REFERENCE:
Studnička M. (2003): Further problem in Genlisea
trap untangled?.- Carniv. Pl. Newslett., Fullerton,
32: 40-45.
Technical Refer eed Contribution
FURTHER PROBLEM IN GENLISEA TRAP UNTANGLED?
MILOSLAVSTUDNICKA • Botanic Garden s Liberec • 46001 Liberec • Czech Republic
• [email protected]
Keywords : ca rnivory: Genlisea hispidula - observation s: Genlisea hisp id ula.
Introduction
It is well k nown that pla nts in th e gen us Genli sea pro duce su bterranean,
Yshaped, ca rnivorous trappi ng organs . The two branches of eac h trap fun ction as
unidirectional cha nnels, directin g prey towards the trap neck. At that poin t , prey
travel al ong the trap neck (a long tunn el) t o the vesicle, wh ich is the enlarged dige sti on chamber.
While these aspects of Genlisea are well know, ma ny as pects of h ow the trap s
work are st ill mysteries. Current research is focused on using ph ysiological experimen ts to t est several hypotheses. For example, it is being investiga te d which (if any )
chemi cal substan ce a ttracts prey int o the traps (Stu dnicka, 2002). Th ere are even
different opinion s as to what kind of prey Genlisea tends to capture most fre quent ly. Recent stu dy suggest s that Genlisea may be specializ ed to capture proto zoa
(Barthlott et al., 1998), while Lloyd (1942 , p. 94) wro te : "The ca pt ures cons ist of
copepods, and the like, sma ll water spiders, ne matodes and plenty of othe r for ms,
many of which I h ave seen in t he Brazilian material studied." I have observed in G.
pyg maea many pr ey organisms, i.e. nema t odes, r em ai n s of arthropods, etc.
(Stud nick a, 1996). Furthermore, while prep aring the photogra ph s of G. uiolacea
glands for this a rticle, I observed nume rous nematod es as well as mobile, unicellular orga nis ms in th e traps . Some Genl isea species pr odu ce traps of two distinctly different sizes; t his see ms to im ply some ki nd of prey specialization that differs
between the trap types (Studni cka, 1996).
Another interesting qu estion is how the Genlisea tra ps re tain the nutrient molecu les obt aine d by digesting pr ey items. Sin ce the tra p a pparen tly remains open,
such nutrient molecul es might diffuse ou t th e t ra p neck a nd would be lost to th e
pla nt. Meyers-Rice (1994) presented a mathem atical arg umen t sugge sting that
traps were active, i.e const a ntly pumping wa te r through vesicle gla nds , so the
resulting flow through the trap neck would overcome diffusion effects. However,
Adam ec (2002) found that the flows predicted by this model were not present in
Genlisea trap nec ks . In th is paper, I presen t a novel explanation of how Genli sea
traps may sa feguard their precious, pr ey-d erived nutrien t molecules .
Hypothesis: A Hitherto Un suspected Valve?
Th e tunnel-shap ed trap s of Genlisea are sit uated in soggy soil and a re thus submer ged in wa ter. Th e prey in the ves icle is processed a n d subs ta nces from it a re dissolve d. Since there is an uninterrupted, free path of water fr om the vesi cle to th e
tr ap ext erior (i.e. thr ough th e open tube to the trap neck ), nutrients released by
digestion proc esses in the vesicle could diffu se th rough the nec k and be lost lost to
the pla n t . Ca reful descriptions of the trap (i.e. Lloyd (1942»)h ave demonstra ted that
the re a re no plant st ructures in place th a t would pr event such nutrien t losses.
Since th ere ar e no structures (base d up on plant ti ssues) that block nutrient
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Carnivorous Plant Newsletter
A
B
Figure 1: Diagram showing the locations of the slices in the comparisons of the traps to
a glass capillary tube. Drawn by E. M. Salvia .
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41
losses from th e traps, I h ave hypothesized that there could be some other kind of
barrier or valve holding the dissolved nut rients nea r the digesting gla nds. This
paper des cribes lab oratory tests and new obs erv ations on the nature of internal trap
glands which support this hypothesis.
Furthermore, I have found it useful to divide the trap neck (i.e. the trap tunnel
that extends from the vesicle to the tra p bifurcation) into two porti ons: the proximal
neck (th e tunnel near the vesicle) and the distal neck (the part of the tunnel that
exte nds from the trap bifurcation to the pro ximal neck a re a ). Previous researchers
h ave not recogniz ed the value of dividing the trap neck in to two such zones .
Material and Methods
I used G. hisp idula in the physiological experiments since it produces the
largest traps of all the plants in our gr eenhouse collection . If th e trap neck were
truly an uninterrupted, fluid filled, hollow tube, it could be consid ered a capilla ry
tube. As such, it should be similar in many ways to a simple glass ca pillary tube.
For my first experi me n t, I used a syringe to pierce the vesicle of an intact trap ,
and inje cted a sm all volume (approximate ly 0.5 mm 3 ) of very dilute gentian anilin
(known al so as methylrosanilini chlorati, a pproximately 40 ppm dilution). Even at
such low concentrations, the purple gen tian a nilin was clearly visible to the un aided eye. Th e diffu sion of th e dye was monitored .
