CONCENTRATIONS OF OXYGEN AND INDOLE-3-ACETIC-ACID IN THE CAMBIAL REGION DURING LATEWOOD FORMATION AND DORMANCY DEVELOPMENT IN PICEA-ABIES STEMS

To manipulate the occurrence of latewood formation and cambial dormanc y in Picea abies (L.) Karst. stems, potted seedlings were transferred from the natural environment on 9 July, when tracheids early in the tr ansition between earlywood and latewood were being produced, and cultu red for up to 5 weeks in a controlled environment chamber having: (1) Warm LD, (25/15 degrees C during day/night) and long (16 h) photoperio d, (2) Warm SD, (25/15 degrees C) and short (8 h) photoperiod, or (3) Cold SD, (18/8 degrees C) and short (8 h) photoperiod. In Warm LD tree s, the radial enlargement of primary-walled derivatives on the xylem s ide of the cambium, as well as xylem production, continued at the same magnitude throughout the experiment, In Warm SD and Cold SD trees, th e radial enlargement of primary-walled derivatives declined and the ca mbium entered dormancy, both developments occurring faster in the Warm SD trees, The concentration of indole-3-acetic acid (IAA) was higher in developing xylem tissue than in cambium+phloem tissues, but did not vary with environmental treatment or decrease during the experimental period, The O-2 concentration in the cambial region followed the orde r of Cold SD>Warm SD>Warm LD trees and was <5%, the threshold for the inhibition of IAA-induced proton secretion, for the first 3 weeks in W arm SD and Warm LD trees. Thus, neither latewood formation nor cambial dormancy can be attributed to decreased IAA in the cambial region, No r does lower O-2 concentration in the cambial region appear to be inhi biting the IAA action that is associated with cambial growth.