Reversible Fine Structural Alterations of Pinto Bean Chloroplasts Following Treatments with Hydrogen Chloride Gas

Abstract

Primary leaf tissue from Phaseolus vulgaris, 8, 12, or 16 days post seeding, was sampled at intervals up to 24 h following 20-min treatments with 6.0-54.2 mg m-3 gaseous hydrogen chloride (HCl). The purposes of the study were to characterize chloroplast fine structure throughout the 24 h response period and to identify reversible chloroplast alterations. Most samples taken immediately after termination of HCl treatment had plasmolyzed mesophyll cells containing chloroplasts with (1) crystals in the stroma, (2) swollen frets and terminal granal compartments, (3) accumulated deposits of electron-dense material between envelope membranes, (4) envelope disruptions, and (5) increased stroma granulation. As the interval between HCl treatment and sampling lengthened, many chloroplasts gradually recovered normal appearance while a few became entirely disrupted. The apparent relative frequencies of normal and moribund chloroplasts 24 h after fumigation were dependent on HCl concentration. The number of chloroplasts with crystals increased with increasing HCl concentration; these crystals disappeared within 4 h following the 21.1 mg HCl m-3 treatment. Estimates of sectional area obtained from micrograph measurements indicated that chloroplasts enlarged following HCl treatment and that, at concentrations below 25 mg m-3, chloroplast length preferentially increased. Although 12-day-old leaves are known to be most sensitive to HCl, no qualitative differences in chloroplast responses between the different ages were discerned. Differences were quantitative: 12-day-old leaves showed more frequent totally disrupted chloroplasts at each HCl concentration. The results indicated that stroma crystal formation, granal compartment swelling, and chloroplast enlargement were reversible responses to HCl treatment. A limited number of breaks in chloroplast envelope may also be repaired. Chloroplasts with frequent disruptions of the envelope and extensive deposits of electron-dense material within the envelope underwent further degenerative changes.