The aim of this study was to evaluate the effect of arginine on sugarcane (Saccharum sp.) somatic embryogenesis, free polyamines and other nitrogenous compounds contents. Segments of leaves were used as explants to establish embryogenic cultures on media with 0 and 50.0 mg l -1 arginine. Somatic embryos formation and free polyamines, free proline and total soluble proteins contents were compared. Arginine significantly induced sugarcane somatic embryogenesis. Free proline and protein levels determined in embryogenic cell masses during embryo differentiation-maturation, showed an arginine-induced promotion associated to the enhancement of the embryogenic process. In addition, free putrescine and, in a minor extent, spermidine and spermine contents were enhanced by arginine.

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The influence of an additional supply of ammonium to a nitrate containing hydroponic solution on the mineral nutrition of greenhouse rose plants (Rosa hybrida cv. ‘Lambada’) has been investigated. The effect on NPK uptake, mineral contents in roots and leaves as well as nitrate reductase (NR) and glutamine synthetase (GS) activities were examined. The addition of ammonium in a nutrient solution containing nitrate produced a total nitrogen uptake increase during shoot elongation, while in the absence of ammonium, nitrate uptake was lower during shoot elongation. Adding ammonium to the hydroponics solution caused an increase of potassium uptake while ammonium absorption was constant. Phosphate uptake was always higher in combined nitrate plus ammonium treatment, likewise in this treatment the most relevant effect on plant mineral content was the increase of P concentration in the roots. In both treatments with or without NH+4, free nitrate was notably higher in the roots than in leaves, indicating that nitrate reduction in rose plants takes place mainly in the leaves. NR activity in the leaves was higher when ammonium was present, whereas the root GS activity was similar in both treatments. The influence of ammonium on phosphate uptake and the subsequent effects on transport of other ions and enzymatic activities are discussed.

The effects of sodium (Na + ) ion concentration on shoot elongation, uptake of ammonium (NH 4 + ) and nitrate (NO 3 -) and the activities of nitrate reductase (NR) and glutamine synthetase (GS) were studied in rose plants (Rosa hybrida cv. Lambada).The results showed that shoot elongation was negatively correlated with sodium concentration, although no external symptoms of toxicity were observed. Nitrate uptake decreased at high sodium levels, specifically at 30 meq litre -1 of sodium. As flower development was normal under high saline conditions, this could suggest that nitrogen was being mobilised from shoot and leaf reserves. Ammonium uptake was not affected by any of the salt treatments applied probably because it diffuses through the cell membrane at low concentrations. Nitrate reductase activity was reduced by 50% at 30 meq litre -1 compared with control treatment, probably due to a decrease in the free nitrate related to nitrate uptake pattern. None of the salt treatments used affected total leaf GS activity (both chloroplastic and cytosolic isoforms) or leaf NPK mineral contents. Nitrate reductase activity in leaves increased at 10 meq litre -1 of sodium and GS activity in roots (cytosolic isoform only) followed the same pattern as NR. It is suggested that the activation of both enzymes at low salt level could be attributed to the beneficial effect of increased sulphur in the nutrient solutions.