Harvested samples of plants were washed and oven-dried at
55 C for 72 h, and the dried plant parts were ground to powder.
For each plant sample, 1.0 g of powder was digested with
10 N HNO3, and the sample digests were subjected to element
analysis by an atomic absorption spectrophotometer (Shimadzu,
AA-670). A flame photometer (Jenway, PFP7) was used
to determine the Na and K contents.