Comparison of different methods of proline application to alleviate the effect of nickel stress on germination and seedling growth of Cucumis melo var. Flexousus

Nickel is an essential microelement, but the increased concentration it in the medium disrupts the germination and growth of plants. In the present study, the effect of pretreatment and exogenous proline in the seedling growth of Cucumis melo under nickel stress was investigated. For this purpose, seeds were divided into two groups. In one group, seeds were sterilized for 24h, then they soaked in 0, 10 mM proline and finally cultured in different nickel concentrations. Another group seeds were soaked in deionized water for 24 hours and then cultured in petri dishes containing the same from one another concentrations of nickel and proline. All seeds were kept for 10 days, then measured germination, and growth parameters and membrane stability. The results showed that germination parameters were not affected by nickel. Radicle was more sensitive to Ni excess than hypocotyl. The amount of malondialdehyde increased with increasing nickel concentration. Add exogenous proline significantly reduces germination percentage and germination index but it increased mean germination time. Proline pretreatment in the presence of nickel treatments improved radical length, root to shoot ratio. But the addition of exogenous proline increased hypocotyl length while radical length and their ratio decreased in lower exposure levels. However, exogenous proline reduced lipid peroxidation and membrane permeability more than similar treatments under nickel treatments. Proline, as a pretreatment as a compatible solution and antioxidant, improves the early stages of growth and reduces the damage caused by nickel toxicity in the early stages of cucumber seedling growth.