Response Mechanism Of The Arabidopsis Thaliana Epicuticular Wax Under Sclerotinia Sclerotiorum, UV-B And Cold Stresses

Plant cuticle plays a role as the medium between plant and environment which can decrease the lease of nutrient substances and slow down metabolism. Epicuticular waxes covering the outer surface of land plants have the functions of waterproof, keeping dry, decreasing UV radiation and protecting the leaf from accumulation of dust and bacteria spores. Epicuticular waxes consist of very long-chain fatty acids, alkanes, primary alcohols, secondary alcohols, aldehydes, ketones and esters. The constituents and amount of wax are affected by many environmental factors. In this study seven wax mutant (cer1, cer3, cer4, kcs1, cer6, cer10and cer20) and wild type of Arabidopsis thaliana were selected to analyze the responses of epicuticular wax in crystal structure, amount and chemical constituent, and wax related gene under Sclerotinia sclerotiorum, ultraviolet radiation and cold stresses. The results of the research lay the foundation for further study of the waxy biological function under the stress condition. The main results were as follows:1After inoculation with S. sclerotiorum, The amounts of alkanes, ketones and secondary alcohols in Arabidopsis decreased, while those contents of primary alcohols increased or unchanged. The result of qRT-PCR showed that the aldehyde decarbonylase gene CER1which catalyzed the synthesis of alkyl compounds decreased after inoculation, while fatty acy1-CoA reductase gene CER4which is responsible for generating primary alcohols increased. In response of Arabidopsis epicuticular wax to disease stress, primary alcohols generated by acyl reduction pathway increased, while alkanes, secondary alcohols and ketones generated by decarbonylation pathway decreased.2Under enhanced ultraviolet-B radiation, the amounts of primary alcohols and aldehydes in A. thaliana epicuticular wax increased, while those of ketones and secondary alcohols decreased generally. The result of qRT-PCR shows that the expression of CER3、CER4、KCS1increased under enhanced UV-B radiation stress, and the greatly expression of CER4promoted the significant increase of primary alcohols. On the other hand, the significant decrease of CER1expression can lead to the accumulation of aldehydes and reduction of alkanes. Arabidopsis can change the specific waxy component secretion in response to enhanced UV-B radiation.3Under cold stress, the total amount of A. thaliana epicuticular wax increased significantly by increasing the amount of alkanes. The qRT-PCR analysis showed that the expression of CER1was induced strongly by low temperature, and thus the up-regulating expression of CER1promoted the synthesis of alkyl compounds in response to cold stress. The increase of alkanes in waxy compounds may be the main response way to cold stress.4Under biotic and abiotic stresses, the density, shape and size of wax crystalloids on stem of mutants and WT changed in different degree. Under UV-B radiation and cold stress, some wax crystal structures melted to flake,and the flake structure increased generally. Under disease stress, some small protuberances appeared on the wax surface.