MAŁGORZATA WIERZBICKA, AGNIESZKA ABRATOWSKA, MARIA PIELICHOWSKA,
ANDRZEJ PODSTOLSKI (authors of photographs)
MAŁGORZATA WIERZBICKA (project manager)

University of Warsaw,
Faculty of Biology, Institute of Experimental Plant Biology, Department of Ecotoxicology;
Miecznikowa 1, 02-096 Warsaw
e-mail: wierzbicka@biol.uw.edu.pl

Description popularizing the research project

As far as the crocodile tears are concerned, let us have a look at plants. We do not mean blood-thirsty Monkey Cups from the depth of Asian jungles, gluttonous Venus Flytrap of North Carolina or our own, and carnivorous, Sundews from deep peat bogs. The only thing they have in common with the saltwater crocodiles, which are famous for their lacrimal glands, is the diet. Neither sundew nor the crocodile weep over the sad remnants of their victims. But in fact there are plants which really cry. Through the pores in lamina they excrete salt crystals which cover the leaves like frost. That is how Armenia maritima, known as thrift, cries. Mesembryanthemum is an even more moving sight when it presents salty droplets. In the microscope picture the drops do not flow down the stem, they attach to the leaves gathered in “tear sacs".
What do the two plants have in common? Well, they both grow in places where excess of salt in soil threats the correct functioning of metabolic processes. We can find them in coastal regions, deserts, mangroves, saline meadows and lead-zinc waste heaps. What do the saltwater crocodile and Mesebryanthemum have in common? It is the fact that the observed tears do not mean remorse, longing, despair or hopelessness. In this way both the halophytic plant and the crocodile remove the excess of salt from the organism. Plants absorb the concentrated solution through their roots, the crocodile because of the distant hunting grounds in the open sea in South- East Asia. For both the plant and the crocodile the excess of salt is harmful. It disturbs metabolism and functioning of cell membranes. It also lowers activity of enzymes. That is why they excrete salt through the glands. Ironically the crocodile has the glands near eyes.
And again rationalism killed the tiny bit of feelings. All we can do is just sit and weep.

Abstract

Research carried out at Department of Ecotoxicology is focused on finding plant species with adaptation allowing them to grow in polluted post-industrial areas, for example - Silesia. We noticed that plants well-known as halophytes more and more often appeared in anthropogenic areas, which are changed as a consequence of the man activity. Halophytes form an interesting group of plants, characterized by ability to colonize salty soils (such as salt marshes for example). Accumulation of salt in cells and tissues is their distinctive feature. Mesembryanthemum crystallinum is an extraordinary example of these interesting adaptation. It is a plant which trails and very often forms carpets. Fleshy stems and leaves enable plant to retain considerable amount of water in tissues. The plant looks like jeweled with diamonds. Thorough observations have showed that leaves are overlaid with vesicular hairs. It can be well seen in a cross-section of the leaf which looks like ornamented with Christmas balls. These are not Christmas ornaments though but epidermal hairs containing huge vacuoles in which salt is stored. These interesting features enable plant to grow in extreme habitats impacted by drought, high salinity and intense insolation. During observations of plants growing on waste heaps we often notice that these plants have leaves densely covered with hairs. Biscutella laevigata - plant accumulating great amount of heavy metals in their leaf hairs - can be an ideal example. Our research has showed that halophytes are predisposed to grow on post-industrial areas polluted with heavy metals.
Our study was performed using stereomicroscope Nikon SMZ - 2T with Nikon digital photography system, scanning electron microscope Leo 1430 VP. The research was supported by research grants from Ministry of Science and Higher Education and from University of Warsaw, Faculty of Biology (intramural funds). Results are part of PhD theses prepared by Agnieszka Abratowska and Maria Pielichowska. Both theses were prepared under tuition of Małgorzata Wierzbicka.