Rapidity of cellular changes induced by zinc in a zinc tolerant and non‐tolerant cultivar of Festuca rubra L.

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Abstract
Summary: 7 day‐old seedlings of a Zn‐tolerant cultivar (Merlin) and a non‐tolerant cultivar (S59) of Festuca rubra L. were transferred to aerated solution culture containing 3 concentrations of Zn (0, 80 and 120 μM). Roots were sampled at 0, 6, 12, 24, 48, 72 and 96 h following transfer. Zn markedly reduced root extension in S59; this inhibition was evident after only 12 h exposure. In contrast Zn stimulated the root extension of Merlin. The length of the apical meristem of S59 was reduced within 12 h after transfer to the Zn‐containing solutions, followed by a further reduction to 69 % and 61 % of that of control roots (0 μM Zn) after 96 h at 80 μM Zn and 120 μM Zn respectively. The meristem length of Merlin was much less affected by Zn. Treatment with 80 μM Zn resulted in a stimulation in the number of lateral root primordia in both cultivars but their formation was depressed relative to the control roots at 120 μM Zn in S59, though not in Merlin. The area of mitotic cells was reduced by 25 % after only 12 h exposure to 120 μM Zn in S59 and this reduction increased with duration of exposure. However, in Merlin, the area of mitotic cells increased with increasing length of exposure to Zn. The protein content of mitotic cells of S59 was reduced by 28 %, relative to that of roots grown in the control solutions, after 12 h exposure to 120 μM. Zn, culminating in a 50 % reduction after 96 h exposure. However, the cellular protein content of Merlin increased progressively with time of exposure to Zn. The sensitivity and rapidity of response of these cellular changes to Zn in S59 may make them useful early markers of metal toxicity in roots.