Search

We analyzed effects of nitrogen availability and form on growth rates, concentrations of polyamines and inorganic ions and glutamine synthetase activity in in-vitro-cultured red spruce (Picea rubens Sarg.) cells. Growth rates, concentrations of polyamines and glutamine synthetase activity declined when either the amount of nitrate or the total amount of N in the culture medium was reduced. When total N in the medium was increased, cell mass increased without significant changes in glutamine synthetase activity or polyamine concentration. Reductions in the amount of nitrate or total N in the culture medium resulted in increased accumulations of Ca, Mn and Zn in the cells, and K accumulation decreased in response to decreasing nitrate:ammonium ratios. The data indicate that changes in total N availability as well as the forms of N play important roles in the physiological responses of in-vitro-grown red spruce cells that mimic the observed responses of forest trees to soil N deficiency and N fertilization.

We determined: (a) the physiological consequences of overproduction of putrescine in transgenic poplar (Populus nigra x maximoviczii) cells expressing an ornithine decarboxylase transgene; and (b) effects of variation in nitrogen (N) concentration of the medium on cellular polyamine concentration in transgenic and non-transgenic cells. Cells grown in the presence of supplemental (to the normal concentrations of N sources in the growth medium) and reduced amounts of NH4NO3 and KNO3 were used to study effects on membrane permeability, mitochondrial respiratory activity, protein accumulation, growth rates and changes in cellular polyamine concentration. The N concentration of the MS medium was not a limiting factor for continued overproduction of putrescine in transgenic cells. However, continued supplies of NH4+ and NO3- were required to maintain homeostatic amounts of putrescine in both cell lines. The presence of high amounts of putrescine in transgenic cells had significant effects on the physiological parameters measured. Compared with non-transgenic cells, transgenic cells had greater plasma membrane permeability, less tolerance to NH4NO3, more tolerance to KNO3, and accumulated higher amounts of soluble protein.

In the absence of added Al, the concentration of succinate in cultured red spruce (Picea rubens Sarg.) cells was 15-20 times higher (> 600 nmol g-1FW) than that of citrate or oxalate and 4-6 times higher than that of malate. Addition of AlCl3 (effective monomeric Al concentrations of 0.23 and 0.48 mM) to 3-day-old suspension cultures significantly increased cellular succinate concentrations with a concomitant decrease in cellular oxalate concentrations. However, in the medium of Al-treated cell cultures, both succinate and oxalate concentrations were significantly higher than in the medium of cell cultures without added Al, and oxalate concentrations were several times higher than succinate concentrations. Aluminum did not significantly affect the cellular concentrations of malate, ascorbate and citrate, and none of these organic acids was present in detectable quantities in the medium. Exogenous succinate alone or with Al had no effect on cellular free polyamine concentrations or cell mass. Aluminum caused a significant increase in cellular putrescine concentrations. Addition of malate had a positive effect on growth and completely reversed the effects of Al on cell physiology. In contrast, the addition of oxalate and citrate only partly reversed the effects of Al.