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We examined the effects of foliar supplementation of different nitrogen sources (urea, Nitamin, N[H.sub.4]N[O.sub.3], and arginine) to study their efficacy as fertilizers for growth of two clonally propagated shrub willow cultivars; namely, 'Fish Creek' (Salix purpurea L.) and 'Preble' (Salix viminalis L. x (Salix sachalinensis F. Schmidt x Salix miyabeana Seemen)). Our objectives were to determine (i) if foliar nitrogen application is an effective method of fertilization for the two shrub willows and (ii) if different nitrogen sources are metabolized similarly by the plants. The analyses involved soluble leaf polyamines, amino acids, total protein, total nitrogen and carbon, and plant biomass in response to short-term treatments with four sources of nitrogen. The effects of foliar nitrogen application on leaf chemistry, biomass, and foliar nitrogen content varied according to the form of nitrogen used. The data indicate that (i) urea is the most suitable nitrogen source for foliar spray (29% higher N accumulation vs. Nitamin), whereas arginine is the least suitable, and (ii) different nitrogen sources are metabolized differently by the plant. While the foliar nitrogen application method could become a practical and sustainable way to fertilize shrub willows and other short-rotation biofuel crops, it may also help reduce nitrogen loss to the environment. Key words: amino acids, foliar application, nitrogen assimilation, polyamines, shrub willows, urea. Nous avons observe les effets de differentes sources d'azote applique directement sur le feuillage (uree, Nitamin, N[H.sub.4]N[O.sub.3] et arginine) pour etudier leur efficacite comme fertilisant pour la croissance de deux cultivars de saule arbustif propages de facon clonale, nommement 'Fish Creek' (Salix purpurea L.) et 'Preble' (Salix viminalis L. x (Salix sachalinensis F. Schmidt x Salix miyabeana Seemen)). Nos objectifs consistaient a determiner (i) si l'application foliaire d'azote est une methode efficace pour les deux saules arbustifs et (ii) si la maniere dont l'azote est metabolise par les plants differe selon la source. Les analyses du feuillage ont porte sur les polyamines solubles, les acides amines, les proteines totales, l'azote et le carbone totaux ainsi que la biomasse des plants en reaction aux traitements a court terme avec quatre sources d'azote. Les effets de l'application foliaire d'azote sur les caracteristiques chimiques, la biomasse et la teneur en azote des feuilles variaient selon la forme d'azote utilisee. Les donnees indiquent que (i) l'uree est la source d'azote la plus appropriee pour un epandage foliaire (accumulation de N 29 % plus elevee qu'avec Nitamin), tandis que l'arginine est la source la moins appropriee, et (ii) differentes sources d'azote sont metabolisees differemment par les plants. Alors que l'application foliaire d'azote pourrait devenir une facon pratique et durable de fertiliser les saules arbustifs et d'autres cultures a courte rotation pour la production de biocombustibles, cela pourrait aussi contribuer a reduire les pertes d'azote dans l'environnement. [Traduit par la Redaction] Mots-cles: acides aminees, application foliaire, assimilation de l'azote, polyamines, saules arbustifs, uree., Introduction Global consumption of synthetic nitrogen (N) fertilizer increased almost 10-fold in 2015 compared with the early 1960s (FAO data, http://www.fao.org/faostat/en/#data/GY). Although the norm, soil application of N fertilizer can [...]

The mechanisms that control polyamine (PA) metabolism in plant cell lines with different embryogenic potential are not well understood. This study involved the use of two Araucaria angustifolia cell lines, one of which was defined as being blocked, in that the cells were incapable of developing somatic embryos, and the other as being responsive, as the cells could generate somatic embryos. Cellular PA metabolism was modulated by using 5mM arginine (Arg) or ornithine (Orn) at two time points during cell growth. Two days after subculturing with Arg, an increase in citrulline (Cit) content was observed, followed by a higher expression of genes related to PA catabolism in the responsive cell line; whereas, in the blocked cell line, we only observed an accumulation of PAs. After 14 d, metabolism was directed towards putrescine accumulation in both cell lines. Exogenous Arg and Orn not only caused a change in cellular contents of PAs, but also altered the abundance of a broader spectrum of amino acids. Specifically, Cit was the predominant amino acid. We also noted changes in the expression of genes related to PA biosynthesis and catabolism. These results indicate that Arg and Orn act as regulators of both biosynthetic and catabolic PA metabolites; however, we suggest that they have distinct roles associated with embryogenic potential of the cells. [ABSTRACT FROM AUTHOR]

Polyamines (PAs) are essential biomolecules that are known to be involved in the regulation of many plant developmental and growth processes as well as their response to different environmental stimuli. Maintaining the cellular pools of PAs or their metabolic precursors and by-products is critical to accomplish their normal functions. Therefore, the titre of PAs in the cells must be under tight regulation to enable cellular PA homeostasis. Polyamine homeostasis is hence achieved by the regulation of their input into the cellular PA pool, their conversion into secondary metabolites, their transport to other issues/organs, and their catabolism or turnover. The major contributors of input to the PA pools are their in vivo biosynthesis, interconversion between different PAs, and transport from other tissues/organs; while the output or turnover of PAs is facilitated by transport, conjugation and catabolism. Polyamine metabolic pathways including the biosynthesis, catabolism/turnover and conjugation with various organic molecules have been widely studied in all kingdoms. Discoveries on the molecular transporters facilitating the intracellular and intercellular translocation of PAs have also been reported. Numerous recent studies using transgenic approaches and mutagenesis have shown that plants can tolerate quite large concentrations of PAs in the cells; even though, at times, high cellular accumulation of PAs is quite detrimental, and so is high rate of catabolism. The mechanism by which plants tolerate such large quantities of PAs is still unclear. Interestingly, enhanced PA biosynthesis via manipulation of the PA metabolic networks has been suggested to contribute directly to increased growth and improvements in plant abiotic and biotic stress responses; hence greater biomass and productivity. Genetic manipulation of the PA metabolic networks has also been shown to improve plant nitrogen assimilation capacity, which may in turn lead to enhanced carbon assimilation. These potential benefits on top of the widely accepted role of PAs in improving plants' tolerance to biotic and abiotic stressors are invaluable tools for future plant improvement strategies.