Seed Priming: New Comprehensive Approaches for an Old Empirical Technique

Seed priming is a pre-sowing treatment which leads to a physiological state that enables seed to germinate more efficiently. The majority of seed treatments are based on seed imbibition allowing the seeds to go through the first reversible stage of germination but do not allow radical protrusion through the seed coat. Seeds keeping their desiccation tolerance are then dehydrated and can be stored until final sowing. During subsequent germination, primed seeds exhibit a faster and more synchronized germination and young seedlings are often more vigorous and resistant to abiotic stresses than seedlings obtained from unprimed seeds. Priming often involves soaking seed in predetermined amounts of water or limitation of the imbibition time. The imbibition rate could be somehow controlled by osmotic agents such as PEG and referred as osmopriming. Halopriming implies the use of specific salts while "hormopriming" relies on the use of plant growth regulators. Some physical treatments (UV, cold or heat,..) also provide germination improvement thus suggesting that priming effects are not necessarily related to seed imbibition. A better understanding of the metabolic events taking place during the priming treatment and the subsequent germination should help to use this simple and cheap technology in a more efficient way

Repression of Floral Meristem Fate Is Crucial in Shaping Tomato Inflorescence

Tomato is an important crop and hence there is a great interest in understanding the genetic basis of its flowering. Several genes have been identified by mutations and we constructed a set of novel double mutants to understand how these genes interact to shape the inflorescence. It was previously suggested that the branching of the tomato inflorescence depends on the gradual transition from inflorescence meristem (IM) to flower meristem (FM): the extension of this time window allows IM to branch, as seen in the compound inflorescence (s) and falsiflora (fa) mutants that are impaired in FM maturation. We report here that JOINTLESS (J), which encodes a MADS-box protein of the same clade than SHORT VEGETATIVE PHASE (SVP) and AGAMOUS LIKE 24 (AGL24) in Arabidopsis, interferes with this timing and delays FM maturation, therefore promoting IM fate. This was inferred from the fact that j mutation suppresses the high branching inflorescence phenotype of s and fa mutants and was further supported by the expression pattern of J, which is expressed more strongly in IM than in FM. Most interestingly, FA - the orthologue of the Arabidopsis LEAFY (LFY) gene - shows the complementary expression pattern and is more active in FM than in IM. Loss of J function causes premature termination of flower formation in the inflorescence and its reversion to a vegetative program. This phenotype is enhanced in the absence of systemic florigenic protein, encoded by the SINGLE FLOWER TRUSS (SFT) gene, the tomato orthologue of FLOWERING LOCUS T (FT). These results suggest that the formation of an inflorescence in tomato requires the interaction of J and a target of SFT in the meristem, for repressing FA activity and FM fate in the IM

Could orphan crops or crop wild relatives help mitigate the impact of climate change on agriculture?

In the context of climate change, an increase in temperature and a decrease in rainfalls are expected. These environmental modifications will have an impact on crops as a consequence of multi-component stress. Broadening our food sources through the integration of neglected crops, such as pseudocereals, will help to mitigate the effects of environmental change and improve qualitative food security. Regarding pseudocereals, we investigate the impacts of heat and drought on buckwheat (Fagopyrum esculentum and Fagopyrum tataricum) and the impact of salinity on amaranth (Amaranthus cruentus). These plants have received renewed interest due to their nutritional and medicinal benefices but the physiological basis of resistance mechanisms to abiotic constraints remain largely unknown in these species. Another strategy to improve crop resistance to abiotic stress is the use of wild crop relatives as a source of resistant genes. Among the tomato clade, Solanum chilense is considered as one of the most promising sources of genes for tomato selection due to its high level of genetic variability and its resistance to harsh environment. We compared the salt, drought and heat resistance of the cultivated tomato (Solanum lycopersicum) and Solanum chilense and investigated the inter-specific reproductive barriers in order to produce hybrids between the two species

Genetical control of flowering in tomato (Lycopersicon esculentum Mill.): a case study of some key genes regulating flowering time and morphogenesis of reproductive structures

