Changes in concentrations of several endogenous phytohormones and metabolites were analyzed in the long shoots of nine genotypes of coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) at five developmental stages: (1) closed buds, (2) flushing buds, (3) rapidly elongating shoots, (4) growing shoots and (5) near full-length shoots during one growing season. When averaged across genotypes, indole-3-acetic acid (IAA) concentration was high at stages 1 and 3. The only pattern that correlated with cone productivity was the one that was unique to IAA, in which high concentrations at stages 3 and 4 were found in all genotypes with high female cone productivity. Concentrations of isopentenyl adenosine (iPA) decreased and zeatin riboside (ZR) concentrations increased as the buds initiated and differentiated; ZR was 30 and 28 ng g−1 dry weight (DW) at stages 1 and 4, respectively, before increasing to 166 ng g−1 DW at stage 5. Isopentenyl adenosine peaked at 92 ng g−1 DW at stage 2 and declined to low concentrations at stages 4 and 5. Zeatin-O-glucoside was 30 ng g−1 DW at stage 1, declined at stages 2 and 3 and increased at stages 4 and 5. High abscisic acid (ABA) concentrations were positively correlated with rapid shoot elongation (stages 1 and 2), but as growth slowed and terminated, ABA concentrations decreased. Abscisic acid was 7 μg g−1 DW at stage 1, increased to 13 μg g−1 DW at stage 2 and then declined. The glucosyl ester (GE) of ABA decreased rapidly in early summer, and increased inversely with an increase in ABA. Between stages 1 and 2, ABA-GE decreased from 10 to 0.2 μg g−1 DW and then increased. Of the ABA catabolites studied, 7′-hydroxy-ABA was about 2 μg g−1 DW at stage 1, declined at stages 2 and 3 and increased at stages 4 and 5; phaseic acid concentrations were low at all stages, whereas dihydrophaseic acid was detected only at stages 4 and 5.
Keywords: long shoot; plant hormones
Journal Article. 5045 words. Illustrated.
Subjects: Plant Sciences and Forestry
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