Impact of Ascorbic Acid on Seed Germination, Seedling Growth, and Enzyme Activity of Salt-Stressed Fenugreek

Fenugreek (Trigonella foenum-graecum) seeds soaked in ascorbic acid had increased germination, seedling shoot length and total chlorophyll under salt stress as compared with seeds not treated with ascorbic acid. Root length, fresh weight, dry weight, proline, and catalase activity (CAT) increased in salt stressed seedling in which seeds were not treated with ascorbic acid. In seeds treated with ascorbic acid, the salt stress effect on CAT activity was decreased. Ascorbic acid pretreatment of seeds counteracted the decrease in ascorbate oxidase (AO) induced by salt stress, but appeared to act synergistically with salt stress to decrease proline dehydrogenase. The application of ascorbic acid to fenugreek seed apparently increased antioxidant activity, leading to an increase in resistance to salt stress. Salt stress and the ascorbic acid treatment of seeds led to metabolic changes in seedlings as evidenced by changes in peroxidase (Prx) and esterase (Est) isozymes associated with increases in salt and ascorbic acid concentrations. Such changes could account for increases in seedling vigor with ascorbic acid seed treatment and the ability of the seedling to grow in the presence of a salt stress. INTRODUCTION Fenugreek (Trigonella foenum-graecum) is grown as a medicinal and food plant in the Mediterranean region and several other Middle Eastern countries. Most of the land areas in which fenugreek is cultivated, however, are subject to desertification and have relatively high salt levels as a consequence of low and random precipitation and incorrect irrigation practices. In addition, many other areas of the world contain arid and semi-arid soils and water resources that are too saline for growth of common economic crops. Salt stress, similar to many abiotic stress factors, is known to induce oxidative damage to plant cells from reactive oxygen species that affect the physiology and biochemistry of plants and that can lead to a reduction in plant yield (AzevedoNeto et al., 2006). The reactive oxygen species can damage membranes and other essential macromolecules, such as photosynthetic pigments, proteins, DNA, and lipids (Fahmy et al., 1998). For stress protection, plants have developed enzymatic and non-enzymatic scavenging mechanisms for the reactive oxygen species (Demiral and Turkan, 2005). These scavenging mechanisms, such as the production of catalase to reduce hydrogen peroxide (Hernandez et al., 2000), enable the plant to maintain growth under stress conditions. Ascorbic acid, an abundant, relatively small molecule in plants, plays multiple roles in plant growth, functioning in cell division, cell wall expansion, and other developmental processes (Asada, 1999; Conklin, 2001; Pignocchi and Foyer, 2003). In addition, ascorbic acid is a key substance in the network of plant antioxidants, including glutathione and enzymatic antioxidants that detoxify H2O2 to counteract oxygen radicals produced by the Mehler reaction and photorespiration (Noctor and Foyer, 1998). Yet, little information is available on the effect of ascorbic acid on salt stress or enzyme activity in fenugreek plants. Behairy et al.: Impact of Ascorbic Acid on Seed Germination, Seedling Growth, and