Effects of cadmium on germination and seedling growth of Prosopis juliflora (Swartz) DC. - A potential metallophyte

Germination and seedling growth of Prosopis juliflora (Swartz) DC is investigated against cadmium toxicity. Cadmium concentration up to 400ppm, in vitro, showed no detrimental effect on germination of abraded seeds, germination velocity was, of course imperial Cotyledonary area per seedling (CAS) remained more or less unaffected (r= -0.0025, NS) but radicle growth was inhibited drastically above 25ppm. Compared to radicle, reduction in growth of hypocotyl was relatively of lower order. In Cd concentrations higher than 50ppm, radicle appeared somewhat dehydrated, turned brown and almost burnt gradually in higher concentrations. TL50 values for Hypocotyl and radicle growth were 288 and 36ppm of Cd, respectively. Such values calculated on the basis of regression for hypocotylar growth turned out to be 300ppm. Radicle length related with Cd curvilinearly indicating 50%, reduction at 45.4ppm of cadmium. Seedling emergence and their growth, for a pe riod of 50 days, were also evaluated in pot containing soil contaminated with 10-100 mg cadmium per kg soil. Soil appeared to provide protection to the seedlings against cadmium in comparison to their, in vitro, vulnerability to cadmium. There was delay in emergence velocity but (CAS) remained more or less unaffected up till 15th day of growth - CAS declined at later stage. Cadmium had no significant effect on hypocotylar growth. There was delay in primary leaf development. Fifty per cent reduction in growth of radicle, epicotyl, shoot (hypocotyl + epicotyl), number of leaves, number of leaflets per seedling and seedling biomass corresponded with 129.5, 136, 249.8, 169.2, 104.9, and 180 mg of cadmium per kg soil, respectively. Cadmium inhibited internodal elongation significantly. One individual each in 80 and 100 mg Cd per kg soil treatments died after 24 days of growth. The results are discussed in eco- physiological context.