MICROTUBULAR CONFIGURATIONS DURING ENDOSPERM DEVELOPMENT IN PHASEOLUS-VULGARIS

Microtubular cytoskeletons in nuclear, alveolar, and cellular endosper m of bean (Phaseolus vulgaris) were analyzed immunocytochemically and by electron microscopy to reveal their function during cellularization . Nuclear endosperm showed a fine network of microtubules between the wide-spaced nuclei observed towards the chalazal pole. Near the embryo , where nuclei were densely packed, bundles of microtubules radiated f rom nuclei. They were formed just before alveolus formation and functi oned in spacing nuclei and in forming internuclear, phragmoplast-like structures that gave rise to nonmitosis-related cell plates. During al veolus formation cell plates extended and fused with other newly forme d walls, thus forming the walls of alveoli. Growing wall edges of cell plates exhibited arrays of microtubules perpendicular to the plane of the wall, initially. When two growing walls were about to fuse, micro tubules of both walls interacted, and because of the interaction of mi crotubules, the cell walls changed their position. When a growing wall was about to fuse with an already existing wall, such interactions be tween microtubules were not observed. It is therefore concluded that i nteractions of microtubules of fusing walls influence shape and positi on of walls. Thus microtubules control the dynamics of cell wall posit ioning and initial cell shaping.