Pressure-Driven Extrusion of Intracellular Substances from Bean and Pea Cotyledons during Imbibition

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Abstract
Intracellular substances leak from imbibing cotyledons of grain legumes during imbibition. This work reports the discovery of a biophysical process by which intracellular substances are driven from cotyledons during imbibition. Light and scanning electron microscopy were used to examine bean (Phaseolus vulgaris L.) and pea (Pisum sativum L.) cotyledons and the material released from them into imbibition water. A large fraction of the visible materials released from excised bean and pea cotyledons during the first 30 minutes of imbibition consisted of convoluted or helical streams of material which rapidly emerged from the cotyledons surfaces. Large streams of material from bean cotyledons contained starch grains and protein bodies, and smaller streams from bean and pea cotyledons probably contained protein bodies. The forms of streams were characteristic of a viscous fluid which had been forced by pressure through irregular orifices. The sites of extrusion from bean cotyledons were multicellular blisters which formed on the surfaces of imbibing cotyledons. In 6 hours, pea and bean cotyledons leaked from 1 to 11 micrograms protein per milligram of seed dry weight. The quantities of protein leaked primarily depended on cultivar.