IN-VITRO AND IN-VIVO POLLEN HYDRATION, GERMINATION, AND POLLEN-TUBE GROWTH IN WHITE SPRUCE, PICEA-GLAUCA (MOENCH) VOSS

Pollen hydration, germination, and pollen tube growth were examined in Picea glauca. Pollen germination and the early stages of pollen tube growth were similar in vitro and in vivo, although germination occurs within hours in vitro but days in vivo. We found no instances in vitro of separation of the stalk cell, movement of the stalk/body cell complex, or division of the body cell nucleus to form two male nuclei. These are all events which occur once the pollen tube has penetrated the nucellus and may be triggered by some interaction between pollen tube and nucellus. The low moisture content and the lack of polysomes in dry pollen may contribute to the relatively slow rate of germination. Once pollen has germinated, a pattern of zonation is established in the pollen tube. The pollen tube becomes branched as it penetrates the nucellus, and we propose that these branches, as well as the plasmatubules located at the distal end of the pollen tube, have a role in the nutrition in pollen-tube growth. The stalk cell initiates the release of the stalk/body cell complex from the intine and may be involved with movement of the body cell in the pollen tube. The male nuclei form while the pollen tube is penetrating the nucellus. A partial cell plate is formed between the male nuclei, but a cell wall is never completed. The male nuclei are lobed and contain tubules located just inside the nuclear membrane. The nuclear lobing and tubules may have a role in nuclear movement through the egg cytoplasm.