Testing The Appetites of Ibicella And Drosophyllum
Keywords: carnivory: Drosera -- carnivory: Drosophyllum lusitanicum
-- carnivory: Ibicella lutea.
Received: 30 October 1998
A simple method of detecting enzymes was used to test
thirteen species. As expected, Drosera, Dionaea, Pinguicula,
and Drosophyllum were all shown to secrete digestive enzymes. The
method was tested on noncarnivorous plants and controls. Ibicella lutea
and Proboscidea parviflora are in the Martynia family, and
the former is sometimes suggested to be carnivorous. Ibicella lutea
and Proboscidea parviflora showed no enzymatic activity.
In 1997, Siegfried Hartmeyer discovered that Byblis
liniflora does not produce digestive enzymes (Hartmeyer, 1997). This
means that B. liniflora is not strictly a carnivorous plant and
he established the hypothesis that it requires the aid of arthropods to
benefit from its captured prey (i.e., Hartmeyer 1998). While his results
were fascinating, the experimental method he used, first developed by
Heslop-Harrison & Knox (1971), was particularly remarkable because
it involved a technique of enzyme testing that is so simple, anyone with
a pair of scissors, tape, and inexpensive black and white film could perform
In summary, this is Hartmeyers approach. He stimulated
the leaves of carnivorous plants into producing digestive enzymes by smearing
a yeast solution onto them. Then he placed photographic film (right out
of the roll with no processing) in contact with the stimulated leaves.
The digestive enzymes from the leaves digested the protein layer of the
film, so after twelve hours or so parts of the previously opaque film
became transparent. Subsequent photoprocessing was optional.
I decided to try the enzymatic test. I bought a roll
of Ilford HP5 ASA 400 film (as Hartmeyer recommended) and a packet of
bakers yeast. I made a 10% solution of yeast by mixing 7 grams of
yeast with 70 ml of distilled water. For each leaf tested, I did the following.
1)I smeared a few drops of yeast solution onto a leaf. Instead of waiting
several hours as did Hartmeyer, I immediately proceeded with the next
step. 2)I taped one edge of a 2-4 cm length of film to a paper backing.
3)I coded the film with holes from a deftly wielded pin and a hole-puncher.
4)I delicately sandwiched the stimulated leaf between the film and the
paper, and taped the other edge of the film to the paper backing. 5)If
the film and paper sandwich was too heavy for the plant, I affixed the
sandwich to an appropriate support pole. 6)I recorded the details of the
trial in my notes, referring to the code I made in step two. 7)I returned
the plant to its normal location in the greenhouse for 24 hours before
removing the film sandwich.
Figure 1: Positive enzyme secretions of Drosera capensis.
Figure 2: Positive enzyme secretions of Drosophyllum lusitanicum
Some important but mundane matters should be mentioned.
First, photographic film consists of an inert plastic layer that functions
as a support for the emulsion. When preparing the individual tests, I
took care that the dull emulsion side--and not the shiny plastic side--was
pressed against the leaf. Even a hungry carnivorous plant cannot digest
plastic! Second, I used acid-free archival cardboard for the backing in
each test (specifically, the sturdy paper used in mounting herbarium specimens).
Third, when making each film-leaf-paper sandwich, I used the tape to make
the sandwich snug enough so it would not slip off the leaf, but not so
snug that the leaf was crushed. Finally, as an alternative to yeast, I
experimented with using a dilute solution of Bovine Serum Albumin (BSA)
to stimulate the plants leaves. The results in all cases were identical
to my yeast trials. (As I dripped BSA onto the glistening leaves I enjoyed
thinking how, decades after I killed my first Venus Flytraps by giving
them hamburger, I was once again feeding cows to my plants, albeit in
the guise of high science!)
The first group of tests included those plants I thought
would certainly demonstrate enzyme production. Specifically, I tested
Dionaea muscipula, Drosera adelae, D. binata var.
multifida f. extrema, D. x californica, D.
capensis (red- and wide-leaved clones), D. spatulata, D.
venusta, and a Mexican Pinguicula hybrid of unknown parentage
(but obviously closely related to P. Sethos. Dionaea
was tested by feeding the traps small pieces of photographic film which
were retrieved from the traps when they reopened a week later. A total
of twenty-four yeast and BSA trials unanimously shouted these plants were
carnivorous. In Figure 1 I show the results of a test using Drosera
capensis (a red-leafed clone). The positive enzyme secretions are
indicated by the clear spots digested into the normally black opaque emulsion.
Six control tests were made upon Abutilon x hybridum
Sugar Plum (a non-carnivorous Malvaceous species), and four
control tests were made where no plant at all was used (yeast solution
or BSA was applied directly to the films emulsion). No relevant
emulsion damage was observed in these tests. These control tests demonstrated
that a lack of enzymatic activity was properly indicated by the method.
