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.P.) seedlings. The greatest degree of hardening to -20 degrees C occurred in seedlings exposed to an 8-h photoperiod at 25 degrees C, and some hardening occurred in seedlings exposed to 5 degrees C in either an 8-h or 18-h photoperiod. Proline accumulated in shoots in response to 5 degrees C and either an 8-h or 18-h photoperiod, whereas Trp accumulated in response to an 8-h photoperiod at either temperature, and Arg only accumulated in shoots in the 5 degrees C + 8-h photoperiod treatment. Only the accumulation of Trp was significantly related to the degree of hardiness to -20 degrees C.