Age-dependent growth and injury responses of pinto bean leaves to gaseous hydrogen chloride

Susceptibility of unifoliate leaves of Phaseolus vulgaris L. to visible injury following acute exposures to anhydrous hydrogen chloride gas (HCl) and the relationship of susceptibility to leaf age and subsequent growth were examined. Plants varying in age from 6 to 12 days postseeding were treated with 25.6 ± 3.3 mg HCl m^-3 for 20 min. Foliar injury consisted primarily of abaxial glazing and bifacial interveinal necrosis. Plants that were 6 days old at the time of exposure were uninjured; the percent of injured unifoliate leaves increased with tissue age at the time of HCl treatment. The relationship was sigmoidal and probit analysis indicated that the estimated stage of maturity at which 50% of the unifoliate leaves became injured (EM₅₀) was 9 days. The rate of leaf expansion between control and fumigated leaves did not differ significantly, but expansion of the fumigated leaves was significantly delayed. The delay was apparently not directly related to visible foliar injury, nor were any differences in the relationship of leaf fresh weight to dry weight noted between control and HCl-treated leaves.