Microsporogenesis and pollen formation in lodgepole pine

Microsporogenesis and pollen formation of three coastal and two interior lodgepole pine (Pinus contorta Dougl.) trees, and microstrobili of the interior trees were studied. Microspore mother cells were at pachytene when first observed and they remained at pachytene until the end of March in the interior trees and until mid-April in the coastal trees. The stages from pachytene to pollen shedding took 1 month in the coastal and interior trees. Several abnormalities were found in chromosome behavior, cell wall formation, and pollen grains. The percentage of abnormalities was higher in the interior trees than in the coastal trees. Abnormalities in chromosome movement seem to be genetically influenced and may be attributed to the large chromosomes, and to the prolonged low temperatures during meiosis and pollen formation. For interior lodgepole pine, the average number of microstrobili per shoot is 19.6 with 8.3 bud scales per microstrobilus, 93.3 microsporophylls per microstrobilus, and 2491 pollen grains per microsporangium. It is estimated that each microstrobilus produces about 465 000 pollen grains and each shoot produces about 9 million. There are about 33.5 million pollen grains per gram of dry pollen in lodgepole pine.