In barley (Hordeum vulgare L.) seedlings, the rate of root growth, osmotic pressure (Π), hydraulic conductance (L p), and longitudinal (δl) and transverse (δD/D) extensibility of root cells were measured. The seedlings were grown on Knop solution with nitrate or without nitrate with addition of 5–10 mM NH 4 + or 0.5–1.0 mM glutamate. Root growth retardation on the 1st–4th days of exposure to NH 4 + was determined by a decrease in δl in the zone of elongation, whereas root thickening was evidently related to an increase in Π. Biphasic dynamics of δl in the presence of NH 4 + was imitated by medium acidification near the root surface to pH 3.7, which confirms a conclusion, we have done earlier, about a non-monotonous pH-dependence of longitudinal extensibility. Root growth retardation during the first day of exposure to Glu was also determined by a decrease in the δl, which was, however, accompanied by an increase in the δD/D and L p. Fast Glu-induced changes of measured root parameters were imitated by root exposure to oryzalin, ionomycin, and inhibitors of the H+-pump. It was supposed that a decrease in δl in the presence of NH 4 + and Glu was related to cortical microtubule disorganization with the involvement of cytosolic calcium Ca cyt 2+ . A decrease in the δD/D and L p in the presence of NH 4 + was related to apoplast acidification and a high activity of the plasmalemmal H+-pump. An increase in the δD/D and L p in the presence of Glu indicates the inhibition of the plasmalemmal H+-pump. On the 2nd–4th days of exposure to Glu, root growth ceased, as distinct from treatment with NH 4 + . This complete root growth inhibition by Glu was possibly related to a rapid uptake of Ca2+ through Glu-sensitive Ca2+-channels, Ca2+-dependent inhibition of the plasmalemmal H+-pump, and a decrease in mitotic activity.
Russian Journal of Plant Physiology – Springer Journals
Published: Mar 12, 2011
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