Carnivores, these plants!

BIOLOGY

Researchers have discovered that the leaves of philcoxia are a snare for ring worms. The plants later feed on the worms, writes K S Someswara.

It is not uncommon to spot carnivorous plants. Their behaviour is marked by luring insects to sit on their leaves which are coated with a sticky substance. However, recently, researchers have discovered a different kind of such plant.

These meat eating plants trap underground nematodes with their leaves buried in the sand. These plants are called philcoxia. They can be seen in patches of white sand which dot Campo Rupestra, a savannah in Brazil’s central highlands.

These strange plants survive in tracts where the soil is poor in nutrients. The plants are spiny in nature and have purple flowers. Also, the plant grows with its leaves buried underground. Researchers have now discovered how the leaves are a snare for ring worms that plants absorb and eat. They thrive in areas where there is white sand.

Sand patches are each about 300 metres wide, and occur in many more areas of Brazil’s mountain savannahs, says plant ecologist Rafael Oliveira of the University of Campine in Sao Paulo, Brazil. But, they are very vulnerable to environmental changes and might be disappearing. What’s interesting is that philcoxia has one-mm wide underground leaves which are still able to photosynthesise despite being covered by soil. But Olivera and colleagues were mystified about where philcoxia got its raw materials.

Harbouring nematodes

Previously, researchers had discovered that philcoxia leaves contain structures that resemble the glands that can be spotted in many carnivorous plants. When they looked at the leaves under an electronic microscope, they noticed tiny roundworms called nematodes sitting on the leaves. To figure out what the worms were doing, these researchers created a miniature food chain. They grew bacteria in a culture containing a variant or isotope of nitrogen that is heavier than the normal element.

They then fed these bacteria to nematodes, which drew the heavy isotope into their own tissues. Finally, scientists placed the nematodes near the leaves of a few philcoxia plants and watched. The next day, worms had crawled into the leaves and the team was able to detect the heavy nitrogen isotope from the worms in the plant tissue within 48 hours and 15 per cent of the heavy nitrogen in the worms had been taken up by the leaves.

This suggests that not only had the plant eaten the worms, but also constituted a very large part of its diet. Olivera says that when he first saw the results, he could not believe that these underground leaves had actually eaten nematodes. They did not find any fungi or other organisms associated with the leaves. Although philcoxia is not the first worm eating plant to be discovered, plants such as bladderworts catch worms and other critters with the trap door in their bubble-like truss. Nematodes are especially important to these plants’ diet, says another ecologist Aaron Ellison.

These plants belong to the family plantagineceae and are found in species such as philcoxia bahiensis, philcoxia goiasensis and philcoxia minensis. These three rare plant specimens are located in Brazil and resemble terrestrial specimens of the genus utriculara.

Each one has been named after the Brazilian state to which it is endemic. These plants are characterised by subterranean stems, peltate leaves at or below the soil surface. Following initial doubts that the plethora of stalked capilate glands on the upper surface of the leaves was an indication that these species may be carnivorous, a study was carried out in 2007.

The study tested philcoxia minesis for protease activity, a typical test for the carnivorous syndrome and could detect none. Later studies detected other digestive enzymes such as phosphates and qualitatively assessed prey digestion and nutrient uptake indicating that it is a true carnivorous plant.

The subterranean leaves each of about the size of a pinhead are able to absorb some light through white soil of the cerrado, a tropical savannah in Brazil.
The high morphology of these plants has led to confusion about the proper taxonomic placement. Various studies in different periods have placed these plants in the tribe gratioleae.

A researcher, Peter Taylor, suggested that the morphology philcoxia resembles that of the carnivorous lentibularcaceae and droseraceae in some aspects.