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Investigations were carried out to evaluate alterations in photosynthetic performance of Salvinia natans (L.) exposed to chromium (Cr) and zinc (Zn) rich wastewater. Accumulation of high levels of Cr and Zn in plants affected photosynthetic electron transport. Photosystem-(PS) II-mediated electron transport was enhanced in plants exposed to Cr rich wastewater while a decline was observed in Zn-exposed plants. Photosystem-I-mediated electron transport increased in plants exposed to Cr and Zn rich wastewater. Efficiency of photosystem II (F v /F m ) measured by fluorescence did not show any significant change in Cr-exposed plants but a decrease was observed in Zn-exposed plants as compared to the control. The enhancement in PS I-induced cyclic electron transport in Cr and Zn exposed plants led to a build up of the transthylakoidal proton gradient (∆pH) which subsequently helped in maintaining the photophosphorylation potential to meet the additional requirement of ATP under stress. The carbon assimilation potential was adversely affected as evident from the decrease in Rubisco (EC 4.1.1.39) activity. The alterations in photosynthetic electron transport affected stromal redox status and induced variations in the level of stromal components such as pyridine nucleotides in plants exposed to Cr and Zn rich wastewater. The present investigations revealed that alteration in the photosynthetic efficiency of Salvinia exposed to Cr could primarily be the result of a decline in carbon assimilation efficiency relative to light-mediated photosynthetic electron transport, though in the case of Zn-exposed plants both these factors were affected equally. Key words: carbon assimilation, electron transport, heavy metals, photophosphorylation, redox status Desempenho fotossintético de plantas de Salvinia natans expostas a água de esgoto rica em cromo e zinco: Avaliou-se o desempenho fotossintético de plantas de Salvinia natans L. expostas a água de esgoto rica em cromo (Cr) e zinco (Zn). O acúmulo de Cr e Zn em altos níveis afetou o transporte fotossintético de elétrons. O transporte de elétrons mediado pelo fotossistema (FS) II aumentou nas plantas expostas ao esgoto rico em Cr, observando-se o oposto nas plantas expostas ao esgoto rico em Zn. O transporte de elétrons mediado pelo FS I aumentou nas plantas expostas ao esgoto rico tanto em Cr como em Zn. A eficiência do FS II (F v /F m ) avaliada por fluorescência não variou significativamente em resposta ao Cr, porém reduziu-se nas plantas expostas ao esgoto rico em Zn, em comparação com as plantas-controle. O aumento do transporte cíclico de elétrons associado ao FS I acarretou em aumento do gradiente transtilacoidal de prótons (∆pH) que, por seu turno, esteve associado com o potencial de fotofosforilação para suportar as necessidades adicionais de ATP sob condições de estresse. O potencial de assimilação do carbono foi decrescido, conforme se deduz da menor atividade da Rubisco (EC 4.1.1.39). As alterações no transporte fotossintético de elétrons afetaram o status redox do estro...

There has been increased use of herbal drugs in recent years. Because of increasing demand and wider use, it is essential that the quality of plant-based drugs should be assured prior to use. When heavy metals contaminate the plants from which herbal drugs are derived, they affect both plant growth characteristics and production of secondary plant metabolites. Plants exposed to heavy metal stress show changes in production of secondary metabolites. High levels of heavy metal contamination in medicinal or other plants may suppress secondary metabolite production. Alternatively, the presence of heavy metals in medicinal plants may stimulate production of bioactive compounds in many plant species. Moreover, some research results suggest that heavy metals may play an important role in triggering plant genes to alter the titers or nature of secondary plant metabolites, although the exact mechanism by which this happens remains unclear. Oxidative stress induced by heavy metals triggers signaling pathways that affect production of specific plant metabolites. In particular, reactive oxygen species (ROS), generated during heavy metal stress, may cause lipid peroxidation that stimulates formation of highly active signaling compounds capable of triggering production of bioactive compounds (secondary metabolites) that enhances the medicinal value of the plant. As usual, further research is needed to clarify the mechanism by which heavy metals induce responses that result in enhanced secondary metabolite production.

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