Cuticle Wax And Its Correlation With Drought In Camellia Sinensis Leaves

Abiotic stresses such as drought seriously affect crop growth and development,cuticle plays a very important role in plant drought tolerance.The relationship between cuticle and drought tolerance of tea plant was studied.Based on the identification of cuticle wax content and its composition,the molecular mechanism of cuticle in plant adaptation to drought stress was further explored.In this study,the cuticle structure and thickness were observed by scanning electron microscopy and transmission electron microscopy.The wax components and their contents were identified by GC-MS and GC-FID.The results were as follows:1.By using Camellia sinensis cv Fuyun 6,we analyzed the cuticle changes with leaf maturation.The goal was to monitor cuticular wax accumulation during leaf development of Camellia sinensis.The second leaf and the fifth leaf in spring new shoot was chosen to represent immature and mature stages,respectively.The thickness of the adaxial cuticle was increased from the second leaf(1.152±0.066 μm)to the fifth leaf(2.477±0.054 μm);similarly,the thickness of the abaxial cuticle also was increased from the second leaf(0.468±0.025 μm)to the fifth leaf(1.048±0.033 μm).During leaf maturation intracuticular wax layer contributed most to this increase,and the epicuticular wax layer only slightly increased.Gas chromatography-mass spectrometry analysis identified 58 wax constituents belonging to 13 chemical classes,including esters,glycols,terpenoids,steroids,fatty acids and their derivatives(primary alcohols,aldehydes,ketones,and alkanes).Wax coverage increased with leaf maturation,from the second leaf(4.76±0.23μg/cm2)to the fifth leaf(15.38±0.25 μg/cm2).Primary alcohols dominated in the immature leaf,then triterpenoids became the major components in the mature leaf.2.We measured the water loss rate in different cultivars of Camellia sinensis in an effort to study the relationship between wax and drought tolerance in Camellia sinensis.We optimized the SWAPDT method,then screened 118 Camellia sinensis germplasm,a known drought-tolerant cultivar Fuandabai and drought-sensitive cultivar Xianggubaihao wereused as positive and negative control,respectively.95 germplasms were identified with lower water loss rate,and 23 germplasms showed higher water loss rate.3.Six with lower water loss rate and six higher water loss were selected,stomata density was observed by scanning electron microscopy,and eight germplasms of Camellia sinensis with similar stomatal density were selected,including 4 low water loss rate germplasms(Wuniuzao,Jinmudan,Jinguanyin and 0316B),and 4 higher water loss rate germplasms(0202-10,0306H,0306A and Hongyafoshou).The wax structure,content and composition of the eight germplasms were analyzed.There were more large chunk of wax crystal distributed around the stomata in Wuniuzao and 0316B,while large crystal structure is relatively sparse in Jinmudan and Jinguanyin.For the 4 germplasms with higher water-losing rate,0202-10 and 0306H had more wax crystal distributed around the stomata,In 0306A and Hongyafoshou,the wax crystal around the stomata was mainly small flaky and short sticks.Generally the germplasms with lower water loss rate had thicker cuticle compared with those germplasms with higher water loss rate,except 0202-10.4.One-year old pot-grown Jinmudan(variety with lower water loss)and Hongyafoshou(variety with high water loss rate)were subjected to drought treatment.Used to analyze the relationship between leaf wax changes and drought stress.The result is as follows:We observed that epidermal wax crystals of both cultivars increased continuously under drought stress,and young leaves showed higher increase in wax crystal number compared with mature leaves,and wax crystal in mature leaves were mainly distributed on the abaxial surface.Meanwhile,cuticle thickness constantly increased at different leaf positions.Cuticle wax content measurement indicated that wax load from both cultivar increased with the prolongation of drought treatment,while this increase in young leaves was more significant compared with mature leaves.The wax components and contents have also undergone significant changes under drought stress.The most significant change is the significant increase in the content of alkane and the formation of other components,suggesting that the decarbonylation pathway for wax synthesis is enhanced by drought treatment.