IS TISSUE-CULTURE A VIABLE SYSTEM WITH WHICH TO EXAMINE ENVIRONMENTALAND 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 co ld acclimation conditions to determine ii this in vitro system would b e viable for dormancy/hardiness studies in woody plants. Low temperatu re induced significant hardiness levels in plantlets to -27 degrees C after 6 weeks at 4 degrees C but did not approach liquid nitrogen leve ls of fully hardened, held-grown buds. Control plantlets were consiste ntly killed at -5 degrees C throughout this period. Significant hardin ess was attained under both short and long day/low temperature conditi ons; however, hardiness was reduced under continuous light or dark tre atments. A pre-exposure to the typical short photoperiod regime of woo dy plants did not significantly increase the rate of acclimation in th ese 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 wee ks in treatment. Addition of abscisic acid (ABA) increased cold hardin ess levels (-12 degrees C) while addition of benzylaminopurine (BAP) t o this hormone-free media decreased hardiness to -5.3 degrees C. A com bination of BAP and ABA treatments produced LT,, values intermediate b etween individual applications of either hormone. Conversely, x-naphth aleneacetic 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 co uld not maintain the hardiness levels of cold-acclimating treatments a nd plantlets de-acclimated to -9 degrees C in BAP + ABA media. Subcult uring in itself significantly elevated cold hardiness in plantlets to -9C degrees C on BAP + NAA media within 3 days after subculture and th ereafter plantlets dehardened to -5 degrees C. While tissue culture ha s value in specific cases, caution should be taken when using tissue-c ultured plantlets as a system co evaluate environmental regulation of cold acclimation in woody plants, in part, due to the influence of phy tohormones in the media.