三种豆科绿肥作物茎和叶角质层蜡质化学组成分析

植物角质层蜡质是一类覆盖于植物表层的疏水有机化合物,在保护植物免受生物与非生物逆境胁迫中发挥着重要作用。为了更好地了解和认识角质层蜡质在夏季绿肥作物抗逆性中的作用,选择柽麻(Crotalariajuncea)、田菁(Sesbania cannabina)和竹豆(Phaseolus calcaratus) 3种夏季豆科绿肥作物,鉴定茎和叶蜡质组分,并分析蜡质总量、各组分含量及碳链分布特征。共鉴定出8类化合物,包括脂肪酸、初级醇、醛、烷烃、烷基酯、二醇、萜类和固醇类化合物,其中前4种以同系物形式存在且为所有植物茎和叶共有成分(柽麻茎中未检出脂肪酸),说明烷合成和醇合成途径是主要的2种蜡质合成途径。田菁茎中鉴定出二醇化合物,其结构初步解析为1,18-30烷醇和1,16-30烷醇。3种绿肥作物茎和叶蜡质总量存在显著种间及部位差异,其中柽麻茎蜡质总含量为16.33μgcm^-2,显著高于田菁茎(6.45μg cm^-2)和竹豆茎(0.72μg cm^-2)。就茎和叶比较,柽麻茎显著高于叶片,其他2种植物茎和叶之间无显著差异。柽麻茎蜡质中,烷烃为优势成分,占蜡质总量的57.38%;叶片以初级醇为优势成分,占蜡质总量的50.12%。田菁茎、叶蜡质中的优势成分均为初级醇,分别占总蜡质的30.12%和71.21%。竹豆茎、叶蜡质中的优势成分均为烷烃,分别占总蜡质的40.79%和39.27%。各组分优势化合物的碳链长度在不同物种、不同部位也存在一定差异,说明参与蜡质合成的基因在物种、器官间有所不同。这些结果为今后从分子水平上揭示角质层蜡质参与夏季绿肥作物抗逆机制提供了理论基础。

Chemical compositions of cuticular waxes on stems and leaves of three legume green manure crops

Cuticular waxes are hydrophobic compounds covering plant surfaces and play vital roles in protecting plants from various biotic and abiotic stresses. However, less is known as related to the cuticular wax on leaves or stems of summer legume green manures. In the current study, stems and leaves from three summer legume green manure crops grown in the fields were sampled, including Crotalaria juncea, Sesbania cannabina, and Phaseolus calcaratus Roxbwere. Using gas chromatography-mass spectrometer (GC-MS), we identified most of the chemical compounds on these plant species. In total, eight classes of wax compounds were identified, including fatty acids, primary alcohols, aldehydes, alkanes, alkyl esters, diols, terpenoids and sterols. Among these compounds, fatty acids, primary alcohols, aldehydes and alkanes with serial homologs could be observed in stems and leaves of all tested plant species excepting fatty acids in leaves of C. juncea, with their weight proportions accounting for more than 60% in total wax. This suggested that alkane forming and alcohol forming pathways were two major biosynthesis pathways in these plants. In stems of S. cannabina, two compounds were identified as diols with the functional hydroxyl group located at 1,18 and 1,16 positions. Using gas chromatography with flam ionized detector (GC/FID), we quantified the total wax and wax compounds. Total wax coverage differed among three plant species and between two organs. The total stem wax coverage was the highest in C. juncea (16.33 μg cm ^-2), followed by S. cannabina (6.45 μg cm ^-2) and P. calcaratus (0.72 μg cm ^-2). The total wax coverage on stems of C. juncea was significantly higher than that on leaves, whereas no significant difference in total wax coverage between stems and leaves was observed in S. cannabina and P. calcaratus. The predominant wax class differed in plant species and organs. For C. juncea, alkanes were the predominant composition in stems accounting for 57.38% of total wax, whereas primary alcohols were the predominant composition in leaves accounting for 50.12%. For S. cannabina, both stems and leaves were dominated by primary alcohols, accounting for 30.12% and 71.21% of total wax, respectively. For P. calcaratus, both stems and leaves were dominated by alkanes, accounting for 40.79% and 39.27% of total wax, respectively. We further analyzed the chain length distributions of the wax classes in stems and leaves. Generally, fatty acids, primary alcohols and aldehydes were consisted of serials of even carbon number homologs, whereas alkanes were consisted of both even- and odd-carbon number homologs with odd number predominance over even number. The predominant compound in each wax class also differed between plant species and organs. The dominant fatty acids on stems and leaves in C. juncea, S. cannabina, and P. calcaratus were C₃₀, C₃₀ and C₂₆, and C₂₈, respectively; the dominant primary alcohols were C₂₈, C₃₀, and C₂₈ and C₃₂ respectively; the dominant aldehydes were C₃₂ and C₃₀, C₃₀, and C₃₀ and C₂₈, respectively; while the dominant alkanes were C₃₁, C₂₉, and C₃₁, respectively. The terpenoids identified in current study were β-amyrin, α-amyrin and lupenol. The variations of predominant wax class and wax compound between plant species and organs implied that genes involved in wax biosynthesis might also be different. These results provide basic knowledges in studying the molecular mechanisms of cuticular waxes in legume green manure crops fronting biotic and abiotic stresses.