Influence of photoperiod and temperature on frost hardiness and free amino acid concentrations in black spruce seedlings.

We investigated the effects of a 4-week exposure to an 8-h or 18-h photoperiod at 5 or 25 degrees C on the development of hardiness to -20 degrees C and the accumulation of proline (Pro), arginine (Arg) and tryptophan (Trp) in shoots of black spruce (Picea mariana (Mill.) B.S.