Deborah Boyar was kind to send me the following article from The New
York Times Science section Tuesday, April 8, 1997 which I think you all
will find interesting.

" Tuning In to the Hidden Message in Some Fruits' Siren Song." by Carol
Kaesuk Yoon.

Evolved over eons entice, a lusciously ripened fruit is pure
temptation.  But as Adam and Eve, as well as other intrepid fruit
samplers discovered, what hangs on vine and tree is not always the
sweet treat it seems and can even be downright dangerous.  Even though
a fruit's job is to be eaten by animals that could transport its seeds
elsewhere, biologists say most fruits in the wild actually range
between horrible tasting and deathly poisonous.
"It's a paradox," said Dr. Martin L. Cipolline, a plant ecologist at
Berry College in Mount Berry, Ga., who has published two studies with
Dr. Doug Levey, an ecologist at the University of Florida at
Gainesville, that are beginning to help solve the mystery. "Why are
some fruits toxic?"
In a study that may begin to explain the awful taste of fruits like the
common holly, known by the scientific name vormitoria, and the wild
cherry known as the chokecheery, the researchers investigated two plant
species in the nightshade family.  In two reports published in the
April issue of the journal Ecology, they found that the foul-tasting
toxins in these fruits from going bad because they are as repellent to
fruitrotting fungi as they are to an animal's tongue.
In addition to putting wild fruits in a new and somewhat distasteful
light, the work explains why the produce at the grocer's, which has
been bred to remove any last traces of sour or bitter chemicals, goes
bad so quickly, stripped as it is of its antifungal defenses.  It also
suggests that fruits may be an important place to look for antifungal
pharmaceuticals because many of them fend off fungi but remain edible
to humans.
Calling the work "straightforward and convincing", Dr.Chris Whelan of
the Morton Arboretum in Lisle, Ill., said: "This is a brand-new field.
They're paving the way for an entirely new approach to looking at the
interaction between fruits and the animals who consume them."
Researchers have long known that unripe fruits, whose seeds are not yet
fully developed, could contain foul-tasting chemicals that prevented
animals from plucking them prematurely.  But many assumed that when a
fruit ripened, most if not all of its toxins disappeared.  As a result,
biologists have all but ignored the role of toxins in this abundant and
important source of food in the wild.
Dr. Cipollini and Dr. Levey studied two common weed species in the
nightshade family, horse nettle and black nightshade.  Both are
relatives of deadly nightshade, but horse nettle contains much higher
levels of the toxins known as glycoalkaloids than does black
nightshade.
The researchers offered the wild fruits, as well as artificial fruits
made with varying amounts of fruits made with varying amounts of
nutrients and toxins, to two bird species. robins and Northern
bobwhites, and two mammal species, deer mice and opossums, which are
all known to eat the wild fruits.  Robins and opossums defecate the
seeds they eat intact, so they serve as good seed dispersers for the
plant.  Mice and bobwhites, on the other hand, typically destroy the
seeds, grinding them up for food.
What researchers found was that all the species, useful or not, were
deterred by the toxins.  All four preferred artificial and natural
fruits with low levels of glycoalkaloids, regardless of how nutritious
the fruit was otherwise.  But it was these same distasteful
glycoalkaloids that researchers found to be quite effective at
inhibiting the growth of fungi, the microbes responsible for most
rotting in fruits.
By putting toxins into their fruits, the two species of nightshade seem
to have struck an evolutionary compromise.  Their fruits carry enough
toxin to prevent rotting, but not so much that animals avoid them
altogether.
In general little is known of the chemicals in wild fruits, but
researchers were able to carry out their study in these species because
they are part of the nightshade family, whose chemistry is well known
because it includes such commercially important species as tomatoes,
potatoes and eggplant.
Glycoalkaloids, thought to be primarily defensive compounds, act as
toxins by binding to and disrupting the cell membranes of the animals
that eat them.  "The first bitterness you taste is damage, direct
tissue damage," Dr. Cipollini said, as the chemicals break down cells
in the tongue and later, the inner lining of the gut.  Fried green
tomato lovers can thank alkaloids for that deliciously tangy
bitterness.
Describing the Ecology reports as among the first of their kind, Dr.
Henry F. Howe, an ecologist at the University of Illinois at Chicago
who helped found this area of research, fruit-frugivore studies, said,
"They've taken a first big step by testing the fruit with very
different vertebrates."  But he noted that a further search could turn
up an animal that found the toxins harmless or even tasty - perhaps the
species best adapted to disperse the plants' seeds.  The fruits' toxins
might repel the animals tested in the study because they are not the
ideal dispersers of the plants' seeds.
Researchers say there is some evidence for chemicals that repel only
the animals that the plants do not want eating their fruits, a kind of
directed poisoning.  The kick in hot peppers is produced by a chemical
known as capsaican. While sought out by some humans, it is extremely
noxious to most mammals.  Birds, however, eat the hottest peppers with
impunity.  Similarly, birds enthusiastically gulp down the fruits of
deadly nightshade, as lethal to humans as the name suggests.
Scientists say both these plants may be specifically screening out
mammals as less suitable seed dispersers than birds.
While the antifungal chemicals in nightshade were distasteful to the
animals in the study, the researchers say that there are probably
protective compounds in other wild fruits that prevent rotting without
spoiling taste, compounds  in other wild fruits that prevent rotting
without spoiling taste, compounds that should be of particular interest
to plant breeders.
"If we can figure out how they do it, " Dr. Levey said, "we wouldn't
have to irradiate fruits or refrigerate them or spray them with waxes
or breed them to be so bland in taste."

Two photos of fruit trees are accompanied by the following text:
Toxic substances may protect some fruits even after they ripen by
warding off damage from fungi.  The horse nettle, Solanum carolinense,
top, has high levels of toxic glycoalkaloids in both ripe and unripe
fruit.  The black nightshade, Solanum americanum, shown in its ripe
stage, has lower levels of the toxic substances.

Best, Peter
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