2.3 Determination of monovalent cations (Na+and K+) content
Leaves were harvested and washed with deionized water. The leaf samples
were dried first at 105°C for 2 h, subsequently at 70°C for 72 h, and
then weighted for dry weight. Lyophilized leaves were milled to powder
for mineral nutrient analyses. Powdered samples were extracted with 10
ml of HNO3 (0.1N) for 60 min at 95 ºC. The resulting
solutions were filtered through Whatman filter paper, diluted and
analyzed for Na+ and K+. Cation
concentrations were determined with an atomic absorption
spectrophotometer (PerkinElmer, PE AAS 900 F).