A plant's wound-sealing liquid can fight fungi—but when researchers grew plant tissue outside that liquid, the defense survived in one species and vanished in another. The surprise was not just which proteins worked, but where their versions came from.

Latex is released when plant tissue is damaged. It contains many active compounds and proteins linked to plant defense. The accumulation of these molecules at high concentrations has led to the idea that latex forms a defensive barrier, both by sealing damage and by storing toxic or antimicrobial compounds.

The study asked whether callus cultures of two latex-producing species could reproduce the antifungal defense system found in their latex. The central finding was that antifungal activity was associated with protein-cutting enzymes and osmotin-related proteins, while the versions expressed in callus tissue differed from those in latex.

That points to a defense system whose activity is tightly linked to the tissue in which it is made. The researchers evaluated antifungal activity against four disease-causing fungi in the reported experiment. The fungi were maintained in the laboratory, then scraped from cultures, filtered, and counted to prepare spore suspensions for testing.

The study compared protein fractions from callus and latex of both plant species for antifungal activity against the fungal species. Proteins from callus tissue of one species strongly inhibited the growth of every fungus tested, while callus proteins from the other species did not inhibit any of them.

The same pattern appeared when the test looked at spore germination: the first callus protein mixture stopped it, while the second showed no inhibition. Latex protein mixtures from both species, however, showed antifungal activity against all the fungi tested.

The results indicate that callus proteins from C. grandiflora contained inhibitors that blocked two kinds of protein-cutting activity in the assay. The active callus mixture blocked one protein-cutting activity but did not affect the other, suggesting that a detectable inhibitor of the second kind was absent.

When the researchers blocked cysteine protein-cutting enzymes, the protein mixtures almost completely lost their ability to cut proteins. At the same time, previously active mixtures lost most of their antifungal activity, supporting a major contribution from these enzymes.

The defense proteins found in latex were also examined at the level of the instructions cells use to make proteins. Those instructions were detected in latex but not in the corresponding callus samples under the conditions tested. This pattern matched the earlier results from the protein tests and immune-based detection.

The results suggest that callus-derived proteins from C. procera retain antifungal activity associated with peptidases and osmotins, whereas callus proteins from C. grandiflora lack that activity. For someone interested in plant-based protection, the results suggest that callus-derived proteins retain antifungal activity in one species but lack it in another.

The antifungal defense was tied mainly to protein-cutting enzymes and osmotin-related proteins, and the versions found in callus tissue differed from those in latex. That helps explain why plant defenses depend on the tissue carrying them.