Plant Materials and Growing Conditions

The seeds of 2 wheat cultivars having the differential metal tolerance capacity ⁵¹ namely, Sahar-2006 and Inqalab-91 were collected from the Ayub Agricultural Research Institute (AARI) Faisalabad, Pakistan. In order to contaminate the dry, sandy loamy soil, the calculated amount of Cd (10 and 25 mg kg^-1) was applied to soil collected from Agriculture Field Faisalabad for spiking process to make contaminated soil artificially for 3 months. Cadmium chloride (CdCl₂) was used as source for Cd stress. Prior to sowing, seeds were washed with Cd free water and then surface sterilized with 10% H₂O₂ to minimize the microbial contamination and rinsed with distilled water thoroughly. The plastic pots containing 25-cm diameter and 15-cm depth were filled with normal and Cd spiked sandy loamy soil (5 kg). The physico-chemical properties of dry sandy loamy soil are given in Table 1. In each pot, 10 seeds were sown in each pot and placed in an open greenhouse. All pots were arranged in completely randomized design with 3 replicate per treatment. An average of 19 ± 3/10 ± 2°C was the day/ night temperatures, an average of 62.0% to 65.1% was the relative humidity, and an average of 10 to 11 was the day length. Upon full emergence, thinning was done and only 5 seedlings were kept in each pot. Then half strength Hoagland’s nutrient solution made in Cd-free water ⁵² was supplied to all plants at every 5 days-interval. Soil pH was adjusted back to control, pH of 6.0 to 6.2 with diluted H₂SO₄. A control group without Cd application was maintained for comparison. Two weeks after germination, plants were sprayed with different concentration of Si (1.5 and 3 mM Si) using 30 mL of Na₂SiO₃ (Merck, pH 11.76) solution to each wheat seedling. An equivalent amount of Na⁺ (as NaCl) was added to the controlled plants to compensate the differences resulting from Na₂SiO₃ application. The controlled plants were sprayed with distilled water in the same amount. The plants were fertilized with a Hoagland nutrient solution to keep the moisture contents. Plants were harvested after 2 weeks of Si application and fresh leaves were kept in a freezer at −20°C for recording of different growth and biochemical attributes.

Mean Values of Physico-Chemical Properties of Dry Loamy Soil.