Morpho-Physiological Changes in Euphorbia hirta L.
in Response to Mercury Exposure
Juliana Janet M. Puzon1*, Elaine R. Tabayoyong2, and Hazel Joy M. Jumawan2
1Institute of Biology, College of Science,
University of the Philippines, Diliman, Quezon City 1101 Philippines
2Natural Sciences Research Institute, University of the Philippines,
Diliman, Quezon City 1101 Philippines
corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.
ABSTRACT
Euphorbia hirta (L.) plants were grown and exposed for three days in Hoagland’s nutrient solution amended with different concentrations of HgCl2, viz: 0.0 ppm (control), 0.1 ppm and 1.0 ppm. The morpho-physiological responses of the different organs to Hg exposure and the ability of the plant to translocate and accumulate Hg in the leaves were examined. No significant morphological responses to mercury exposure were observed specifically in root length, length of mature stems, and surface area of the young and mature leaves, as well as in the biomass of the roots, mature stems, flowers, young leaves and mature leaves. The length of young stems, however, increased with increasing concentration of Hg treatment. The levels of photosynthetic pigments, viz., chlorophyll a and b, total chlorophyll and carotenoids of the leaves and flowers were not significantly affected by Hg treatments, except for the chlorophyll a of flowers, the chlorophyll b and total chlorophyll of the mature leaves. No significant changes in total chlorophyll content of the stems and in carotenoid contents of the young leaves, mature leaves and flowers were observed in response to increasing HgCl2 concentrations. Anthocyanin content in young stems was higher in the control plants compared to their Hg-treated counterparts, while the reverse trend was observed in mature stems. Based on these results, the maintenance of carotenoid levels in the leaves and flowers, the increase in chlorophylls in the mature leavesand flowers, as well as the increase in anthocyanin content in the mature stems serve as protective, adaptive response mechanisms against Hg toxicity. Therefore, the overall morpho-physiological responses of the various organs of E. hirta reveal its tolerance to Hg exposure. Atomic absorption spectrophotometry (AAS)-hydride vapour generation method revealed the ability of E. hirta to translocate and accumulate Hg in its leaves. The results of this study have important implications on the utilization and cultivation of the plant for medicine and for mercury phytoremediation.
INTRODUCTION
Natural processes such as soil erosion, volcanic eruption and evaporation from the ocean release heavy metals to the environment. The overall amount emitted by these, however, are not enough to produce alarming levels and cause notorious impacts on human health and on the environment. The main causes of heavy metal pollution are anthropogenic activities that pertain to industrialization and modernization, for example, the burning of fossil fuels, mining and extraction of minerals, and application of artificial fertilizers and pesticides . . . . read more
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