Appropriate ultra-low seed moisture content stabilizes the seed longevity of Calocedrus macrolepis, associated with changes in endogenous hormones, antioxidant enzymes, soluble sugars and unsaturated fatty acids

Abstract

Calocedrus macrolepis Kurz is a relic and endangered woody plant, which is naturally distributed in southwestern China and adjacent regions, and is known for its valuable timber. There is a serious bottleneck in C. macrolepis conservation: its seed vigor is lost rapidly after harvesting. To explore the feasibility of ultra-dry storage of the seeds of this species, seeds were dehydrated to five different moisture contents (MCs, 1–5%), and stored at ambient temperature for 5 years. Seeds stored at 2.1% or 3.0% had higher percentage germination than those stored than the non-dehydrated seeds. Furthermore, we measured quantitative changes in metabolic products, namely endogenous hormones, soluble sugars and fatty acids, and activities of antioxidant enzymes. Among four endogenous hormones investigated, the concentration of the auxin indole-3-acetic acid was not significantly different at different MCs, while there was a negative relationship between percentage germination and both gibberellic acid and cytokinin zeatin riboside concentrations, and a positive relationship between abscisic acid concentration and percentage germination. Seeds with MCs of 2.1 or 3.0% contained higher activities of the antioxidant enzymes glutathione reductase, ascorbate peroxidase, superoxide dismutase and catalase, corresponding to lower concentrations of malondialdehyde. Compared with seeds at other MCs, higher concentrations of sucrose, glucose, trehalose (but not fructose) and unsaturated fatty acids were maintained in seeds at 2.1% and 3.0% MCs. Therefore, we suggest that levels of certain endogenous hormones, antioxidant enzymes, soluble sugars and unsaturated fatty acids may help stabilize longevity of seed at ultra-low seed moisture content. Storage of seed of C. macrolepis at 2–3% MC at room temperature may be a useful method for conserving germplasm of this species and in facilitating nursery operations.