Effects of the culture medium pH and ion uptake in in vitro vegetative organogenesis in thin cell layers of tobacco

Thin cell layers (TCL) of Nicotiana tabacum L. cv. Samsun were cultured in vitro to evaluate the effect of the pH of the culture medium and ionic uptake on vegetative organogenesis. The chromatographic analysis showed important variations during culture in the concentrations of the ions in the tissues of the explants grown at different pH levels. After 25 days of culture, shoots with regular development were obtained especially from the explants grown on the media with an initial pH (pH(i)) of 4.0 and 5.0. At pH(i) 7.0, the shoots were often grouped into tufts, lacking apical dominance and vitreous in appearance, probably due to a high uptake of ammonium in the first 48 h of culture and a low level of calcium in the first 24 h of culture. Regardless of the origin, (i.e. subepidermal chlorenchyma cells or wound callus generated by the outermost parenchyma layers) vegetative buds differed according to the pHi level. Direct superficial origin was observed only at pHi 4.0 and 5.0, whereas indirect cicatritial origin was observed at all pH levels.