The growing conditions of a parent plant may affect the degree of dormancy of its seeds. This has been demonstrated in numerous species, both wild and cultivated. The evidence comes from field observations and controlled experiments. A survey of the literature shows that some well defined patterns emerge, with certain environmental factors tending to have similar effects over a wide range of species. Lower dormancy (i.e., increased germinability) is generally associated with the following environmental conditions during seed development: high temperatures, short days, red light, drought and high nitrogen levels. The effects are probably the result of changes in the quantity, mobility or activity of growth substances such as abscisic acid. The ecological implications of the phenomenon are briefly discussed.

Low and high moisture kernels and embryos were imbibed by soaking in distilled water at 5°C and 25°C. Leaching of seeds and embryos was measured by ion conductivity of imbibition water after fixed time intervals. Imbibed kernels were placed on moist filter paper after 1 h imbibition and embryos on a solid culture medium after 15 min imbibition and germinated at 25°C. Primary root length was measured 3 days after germination.

The leakage from seeds or embryos was correlated with the velocity of water uptake but did not show its highest values when low moisture seeds or embryos were imbibed at chilling temperature. Furthermore germination was apparently not affected by imbibitional chilling of either low moisture content seeds or embryos. In one of the three genotypes tested (B73) seedlings from low moisture content seeds imbibed at 5°C showed a reduction of the primary root growth. However, this reduction was also seen in seedlings from low moisture B73 seeds imbided at 25°C and resulting in higher level of leaching. Thus, injury by imbibition of low moisture seeds appears independent of chilling temperature and not due to loss of semipermeability of membrane lipids. Our results suggest that, in the case of embryos, water inrush into the cells reaches levels injurious for membrane integrity independently of the two moisture contents and temperature considered.

Utilization of lipid and protein storage reserves was examined during germination and early growth of somatic and excised seed embryos in vitro, and seed of interior spruce. High germination frequencies were recorded for somatic and excised seed embryos, and elongation of radicles and hypocotyls observed for both embryo types. Although elongation of the embryo types differed (i.e. somatic ≤ excised seed < seed), fresh weight gain was similar. Utilization of triglycerides in somatic embryos was more rapid than in excised seed and seed embryos, thus it appeared to be under embryo infuence. By contrast, depletion of storage proteins appeared to be influenced by the megagametophyte, with hydrolysis in somatic and excised seed embryos preceding that of the seed embryo by 2 days. Differential utilization of the storage reserves was temporally associated with differences in growth patterns of somatic and seed embryos. The evidence presented indicates that the in vitro germination medium does not entirely supplant the role of the megagametophyte during germination and early growth. The relevance of these results to artificial seed technology is discussed.

Seed viability was maintained in four cultivars of oil palm (Elaeis guineensis Jacq.) during 12 months of hermetic storage at 15°C with 10–12% moisture content (embryo moisture contents of 19–21%). The viability of both these and drier seeds was reduced greatly during this period at cooler storage temperatures of 0°C and −20°C, however. For example, intact seeds at 6.1–7.4% moisture content (embryo moisture contents of 9.1–12.0%, at which freezing damage would not be expected) lost viability more rapidly at 0°C and −20°C than at 15°C. Moreover, desiccation to 4–5% moisture content (4–6% embryo moisture content) reduced seed lot viability in some but not all cultivars. The results confirm earlier reports that oil palm is not recalcitrant, but neither is it orthodox. Thus, seed storage behaviour in oil palm appears to be intermediate between these categories. Additional results are presented which suggest that the seeds of the royal palm (Oreodoxa regia HBK) may also show intermediate seed storage behaviour.

Osmotic and ionic effects of NaCl were investigated in germinating wheat. Approximately isotonic solutions of NaCl and sorbitol inhibited germination and seedling growth to similar degrees. When dry kernels were pre-imbibed in salt for 24 h and then transferred to water, germination was equivalent to that of kernels imbibed continuously in water and the development of embryos was delayed to about the same extent as kernels pre-imbibed in sorbitol for 24 h. Measurements of water uptake, respiration, biosynthetic activities and rubidium uptake in embryos dissected from grains imbibed in NaCI or sorbitol for the first 24 h demonstrated that salt supplied to dry kernels closely mimicked sorbitol in counteracting the reactivation of embryo metabolism. No toxic effects of salt were observed when dry kernels were pre-imbibed in very high NaCI concentrations for 24 h and then transferred to water, even though embryo sodium contents increased considerably. Ultrastructural observations of embryo tissue further showed that salt influx into dry grains did not produce ion-specific damage in cell organization. On the other hand, salt specific effects became evident when the 24 h salt exposure was applied to kernels pre-hydrated for 24 h and, even more, for 30 h. We conclude that in wheat the inhibition of germination by salt corresponds to that induced by an osmoticum, provided that the caryopsis has not reached the stage of germination associated with active embryo expansion.

We have studied by means of cytology and autoradiography the effect of benzyladenine (BA, a synthetic cytokinin) on DNA metabolism during early maize germination.The data indicate that BA stimulates nuclear DNA replication. The doubling of the amount of nuclear DNA in BA-treated axes occurs earlier than in nontreated axes, and there is a three-fold increase in the mitotic index at 24 h of germination. These results provide further corroboration for the suggestion that the stimulation of DNA synthesis observed relates to a nuclear replicative type of synthesis. Possible mechanisms of action of BA are discussed.

Identification of discrete stages during embryogenesis is important for the consistent and repeatable selection of seeds having similar developmental characteristics. A timetable for staging developing seeds of alfalfa (Medicago sativa L.) has been developed. Morphological characteristics, fresh and dry weights, SDSpolyacrylamide gel electrophoretic protein patterns and total protein content were recorded at various times between fertilization and 36 d after pollination (maturity), stages I–IX. A full complement of storage proteins (2S, 7S, 11S) is synthesized in both developing cotyledons and radicles. Low-salt soluble (S1) and high-salt soluble (S2) storage proteins first appear during embryo elongation. The proportional amounts of some S1 storage proteins change during alfalfa seed development. Markers are thus provided as uniform reference points for staging from the time of anthesis to seed shedding.

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.