In the present work, we initiated a study of the genetic control of various aspects of the reproductive process in tomato, including the flowering time, the structure of the inflorescence and some floral traits. We investigated 5 mutants known to be affected in their flowering response: uniflora (uf), blind (bl), compound inflorescence (s), single flower truss (sft) and jointless (j). For most of these mutant plants, both the flowering time and the reproductive structure were altered. The recording of their flowering time phenotype suggested that UF, BL, SFT and to a lesser extent J and S are flowering promoters. Regarding the initiation of the reproductive structures, UF may participate in the identity of the inflorescence meristem; BL, J and SFT most likely control the maintenance of the inflorescence meristem and S appears to be a floral meristem identity gene. The uf:s, uf:j, uf:sp and uf:bl double mutants were produced, and instead of inflorescences, they all developed solitary flowers just like the parental uf plants. These results suggest that UF may be a key gene that acts upstream of BL, S, J and SP in specifying the structure of the inflorescence. All the investigated mutants (simple and double) exhibited a delayed flowering on the various sympodial segments suggesting in most cases an interaction between the additional affected genes and SELF PRUNING (SP). Indeed, SP controls the sympodial growth of tomato and belongs to the CETS genes family. In addition to SP, this family contains 5 other members in tomato (the functions of which are yet unknown). We analysed the expression of the tomato CETS genes in different organs of the sp, uf, bl, s, j mutants and the generated double mutants. Our results indicate that qualitatively, mutation of UF, S, J and BL did not significantly affect the expression of members of the CETS family. The apparent absence of striking interactions at the transcriptional level may not preclude possible protein-protein interactions between SP and any of the UF, S, J or BL product. At the flower level, we extended observations reported in the literature and indicating that different floral traits are linked to the Lycopersicon incompatibility S-locus. We showed that the floral organs size and the number of flowers per inflorescence are genetically linked to the S-locus suggesting that a complex of tightly linked genes affecting separate aspects of reproductive biology may be located on tomato chromosome 1.Doctorat en sciences (sciences biologiques) (BIOL 3)--UCL, 200

Comparison of Heat and Drought Stress Responses among Twelve Tartary Buckwheat (Fagopyrum tataricum) Varieties

The use of orphan crops could mitigate the effects of climate change and improve the quality of food security. We compared the effects of drought, high temperature, and their combination in 12 varieties of Tartary buckwheat (Fagopyrum tataricum). Plants were grown at 21/19 °C or 28/26 °C under well-watered and water-stressed conditions. Plants were more discriminated according to environmental conditions than variety, with the exception of Islek that was smaller and produced fewer leaves, inflorescences, and seeds than the other varieties. The combination of high temperature and water stress had a stronger negative impact than each stress applied separately. The temperature increase stimulated leaf and flower production while water stress decreased plant height. Leaf area decreased with both temperature and water stress. High temperature hastened the seed initiation but negatively affected seed development such that almost all seeds aborted at 28 °C. At 21 °C, water stress significantly decreased the seed production per plant. At the physiological level, water stress increased the chlorophyll content and temperature increased the transpiration rate under well-watered conditions. High temperature also increased the polyphenol and flavonoid concentrations, mainly in the inflorescences. Altogether, our results showed that water stress and temperature increase in particular negatively affected seed production in F. tataricum

Comparison of common buckwheat and tartary buckwheat cultivation and pollination under field conditions in belgium

