Endogenous Sugar Levels and Their Effects on Root Formation and Petiole Yellowing of Detached Mustard Cotyledons

Detached cotyledons of Sinapis alba rooted readily in water in petri dishes in the light. The addition of (6 × 10−2M) galactose, mannose or 2‐deoxy‐D‐glucose to the culture medium proved toxic to cotyledon growth. Of the other sugars tested that were not toxic, sucrose was the most inhibitory to root formation and increased petiolar yellowing to the greatest extent. Glucose was more inhibitory than fructose which in turn increased petiolar yellowing more than methyl‐D‐glucose. Sucrose, glucose, or fructose at 6 × 10−2M in the culture medium gave rise to very substantial increases in the cotyledon petiole of reducing sugar and starch with smaller increases in sucrose. Methyl‐D‐glucose had much less effect on internal sugar levels. It was found that the higher the internal level of glucose the more rapid the rate and final extent of petiolar yellowing. In general, the degree of petiolar yellowing was inversely related to the ability of the cotyledon to root. Methyl‐D‐glucose differed from the other sugars in that it delayed and reduced root formation but had very little effect on petiolar yellowing.