UV-B辐射增强对拟南芥表皮蜡质的影响

Abstract

Due to the depletion of stratospheric ozone( O3),the quantity of UV-B radiation reached the earth's surface has increased significantly. Enhanced UV-B radiation influenced plant growth,development and productivity by damaging DNA,RNA,and proteins. Plants are thought to employ a variety of UV-B protective mechanisms,including accumulation of a range of secondary metabolites and adaptive changes in plant morphological features. As the outer surface of aerial plant tissues,the epicuticular wax is believed to play an important role in protecting plants against ultraviolet-B radiation.Epicuticular wax was composed primarily of saturated free fatty acids,aldehydes,alkanes,primary alcohols,secondary alcohols,ketones,and wax esters. Arabidopsis,as a model system to study the genetics and the molecular biology,has the typical structure and composition of cuticle,and it should be a model system to study the ecology of epicuticular waxes.However,little is known as to the responsees of different wax constituents to enhanced UV-B radiation,and the role of epicuticular waxes in providing protection for Arabidopsis from UV-B has not been examined either. Therefore,in the current study,seven wax mutants( CER1,CER3,CER4,CER6,CER10,CER20 and KCS1) and wild type of A. thaliana were selected to analyze the responses of epicuticular wax in crystalloid structure,content and constituents,and wax related gene to UV-B radiation( 50 μW / cm2). The plants accepted UV-B radiation 2 h every day for consecutive 10 days. The resultsshowed that enhanced UV-B radiation altered the crystalloid structure of epicuticular wax on Arabidopsis stems. Under the enhanced UV-B radiation,amounts of pine needle-shaped crystalloids( CER1),columnar-shaped crystalloids and rods( CER3、CER10 and KCS1) decreased significantly. Some small globular-shaped crystalloids appeared on the surface of CER6 mutant. Some irregular plate- and membrane-shaped structures covered the surface of KCS1 and CER10. No significant change of crystalloid types was observed on the stem of the Arabidopsis wild type; however,many horizontal rod and tube crystalloids accumulated in specific zones,which increased the thickness of cuticle. Enhanced UV-B radiation also altered the secretion quantities of wax constituents. Under UV-B radiation,the contents of primary alcohols,fatty acids and aldhydes in Arabidopsis wild type increased significantly,the contents of alkanes,secondary alcohols and ketones decreased significantly,while the contents of total wax changed insignificantly. Under UV-B radiation,the increase of primary alcohols and the decrease of secondary alcohols and ketones were universal in Arabidopsis mutants. Enhanced UV-B radiation upregulated the expression of CER3,CER4 and KCS1,which promoting the accumulation of primary alcohols,fatty acids and aldehydes. The decreased expression of CER1 under UV-B radiation might lead to the reduction of products from alkanesynthesizing branch of the pathway,including alkanes,secondary alcohols and ketones. The decreased expression of WIN1 under UV-B radiation had no effect on the content of total wax,implying that the accumulation of total wax was a result of comprehensive effects of multi genes involved in wax synthesis pathway. Enhanced UV-B radiation shunted wax precursors away from the alkane-synthesizing branch to primary alcohol branch of the pathway.