Seeds of Celosia argentea L. displayed an absolute requirement for light for germination. Germination could be induced by far-red light as well as red light, and therefore, the effect of red light was not completely reversible by far-red light. A considerable proportion of the seed population was sensitive to red light within the range 0.01–0.1 μmol m−2, which suggested that phytochrome was operating in the very low fluence response mode. Seeds showed a gradual increase in germination in response to red light with an increasing duration of previous dark imbibition. Interruption of the dark imbibition period with very low fluence (10−4−10–1 μmol m−2) or low fluence (1–103 μmol m−2) red light prevented germination subsequent to a terminal, saturating red light irradiation. Increasing responsiveness to red light with increase in imbibition temperature and inhibition of development of photosensitivity by cycloheximide suggested that phytochrome synthesis occurred during the dark imbibition period. An absolute requirement for light for seed germination, inhibition of seed germination on interrupting the dark imbibition period with very low fluence or low fluence red light, and the recovery from photoinhibition of seeds in darkness are consistent with the hypothesis that PhyA is the principal phytochrome involved in the photoregulation of seed germination in C. argentea.

Freshly harvested tomato (Lycopersicon esculentum Mill, cv. Moneymaker) seeds were osmotically primed for 8 d in −1.0 MPa PEG-6000 solution and dried to about 6% water content for storage. Such so–called ‘fresh PEG priming’ enhanced seed germination and improved seedling performance as compared with the untreated control. Fresh PEG priming neither alleviated seed dormancy nor promoted DNA replication as was the case when seeds were dried upon harvest and subsequently primed in PEG (normal PEG priming). However, the addition of 10 μM GA4+7 to the osmotic priming solution triggered replicative DNA synthesis of fresh-priming seeds and further enhanced the germination process. After 5 months of storage in ambient temperature conditions, fresh PEG-primed seeds maintained more positive effects gained from priming, whereas, normal PEG-primed seeds had lost the promoting effects on germination. Normal PEG-primed seeds were much more susceptible to controlled deterioration than fresh PEG-primed seeds. It is suggested that the advancement of germination is negatively correlated with seed storability. The mechanisms of seed priming in relation to nuclear replication activities and physical changes are discussed.

Storage of tomato seeds under deteriorating conditions reduced the rate of germination, the uniformity of germination, total germination and the proportion of normal seedlings. Pre-storage humidification and hydropriming of seeds resulted in a significant increase in resistance to deterioration. In contrast, osmoprimed seeds were more deterioration sensitive. Humidification or hydropriming for one day did not allow nuclei to enter the S phase of the cell cycle. Osmopriming strongly increased the percentage of nuclei with replicated DNA in the embryonic root tip, indicating initiation of the cell cycle and progression towards the G2 phase. The interaction between the prestorage treatments, cell cycle progression and deterioration resistance, is discussed. Based on the changes in moisture content equilibrium and cell cycle activity it is hypothesized that the beneficial effects of pre-storage humidification and hydropriming were related to metabolic activities induced by the partial hydration and that the adverse effects of osmopriming were caused by a decrease in DNA repair activity due to progression in the cell cycle.

Predispersal seed predation may have implications for plant population dynamics and the evolution of plant traits, but assessing the level of seed predation for an individual plant is not always straightforward. Seeds of Lotus corniculatus (Fabaceae) are often only partially eaten by a weevil seed predator, Apion loti. Samples of these seeds were tested for viability and subsequent seedling vigour. A large proportion of these damaged seeds were viable, and the resulting seedlings almost as vigorous as those from undamaged seeds. The ubiquity of these findings, and their ecological significance, is discussed.

The need to conserve plant genetic resources can no longer be in doubt. The destruction of natural habitats, the replacement of multiple cropping systems with monocultures, the replacement of traditional varieties with uniform high-yielding cultivars all lead to genetic erosion and the loss of crop and plant diversity. Genetic resources are vital for crop breeding programmes as sources of new genes for, for example, disease and pest resistance. They are also vital as sources of pharmaceutical and novel industrial and food products. In their own right they may have potential as new crops.