Dynamics of Imbibition in Phaseolus vulgaris L. in Relation to Initial Seed Moisture Content

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Abstract
The seed moisture the onset on imbibitional injury (breakpoint) was determined for two cultivars of Phaseolus vulgaris L. cvs ''Tendercrop'' (TC) and ''Kinghorn Wax'' (KW). At 20.degree.C the breakpoints were 0.15 gram H2O/gram dry weight (gram per gram) for TC and 0.11 per gram for KW. When seeds were imbibed at 5.degree.C, the breakpoints were 0.19 gram per gram (TC) and 0.16 gram per gram (KW). Below the breakpoint germination rates were maximal at 0.07 gram per gram and 0.33 gram per gram after 20 mintues imbibition. Rates of electrolyte leakage were correlated with the imbibition rate maximum at 0.33 gram per gram. The transition from tightly bound to semibound water occurred at 0.09 per gram and 0.11 gram per gram for KW and TC, respectively. T1 values increased exponentially as seed moisture decreased from 0.47 gram per gram to 0.05 gram per gram. 13C-NMR sugar signals and plateaued at approximately 0.33 gram per gram seed moisture. These results suggest that the breakpoint moisture level for imbibitional damage is a function of temperature while the injury process is similar at both 5 and 20.degree.. Imbibition and leakage rate maxima reflect transitions in the states of seed water. NMR data support the application of the Water Replacement Hypothesis to seeds. Thus, imbibitional injury may be related to specific, temperature dependent moisture levels that are determined by water binding characteristics in the seed tissue.