RESUMO
Toxic heavy metals viz. lead, mercury and cadmium induced differential accumulation of proline in lemongrass (Cymbopogon flexuosus Stapf.) grown in soil amended with 50, 100, 200, 350 and 500 mg kg-1 of the metals have been studied. Proline accumulation was found to be metal specific, organ specific and linear dose dependant. Further, proline accumulation following short term exposure (two months after transplantation) was higher than long term exposure (nine months after transplantation). Proline accumulation following short term exposure was 2.032 to 3.839 μ moles g-1 for cadmium (50 -200 mg kg-1); the corresponding range for mercury was 1.968 to 5.670 μ moles g-1 and 0.830 to 4.567 μ moles g-1 for lead (50 -500 mg kg-1for mercury and lead). Proline accumulation was consistently higher in young tender leaf than old leaf, irrespective of the metal or duration of exposure. For cadmium treatment proline level was 2.032 to 3.839 μ moles g-1 for young leaves while the corresponding value for old leaf was 1.728 to 2.396 μ moles g-1 following short term exposure. The same trend was observed for the other two metals and duration of exposure. For control set proline accumulation in root was 0.425 μ moles g-1 as against 0.805 and 0.533 μ moles g-1 in young and old leaves respectively indicating that proline accumulation in root are lower than leaves, under both normal and stressed condition.