The Effects of Light Intensity and Sucrose on Root Formation, Photosynthetic Ability, and Senescence in Detached Cotyledons of Sinapis alba L. and Raphanus sativus L.

The ability of detached cotyledons cultured in the light toassimilate ¹⁴CO₂, was reduced by the presence of sucrose inthe culture medium. This was due, at least in part, to an increasedrate of chlorophyll loss and yellowing of the blade. When cotyledondiscs were used, the inhibition of ¹⁴Carbon fixation by sucrosewas even more marked than in entire cotyledons. This could bedue to a higher level of penetration of the sucrose into discsor to the absence of the petiole which normally accumulatesphotosynthetic products. Sucrose culture also inhibited root production in cotyledonscultured in the light but promoted root formation in dark-grownor DCMU-treated cotyledons. The DCMU-inhibition of ¹⁴Carbonfixation by the blades was alleviated to some extent by sucroseculture. The sucrose effect on rooting was not permanent inthat transfer into water from sucrose led to root formationalthough this was delayed and present in a lower proportionof cotyledons than the controls. Thus, although a carbohydrate source either from photosynthesisor as applied sucrose, is essential for root production to takeplace, the combination of culture in the light with the presenceof sucrose in the medium may lead to an accumulation of carbohydrateto a level which directly or indirectly increases blade yellowingand inhibits root production.