Ginkgo biloba
Some plants hibakujumoku were already prepared for the worst, suggests a new study.
The two US nuclear bombings of Japan caused, according to estimates, more than two hundred thousand human deaths. However, trees and other plants survived the unprecedented massacre of Hiroshima and Nagasaki.
A recent study, decades after these two historical events, seeks to explain how this happened to part of the Japanese flora.
In the center of Hiroshima, there are still so-called hibakujumokua Japanese term that designates “trees bombed by the atomic bomb”. The name results from hibaku“hit by the bomb”, and jumoku, “trees” or “bushes”.
These trees became a symbol of resistance and rebirth in a city devastated by the North American nuclear attack on August 6, 1945.
At 8:15 am local that day, the bomb dropped on Hiroshima, with a power equivalent to 15 kilotons of TNT, released extreme levels of heat and radiation. According to the now revised Progress in Biophysics and Molecular Biologythe temperature around three kilometers from the hypocenter could have reached between 3,000 and 4,000 degrees Celsius in the first moments after the detonation. The explosion also exposed the area to around 240 grays (Gy) of radiation — a value well above the potentially lethal dose for humans, which can start at five Gy.
Given these numbers, many experts believed, at the time, that the region’s vegetation would not recover for decades. Some predictions pointed to a gap of up to 75 years before plant life returned. However, to his surprise, shoots began to emerge a few months after the bombings.
It is precisely this rapid recovery that intrigues scientists now. Unlike what occurred in Chernobyl and Fukushima, areas marked by chronic and prolonged contamination, Hiroshima and Nagasaki were hit by an acute and extremely intense load, followed by a rapid drop in radiation levels. This difference changes the scientific question: Instead of studying adaptation to prolonged exposure, researchers want to understand, according to , how certain plants survived an immediate extreme shock.
How plants may have survived
The new paper suggests that the explanation may lie in what the authors call “constitutive resilience”that is, defense mechanisms already present in plants before the attack.
Among these mechanisms may be effective DNA repair systems, greater antioxidant capacity and protective morphological characteristics.
Instead of a generational adaptation, as observed in other nuclear scenarios, survival may have depended on pre-existing biological strategies, the exact location of each specimen or even microenvironments that offered some protection.
Among the species that have recovered are the Ginkgo bilobaone of the oldest tree species in the world, as well as weeping willows, Japanese hackberry trees and various herbs, such as Japanese silverweed. Some regenerated from protected seeds; others benefited from rhizomes preserved in the soil.
The authors advocate carrying out more detailed studies on these trees, including genomic and epigenetic analyses, to identify the molecular mechanisms that allowed survival.
