In order to determine the functional significance of regulated ethylene biosynthesis to environmentally induced abscission, we are modulating expression of specific biosynthetic enzymes and assessing the consequences in transgenic plants. Transgenic analysis of altered gene expression provides us with fundamental information about how ethylene coordinates plant responses to water stress and also suggests molecular strategies whereby premature abscission due to stress might be reduced for crop improvement purposes. These approaches have led to a partial reduction in abscission but have failed to approach levels desired, possibly due to a current lack of understanding of the fundamental biochemistry of cell wall dissolution. Hormonal control, if done properly, offers the potential of more global control. The Classical Genetic Approach Classical genetic approaches to environmental cell separation complement our transgenic studies.
Dehiscence is a cell separation program that occurs in seedpods to disperse seed.
Like abscission, it is environmentally regulated and stress can cause release of immature seed by inducing premature dehiscence. Upon conclusive identification of Arabidopsis gene sequences whose interruption by foreign T-DNA leads to incomplete or delayed dehiscence, cDNAs will be cloned that correspond to homologous genes in soybean. This strategy promises to reveal novel determinants of dehiscence, some of which are regulated by ethylene and others that may lie outside hormonal control. The rapid, annual life cycle of Arabidopsis puts constraints on its use in our transgenic studies to elucidate the role of ethylene in promoting long-term adaptive responses to environmental stress. The longer life cycle of soybean and its tendency to dehisce and abscise in response to a variety of stresses renders it ideal for functional analyses of ethylene-regulated cell separation as a survival strategy.