Seasonal fluctuation of organic and inorganic components in xylem sap of Populus nigra

Deciduous trees show annual periodicity in shoot growth and development, but such periodicity is not well investigated in roots. To clarify the seasonal fluctuation in root functions, xylem sap from Populus nigra branches was analyzed for 2 years. Various xylem sap components including calcium, potassium, glucose, and proteins showed seasonal fluctuations with peaks from winter to spring. Abscisic acid (ABA) was the most abundant hormone in the xylem sap throughout all seasons and showed two peaks from late autumn to spring. We hypothesize that low temperature in winter promotes metal loading into the xylem sap and the synthesis of proteins and sugars in roots as an adaptation to the winter environment and to prepare for spring bud burst. acetic acid; IA-Ala, indole-3-acetyl- L-alanine; IA-Ile, indole-3-acetyl-L-isoleucine; IA-Leu, indole-3-acetyl- L-leucine; IA-Asp, indole-3-acetyl-L-aspartic acid; IA-Trp, indole-3-acetyl-L-tryptophan; IA-Phe, indole- 3-acetyl-L-phenylalanine; GA, gibberellic acid; ABA, abscisic acid