The control of food mobilisation in seeds of Cucumis sativus L. : II. The role of the embryonic axis.

Removal of the embryonic axis from germinated cucumber seeds, either on the second of fourth day after imbibition, subsequently results in reduced rates of lipid and protein degradation and in the accumulation of free sugars and amino acids in the cotyledons. These isolated cotyledons show an inherent capacity for expansion growth which apparently results from an increased rate of water uptake. When water uptake is inhibited by incubating samples in polyethylene glycol the rate of lipid degradation is further reduced. This is accompanied by an additional increase in the reducing sugar and sucrose content of the cotyledons. Protein degradation in isolated cotyledons is inhibited to the same extent whether samples are incubated in water or polyethylene glycol. Furthermore, amino acid levels show appreciable and almost identical increases in both incubation media. Evidently an inverse correlation exists between rates of reserve mobilisation and levels of end products. It is suggested that the axis controls food mobilisation through a sink effect by reducing the levels of end products in the cotyledons.