As a bonus, these control tests illustrated that when kept wet for 24
hours, film emulsion becomes delicate and is easily damaged. Do not mistake
such damage for enzyme activity!
The third test group consisted of three species which
particularly interested me: Drosophyllum lusitanicum, Ibicella
lutea, and Proboscidea parviflora. In each of its five tests,
the Drosophyllum digested all the emulsion it contacted (Figure
2) and left only the transparent plastic substrate--the evidence of enzymes
was clear! Seven trials were made of Ibicella, and seven of Proboscidea,
targeting leaves both very young and mature. At the end of the twenty-four
hours the films were examined, and showed numerous tiny clear dots or
dashes, unlike any seen in the other tests (Figure 3). However, these
dots were not the result of enzymes. Instead they were caused by the leaf
hairs being driven into the emulsion (although I could not tell if the
marks were due to the glandular or the longer, eglandular hairs). The
stiff hairs had left their imprints in the emulsion! (As noted above,
after a day of exposure to water, the emulsion layer becomes mushy and
very susceptible to such mechanical damage.) In some cases I used paper
clips to hold the film sandwiches onto the leaves. I noted the clear marks
were often clustered around where the paper clip had been, further indicating
the marks were a result of mechanical damage and not enzymatic activity.
Soaking the leaf with water so the film detached more easily still resulted
in some tearing damage.
Ibicella and Probiscidea tests in which
film was left on the leaves for another twenty-four hours still resulted
in no enzymatic damage to the film.
Figure 3: Negative enzyme secretions of Ibicella lutea under
high power. The horizontal bar indicates 1 mm.
4: A close-up view of a leave of Ibicella lutea, with trapped
whitefly and fungus gnats.
My tests have verified the effectiveness of Hartmeyers
method of enzymatic detection, and extended them to show enzymatic activity
in a few new genera. A significant oversight in Hartmeyers work
was a lack of appropriate control tests and null tests. I have addressed
this by showing his method does not falsely detect enzymes when none are
present. While he did test Roridula as a noncarnivorous species,
this plant has a suspicious history in the annals of plant carnivory,
and also damaged the emulsion mechanically. More appropriate controls
needed to be tested.
Plants in the Martyniaceae, in particular Ibicella
lutea, did not show any indication of producing digestive enzymes.
Is Ibicella just another sticky, but non-carnivorous plant? Probably.
But it might be carnivorous in one of three ways and still have slipped
past my enzyme tests.
First, it is possible Ibicella is not carnivorous
its entire life and I may have tested it during the wrong time. While
both young and old leaves were tested for enzyme activity, might it be
that overall plant age is relevant? For example, Triphyophyllum peltatum
is usually carnivorous only prior to changing its growth form into a climbing
plant. However, unlike Triphyophyllum, Ibicella has no habit
change so clearly marked. Leaves on branches bearing flowers, fruit, or
no reproductive organs were all tested. No enzymatic behavior was detected.
Second, it is possible only specific parts of the plant
are carnivorous and were overlooked by my tests. Indeed, small insects
are trapped on all parts of the plants except the petals (Figure 4), but
only the leaves were tested. Nonetheless, the trapped insects on these
untested areas do not appear any more digested than the insects on the
leaves. If carnivory were a factor, it would be much more likely to occur
over the large overall leaf surface area than the relatively small amount
of stem, petiole, or inflorescence surface areas.
Finally, it is possible that Ibicella requires
an arthropod analogous to those observed on Roridula (Hartmeyer,
1998). No arthropod candidates were observed on the plants grown outdoors
in Davis, California or Tucson, Arizona. It may be that the appropriate
arthropods are only found in the plants native range in South America,
but no such fauna has ever been observed on the related Proboscidea,
which I have grown for many years well within its native range.
In conclusion, I have found no sturdy evidence that Ibicella
and Proboscidea are carnivorous. Personal communication with Jan
Schlauer (1998), revealed he had been unable to detect any enzymatic activity
when he applied peptone to the leaves of Ibicella lutea and Proboscidea
louisianica. These are interesting plants, but I have no room for
them in my carnivorous garden. The seeds I will send to the ICPS seedbank
will be my last.
I would like to thank Tim Metcalf and the staff at the
University of California at Davis Botanical Conservatory for the use of
their facilities for this experiment. A particular apology is due to any
of the staff who brushed against the foul-smelling Ibicella lutea
plants the long year I grew them at the greenhouses.
Hartmeyer, S. 1997, Carnivory of Byblis Revisited--A
Simple Method For Enzyme Testing On Carnivorous Plants, Carniv. Pl.
Newslett., 26: 39-45.
Hartmeyer, S. 1998, Carnivory in Byblis Revisited
II: The Phenomenon of Symbiosis on Insect Trapping Plants, Carniv. Pl.
Newslett., 27: 110-113.