Characteristics of systemic growth activation by 9,10-ketol-12(<i>Z</i>),15(<i>Z</i>)-octadecadienoic acid (KODA) in <i>Populus alba</i> cultured in vitro

α-Ketol octadecadienoic acid (KODA), an oxylipin, is generated from linolenic acid by 9-specific lipoxygenase, while jasmonic acid is ultimately synthesized from the same linolenic acid by 13-specific lipoxygenase. KODA has a unique action different from jasmonic acid, such as promotion of flower formation, activation of rooting, increase of shoot germinating in spring, and breaking endodormancy. We report here that KODA promotes the systemic growth in juvenile <i>Populus alba</i> cultured in vitro probably through the activation of immature tissue. Two newly growing shoots emerging from axillary buds of <i>Populus alba</i> shoots cultured in vitro, were cut off. One was immersed in 10 µM KODA for 3 min while the other in water as a control. The growth of the plants developing from the shoots was observed one month later. KODA strongly promoted the growth of the primary roots and the aerial parts, in which leaves were mainly contributed. Measurement of the length of each internode revealed that KODA significantly acted on the elongation zone in the stem; clearly extending the length of the second and the third position of internode. The total node number was not significantly different from that in the control. Accordingly, KODA had little effect on the height of the whole shoot. Combined with the previous research of KODA, these findings suggest that KODA application systemically promotes the growth of <i>Populus alba</i> cultured in vitro by improving the growth of immature tissues of all organs including roots, stem, and leaves.