Winter chilling in the field removed the primary dormancy in common ragweed (Ambrosia artemisiifolia L.) seeds and allowed them to germinate in both light and darkness. A secondary dormancy was induced in the spring and seeds again failed to germinate in light or darkness. Kinetin (K) + ethephon (E) + gibberellin A4 + A7 (GA4+7) applied to the soil in December prevented secondary dormancy. The following May only 20% of the seeds at the 15-cm depth remained viable. The rest had germinated or decayed. In contrast, 89% of the untreated seeds remained viable. Application of K + E + GA4+7 on April 22 and May 2 also broke the secondary dormancy. Gibberellin A3 (GA3) was less effective than GA4+7 in preventing or breaking secondary dormancy.

Untreated (control) tomato seeds germinated at temperatures ranging from 15 to 35°C. There was a positive linear relationship between the rate of germination (expressed as the reciprocal of time to obtain 50% germination) and temperature up to the thermal optimum. At higher temperatures, the negative relationship was also linear. The thermal optimum for seed germination was 27–28°C and the lower and maximal temperatures were around 9 and 40°C, respectively. Germination was strongly reduced in atmospheres containing less than 10% oxygen. After pretreatment at 15°C in a polyethylene glycol-8000 solution at –1.0 MPa, seeds germinated faster in a wider range of temperatures, and this stimulatory effect remained after drying back the seeds. Such a pretreatment did not change the optimal and maximal temperatures of germination, but decreased the lower temperature to about 6°C. The beneficial effect of osmoconditioning increased as the duration of the treatment increased and was maximal after 5–7 days. Osmotic pretreatment also reduced the sensitivity of seeds to oxygen deprivation; 50% of the seeds germinated within 7 days in 5% oxygen. The range of temperatures and the concentrations of oxygen which were effective in osmoconditioning were very similar to those which allowed the germination of untreated seeds. In particular, the optimal temperature (27–28°C) and oxygen concentrations (more than 10%) for osmoconditioning and germination were the same. These results confirm that the beneficial effect of osmotic pretreatment (priming) corresponds to the realization of germination sensu stricto (phase II of the germination process).

This paper is a résumé of research on imbibitional chilling injury of seeds. The following summarizes the experimental results obtained and some views and concepts derived from the studies conducted at Beijing Botanical Garden during the last decade. A lot of evidence has supported and confirmed the hypothesis for imbibitional chilling injury in seeds, i.e. the primary target of harmful effects during the chilling rehydration in seeds is the membrane systems, and the subsequent degree of lasting damage depends highly on the repair of the membrane systems themselves. The two processes of repair, physical and physiological–biochemical processes, can complement each other to a certain extent.