Physiological and Genetic Analysis of Leaves from the Resprouters of an Old Ginkgo biloba Tree

Ginkgo biloba is a well-known long-lived tree with important economical, ornamental and research value. New stems often resprout naturally from the trunk or roots of old trees to realize rejuvenation. However, the physiological and molecular mechanisms that underlie the resprouting from old trees are still unknown. In this study, we investigated a 544-year-old female ginkgo tree with vigorous resprouters along the trunk base in Yangzhou, China. We compared the morphological and physiological traits of leaves between resprouters (SL) and old branches (OL) and found a significantly higher thickness, fresh weight, and water content in SL. In particular, the depth and number of leaf lobes were dramatically increased in SL, suggesting the juvenile characteristics of sprouters in old ginkgo trees. Transcriptome data showed that the expression of genes related to photosynthetic capacity, the auxin signaling pathway, and stress-associated hormones was upregulated in SL. Importantly, levels of the most important secondary metabolites, including kaempferol, isorhamnetin, ginkgolide A, ginkgolide B, and ginkgolide C, were significantly higher in SL. We also identified high expression of key genes in SL, such as PAL and FLS, which are involved in flavonoid synthesis, and GGPS, which is involved in the synthesis of terpene lactones. These findings reveal the distinct physiological and molecular characteristics as well as secondary metabolite synthesis in leaves of resprouting stems in old ginkgo trees, providing new insight into rejuvenation physiology in old tree aging.