Variations saisonnières du pH et du contenu en acides aminés de la sève xylémienne dePopulusxeuramericanaI.214

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Abstract
The vascular sap of Populus x euramericana I.214 was used to study the pH changes and the variations in amino acids content during the annual cycle. In late winter, during the growth of catkins, the amides and amino acids amounts increased dramatically. They reached a peak value at the beginning of April. In the same way, the pH draped from neutrality to its minimal value (pH 5.3). At this time glutamine was the dominating N-compound, constituting up to 60 % of the nitrogen compounds of the vascular sap. Then, from April to August, the amount of amides and amino acids decreased progressively. From September to late February, only very low amounts of soluble N were detected and glycine was the main amino acid. During all this time sap pH was again close to neutrality. These pH and amino acids variations are discussed in relation to the activity of the meristematic tissues.