Dormancy-induced temporal up-regulation of root activity in calcium translocation to shoot in Populus maximowiczii

To explore seasonality of root functions, we analyzed the concentrations of 8 minerals in leaves of Populus maximowiczii (Japanese native poplar) by inductively coupled plasma atomic emission spectroscopy. These concentrations were used as indices of root mineral translocation activity. In leaves close to the shoot apex, dramatic increases in Ca concentration, and similar but slight increase in Mg and Mn, were observed after the onset of dormancy. Because of the constant concentration of Na, which is not essential for plant growth, the increase of Ca concentration was mainly derived from not by the increase of transpiration rate but by the enhancement of root activity of xylem loading. Leaf Ca concentration in August 2010 was approximately fivefold higher than before dormant bud formation. To investigate the shifts in Ca-translocation activity during dormancy induction, we grew saplings hydroponically under lightand temperaturecontrolled conditions and subsequently analyzed the distribution of Ca absorbed by roots using a Bio-Image Analyzer. In this pulse chase experiment, the enhancement of Ca translocation to the shoot was not observed in early dormancy. This suggested the increase of leaf Ca in early dormancy was caused by the Ca loading into root xylem vessels using the root Ca absorbed before the onset of dormancy. These changes in mineral translocation activities indicate that alterations in Ca distribution are most probably triggered by bud dormancy. Furthermore, several root functions were regulated by the dormancy induction process.