Chemical Warfare

by Michael Todd

It’s the kind of media attention scientists drool over – high-profile television, radio, print and online coverage of their work, both at home and abroad – which is apropos since the subject of the research is drool itself, specifically moose and reindeer saliva.

Certain plants use chemical deterrents as a means of self-preservation, and it seems saliva from big, hoofed animals (ungulates) is able to suppress and even disarm their defences.

Moose are big. And to keep all that moose mass running smoothly they have to eat a lot of grass and twigs. Some yummy plants such as red fescue, a common grass, have a symbiotic relationship with a “live-in” fungus, and when eaten together, they produce alkaloid toxins strong enough to make the hooves of animals fall right off. Those toxins don’t seem to bother moose or reindeer, however, and nobody knows why.

York researchers Dawn Bazely and Mark Vicari and their colleagues may be shedding some light on how certain ­herbivores manage to defuse the toxic effect.

Little is understood about fungal endophytes and their relationship with plants since they have only recently been identified as the cause of many livestock illnesses and mortality. (Red fescue isn’t the only plant that has a relationship with endophytes.)
“Most plants contain bacterial and fungal endophytes,” says Vicari. “They feed on nutrients within plant tissues but cause no symptoms of infection.”

Endophytes can be beneficial to the plant by repelling grazing animals or insects. In protecting the plant, the fungus also protects its own food source, but if the fungus can make chemicals to combat its herbivore rivals, why not vice versa? “That’s a question we were interested in exploring,” says Vicari.
His colleague Andrew Tanentzap obtained moose saliva courtesy veterinarians at the Toronto Zoo. It was collected from sedated animals during their annual checkups.

It seems moose, like people, drool while asleep, and York biologists only needed a ­couple of tablespoons for their research purposes.

The drool was then applied to red fescue grown in the York greenhouse and also to Petri dishes teeming with colonies of the fungus Epichloë ­festucae. Compared to fungal samples treated with water (as a control), the moose saliva slowed the growth of the fungal colonies.

When applied to clipped fescue grass to simulate browsing by moose, the drool reduced the production of the fungal toxin ergovaline between 41 and 70 per cent compared to unclipped plants untreated with saliva, or treated with plain water.
Most plants that have been tested harbour endophytes, says Vicari. In fact, scientists believe there may be on average about four species of endophytic fungus for every species of plant. “That’s about a million fungal species, most of which have yet to be discovered,” he explains.

The specific secret of moose spit that enables it to suppress toxins remains a mystery. Researchers suspect that compounds in moose saliva interfere with the chemical signals that switch on toxin production when the plants get eaten.
Vicari says their next step will be to identify the chemical(s) in herbivore saliva that are antagonistic to endophytes. Those chemicals might turn out to be useful antimicrobial compounds.
Will we see fields being sprayed with moose spit anytime soon? Not likely, but you can bet that if endophyte research can save farmers money, it’s sure to make them salivate.  ■

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