Control of Rooting and the Pattern of Senescence in Detached White Mustard Cotyledons

Senescence of detached mustard cotyledons was greatest in full light or at low light intensity but was reduced at intermediate light intensities. The location of yellowing in the blade depended on the conditions in which it was maintained after excision. Cotyledons cultured at full light intensity in the absence of exogenous nutrients formed roots at the base and yellowed around the margins. Reduction in light intensity and increasing nutrient concentrations resulted in an increasing proportion of the cotyledons yellowing from the base upwards, and fewer developed roots. At low light intensity with high nutrient levels rooting was suppressed and basal senescence predominated. The location of yellowing in the cotyledon may be associated with mobilisation gradients induced by the differential effects of light and mineral nutrient level on root initiation and blade growth.