Effect of Ethephon and Gibberellin a 3 on Amaranthus Caudatus Seed Germination and Α - and Β - Amylase Activity under Salinity Stress

Salinity is one of the major environmental stresses for plants (Greenway and Munns, 1980). Based on their ability to grow on salt medium, plants, including crop species, are traditionally classified as glycophytes, showing the effects of salt at concentrations less than 50 mM, or halophytes which can complete their life cycles at 500 mM (Flowers, 1985; Maas, 1986). Although glycophytes generally are more sensitive to saline stress, they range widely in tolerance between species and varieties (Greenway and Munns, 1980). Plant growth is affected by salinity at all stages of development, but sensitivity varies greatly at different stages (Caravajal et al., 1998; Akram et al., 2002; Akinci et al., 2004). Germination is a critical stage in the growth cycle of plant species; it determines plant establishment and final crop production (Pearen et al., 1997). Increasing salinity generally reduces germination of glycophytes (Basalah and Mohammad, 1999; Almansouri et al., 2001; Akinci et al., 2004; Jamil et al., 2006; Siddiqui et al., 2006). This reduction is caused by two components of salt stress: osmotic effects due to restricted supply of water, creating water stress, and ionic effects due to seed ion uptake and/or accumulation (Ungar, 1996; Dodd and Donovan, 1999; Almansouri et al., 2001). Both components of salt stress can reduce seed germination by limiting water absorption (Dodd and Donovan, 1999; Duan et al., 2004), altering the mobilization of stored reserves (Lin and Kao, 1995), or other metabolic and molecular responses (Ramagopal, 1990). α-mylases (E.C. 3.2.1.1), which randomly attack the internal α-D-(1→4) O-glucosidic linkages, and β-amylases (E.C. 3.2.1.2), which hydrolyze α-D-(1→4) O-glucosidic linkages from the nonreducing end, are enzymes that play a major role in the mobilization of insoluble starch granules (Duedahl-Olesen et al., 2000). Under salinity, decreased α-amylase activity has been reported in Hordeum distichum (Tipirdamaz et al., 1995), Triticum aestivum (Siddiqui et al., 2006), Triticum durum seeds (Almansouri et al., 2001), Vigna radiata cotyledons (Promila and Kumar, 2000) and