Increasing NaCl and CaCl2 concentrations in the growth medium of quince leaves: II. Effects on shoot regeneration

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Abstract
The effects of NaCl and CaCl2 on shoot regeneration from quince (Cydonia oblonga BA L29 clone) leaves were investigated. Caulogenesis was induced on in vitro-grown leaves treated for 2d in liquid Murashige and Skoog (MS) medium with 11.3 μM 2,4-dichlorophenoxyacetic acid and cultured on MS gelled medium supplemented with 4.5 μM thidiazuron and 0.5 μM naphthaleneacetic acid. Three experiments were performed: in the first, we compared the effects of NaCl at 0, 25, 50, 100, and 200 mM in factorial combination with 3, 9, and 27 mM CaCl2. In the second, NaCl was tested at 0, 5, 10, 20, 40, and 80 mM with CaCl2 at 0.3, 1.0, and 3.0 mM. The third experiment was carried out with the same experimental design as the second one but replacing NaCl with Na2SO4. Shoot regeneration was evaluated after 50 d of culturing: 25 in darkness and 25 in white light. In the first experiment, shoot regeneration was very poor and was observed only at the lower salt concentrations. In the second experiment, the percentages of caulogenic leaves were much higher, but decreased with increasing NaCl concentration. The more pronounced negative effect of the highest NaCl concentrations appeared to be partly mitigated by CaCl2 at 1 and 3 mM. The presence of 3 mM CaCl2, in the experiment with Na2SO4, appeared to be even more effective in reducing the adverse effect of sodium stress on caulogenesis. This result was attributed to the lower Cl− concentration in the growth medium, which resulted from replacing NaCl with Na2SO4. NaCl applied at low concentrations (5 and 10 mM) in combination with 3 mM CaCl2 exerted a favorable effect on adventitious shoot regeneration. As regards the Na+ and Ca2+ interaction, when the Na+/Ca2+ ratio was below roughly 35 and 20, with NaCl and Na2SO4, respectively, at least 60% of leaves showed regenerating capacity, but optimal values of this ratio were not derived.