Expression profiles of the Populus OPT genes. A. Dynamic expression profiles from GEO: GSE21481 of the 20 OPT genes in different tissues. RT, roots from tissue culture; RF, roots from field trees; MF, male floral bud initials; FF, female floral bud initials; S, seedling 43 hr post-imbibition; AB, axillary buds; SA, shoot apex. B. Expression profiles from GEO: GSE13043 of the 20 OPTs in different internodes. IN9, internode 9; IN5, internode 5; IN4, internode 4; IN3, internode 3; IN2, internode 2.