THE SEQUENTIAL ONSET OF TERPENOID BIOGENESIS IN SEEDLINGS: IMPLICATIONS FOR MELALEUCA ALTERNIFOLIA CHEMOTYPE IDENTIFICATION PRIOR TO PLANTATION ESTABLISHMENT

The producers of medicinal and aromatic plants need to ensure that their plantation is stocked exclusively with the desired commercial chemical variety.
Planting the wrong variety can only be remedied by costly crop removal and replanting operations.
The examination of germinants at successive stages of development gave an indication of the chemical changes that take place between germination and harvest.
Using Australian tea tree (Melaleuca alternifolia) as an example, terpenoid biogenetic pathways were found to be initiated at different stages of ontogeny.
The cotyledon leaves of commercial terpinen-4-ol chemical variety seedlings were rich in -pinene (7.4%), -pinene (12.0%) and terpinolene (27.3%). The non-commercial terpinolene variety was found to be rich in 1,8-cineole (12.5%) and terpinolene (25.4%) and the 1,8-cineole variety rich in 1,8-cineole (37%) with significant quantities of -pinene (15.5%), -pinene (23.3%) and terpinolene (10.9%).
Individual leaves of all three chemical varieties were then examined from the emergence of the first true leaves, through to six-week-old leaf-set-ten material.
In the terpinen-4-ol variety, the higher concentrations of terpinolene, -pinene and -pinene and lower concentrations of terpinen-4-ol, sabinene and cis-sabinene hydrate gradually changed, firstly with the emergence of each new leaf set and then again as each leaf set aged.
By the time that leaf-set-ten was 6 weeks old, terpinolene, -pinene and -pinene levels had fallen, cis-sabinene hydrate risen and then fallen and terpinen-4-ol increased so that all components were now present in concentrations similar to those of mature leaf.
In the 1,8-cineole and terpinolene chemical varieties, some differences were evident, but early leaves better reflected the chemical quality of the mature tree.
The cotyledon and early seedling leaf composition, when compared with that of mature leaf from the same chemical variety, was found to be biased toward pinene and terpinolene biogenetic pathway constituents.
Hence pinene and terpinolene biogenesis commences prior to the onset of sabinene hydrate and terpinen-4-ol formation.
Consequently early seedling leaf microanalysis is not a good indicator of mature tree quality unless the sequential onset of the biogenetic pathways in tea tree is taken into consideration.

International Conference on Medicinal and Aromatic Plants (Part II)

I.A. Southwell, M.F. Russell

Australian tea tree, biogenesis, chemotype identification, cotyledon leaf, essential oil, Melaleuca alternifolia, plantation quality, terpenoid pathways

https://doi.org/10.17660/ActaHortic.2003.597.3