Study On The Correlation Between Cuticular Wax Composition And Cuticular Transpiration In Camellia Sinensis Leaves

The plant cuticle is an extracellular lipid mixture,which covers aerial organs.The primary function of cuticular wax is to limit cuticular transpiration,and contribute to the drought tolerance.Understanding the relationship between cuticular transpiration and cuticle composition is important for tea tree breeding,cultivation and production.In this study,tea tree leaves were used as experimental materials.Cuticle ultrastructure was observed by TEM and SEM observation,and the cuticular wax composition was measured by GC-MS and GC-FID analysis..Correlation analysis was used to find the key cuticular waxes that affect the cuticular transpiration barrier.The results were as follows.1.We developed a new method that can measure the cuticular transpiration from different leaf surface simultaneously.We showed that the cuticular transpiration rate of abaxial surface of Fuyun 6 tea tree was about 1.8 folds higher than that of the abaxial surface.Data analysis showed that the intracuticular wax of adaxial surface and the epicuticular wax of abaxial surface were the major cuticular transpiration barriers.The coverages of primary alcohols,aldehydes and alkanes in the adaxial intracuticular wax were significantly higher than that in the abaxial,which may attribute to its lower transpiration rate.2.Cuticular transpiration and wax composition were analyzed fromeight tea tree germplasms under normal growth condition,we found that the cuticular transpiration rate of the abaxial surface was about 1.8-3.3 times that of the adaxial surface.We also showed that the cuticular transpiration rate from abaxial intracuticular wax was the highest among the four transpiration layers.We concluded that the abaxial surface of the tea tree leaves,especially the epicuticular wax layers,is the main trnaspiration barrier to limit non-stomatal water loss.We also found the intracuticular wax of adaxial surface and the epicuticular wax of abaxial surface were the main cuticular transpiration barriers in eight tea tree germplasms.Through correlation analysis,we found that the VLCFAs was significantly negatively correlated with cuticular transpiration.However,no correlation was found in alicyclic compounds such as sterols and triterpenes.Therefore,our data suggested that VLCFAs is the main substances constituting the cuticular transpiration barrier.3.Cuticular transpiration and wax composition were measured during water deprivation,we found that cuticular wax modification in tea trees are reversible in response to soil water status.Wax lipid analysis showed that the coverage of abaxial intracuticular wax(primary alcohols and triterpenoids)significantly increased after drought stress.The increase of these wax composition significantly improved the barrier properties of the abaxial intracuticular wax.Correlation analysis results also showed that the aliphatic compounds had a greater contribution to the enhancement of cuticular transpiration barrier under drought stress.At the same time,we also found that drought stress can promote the deposition of alicyclic compounds in the intracuticular wax,and which is related to the cuticular transpiration.By combining the results of the previous experiments,we concluded that under normal growth conditions,VLCFAs are the main substances that constitute cuticular transpiration barrier under normal growth condition.However,when tea tree is exposed to drought stress,alicyclic compounds can improve the mechanical strength of cuticle;thus,to maintain the integrity and stability of the cuticular transpiration barrier and improve the efficiency of barrier.