ROLE OF PROLINE ACCUMULATION IN RESPONSE TO TOXIC COPPER IN CHLORELLA SP. (CHLOROPHYCEAE) CELLS

Abstract

The green alga Chlorella sp. (strain 2350) was found to accumulate proline, up to a maximum of 0.027 fmol·cell Ϫ1 , under stressful concentrations of cupric ions. The function of the accumulated proline was studied with respect to its effect on copper (Cu) uptake. By induction with salt stress, cells with various levels of intracellular proline were used for this study. It is shown that the amount of Cu taken up by the cells was reduced when the intracellular proline levels were enhanced. When proline was exogenously supplied prior to Cu treatment, the adsorption of Cu was markedly reduced. When exogenous proline was supplied after Cu treatment, it resulted in a remarkable desorption of the adsorbed Cu immediately after the addition of proline. The results of the present study indicate that proline may exert some action on the cell surface and suggest that one function of accumulated proline is to reduce the uptake of metal ions. The accumulation of proline may be related to a tolerance mechanism for dealing with Cu stress.

Heavy‐metal‐induced proline accumulation and its role in ameliorating metal toxicity in Chlorella vulgaris

“…The hierarchy of metal toxicity in the present study was similar to that reported previously (Rai et al, 1981 ;De Filippis & Pallaghy, 1994). Metal-induced enhancement of the concentration of intracellular proline in C. vulgaris agreed with reports on higher plants (Alia & Pardha Saradhi, 1993 ;Bassi & Sharma, 1993a,b ;Costa & Morel, 1994), algae (Chang, 1991 ;Wu et al, 1998) and cyanobacteria (Wu et al, 1995). Proline accumulation was highest in cells treated with Cu and Cr, followed in decreasing order by Ni-and Zn-treated cells.…”

“…Wu et al (1995) showed that Cu-induced efflux of K + in Anacystis nidulans was minimized in the presence of proline, suggesting that proline possibly protected the plasma membrane from Cu toxicity, or that it perhaps complexed Cu# + thereby decreasing the concentration of free Cu# + in the external environment. In a subsequent paper, Wu et al (1998) demonstrated reduced Cu uptake by cells containing high concentrations of proline, suggesting that proline stabilized the plasma membrane and also reduced the uptake of Cu by algal cells. The present work is not in agreement with those findings, since proline-pretreatment, instead of reducing, caused a slight enhancement (12 %) of Cu uptake in C. vulgaris.…”

“…After harvesting algal cells, CsCl (0.1 %, w\v) was added to the filtrate before measuring its K + content by atomic absorption spectrophotometry. Wu et al (1998) showed that Cu# + uptake was inhibited by intracellular proline ; to assess the effect of proline pre-treatment on Cu uptake, C. vulgaris was exposed to 1 mM proline for 1 h, followed by measurement of Cu# + uptake by the method already described.…”

Role of proline under changing environments

“…Proline accumulated when different algae were exposed to metals such as Cu in Anacystis nidulans, 128 Chlorella sp. 129 and Chlorella vulgaris.…”

Influence of copper ions on growth, lipid peroxidation, and proline and polyamines content in carrot rosettes obtained from anther culture

“…High level of endogenous proline and lower Cu content in the 1014 line rosettes resulted in better growth regeneration capacities in the presence of 10 lM Cu. In this context, suggestions have been made that proline provides protection by (a) maintaining the water balance, (b) chelating Cu in cytoplasm, or (c) reducing metal uptake (Wu et al 1998). Decline in proline content in the 1014 line grown in the presence of 100 lM Cu for 24 weeks may indicate that a certain threshold of intracellular Cu was crossed, or antioxidative systems were unable to cope with the oxidative stress induced by Cu excess.…”