SAHITO AND KHAN (2013), FUUAST J. BIOL., 3(2): 11-24 GROWTH OF WIRY WATTLE SEEDLINGS UNDER SALT STRESS ZULFIQAR ALI SAHITO AND D. KHAN Department of Botany, University of Karachi, Karachi-75270, Pakistan. Abstract The experiment was conducted to observe the influence of Sea salt salinity (0, 0.15, 0.3, 0.6, 0.9 and 1.2% corresponding to ECiw of 0.6, 3.51, 5.24, 9.23, 12.81 and 16.67 dS.m -1 , respectively) on seedling growth and the physiological, biochemical and mineral parameters of growth in Acacia coriacea subsp. pendens. On average basis, 50% reduction in seedling growth performance in coastal sandy soil corresponded to ECiw: 14.94 ± 2.18 dS.m -1 . Phyllode concentrations of protein, total soluble sugars, proline and phenols increased significantly with the salt stress and the pigments (chlorophylls and carotenoids) concentrations posed a fluctuating behaviour. There was substantial increase in Na and Cl contents of phyllode (306.59 and 213.67 % over control, respectively) in extreme salinity of ECiw: 16.67 dS.m -1 . K contents declined under saline environment. K/Na ratio although declined in salinity treatments as compared to the control, it didn’t vary practically amongst the salinity treatments of ECiw: 3.51 to 16.67 dS.m -1 . The results are discussed in physiological context. Introduction Some 48 species of Acacia have been screened in relation to salinity (Niknam and McComb, 2000). Craig et al. (1990) have tested ten taxa of Acacia. A. cyclops, A. brumalis, A. redolens and A. aff. lineolata had survival rate of 100% after 12 weeks irrigation with saline solution of 9.5 dS.m -1 . A. saligna, A. stenophylla and A. salicena have also been shown to be salt tolerant (Aswathappa et al., 1987; Hussain and Gul, 1991; Gill and Abrol, 1991; Hafeez, 1993; Singh et al., 1994; Marcar et al., 1995; Shirazi et al., 2006). Sahito et al. (2013) have reported 50% decline in growth of A. stenophylla to correspond with Seawater dilution of ECiw: 12.51 ± 0.51dS.m -1 . Six species of Acacia have been grown in Riyadh under irrigation for four years and compared for their growth and biomass production by Aref et al. (2003). Survival and growth of 24 native species of Australia including some Acacias have been tested near Wellington in Central-West-New South Wales on a saline discharge site by Marcar et al. (2003). Acacia coriacea (wire wood, desert oak, dogwood or wiry wattle) is one of the desert species of Australia - reported from the Pilbara coast as well (www.kimseed.com.au) - has been studied for its salt tolerance at germination stage. Rahman et al. (1997) found the effects of NaCl on seed germination of Acacia coriacea to be adverse due to internal osmotic and toxicity rather than from a restriction of imbibition. Harris et al. 1998) tested effects of hardening by soaking seeds of nine species of Acacia in water. The treatment showed varying effects of hardening on seed germination in distilled water and NaCl – high rate of germination in A. tortilis; low reduced rate of germination in A. elata and no significant effect on germination in other species including A. coriacea were recorded. LD 50 concentration of NaCl in case of A. coriacea seed germination was reported to be 125mM (Rahman et al., 1998a). It was rated as salt sensitive species at germination stage (Rahman et al., 1998 b). Since many species including some halophytes are reported to be differentially tolerant to salinity at germination and subsequent growth phase (Ayers and Hayward, 1948; Azizov, 1974; Ungar, 1974; Mahmood and Malik, 1986; Khan and Ahmad, 1998; Khan et al.,1987; Prado et al., 2000; Ali et al., 2013a) and there is involvement of multiple biochemical pathways in the salt tolerance of plants facilitating retention or acquisition of water, protection of chloroplast functions, maintenance of ion homeostasis, scavenging of oxygen radicals and the peculiarities of secondary metabolism under salt stress (Parvaiz and Satyawati, 2008; Ramakrishna and Ravishankar, 2011; Mane et al., 2011; Aslam et al., 2011; Rahdari and Hoseini, 2011; Zielinska, 2012), experimental investigations related to the growth of wiry wattle (Acacia coriacea DC. subsp. pendens Cowan and Maslin) at seedling stage while irrigated with Seawater dilutions in pots have been undertaken to assess its salt tolerance and its possible scope in afforestation on Pakistan coast under multiple salts salinity of Seawater dilutions in coastal sandy soil. Besides some important biochemical parameters of growth, phyllode contents of Na + , K + and Cl - ions are also investigated. Materials and Methods The seeds of A. coriacea subsp. pendens collected from its tree growing in the Botanical Garden, University of Karachi, during March, 2012 were sterilized with sodium Hypochlorite (2%) for two minutes and stored in brown aseptic bottles for around two months.