Sugars help rice leaves sustain production of antimicrobial compounds

Rice produces antimicrobial compounds called phytoalexins in response to biological and non-biological triggers. A preprint by Naoya Misawa and colleagues examines how light and sugar availability support this response. This briefing is based only on the abstract, not the full manuscript.

The researchers treated rice leaf disks with copper chloride, or CuCl2, to induce production of three groups of phytoalexins: phytocassanes, momilactones and sakuranetin. Darkness strongly reduced both their accumulation and the activation of genes involved in making them.

In darkness, sucrose, glucose and fructose levels fell to just 3%–8% of those measured in the light. Yet early accumulation of two defense-signaling molecules, jasmonic acid and JA-Ile, was not detectably reduced. That contrast suggests the reduced production did not simply reflect a loss of these early signals.

Adding sucrose restored phytoalexin accumulation and expression of the suppressed biosynthetic genes in darkness, with larger doses producing greater restoration. Mannitol at an equivalent concentration did not help. Glucose restored sakuranetin accumulation but only partly restored the other two groups.

The team also used DCMU, an inhibitor of photosynthetic electron transport. In illuminated leaf disks, it depleted soluble sugars and suppressed phytoalexin accumulation; added sucrose reversed that suppression.

Importantly, sugars alone induced little phytoalexin accumulation. The authors therefore interpret carbohydrates as supporting an already-triggered response rather than initiating it. They conclude that photosynthesis-derived carbohydrate supply largely accounts for the response’s dependence on light. The reported experiments concern chemically treated leaf disks; the abstract does not establish whether adding sugar improves disease resistance in whole rice plants.