Indian Journal of Plant Physiology

Seeds of rice (Oryza sativa L.) cv IR- 36 and Ratna subjected to heavy metal (Pb²⁺ and Hg²⁺) stress showed inhibition in germination percentage, shoot and root length and their fresh and dry mass after 7 days. Both Pb²⁺ and Hg²⁺ inhibited starch hydrolysis due to inhibition of α-amylase. Hg²⁺ was more effective than Pb²⁺ in inhibiting germination, and IR-36 was more tolerant than Ratna to these heavy metals. When metal- treated embryos were grown in vitro, 2% sucrose in the medium could overcome the inhibitory effect of Pb²⁺ on embryo growth while the same could not erase the inhibitory effect of Hg²⁺ on embryo growth significantly. Thus, Pb²⁺ seemingly inhibited germination and seedling growth by impairing the hydrolysis of endosperm starch without significantly affecting the embryo, while Hg²⁺ inhibited the same by damaging the embryo itself. Thus, Hg²⁺ is potentially more lethal than Pb²⁺ in inhibiting germination of rice seeds.