PROLINE ACCUMULATION UNDER HEAVY-METAL STRESS

The effect of nitrate salts of the four heavy metals cadmium, cobalt and zinc in B5 medium and lead in distilled water was tested on seed germination and seedling growth in Cajanus cajan (cv. BS-15), Vigna mungo (cv. T-9) and Triticum aestivum (cv. C-306) under controlled sterile conditions. All four heavy metals caused proportionate reduction in growth depending on the concentration. However, zinc stimulated the growth of seedlings at low concentrations. A considerable and proportionate increase in proline content was recorded with increase in concentration of heavy metals. Cadmium proved to be the strongest inducer for proline accumulation, zinc the weakest. Equimolar concentrations of potassium did not show any proportionate change in the level of proline when compared with controls. It is therefore inferred that proline accumulation can be used as a marker to test the level of heavy metal pollution. Accumulation of large quantities of proline in seedlings raised in media with lead nitrate having higher osmotic potential compared with those grown in B5 medium (not supplemented with heavy metal) having lower osmotic potential suggests that proline accumulation is not related to osmotic adjustment.