THE INDUCTION OF FREEZING TOLERANCE IN JACK PINE-SEEDLINGS - THE ROLEOF ROOT PLASMA-MEMBRANE H-ATPASE AND REDOX ACTIVITIES()

The acquired freezing tolerance of jack pine seedlings (Pinus banksian a Lamb.) conditioned at low nonfreezing temperatures and short photope riods was determined by comparison of seedling survival to that of non conditioned (control) seedlings following exposure to -5 and -10 degre es C. Compared to that of controls, survival of conditioned seedlings was markedly increased following exposure to freezing temperatures. A 1-week conditioning treatment significantly increased the survival of the seedlings after exposure to -5 degrees C, but was less effective o n seedlings exposed to -10 degrees C. Conditioning periods of 2 and 4 weeks resulted in higher survival of seedlings exposed to both -5 and -10 degrees C. The changes of two root-plasma-membrane-associated enzy me activities, H+-ATPase and NADH-dependent ferricyanide reductase, we re studied in enriched plasma membrane fractions during conditioning a nd after freezing. Post-freezing activities of both enzymes were enhan ced by conditioning at low temperatures and short photoperiods. These changes may be related to the increased frost hardiness also induced b y conditioning.