Chloride localization in Phaseolus vulgaris leaves exposed to HCl gas

An investigation of chloride accumulation and distribution in unifoliate leaves of Phaseolus vulgaris following supra-acute exposures to gaseous hydrogen chloride (HCl) was conducted. Plants which were 8-22 days old (post-seeding) were exposed for 20 min to HCl gas in concentrations ranging from 6.0-54.2 mg m-3 in different combinations of age and concentration. Aqueous extracts of treated unifoliates contained more chloride than was present in control leaves. In both 8 and 12-day-old leaves, the amount of chloride accumulated was proportional to the exposure concentration of HCl, but 12-day-old plants accumulated less chloride than 8-day-old plants. The number of leaves with macroscopic injury symptoms (epidermal glazing and interveinal necrosis) was also related to chloride content. Precipitation of chloride ions by silver salts was employed to examine the ultrastructural distribution of chloride. Deposits of AgCl were present in cell walls, ground plasm, vacuoles, and chloroplasts of both control and HCl-treated leaf tissues. In leaves sampled immediately after treatment, chloroplastic AgCl precipitates were less than in controls, but as sampling was delayed from the HCl treatment, AgCl deposits in chloroplasts regained control levels. The frequency and distribution of AgCl deposits indicated that chloride passed through the leaf cuticle and migrated through the apopolast. Chloride also entered the cytoplasm of cells and appeared to be sequestered in vacuoles of treated cells.