Priming applied to commercial seed lots is widely used by seed technologists to enhance seed vigour in terms of germination potential and increased stress tolerance. Priming can be also valuable to seed bank operators who need improved protocols of ex situ conservation of germplasm collections (crop and native species). Depending on plant species, seed morphology and physiology, different priming treatments can be applied, all of them triggering the so-called ‘pre-germinative metabolism’. This physiological process takes place during early seed imbibition and includes the seed repair response (activation of DNA repair pathways and antioxidant mechanisms), essential to preserve genome integrity, ensuring proper germination and seedling development. The review provides an overview of priming technology, describing the range of physical–chemical and biological treatments currently available. Optimised priming protocols can be designed using the ‘hydrotime concept’ analysis which provides the theoretical bases for assessing the relationship between water potential and germination rate. Despite the efforts so far reported to further improve seed priming, novel ideas and cutting-edge investigations need to be brought into this technological sector of agri-seed industry. Multidisciplinary translational research combining digital, bioinformatic and molecular tools will significantly contribute to expand the range of priming applications to other relevant commercial sectors, e.g. the native seed market.

Seed priming: state of the art and new perspectives.

When seeds deteriorate, they lose vigour and become more sensitive to stresses upon germination. Eventually seeds lose the ability to germinate. The factors which determine the rate of this ‘aging’ are the temperature and moisture content at which seeds are stored and an ill-defined parameter, seed quality. While it has been known for many years that manipulation of these factors influences the longevity of seeds, the precise interactions among them are so poorly understood as to preclude the prediction of longevity for a particular seed lot. Concepts from studies of materials and food stability can be applied to seed aging research, and this may help us take a more integrative approach to understanding the kinetics of seed deterioration. These concepts describe the physical environment of the seed matrix in response to changing water contents and temperature. Water activity models describe the state of water in the seed, while the glass models describe the state of the aqueous solution. Both models presume that changes of state affect the nature and kinetics of chemical reactions. Thus, the physical and chemical environment within the seed are inextricably linked.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S096025850000413X

Understanding the mechanisms and kinetics of seed aging

Aquatic plants include a variety of life forms and functional groups that are adapted to diverse wetland habitats. Both similarities and differences in seed and seed-bank characteristics were discovered in comparisons of Australian (New South Wales) temporary upland wetlands with a North American (New Jersey) tidal freshwater marsh having both natural and constructed wetlands. In the former, flooding and drying are unpredictable and in the latter water levels vary diurnally and substrate is constantly moist. The hydrologic regimen provides the overriding selective force, with climate an important second factor. Other factors related to water level, such as oxygen availability, temperature and light, vary spatially and temporally, influencing germination processes, germination rates and seedling establishment. Seed and seed-bank characteristics (size, desiccation and inundation tolerance, germination cues and seed-bank longevity and depletion) differ, with the Australian temporary wetland being more similar to the small-seeded persistent seed bank of the constructed wetland site than to the natural tidal freshwater site with its larger seeds, transient seed bank and seasonal spring germination. Some non-spring germination can occur in the tidal constructed wetland if the soil is disturbed. In contrast, seeds in the temporary Australian wetlands germinated in response to wet/dry cycles rather than to season. Functional groups (e.g. submerged, amphibious) are more diverse in the Australian temporary wetlands, where all species tolerate drying. We suggest that the amphibious zone, with its hydrologic gradient, is the site of selection pressure determining establishment of wetland plants from seed. In this zone, multiple selective factors vary spatially and temporally.

Ecological and evolutionary trends in wetlands: Evidence from seeds and seed banks in New South Wales, Australia and New Jersey, USA

Priming and re-drying improve the survival of mature seeds of Digitalis purpurea during storage.

Seed maturity and the effects of different drying conditions on desiccation tolerance and seed longevity in foxglove (Digitalis purpurea L.)

Priming in polyethylene glycol (PEG, −1.5 MPa) for 7 d followed by drying, led to a 4–5 fold increase in mean longevity when achenes (seeds) of Ranunculus sceleratus L. were subsequently stored at 35°C and 9.2% moisture content on a fresh weight basis (67.1% equilibrium relative humidity). The increase in longevity was due to an increase in the standard deviation of the frequency distribution of individual seed lifespans (decrease in the slope of transformed survival curves) and to a lesser extent to an increase in the intercept of survival curves. Priming for 1 d resulted in a smaller but significant increase in longevity independent of whether seeds were primed in PEG, distilled water or a saturated atmosphere (100% RH).The effects of priming were not due to the prevention of imbibition injury, and there was no evidence that the water relations of whole achenes was affected by priming. The effects of a 7 d priming treatment were dependent on the temperature and nature of the priming medium. However, no differences were recorded between corresponding treatments which were primed in PEG or distilled water. Moreover, the survival and responsivity to priming of R. sceleratus seeds was not related to dormancy status. The effects of priming on the longevity of R. sceleratus seeds are apparently unrelated to seed quality as the response of seeds previously aged for 8 d at 35°C and 7.9% moisture content was similar to that for unaged seeds.Priming followed by drying did not increase seed longevity in the related species R. acris L. The promotive effects of priming on seed survival appear to be species specific and may be related to ecological factors.

G. E. Wechsberg

Papers

The effects of priming on seed longevity in Ranunculus sceleratus L.