VARIABLE SEED GERMINATION AND SEEDLING GROWTH RESPONSES OF HIPPOPHAE RHAMNOIDES AND H. SALICIFOLIA TO CADMIUM

Owing mainly to diverse anthropogenic but also to natural sources, the concentrations of heavy metals (HMs) such as Cd, Pb, Hg etc. have tremendously increased in soil and water (Sharma and Dietz 2006; Marschner 2012). HMs are taken up by plants often via transport pathways meant for essential metal ions. For 2+ example, Cd employs Ca channels for entering the cell (Perfus-Barbeoch et al. 2002). Even the essential HMs such as Zn, Cu, Ni etc. turn toxic as and when their concentration exceeds certain threshold values. HMs eventually pose a threat to human and animal health through food chain. HM-dependent phytotoxicity and associated yield losses are well documented (Sharma and Dietz 2006). Following uptake, HMs interfere with multiple cellular and metabolic activities through various mechanisms. The latter mainly include (i) disruption of enzyme functions due to thiol affinities of HMs, (ii) imposition of redox imbalance and resultant oxidative stress and (iii) displacement of essential metal ions from respective functional sites (Sharma and Dietz 2009). In last some years, phytoremediation, a plant based technology aimed at reducing the environmental HM burden, has emerged as an environment friendly way out (Pilon-Smits, 2005). A clearer understanding of plant responses to HMs is expected to facilitate an optimized realization of phytoremediation. In this context, effects of HMs on crop plant species have often been reported (Sharma 1985a,b, Sharma et al. 2004; Thakur and Sharma 2015). Diverse plant processes are suppressed by heavy metals including seed germination (Thakur and Sharma 2015), photosynthesis (Bazzaz et al. 1974; Kumar et al. 2019), transpiration (Bazzaz et al. 1974) and essential ion homeostasis (Sharma et al. 2004). Occasionally, lower concentrations of non-essential HMs have been reported to stimulate processes like seed germination (Sharma, 1985a). There is, however, a dearth of information concerning the responses of wild The phytotoxic effects of heavy metals (HMs) and metalloids in crop plant species are well documented. There is, however, a dearth of information concerning HM toxicity in wild plants of medicinal and economic importance particularly those from high altitude regions. Here, we have assessed the effects of a range of Cd concentrations on seed germination, seedling growth and certain associated metabolic parameters of Hippophae salicifolia (Kinnaur) and two populations of H. rhamnoides namely, Kinnaur and Lahaul (Himachal Pradesh, India). The stated Hippophae (seabuckthorn) species, distributed in Himalayan states of India including Himachal Pradesh, possess tremendous medicinal value, fix atmospheric nitrogen and reduce soil erosion. Higher Cd concentrations differentially suppressed the seed germination of the tested Hippophae species/populations with the lowest effect being in case of H. salicifolia. The lower Cd concentrations stimulated the germination in H. salicifolia and H. rhamnoides Kinnaur. The seedling growth was suppressed by Cd with organand species/population specific differences. The magnitude of root growth inhibition was invariably greater than that of shoot and H. salicifolia proved more tolerant to Cd than both the H. rhamnoides populations. The TTC reduction ability of embryos excised from Cd treated seeds was marginally suppressed by Cd while α-amylase activity was substantially inhibited. Due to Cd treatment, the MDA contents, activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and proline contents increased in the seedling tissue. No marked species/population specific differences were evident in these parameters except that MDA contents did not change due to lower Cd concentration in H. salicifolia. The relative Cd tolerance of H. salicifolia has implications for its better survival in an HM-contaminated scenario.