| Sunflower（Heliauthus annuus L.）is one of the important oil crops in our country.Drought and salt stresses affect the growth and development,and ultimately lead to yield and quality defects of sunflower.Plant cuticular wax covers the surface of plant tissues,reduces the rate of plant water loss and improve the adaptability to water-deficient environments.In this study,the leaf cuticular wax content and components of oil sunflower inbred lines under drought,salt and PEG6000 stresses were detected and analyzed by gas chromatography-mass spectrometry（GC-MS）.Water loss rate and chlorophyll leaching rate were determined to evaluate the leaf permeability of sunflower after stress treatments.In the meantime,genes related to the synthesis of alkanes,an important wax component,were screened out from the sunflower genome,and the identified genes were subjected to bioinformatic analysis.The expression patterns of two candidate genes under the treatment of Na Cl and PEG6000 were analyzed by quantitative real-time PCR（q RT-PCR）.Finally,Ha CER3-1 was functionally characterized by being overexpressed in Arabidopsis.The results of the study are as follows:1.The main components of leaf epidermis wax of sunflower seedlings are primary alcohols,alkanes,fatty acids,etc.Among them,the primary alcohols are the highest content,accounting for 70%～80%of the total wax,the alkanes and fatty acids account for 10%～14%and about 10%,respectively,of the total wax.The carbon chain length analysis revealed that the carbon chain lengths of primary alcohols are distributed between 22～34,among which C24,C26,and C28 are the main ones;the carbon chain lengths of alkanes are distributed between25-35,and the content of C27,C29,and C31 alkanes is the highest;Fatty acid carbon chain lengths are distributed between 16～28,of which C16 and C24 are the highest.2.After 10 d of drought and salt stresses,the total amount of epidermal wax in sunflower leaves was significantly increased by more than 8%compared with the control.After drought stress,the alkane content increased by 62.5%,and the fatty acid increased by 45%;after salt stress,the alkane content increased by 47%,and the fatty acid content increased by 49%;the primary alcohol showed no significant alterations.Moreover,drought and salt stresses only affected the quantity of epidermal waxes without alterations of the content types.The non-stomatal water loss rate and chlorophyll leaching rate of sunflower leaves under drought and salt stress were significantly decreased than those under control conditions.3.There are 6 candidate genes for alkane synthesis were identified in the sunflower genome.Phylogenetic tree analysis showed that 6 genes were divided into 2 groups,3 were CER1 homologs,and the other 3 CER3 homologs.Ha CER3-1 showed the highest identity to Arabidopsis CER3 among the 3 CER3 homologous genes.Transcriptomic analysis showed that Ha CER1-1,Ha CER3-1 and Ha CER3-2,which were probably involved in alkane synthesis,were highly expressed in sunflower leaves and stems.q RT-PCR results showed that Ha CER1-1 and Ha CER3-1 were significantly up-regulated after salt stress and PEG6000treatment:At the 12th hour of treatment,Ha CER1-1 was up-regulated by more than 30 times,and Ha CER3-1 was up-regulated by more than 10 times.4.Overexpressing the Ha CER3-1 in wild-type Arabidopsis increased the alkane content of rosette leaves but reduced leaf permeability.The water-deficient experiment proved that the overexpression of Ha CER3-1 decreased the wilting rate of Arabidopsis under the water-deficient environment. |
