GROWTH, PHOTOSYNTHESIS AND PROLINE ACCUMULATION OF METAL-ACCUMULATOR WEEDS

Abstrak

Intensive use of heavy metals, particularly lead and mercury, in industrial activities and mining extraction has caused the widespread distribution of these contaminants, thereby threatening the environment. Consequently, the growth and several physiological responses of five metal-accumulator weed species were examined in response to mercury (Hg) and lead (Pb) treatments. The weed species Brachiaria mutica, Cyperus kyllingia, Ipomoea aquatica, Mikania micrantha, and Paspalum conjugatum were grown in water culture using half-strength Hoagland's solution and subjected to Hg(NO₃)₂ and Pb(NO₃)₂ at concentrations of 0, 0.25, and 0.5 mM for 3 weeks. Plant growth, photosynthesis, lipid peroxidation, and proline content were observed. Both Hg and Pb significantly reduced plant growth, but the decrease was more pronounced under Hg treatment than under Pb. Hg dramatically reduced the photosynthetic rate under different photosynthetic photon flux densities, indicating that Hg up to 0.5 mM damaged the photosynthetic apparatus in almost all species except I. aquatica. Hg and Pb treatments caused a dramatic increase in leaf MDA content, which was associated with a significant decrease in chlorophyll content. Most species were tolerant to Pb up to 0.5 mM except M. micrantha, while only C. kyllingia and I. aquatica were tolerant to Hg treatment up to 0.5 mM. Hg treatment also induced higher proline accumulation in leaves, although without a clear increment pattern among species, suggesting that proline may function as a stress alarm rather than as a tolerance indicator.