Anatomical and respiratory changes in shoot tips of interior and coastal Douglas fir (Pseudotsuga menziesii (Mirb.) Franco.) seedlings during bud development
Date
1986
Authors
Fielder, Peter
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Abstract
Bud development, embryonic shoot respiration and root elongation of coastal and interior seedlots of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco.) were compared from September through March after four months growth under nursery production conditions. Apical development was described in terms of morphology, mitotic index, and cell numbers. Embryonic shoot development was described in terms of number of leaf primordia, and cell divisions in leaf primordia. Respiratory rates of shoot tips were measured during primary leaf initiation, bud-scale initiation, preformed leaf initiation and dormancy.
Morphological and anatomical stages of bud development in the interior variety occurred about four weeks in advance of the coastal variety. Respiratory rates of developing embryonic shoots decreased rapidly during preformed leaf initiation in both varieties. The interior variety decreased more rapidly, reflecting the earlier morphological development, and reached a basal rate in November, about four weeks in advance of the coastal variety. The lowest levels of respiration in the embryonic shoot coincided with the end of cell divisions in the apex. Cell divisions resumed in mid-February in both varieties. Cells in all apices were dividing by March 1. Flushing was variable but occurred more rapidly in the interior variety. Respiration rates increased in early-March during shoot elongation in both varieties but the interior variety had lower respiratory rates than the coastal variety.
Root elongation showed two peaks of activity, one in the fall and one in the spring, and decreased to a minimum in December in both varieties. The interior variety ceased root elongation completely whereas, the coastal variety continued at a reduced level during the winter. On March 1 root elongation in the interior variety increased rapidly coinciding with the resumption of rapid cell division in the shoot apex. The relationship was less marked in the coastal variety. The relationship between these findings and current definitions of dormancy are discussed.