Abscisic acid in shoots and roots of Scots pine (Pinus sylvestris L.) seedlings grown in controlled long-day and short-day environments.

Scots pine (Pinus sylvestris L.) seedlings grown in nutrient solution in controlled-environment chambers were used. The effects of a shortday (SD, early autumn) treatment on growth and the content of "free" and alkaline hydrolysable abscisic acid (ABA) in shoots and roots were investigated. The weekly relative growth rates of seedlings grown continuously under long-day (LD, summer) conditions were stable at approx. 0.08 g g(-1) d(-1) between weeks four and eight from germination. Weekly relative growth rates of seedlings transferred to SD conditions decreased rapidly to a then stable level of approx. 0.04 g g(-1) d(01). Shoot elongation ceased within two weeks of SD treatment. The content of both "free" and alkaline hydrolysable ABA was approx. 40-50% higher in shoots of seedlings grown for five weeks in LD plus one week in SD than in shoots of seedlings grown for five or six weeks in LD. Two additional weeks of SD did not change the "free" ABA content. Three weeks in simulated late autumn (SD but decreased temperatures) and three weeks in simulated winter (lower light intensity and temperature) further increased the content of "free" ABA in the shoots. A transfer back to LD conditions reduced the ABA content to a level equal to the level found during the first LD period. The recovery of radioactive ABA at certain times after application ofr[(3)H] ABA was the same in shoots and roots of LD-grown and SD-treated seedlings.