Development of the embryo proper and the suspensor during plant embryogenesis

Abstract

Seed plant zygotes differentiate into two components, the embryo proper and the suspensor. Previous studies have led to the generally accepted view that development of the embryo proper is regulated by the suspensor connecting the embryo proper to donor tissue. However, biochemical, biological, and molecular analyses of embryogenesis are difficult, since zygotic embryos in higher plants are deeply embedded in mother tissues. To find a way out of the difficulties, some embryo-defective mutants of Arabidopsis have been used to discuss embryogenesis and suspensor function. On the other hand, somatic embryogenesis is widely used as a model system for studying the process of zygotic embryo formation. Because somatic embryo of gymnosperms has a well-developed suspensor, it has been successfully used to observe the suspensor directly and to identify factors modulating the interaction between the embryo proper and the suspensor. Various stimulatory and inhibitory factors are correlated with the interaction. Here, we review the results of studies employing Arabidopsis mutants and some gymnosperm tissue culture, and we discuss the possibility of using somatic embryogenesis as a new model for studies of suspensor biology.