leaves were evaluated.Under drought stress,there was a weak positive correlation between the drought resistance index?DI?and the ratio of diketone?r=0.26?.DI did not relate to diketone ratio under control irrigation conditions.There was a significant positive correlation between DI,electron transport efficiency?r=0.32?,and intrinsic water use efficiency?r=0.23?under drought stress.Wheat line of glaucous phenotype is not always show drought-resistance.The total wax content of wheat flag leaves was positively related to intercellular CO₂ concentration?r=0.55?,intracellular CO₂ concentration?r=0.40?,i WUE?r=0.28?,and intrinsic water use efficiency?r=0.53?.Intercellular concentration was positive related to the content of primary alcohols?r=0.49?and diketones?r=0.32?.The ratio of alkane was positive related to transpiration rate?r=0.40?and relative water content of leaves?r=0.26?.Therefore,it is speculated that wax compositions play an important role in gas-water exchange process of photosynthesis.Evaluation of glaucousness in wheat drought breeding should be combined with its photosynthetic characteristics.4. Through high-throughput sequencing technology,BSR-seq transcriptome analysis of flag leaves mixed pools of glaucous and non-glaucous line of wheat was performed to select target gene of glaucous phenotype.According to the analysis of FPKM value,a sequence related to waxy synthesis,Ta FAR3,was detected.This sequence was located at the end of chromosome 7A and could be significantly expressed in two non-glaucous line.The ratio of primary alcohol of non-glaucous lines was significantly higher than the alcohol ratio of glaucous lines.By analyzing the differential mutation sites between two mixed pools,there were four significant difference sites that located on 2A,2B and 3D chromosomes of wheat.There were candidate gene groups that related to waxy synthesis such as FAS1,FAD,CP450and FAR1 on the designated regions of 2A chromosome.All in all,this study illustrates the role of both wax and photosynthesis in the potential mechanism of drought resistance through analyzing the effect of drought stress to glaucous and non-glaucous wheat varieties and lines on wax and photosynthesis,which provides theoretical basis for the usage of glaucous wheat in breeding.The digging of candidate genes for wheat wax synthesis provides new resources for wheat molecular breeding.