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The objective of the present study was to characterize intrinsic physiological and biochemical properties of the wall-less unicellular cholorophyte Dunaliella salina isolated from a hypersaline Sambhar Lake. The strain grew optimally at 0.5 M NaCl and 16:8 h L:D photoperiod along with maintaining low level of intracellular Na even at higher salinity, emphasizing special features of its cell membranes. It was observed that the cells experienced stress beyond 2 M NaCl as evidenced by increased intracellular reactive oxygen species and antioxidative enzymes, nevertheless proline and malondialdehyde content declined sharply accompanied by higher neutral lipid accumulation. Salinity exceeding 2 M resulted decrease in photosynthetic quantum yield (Fv/Fm) and enhanced glycerol synthesis accompanied by leakage. Super oxide dismutase seemed to play a pivotal role in antioxidative defense as eight isoforms were expressed differentially while catalase and glutathione peroxidase showing no significant change in their expression at higher salinity. The ability of D. salina to grow in range of salinities by sustaining healthy photosynthetic apparatus along with accumulation of valuable products made this alga an ideal organism that can be exploited as resource for biofuel and commercial products.

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Artemisia absinthium and Psidium guajava are powerful sources of secondary metabolites, some of them with potential allelopathic activity. Both the species grow together in India with a weed (Parthenium hysterophorus) that is becoming extremely invasive. The aim of the present research was to test the allelopathic effect of A. absinthium and P. guajava aqueous leaf extracts on seed germination, seedling growth (shoot and root length), as well as some biochemical parameters (enzymatic and non-enzymatic antioxidants, photosynthetic pigments, osmolytes, and malondialdehyde by-products) of P. hysterophorus plants. Leaf extracts of both A. absinthium and P. guajava constrained the germination and seedling development (root and shoot length), affected pigment content (chlorophylls, carotenoids), stimulated the activity of antioxidant enzymes, and increased the level of malondialdehyde by-products of P. hysterophorus plants. Non-enzymatic antioxidants (glutathione and ascorbic acid) in P. hysterophorus leaves were, conversely, negatively affected by both leaf extracts tested in the present experiment. Although A. absinthium was more effective than P. guajava in impacting some biochemical parameters of P. hysterophorus leaves (including a higher EC50 for seed germination), P. guajava extract showed a higher EC50 in terms of root inhibition of P. hysterophorus seedlings. The present study provides the evidence that A. absinthium and P. guajava extract could be proficiently exploited as a botanical herbicide against P. hysterophorus.

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