Anatomy and histochemistry of Abies balsamea cambial zone cells during the onset and breaking of dormancy

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Abstract
The anatomy and histochemistry of fusiform cambial zone cells were investigated (i) in shoots producing latewood tracheids at the time of collection in July and (ii) in dormant shoots. The latter were naturally or artificially chilled to obtain different stages along the rest–quiescence continuum, then placed for 4 weeks under environmental conditions favoring growth. The transition from active growth to rest was associated with increases in RNA, protein, and total insoluble carbohydrates and in peroxidase and succinic dehydrogenase activities. The rest–quiescence transition was correlated with additional increases in RNA and protein, an increase in lipid staining, radial wall thickness and plasmalemma infolding, and a decrease in vacuolar size. The DNA level did not appear to change; however, a distinct color shift occurred in nuclei stained for total protein. During the 4-week growth period, RNA, protein, total insoluble carbohydrates, and lipids decreased, most obviously in cambia that were fully quiescent at the start of the period. Xylem production and percentage of buds flushing during the growing period increased as the initial dormancy stage changed from rest to quiescence. Little, if any, xylem production occurred in debudded shoots unless indol-3-ylacetic acid (IAA) was supplied. Endogenous and exogenous lAA induced the same anatomical and histochemical responses.