Physiological behavior of Scenedesmus sp. during exposure to elevated levels of Cu and Zn and after withdrawal of metal stress |
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Authors: | B N Tripathi J P Gaur |
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Institution: | (1) Department of Bioscience and Biotechnology, Banasthali Vidyapith, Banasthali, Rajasthan;(2) Laboratory of Algal Biology, Department of Botany, Banaras Hindu University, Varanasi, Uttar Pradesh |
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Abstract: | Summary. A 48 h exposure of Scenedesmus sp. to sublethal concentrations of Cu (2.5 and 10 μM) and Zn (5 and 25 μM) caused a concentration-dependent inhibition of
growth, photosynthesis, respiration, NO3
− uptake, and nitrate reductase (EC 1.6.6.1) activity, and a reduction in protein, carbohydrate, and photosynthetic-pigment
levels with a concomitant increase in intracellular levels of the test metals. After exposure, algal cells were transferred
to the basal medium without the excess level of test metals, to study the recovery of various processes. The growth of the
test algae had not recovered up to 12 h after transfer to the basal medium, but some physiological parameters such as photosynthesis
and respiration recovered within 6 h. The quicker recovery of photosynthesis and respiration might be used as acclimatory
responses as they prepare a background for the recovery of other parameters, including growth, of the test alga by generating
energy, forming photosynthate, and establishing the usual catabolism to attain normal conditions. Most of the processes recovered
completely or almost completely after being stressed with 2.5 μM Cu or 5 μM Zn. However, the maintenance of a relatively high
level of Cu and Zn in the cells previously exposed to 10 μM Cu and 25 μM Zn slowed down the recovery of different processes,
which did not fully recover even at the end of the experiment after 96 h. The present study demonstrates that a chain of metabolic
events, beginning with respiration and photosynthesis and continuing with assimilation and uptake of nutrients and subsequent
restoration of other metabolic processes, is involved in the recovery of the algae from Cu and Zn stress. Each studied parameter
seems to play an important role in balancing the cellular homeostasis during recovery from metal stress.
Correspondence and reprints: Department of Bioscience and Biotechnology, Banasthali Vidyapith, Banasthali 304 022, Rajasthan,
India. |
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Keywords: | : Alga Copper Recovery Scenedesmus sp Toxicity Zinc |
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