Printed in Great Britain THE ORGANIZATION AND POLARITY OF POLLEN MOTHER CELLS OF TRITICUM

Colchicine has been applied to young developing anthers of Triticum aestivtim at varying stages of maturity from the last premeiotic mitoses of the archesporial and tapetal cells to the second meiotic divisions of the pollen mother cells. The developmental stage of the archesporium at which colchicine took effect was determined by cytological examination of the ploidy levels of the nuclei of the adjacent tapetal cells. The type of pollen abnormality induced depended on the time of application and the concentration of colchicine. Uninucleate monads with 4 randomly positioned pores and uninucleate monads without pores were obtained with 0 5 % colchicine. Multipored polyads and multipored uninucleate monads were observed together in anthers treated with o-oi % colchicine. Naturally occurring aberrant pollen types in hybrids of Triticum aestivum x Aegilops mutica or T. aestivum x Aegilops sharonensis have revealed a constant relation-ship between the disposition of the meiotic spindles and the siting of the pollen pores. The colchicine-induced abnormalities have further clarified the nature of this relationship leading to the interpretation that both the positioning of the spindles and the siting of the pores are pre-determined by events taking place in the premeiotic interphase at a time just after the last mitosis of the pollen mother cells and the penultimate mitosis of the tapetum. A reorganization of the archesporial cells (sensitive to colchicine) possibly occurs at this time. Various subsequent meiotic events are dependent on the reorganization. Two of these events- the organization of meiotic spindles and the establishment of pollen symmetry- are discussed