WATER AND SUCROSE REGULATE CANOLA EMBRYO DEVELOPMENT

The effect of water and sucrose on the growth and development of zygot ic, 30-day-old canola (Brassica napus L. cv. Bounty) embryos was exami ned in vitro by manipulating the levels of sucrose and/or sorbitol pre sent in the culture medium. In some experiments, the medium water pote ntial was allowed to vary with sucrose concentration, while in other e xperiments, the medium water potential was held constant by adding sor bitol to varying amounts of sucrose. Our results showed that embryos c ultured on sorbitol alone exhibited two developmental patterns: embryo s germinated precociously on media containing up to 0.70 M sorbitol, w hereas embryos became yellow and quiescent on media with higher concen trations of sorbitol. For embryos cultured on media containing sucrose alone, three distinct developmental patterns were noted: at low sucro se concentrations, embryos germinated precociously; at intermediate co ncentrations, embryos continued to grow in an embryonic mode; and, at high concentrations, embryos became yellow and quiescent. Continued em bryonic growth was never observed in embryos cultured on media contain ing sorbitol alone. Embryos never germinated precociously when culture d on media maintained at a constant water potential of -1.4 MPa, rathe r dry weight increased in these embryos with an increase in sucrose co ncentration. We envision the effect of sucrose on embryo growth and de velopment to be nested within the effect of water availability When wa ter availability is restricted, embryos become quiescent. When water i s available, embryos have the potential to grow, but the developmental growth pattern depends on the availability of sucrose. In the absence of sucrose, embryos germinate and initiate the transition to autotrop hy. If sufficient sucrose is available, embryos remain photoheterotrop hic and continue to grow in an embryonic mode.