Tree of Life?
The Ginkgo biloba is a fascinating tree that has been around for well over 200 million years. Not only has the species survived both the dinosaur extinction and the bombing of Hiroshima, several specimens have been found to be living for over 1,000 years. In addition, comparisons between fossilized and modern ginkgoes show very little differences.1,2 Ginkgoes do not seem to have many processes associated with aging, unlike those seen in other organisms, like humans. External threats are the main stressors to these trees; and, as a result, they have developed an immune system geared towards survival.3
In order to protect from microorganism invasion, organisms have an inborn immunity, or innate immunity, as a built in defense system. Among these are host defense peptides (HDPs), or defensins, including a variety of antimicrobial peptides (AMPs). In addition to these trees facing microbial threats, they also need safeguards against insects. In most organisms, eventually the immune system slows down and becomes less efficient, along with the other aging processes. This does not seem to be the case in the Ginkgo biloba.
In a new publication in PNAS, Li Wang and colleagues take a deeper look into the immune system of the Ginkgo tree. In trees, height is controlled by the meristem, and, as a tree ages, external stressor damage to the meristem eventually begins to limit tree height. On the other hand, girth is regulated by the vascular cambium. Less affected by external stressors, the vascular cambium allows a tree to continue to expand in circumference. Additionally, in most trees, male fertility declines with age. This was not seen in the ginkgo, where pollen levels were relatively steady. It was also surmised that lignans and other defensive agents are preserved in aging ginkgo trees, as seen in maintained antimicrobial and antioxidant secondary metabolite production and sapwood growth.4
- L. Wang, et al., PNAS Latest Articles, https://www.pnas.org/content/early/2020/01/07/1916548117