Influence of Aqueous SO2 on Changes in the Leaf Discs of Free Amino Acid Composition and Free Organic Acid Metabolism under Light and Dark Conditions of Cajanus Cajan and Amaranthus Paniculatus

Abstract

The influence of elevated aqueous SO₂ (0, 10, 20, 30, 40, 50, 100 and 250 ppm) on free amino acid composition, proline content and free organic acid content of pigeonpea (Cajanus cajan (L.) Millsp. cv. PDM1), a C₃ plant and amaranth (Amaranthus paniculatus L. a local cultivar), a C₄ plant leaf discs under light and dark conditions has been studied. The studies of free amino acid composition were carried out at 0, 30 and 100 ppm aqueous SO₂ treated leaf discs in both pigeonpea and amaranth. Though small quantitative variations appeared among individual amino acids, the total quantity of amino acids increased in both the plant species with increasing SO₂ concentration and duration of exposure. Cysteine was absent in the light incubated amaranth but it appeared in the dark incubated SO₂ treatments. In pigeonpea, though initially absent cysteine appeared in the higher concentrations of SO₂. Methionine content was more in amaranth than in pigeonpea. Enhanced levels of proline content were registered at all SO₂ concentrations both in light and dark exposed leaf discs in pigeonpea than amaranth. The accumulation of free organic acid content was more conspicuous in amaranth than in pigeonpea under dark conditions rather than under light conditions in response SO₂.