Relationship between the composition and distribution of nutritional substances, secondary metabolites, and internal secretory structures in the bark tissues of Larix gmelinii var. japonica, L. kaempferi, and their F₁ hybrid and susceptibility to vole herbivory

ABSTRACT

We investigated the quantitative composition and distribution of nutritional substances (soluble sugars, starch, and protein), secondary metabolites (terpenoids and phenolic compounds), and the length, area, and density of internal secretory structures (resin ducts and cavities) in the rhytidome (outer bark) and secondary phloem (inner bark) of Kuril larch (Larix gmelinii var. japonica), Japanese larch (L. kaempferi), and their F₁ hybrid (L. gmelinii var. japonica × L. kaempferi) in order to clarify the relationship of these parameters to susceptibility to red-backed voles’ herbivory in Hokkaido, Japan. The amounts of most nutritional substances in each of both bark tissues were not significantly different among the three larch taxa. The amounts of carane-type monoterpenoid and labdane-type diterpenoid in both bark tissues of L. gmelinii var. japonica and the F₁ hybrid were significantly higher than those of L. kaempferi. The amounts of phenolic compounds in both bark tissues of L. gmelinii var. japonica were significantly lower than those of L. kaempferi. The quantitative composition of most secondary metabolites in both bark tissues of the the F₁ hybrid were between L. gmelinii var. japonica and L. kaempferi. The area and density of the resin ducts and cavities, which were containing terpenoids, in both bark tissues of L. gmelinii var. japonica and the F₁ hybrid were significantly larger and higher than those of L. kaempferi. These results suggest that L. gmelinii var. japonica and the F₁ hybrid utilize some predominant constitutive mono- and diterpenoids as chemical defensive substances in the bark tissues against the voles.

KEYWORDS:

• Constitutive chemical defense
• bark tissue
• terpenoid
• Larix
• F₁ hybrid
• Myodes voles

Acknowledgments

The authors greatly thank Mr. Tsugio Oshima of Hokkaido Forest Tree Breeding Association for his advice of sampling the specimens. We are highly grateful to Dr. Oki Higuchi of Biodynamic Plant Institute Co. Ltd. for his support of identification of some flavonoids.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by Grants-in-Aid for Scientific Research (KAKENHI) from the Japan Society for the Promotion of Science (JSPS) [Grant numbers: JP20580166 and JP25450221].