Buckwheat is a pseudocereal with high nutritional and nutraceutical properties. Although common buckwheat (Fagopyrum esculentum) is the main cultivated species, Tartary buckwheat (Fagopyrum tataricum) is attracting more and more interest. The two buckwheat species differ in their reproduction: F. esculentum is self-incompatible, heterostylous and entomophilous and produces white to pink flowers while F. tataricum is self-compatible and produces small greenish homostylous flowers. Thus, insects are necessary for pollination and reproduction of F. esculentum, but their contribution to the reproduction of F. tataricum has not been studied so far. To improve our understanding of the reproduction of both species, we compared plant growth, yield parameters and pollination of two varieties of F. esculentum ('La Harpe' and 'Darja') and F. tataricum ('Islek' and 'Zlata') under field conditions in Belgium. Fagopyrum esculentum flowered earlier, produced fewer nodes, fewer branches, fewer inflorescences, but more flowers per inflorescence than F. tataricum. Yield was higher in F. tataricum, while thousand kernel weight was higher in F. esculentum. Yield ranged from 2037 kg/ha to 3667 kg/ha depending on species and year. With respect to pollination, F. esculentum attracted a greater diversity of insects than F. tataricum, which generally attracted smaller insects. Syrphidae were the primary visitors to both buckwheat species. In addition, Syrphidae were the most common insects in terms of density and foraging time on F. tataricum. No differences in pollinators or visiting behavior were observed between varieties for any species. Fagopyrum esculentum produced nectar to attract pollinators, but nectar could not be extracted from F. tataricum under field conditions. Our results showed that both species grow well under Belgian conditions and that both species are visited by insects, suggesting that they may also contribute to the reproduction of F. tataricum as observed for F. esculentum

Temperature rise and water stress effects on two buckwheat species (Fagopyrum esculentum and Fagopyrum tataricum)

Buckwheat is a pseudocereal with high nutritional and nutraceutical properties. Although common buckwheat (Fagopyrum esculentum) is the main cultivated species, Tartary buckwheat (Fagopyrum tataricum) is gaining interest. In most western European countries, buckwheat production has declined during the 20th century with the development of more productive crops, but it is currently receiving renewed attention for its nutritional and environmentally friendly qualities. Both species were cultivated under field conditions in Belgium and showed good yield (2037 kg/ha - 3667 kg/ha) and good seed quality (Aubert et al., 2021). Fagopyrum esculentum flowered earlier, produced less nodes, less branches, less inflorescences, but more flowers per inflorescence than F. tataricum. The yield was higher in F. tataricum, while the thousand-grain weight was higher in F. esculentum. Both species differed by their reproduction: F. esculentum is a heterostylous and self-incompatible species mainly pollinated by insects while F. tataricum produces one type of flower that can self-fertilize. However, we observed that insects visited both species: F. esculentum was twice as visited and attracted a greater diversity of insects than F. tataricum, which generally attracted smaller insects. In the context of ongoing climate change, expected temperature rise and increase of drought periods may significantly limit plant growth and productivity of crop species. We investigated the effects of a sub-optimal temperature (27°C vs. 21°C) and of water stress (<20% vs. 40-50% soil water content) on F. esculentum and F. tataricum under controlled conditions (Aubert et al., 2020a, b). High temperature increased leaf production mainly in F. tataricum but decreased leaf area in both species. Water and photosynthesis-related parameters were affected by high temperature but our results suggested that although transpiration rate was increased, adaptive mechanisms were developed to limit the negative impact on photosynthesis. High temperature mainly affected the reproductive stage. It delayed flowering time but boosted inflorescence and flower production. Nevertheless, flower and seed abortions were observed in both species at 27 °C. Regarding flower fertility, heat affected more the female stage than the male stage and reduced the stigma receptivity. Pollen production increased with temperature in F. esculentum while it decreased in F. tataricum. Both species increased their antioxidant production under high temperature to limit oxidative stress. Total flavonoid content was particularly increased in the leaves of F. esculentum and in the inflorescences of F. tataricum. Regarding water stress, our results suggested that F. tataricum was more resistant to water stress than F. esculentum and that F. esculentum had characteristics of drought avoidance, while F. tataricum exhibited traits of drought tolerance. The vegetative growth was affected in F. esculentum but not in F. tataricum as water stress decreased leaf production, leaf fresh, and dry weight, stomatal conductance, transpiration rate, and photosynthesis rate in the former but not in the latter. However, chlorophyll fluorescence parameters were not affected by water stress, whatever the species, and the chlorophyll content increased in water-stressed plants in both species. Oxidative stress was observed in both species in response to water stress, and antioxidant content was increased in F. tataricum. The reproductive phase was affected by water stress in both species: the number of inflorescences and pollen production decreased, mainly in F. esculentum. Altogether, our results showed that abiotic stress response differed between buckwheat species and that reproductive stage was more affected than vegetative stage in both species but antioxidant production was boosted by abiotic stress, which could be interesting from a nutraceutical point of view