THE INFLUENCE OF AN INHIBITOR OF PHYTOCHELATIN SYNTHESIS ON ROOT-GROWTH AND ROOT MERISTEMATIC ACTIVITY IN FESTUCA-RUBRA L IN RESPONSE TO ZINC

Six-day-old seedings of three cultivars of Festuca rubra L. (Merlin, Hawk and S59) were grown in aerated calcium nitrate solution at various concentrations of Zn in the presence or absence of buthionine sulfoximine (BSO), a potent inhibitor of phytochelatin synthesis. In the absence of BSO, increasing Zn concentrations reduced the root length of all three cultivars but the Zn-sensitive cultivar (S59) showed the greatest Zn-induced reduction and the Zn-tolerant cultivar (Merlin) the least. The presence of BSO in the medium, contrary to expectation, ameliorated the inhibitory effect of Zn on root growth in all three cultivars. Treatment with 0.2-mu-g Zn cm-3 reduced the length of the root apical meristem in Merlin and S59. The presence of BSO in the culture solution did not affect the length of the apical meristem in Zn-treated roots in any cultivar but, in the absence of Zn, BSO increased the length of the apical meristem by an average of 14.0 % compared with the controls (0 Zn minus BSO). The mean length of epidermal cells in the region between the proximal boundary of the root meristem and the first root hair was reduced by an average 43 % in the three cultivars following treatment with 0.2-mu-g Zn cm-3. However, the presence of BSO in the rooting medium did not influence epidermal cell length in Zn-treated or untreated roots in any cultivar. The presence of BSO resulted in an average 1.7-fold increase in the mitotic index in the root meristem of Zn-treated roots; a comparable BSO-induced stimulation of mitotic index has been found in roots grown without Zn. However, BSO did not affect the relative frequency of the four stages of mitosis. This preliminary evidence suggests that BSO stimulates cell division activity in roots of F. rubra. The unexpected effect of the phytochelatin-inhibitor, BSO, in increasing the Zn-tolerance of roots argues against a key role of phytochelatins in the Zn-tolerance mechanism of roots of F. rubra