Expression of a Rice Histone Gene during Pollen Developmental Transformations inHyoscyamus niger (Henbane)

Abstract

It is now well-established that pollen grains of angiosperms follow two diverse developmental pathways. One of these involves the familiar set of events leading to an asymmetric division of the pollen grain into a large vegatative cell and a small generative cell, germination of the pollen grain, division of the generative cell into two sperm and finally, double fertilization in the embryo sac, resulting in the fusion of one sperm with the egg nucleus and of the other sperm with the polar fusion nucleus. An alternate pathway of development displayed by pollen grains of a few angiosperms results int heir repeated division leading to the production of embryo like structures (embryoids) and plantlets with the haploid set of chromosomes. This pehnomenon, known as pollen embryogenesis occurs when anthers excised at an appropriate stage of development--generally at the uninucleate stage--are cultured in a mineral salt medium with or without hormonal supplements. Thus, the pollen grain provides an interesting system to study the control of gene expression during its normal ontogeny and during induced embryogenesis (Raghavan, 1986 for review).