Compared responses of poplar cuttings and in vitro raised shoots to short-term chilling treatments

In woody plants, chilling stress occurs during the early spring growth and can have important economic consequences. The aim of this study was to comp are the reliability of two different experimental systems, 3-month-old soft wood cuttings and in vitro-grown shoots, to study chilling effects in a pop lar clone (Populus tremula x P. tremuloides cv. Muhs1). Different parameter s were recorded: lignin content, sucrose concentration and protein and fres h weight variation, during a 2-week treatment at 10 degreesC. Two families of polypeptides of high molecular weight (110 and 116 kDa) were shown to ac cumulate in response to chilling in both cuttings and microshoots. For some of the parameters studied, i.e. appearance of some groups of polypeptides and reduction of fresh weight gain, both in vitro and ex vitro systems were suitable and produced similar results. In contrast, for some other observa tions, i.e. on sucrose concentration and lignin content, the systems led to different conclusions. While sucrose and lignin contents were shown to inc rease in cuttings submitted to chilling, no variation in lignin and only a small temporary peak of sucrose could be observed in microshoots kept under chilling. These parameters seem not to be suitable for studying the respon se of poplar in the in vitro system in such a shortterm study.