In my second experi men t , I prepared a small frame to hold both glass capillary
tubes and Genlisea traps in a vertical orie ntation, a bove a gla ss Petri bowl filled
with water. I prepared a glass capillary tube with the same approximate inner diameter of a Genlisea trap ne ck (i.e. a ppr oximate ly 0.2 mrn). I also prepared two G.
hi spidula trap necks. On "Trap A:' I removed the vesicle an d proxim al neck (i.e. the
cut was made through th e central n eck portion ), whil e on "Tra p B" I cut through the
vesicle (see Figure 1). The glass capillary tube and the prep ared trap fragments (ori ente d cut- side downward) were mounted on the fr ame, and were then lowered so the
ends of all three contacted the water in th e glass Petri bowl. Wat er was immediately drawn into the tubes by capillary action, so the three tubes could be considere d
similar, water-filled capillary tubes. Subsequently, sever al drops of violet anilin solution were added to the water in th e Petri bowl.
Surprising Results
In the first experiment (whe re purple a nilin dye was injecte d into the Genlisea
vesicle) , th e colouring did not spread beyond the proximal neck area (see Figure 2).
Even after a n hour had passed , th e anilin dye did not spread beyond the proximal
neck area. This experimental re sult was the same whether the tr ap was submerge d
in water or kept in the air.
In the second experi me nt, in volving the glass ca pillary tube, G. hi sp idula Trap
A, an d G. hi spidula Trap B, there was a very interesting result. The glass capillary
rapidly became colour ed as the dye solu tion diffused into the water column.
Similarly, in Trap A, the a nilin quickly diffused throughout the distal ne ck (see
Figure 3). In contrast, in Trap B, the dye was unabl e to diffu se out of the vesicle an d
pr oximal n eck area!
Gland Observations
The trap neck has numerous glands on the internal tube surface. The glan ds of G.
violacea were studied by colorin g th em with iodine tincture, which stains cellulose in
particular. The heads of the glands in the proximal neck area of the Genlisea trap are
multicellular (see Figure 4). Searching for similar glands in related genera, we find near42
Carnivorous Plant Newsletter
Figure 2: The Genlisea hispidula vesicle and proximal neck area after the injection of
purple anilin into the trap vesicle . The dye cannot diffuse into the central neck area .
Figure 3: Diffusion of the violet anilin colour into the glass capillary tube (left) and Trap
A (center) . No diffusion is evident in Trap B (right) .
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Figure 4: Glands in the proximal part of the Genlisea violacea trap neck.
Figure 5: Glands in the distal part of the Genlisea violacea trap neck.
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Carnivorous Plant Newsletter
ly th e sa me glan ds in Pinguicula (i.e. th e sessile digest ing glands; see J uni per, Robins
& Joel 1989: 153).
In contrast, th e heads of th e glands in th e dist al portion of the trap neck are only
2-celled (see Figure 5), and ra ther resembl e th e bifid glands found near th e mouth of
Utricularia bladders (Lloyd, 1933: 45; Sydenh am & Findl ay, 1975: 348).
Interpretation of the Experiments
It seems very likely that the two different gland types have two different functions.
If we fix our attention on the glands in the proximal neck, we may infer that they
may serve th e same fun ction as the similar glands found in plants in th e related genus
Pingu icula. Specifically, they may secrete a viscous compound which is not too easily
miscible with water. (Indeed, Genlisea are well known to secrete mucous in othe r contexts, i.e. from th e photosynthetic leaves, e.g. in Genlisea aurea as reporte d by Rivadavia
(2002» . It is possible that such secretions would partially or even complete ly block the
capill ary-like trap tunnel. If thi s is indeed the case, nutrients dissolved in the vesicle
would be prevented from diffusing from the vesicle and pr oximal neck into th e distal
neck (and, subsequently,escaping into the environment). On the other hand, an agile little animal could pen etrate this viscous area by mean s of it s own force. The secre tion
funct ions simila rly to a semi-perm eable membrane.
The inability of th e anilin dye to diffuse from th e vesicle and proximal neck are as
into the distal neck areas (as shown by my experiments) supports thi s interpretation.
Th e presence of similar glands in both th e vesicle a nd the proximal neck area in th e
Genlisea traps suggest a share d nature-indeed, the proximal neck may be a n extension of th e vesicle
It is still unclear what th e function might be for th e gla nds in the distal neck ar ea s.
Acknowledgement
I would like to thank Barry Rice for reviewing and imp roving both thi s and my previous Genlisea articles that appeared in Carnivorous Plant Newsletter.
References
Adam ec, 1. 2002, Zero water flows in the carnivorous genus Genlisea, Carniv. PI.
Newslett. , 32: 46-48.
Barthlott, W, Porembski , S., Fischer, E., and Gemm el, B. 1998, First protozoa- trapping
plant found, Nature, 392: 447.
Juniper, B.E., Robins, R.J. a nd Joel , D.M. 1989, The Carnivorous Plants - London :
Acad emic Press.
Lloyd, l<~E. 1933, The Car nivorous Plants - A Review with Contributions , Tr an sact.
Royal Soc. Canada, ser. 3., vol. 27: 1-67.
Lloyd, F.E. 1976, The Carniv orous Plants.- New York: Dover Publications, Inc. (reprint,
orig. 1942.)
Meyers -Rice, B. 1994, Are Genlisea traps active? A crud e calculation, Carniv. PI.
Newslett., 23: 40-42.
Rivad avia , F. 2002 , Genlisea aurea St.Hil. , Carniv. PI. Newsl ett., 31: 54-56.
Studnicka, M. 2002, Genlisea Traps-A New Piece of Knowledge, Carniv. PI. Newslett. ,
32: 36-39.
Studnicka, M. 1996, Several ecophysiological observ ations in Genlisea. Carniv. PI.
Newslett. 25: 14-16.
Sydenham , P.H. and Findlay, G.P. 1975, Transport of Solutes an d Wat er by
Resetting Bladders of Utricularia. Aust. J. Pl ant Physi ol. 2: 335-351.
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