Materials and Methods

Plant material

Current harvest of soybean (cv. Aijiaozao) seeds were obtained from the Oil Crops Research Institute of the Chinese Academy of Agricultural Sciences (Wuchang, Hubei) and were kept at 15°C until used. The seeds were surface-sterilized in a solution of 1% hypochlorite, rinsed three times in sterile water, and then imbibed by placing the seeds in a shallow layer of distilled water or treatment solution (Ca2+, EDTA, etc.) such that half the seed was immersed. Axes were excised from the seeds that had been imbibed for different times and were then treated as indicated below. All manipulations and germination studies were conducted at room temperature (20°C).

Water content determination

Water contents of 20 individual seeds or axes were determined gravimetri-cally (80°C for 48 h). Water contents are expressed on a dry mass basis (g H2O/g dry mass) (g/g).

Desiccation treatment

Desiccation of the differentially pre-imbibed seeds was achieved by burying them for different times in activated silica gel within a closed desiccator. Rapid drying of excised axes was achieved by placing axes over activated silica gel for different times within a closed desiccator in which there was a small fan. Slow drying of excised axes was achieved by placing axes over saturated sodium chloride (relatively humidity 75%) within a closed container. The temperature when axes were dried was 20 ± 1°C.

Assessment of germination and survival

Batches of 30 treated seeds and/or axes were germinated on moist filter paper in Petri dishes for 5 days (20°C, dark). Seeds showing radicle emergence and axes showing a marked increase in length and volume were scored as germinated and thus as having survived the treatment. Although dried seeds and axes take up water during the early stages of re-imbibition, those seeds and axes that were injured by desiccation deteriorated progressively during continued re-imbibition.

Conductivity test

Electrolyte leakage from batches of 15 treated seeds and axes was measured for 3 h in 30 ml distilled water using a DDS-11A conductivity meter (Shanghai, China). The conductivity of the leachates was measured immediately after the drying treatments and leakage rates were expressed as |S/cm/g dry weight/h.

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