Is tissue culture a viable system with which to examine environmental and hormonal regulation of cold acclimation in woody plants?

In vitro-grown saskatoon berry (Amelanchier alnifolia Nutt.) plantlets were exposed to various hormonal treatments, dormancy-inducing and cold acclimation conditions to determine ii this in vitro system would be viable for dormancy/hardiness studies in woody plants. Low temperature induced significant hardiness levels in plantlets to -27 degrees C after 6 weeks at 4 degrees C but did not approach liquid nitrogen levels of fully hardened, held-grown buds. Control plantlets were consistently killed at -5 degrees C throughout this period. Significant hardiness was attained under both short and long day/low temperature conditions; however, hardiness was reduced under continuous light or dark treatments. A pre-exposure to the typical short photoperiod regime of woody plants did not significantly increase the rate of acclimation in these plantlets. The presence/absence of phytohormones in the media have a pronounced influence on the ability of plantlets to cold acclimate. Hormone-free media increased hardiness to -10.5 degrees C after 2 weeks in treatment. Addition of abscisic acid (ABA) increased cold hardiness levels (-12 degrees C) while addition of benzylaminopurine (BAP) to this hormone-free media decreased hardiness to -5.3 degrees C. A combination of BAP and ABA treatments produced LT,, values intermediate between individual applications of either hormone. Conversely, x-naphthaleneacetic acid (NAA) could not counteract the ABA-induced hardiness. ABA treatments alone were not able to harden plantlets to the extent attained under low temperature acclimation conditions. Further, ABA could not maintain the hardiness levels of cold-acclimating treatments and plantlets de-acclimated to -9 degrees C in BAP + ABA media. Subculturing in itself significantly elevated cold hardiness in plantlets to -9C degrees C on BAP + NAA media within 3 days after subculture and thereafter plantlets dehardened to -5 degrees C. While tissue culture has value in specific cases, caution should be taken when using tissue-cultured plantlets as a system co evaluate environmental regulation of cold acclimation in woody plants, in part, due to the influence of phytohormones in the media.