Effect of temperature and state of hydration on rate of imbibition in soft seeds of yellow serradella

Abstract

Seeds were removed by hand from pods of yellow serradella (Ornithopus compressus L.) cvv. Santorini and Charano and accession GRC5045-2-2 that were taken from the field on 26 March after burial treatment to initiate seed softening. Times taken for soft seeds to imbibe were determined at constant temperatures of 8°, 20°, and 30°C. Rates of moisture uptake and loss were measured in seeds held in a moist (76% RH) or dry (over sulfuric acid) atmosphere and the effects of hydration and dehydration on subsequent imbibition times determined at 20°C.

Temperature had negligible effect on imbibition times in GRC5045-2-2, in which nearly all soft seeds imbibed within 24 h of wetting. Imbibition times in individual seeds of both Charano and Santorini varied from a few days to more than 200 days and were markedly reduced by increasing temperatures. Times taken to approach constant weight in the moist atmosphere were approximately 75, 165, and 430 days in GRC5045-2-2, Charano, and Santorini, respectively. By contrast the rate of moisture loss in the dry atmosphere was similar in all lines. Imbibition times in GRC5045-2-2 were little affected by state of hydration, but in both Santorini and Charano, imbibition was delayed by dehydration and accelerated by hydration.

It is proposed that slow imbibition is attributable to the presence of a minute opening in the seed at an as yet unidentified site (possibly the micropyle or hilum) that restricts moisture uptake until a threshold is reached when seeds in contact with water imbibe rapidly. It is hypothesised that the moisture threshold coincides with the build up of sufficient moisture in tissues associated with the underside of the lens, to cause its rupture, thereby allowing rapid uptake of free water.