GROWTH, PHOTOSYNTHESIS AND PROLINE ACCUMULATION OF METAL-ACCUMULATOR WEEDS

Abstract

Intensive utilization of heavy metals, particularly lead and mercury in industry or extraction in mining areas, have caused the wide spread of these contaminants, thereby further threatening the environment. Consequently, the growth and some physiological responses of five metal-accumulator weed species were examined in response to mercury (Hg) and lead (Pb) treatments. These weed species (Brachiaria mutica, Cyperus kyllingis, Ipamosa 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 0, 0.25 and 0.5 mM for 3 weeks. The plane growth, photosynthesis, lipid petoxidation and praline content were observed. Both Hg and Pb significantly decreased the growth, but the response was more remarkable in Hg than in Pb treatments. Hg treatment reduced photosynthetic rate dramatically under different photosynthetic photon flux density suggesting that heavy metal He up to 0.5 mM had damaged the photosynthetic apparatus in almost all species except in I. aquatica. Hg and Ph treatments caused dramatic increase in leaf MDA content, which was associated with the significant decrease of chlorophyll content, Most of the species were tolerant to Pb treatment up to 0.5 mM except M. micrantha, while only C. kyllingia and I. aquatica were tolerant to He treatment up to 0.5 mM. The Hg treatment also induced a higher proline content in the leaves of treated plants, Even without a clear increment pattern among the species, this suggested that proline may have a role as alarm stress rather than as tolerant indicator.