Department of Metabolic and Structural Biology, CSIR-Central Institute of Medicinal and Aromatic Plants, Lucknow, 226015, India.
CSIR- Human Resource Development Centre Campus, Academy of Scientific and Innovative Research (AcSIR), Sector 19, Kamla Nehru Nagar, Ghaziabad, Uttar Pradesh, 201002, India.
Protoplasma. 2019 Jul;256(4):893-907. doi: 10.1007/s00709-018-01338-y. Epub 2019 Jan 18.
Ocimum species commonly referred to as "Tulsi" are well-known for their distinct medicinal and aromatic properties. The characteristic aroma of Ocimum species and cultivars is attributed to their specific combination of volatile phytochemicals mainly belonging to terpenoid and/or phenylpropanoid classes in their essential oils. The essential oil constituents are synthesized and sequestered in specialized epidermal secretory structures called as glandular trichomes. In this comparative study, inter- and intra-species diversity in structural attributes and profiles of expression of selected genes related to terpenoid and phenylpropanoid biosynthetic pathways have been investigated. This is performed to seek relationship of variations in the yield and phytochemical composition of the essential oils. Microscopic analysis of trichomes of O. basilicum, O. gratissimum, O. kilimandscharicum, and O. tenuiflorum (green and purple cultivars) revealed substantial variations in density, size, and relative proportions of peltate and capitate trichomes among them. The essential oil yield has been observed to be controlled by the population, dominance, and size of peltate and capitate glandular trichomes. The essential oil sequestration in leaf is controlled by the dominance of peltate glandular trichome size over its number and is also affected by the capitate glandular trichome size/number with variations in leaf area albeit at lower proportions. Comprehension and comparison of results of GC-MS analysis of essential oils showed that most of the Ocimum (O. basilicum, O. tenuiflorum, and O. gratissimum) species produce phenylpropanoids (eugenol, methyl chavicol) as major volatiles except O. kilimandscharicum, which is discrete in being monoterpenoid-rich species. Among the phenylpropanoid-enriched Ocimum (O. basilicum, O. gratissimum, O. tenuiflorum purple, O. tenuiflorum green) as well, terpenoids were important constituents in imparting characteristic aroma. Further, comparative abundance of transcripts of key genes of phenylpropanoid (PAL, C4H, 4CL, CAD, COMT, and ES) and terpenoid (DXS and HMGR) biosynthetic pathways was evaluated vis-à-vis volatile oil constituents. Transcript abundance demonstrated that richness of their essential oils with specific constituent(s) of a chemical group/subgroup was manifested by the predominant upregulation of phenylpropanoid/terpenoid pathway genes. The study provides trichomes as well as biosynthetic pathway-based knowledge for genetic improvement in Ocimum species for essential oil yield and quality.
被称为“泰尔西”的奥罗莫物种以其独特的药用和芳香特性而闻名。奥罗莫物种和品种的特征香气归因于其挥发性植物化学成分的特定组合，主要属于萜类和/或苯丙素类在其精油中。精油成分是在称为腺毛的专门表皮分泌结构中合成和隔离的。在这项比较研究中，研究了与萜类和苯丙素生物合成途径相关的选定基因的结构属性和表达模式的种间和种内多样性。这是为了寻求精油产量和植物化学成分变化的关系。奥罗莫·巴西利库姆、奥罗莫·格拉蒂西库姆、奥罗莫·基利曼沙里库姆和奥罗莫·特尼弗洛鲁姆（绿色和紫色品种）的毛状体的微观分析表明，它们之间的毛状体密度、大小和盾状和头状毛状体的相对比例存在很大差异。已观察到精油产量受盾状和头状腺毛密度、优势和大小的控制。叶中的精油贮藏受盾状腺毛大小对其数量的优势控制，并且还受头状腺毛大小/数量的影响，尽管叶片面积的变化较小，但也会影响精油贮藏。对精油 GC-MS 分析结果的理解和比较表明，除奥罗莫·基利曼沙里库姆（一种富含单萜的独特物种）外，大多数奥罗莫（奥罗莫·巴西利库姆、奥罗莫·特尼弗洛鲁姆和奥罗莫·格拉蒂西库姆）物种都产生苯丙素（丁香酚、甲基丁香酚）作为主要挥发物。在富含苯丙素的奥罗莫（奥罗莫·巴西利库姆、奥罗莫·格拉蒂西库姆、奥罗莫·特尼弗洛鲁姆紫色、奥罗莫·特尼弗洛鲁姆绿色）中，萜类化合物也是赋予特征香气的重要成分。此外，还评估了苯丙氨酸（PAL、C4H、4CL、CAD、COMT 和 ES）和萜烯（DXS 和 HMGR）生物合成途径关键基因的转录物的相对丰度与挥发性油成分的关系。转录物丰度表明，通过苯丙氨酸/萜烯途径基因的主要上调，表现出其精油中特定化学组/亚组的特定成分的丰富度。该研究提供了毛状体以及基于生物合成途径的知识，可用于奥罗莫物种的遗传改良，以提高精油的产量和质量。
