Seasonal Changes of the Metabolites in the Leaves, Bark and Xylem Tissues of Olive Tree (Olea europaea. L) I. Nitrogenous Compounds

The changes of total nitrogen and free amino compounds were examined in leaves, bark and xylem tissues of olive tree during a complete annual cycle. In leaves total nitrogen decreased in spring/early-summer but reached the highest level in autumn-winter periods. In bark tissues total nitrogen fluctuations were mainly related to the periodical cambial activities. In xylem tissues total nitrogen was detected in low levels with no fluctuations over the year. The free amino compounds in leaves showed seasonal peaks during the spring and autumn stem elongations, while a considerable restriction of their levels was detected in summer. Glutamate, aspartate, proline, alanine, serine and γ-aminobutyrate are the predominant amino acids detected in leaves. Glutamate and aspartate increased considerably in spring and autumn periods but disappeared in summer. Proline remained almost unchanged over the year. Alanine, in addition to the spring and autumn fluctuations, also fluctuated in summer, γ-aminobutyrate was detected at highest levels in winter. In bark tissues, the pattern of fluctuations and the composition of the free amino compounds were similar to those of leaves. In xylem tissues free amino compounds were detected in high levels over the year except for the drops in spring and summer cambial activity periods. Xylem was the most important reservoir for the readily transportable soluble nitrogen being accumulated during the maturing of the produced new xylem. Arginine, glutamine, alanine, glutamate, aspartate, serine, γ-aminobutyrate and proline are the most prevalent amino compounds in xylem. Arginine and glutamine showed extensive interchanges. Arginine increased in autumn while glutamine and alanine showed low levels in the same period.