*Department of Plant Science, The University of Tasmania, Hobart TAS 7001 Australia; ‡Worcester Foundation for Biomedical Research, Shrewsbury, Massachusetts 01545; §Misaki Marine Biological Station, The University of Tokyo, Kanagawa 238-02 Japan; and ‖Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo 113 Japan (At 1997-06-02)