Solute leakage from susceptible and tolerant cultivars of Phaseolus vulgaris following ozone exposure

Abstract

The leakage of total electrolytes, potassium, calcium, sugars, and amino acids from primary leaf discs of Phaseolus vulgaris L. cv. Seafarer (ozone susceptible) and cv. Goldcrop (ozone tolerant) was monitored following exposure to 40 parts per hundred million (pphm) ozone for 4 h. Significant differences in cultivar response were not detected until 24 h after exposure. At that time, leakage from cv. Seafarer leaves was 220% for total electrolytes, 230% for calcium, 260% for potassium and sugars, and 400% for amino acids relative to controls, whereas the leakage from cv. Goldcrop leaves remained at control levels. The water-soluble sugar and free amino acid content of a leaf homogenate also increased at the 24-h sampling time. These accumulations may result from a reduced rate of phloem translocation. Rates of leakage and leaf-solute contents returned to control levels by 48 and 72 h after exposure.Kinetic analysis of solute efflux from leaf discs sampled from both cultivars immediately after ozone exposure indicated that these leaves contained an increased quantity of solutes which could be rapidly leached within 0.5 h. However, the subsequent linear rate of leakage between 0.5 and 4 h did not increase except in leaf discs sampled from cv. Seafarer 24 h after exposure. The results are discussed in relation to the mechanism of ozone injury in cv. Seafarer and the basis of ozone tolerance in the cv. Goldcrop.