Tree Physiology

A scorched leaf policy? A mangrove tree uses oxidative stress against an insect pest

One major pest of mangrove forests in China is a leaf-mining insect, which burrows into the upper layer of the leaf. Insect attack not only causes physical damage, but also causes the accumulation of reactive oxygen species (highly reactive forms of oxygen that can damage enzymes and DNA) which can cause further damage to plant tissue. We might then expect that trees would increase their ability to neutralize reactive oxygen species when under insect attack.

Scorched leaf
Mangrove leaves before (non-mined leaf), and after leaf miner attack (non-mined and mined portion).

In a new study in Tree Physiology, Zheng et al. (2016) found that in mangrove (Avicennia marina) leaves attacked by a leaf miner (Phyllocnistis citrella), the damaged portion of leaves reduce their antioxidant defenses to allow hydrogen peroxide (a reactive oxygen species) to build up, which then acts as a signal to the intact portion of the leaf to increase its antioxidant and anti-herbivory defenses. This ‘scorched leaf policy’ is reminiscent of the scorched earth policy used by Russians in the early 19th century to successfully repel Napoleon’s army. It seems military strategy is another invention where Nature got there first.

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