Pitcher Plant and the weird world inside it

A plant is considered carnivorous if it receives any noticeable benefit from catching small animals. The morphological and physiological adaptations to carnivorous existence are most complex in plants, thanks to which carnivorous plants have been cited by Darwin as ‘the most wonderful plants in the world’.

When considering the range of these adaptations, one realizes that the carnivory is a result of a multitude of different features. Pitcher plant’s prey-trapping mechanism features a deep, bulbous cavity filled with digestive fluid. There are two types of trapping named:

v  Passive trapping

v Active trapping

In passive traps there is no motion while trapping and enzyme secretion is constitutive, i.e. independent of the presence of prey. In the presence of prey, however, the basal level of secretion increases. Moreover, the amount of enzymes released seems to be correlated to the size of the prey. In other words, the expression/secretion of digestive enzymes is regulated by a signal transduction mechanism.

Pitcher plant

This lets the plant respond to the availability of food resources and thus adjust the cost-benefit ratio efficiently. Nevertheless, passive traps can be viewed as the containers of digestive fluid: pitfalls (Sarracenia, Darlingtonia, Heliamphora, Cephalotus, Nepenthes), tanks (Brocchinia, Catopsis), vesicles (eel-traps of Genlisea) and fly-papers (Drosophyllum, Triphyophyllum, Byblis, Roridula, majority of Pinguicula spp.).

The pitfalls of dicots have the shape of pitchers (Fig. 1A, C, D, E), in which at least three distinctive zones can be recognized. A rim of a slick surface covered with nectaries and trichomes both lures and deceive; when wet, the rim is especially slippery; moreover,

(A) pitcher of an Albany pitcher plant Cephalotus follicularis;
(B) Brocchinia reducta as an example of carnivorous bromeliads  

Sarracenia flava nectar contains coniine (an alkaloid anesthetic to insects) to increase prey-capture efficiency. The waxy zone directly beneath the rim prevents escape; for this, its walls may be covered 

(C)Nepenthes merrilliana; (D) Nepenthes hybrid ‘Miranda’;
(E) North American pitcher plant Sarracenia purpurea  

with waxy scales (Nepenthes), protruding aldehyde crystals (Sarracenia, Darlingtonia), cuticular folds (Nepenthes, Cephalotus, Heliamphora), downward-pointing hairs (Heliamphora, Sarracenia, Darlingtonia) or guard-cell-originating lunate cells (Nepenthes). In Nepenthes, alkaloid fumes promote successful capture, while fluid viscosity increases its retentive properties. The lowest part of the pitcher, the digestive zone harbors numerous digestive glands (Fig. 2A–D) or a glandular epithelium (Sarracenia). 

(A) Three large and numerous small digestive glands of the pitfall type of the Cephalotus follicularis trap – note
strong auto-fluorescence of the apical part of the large glands under UV light; scale bar ¼ 200 mm. (B) Numerous small glands from the pitcher of Cephalotus follicularis – note red anthocyanine in the epidermal cells, which surround glands; scale bar ¼ 50 mm. 

Nepenthes, Sarracenia, and Cephalotus follicularis protect their enzymes (proteases, peptidases, phosphatases, esterases, chitinases, nucleases) from rainfall dilution by covering the pitchers with lids.

(A) Three large and numerous small digestive glands of the pitfall type of the Cephalotus follicularis trap – note
strong auto-fluorescence of the apical part of the large glands under UV light; scale bar ¼ 200 mm. (B) Numerous small glands from the pitcher of Cephalotus follicularis – note red anthocyanine in the epidermal cells, which surround glands; scale bar ¼ 50 mm. 

As most Heliamphora species do not produce enzymes, its lid has reduced in size to become a small ‘nectar spoon’ while excess rainwater is drained off through a slit. Deprived of its own enzymes, too, Darlingtonia californica is unique in that it regulates the pitcher water level by pumping it up through its roots. As low pH promotes the action of proteolytic enzymes and the uptake of organic substances the pitcher fluid is highly acidic. Additionally, oxygen-free radicals produced by the pitcher plants aid in the digestion of prey bodies.

Despite being of little economic importance, carnivorous plants have long held a fascination, being among the most popular plants in cultivation. They still draw the attention of many scientists as convenient model plants for such topics as fast movements negative excitability–photosynthesis coupling  enzyme secretion  nutrient absorption heavy metal phytotoxicity food–web relationships plasticity and genetic radiation phylogenetic and intergeneric relationships trade-off assessments and structural and mineral investment in carnivory.