Seed Priming: An Interlinking Technology between Seeds, Seed Germination and Seedling Establishment

Biologically seed is a small embryonic plant along with either endosperm or cotyledons, enclosed with in an outer protecting covering called seed coat. During the time of seed development large metabolic conversions take place, including proper partitioning of photo-assimilates and the formation of complex polymeric forms of carbohydrate, protein and fats for storing as seed reserves. In developing phase of seeds, every detail information stored in the embryonic plant are genetically and sometimes epigenetically also predetermined and influenced by various environmental/external factors already faced by the mother plant. In the growth cycle of plants, seed germination and seedling establishment are the two critical phases where survivability of the seedlings in natural habitats is a matter of question until the onset of photosynthesis by the established seedling. The various sequence of complex processes known to occur in both the phases i.e., an array of metabolic activities are initiating which eventually leads to the renewal of embryo growth of the dormant seeds and ultimately seedlings are established. Efficient seed germination is an important factor for agricultural sciences and successful establishment of germinated seedling requires a rapid and uniform emergence and root growth. With these aspects of seed physiology kept in mind the present chapter will be designed in such a way where, a gap filling, inter linking, eco- and farmers\' friendly technology i.e., ‘seed priming’ (a pre-sowing partial hydration of seeds) will be considered to improve the rate and uniformity of germination and seedling establishment. Under optimal and adverse environmental conditions, the primed seeds of diversified species lead to an enhanced germination performance with increased vigor index has been reported by various scientists which indicates a good establishment of seedlings in the field and thereafter enhance the performance of crops as a whole.

Crosstalk during the Carbon–Nitrogen Cycle That Interlinks the Biosynthesis, Mobilization and Accumulation of Seed Storage Reserves

Carbohydrates are the major storage reserves in seeds, and they are produced and accumulated in specific tissues during the growth and development of a plant. The storage products are hydrolyzed into a mobile form, and they are then translocated to the developing tissue following seed germination, thereby ensuring new plant formation and seedling vigor. The utilization of seed reserves is an important characteristic of seed quality. This review focuses on the seed storage reserve composition, source–sink relations and partitioning of the major transported carbohydrate form, i.e., sucrose, into different reserves through sucrolytic processes, biosynthetic pathways, interchanging levels during mobilization and crosstalk based on vital biochemical pathways that interlink the carbon and nitrogen cycles. Seed storage reserves are important due to their nutritional value; therefore, novel approaches to augmenting the targeted storage reserve are also discussed.

Quantitative Determination of the Effects of He-Ne Laser Irradiation on Seed Thermodynamics, Germination Attributes and Metabolites of Safflower (Carthamus tinctorius L.) in Relation with the Activities of Germination Enzymes

The present investigation was undertaken to assess the effects of different doses (100, 300, and 500 mJ) of low power He–Ne laser (632.8 nm) irradiation on seed germination and thermodynamics attributes and activities of potential germinating enzymes in relation with changes in seed metabolites. He–Ne laser seed irradiation increased the amylase (Amy), protease (Pro) and glucosidase (Gluco) activities, with a significant improvement in seed thermodynamics and seed germination attributes. A fast increase was found in free fatty acids (FFA), free amino acids (FAA), chlorophyll (Chl), carotenoids (Car), total soluble sugars (TSS) and reducing sugars (RS) in laser treated seeds in parallel with fast decline in seed oil contents and total soluble proteins (TSP). Significant positive correlations were recorded in laser-induced enhanced seed energy levels, germination, activities of germination enzymes with levels of FAA, FFA, Chl, TSS and RS, but a negative correlation with the levels of TSP and oil. In conclusion, the seed treatment with 100 and 300 mJ He–Ne laser was more effective to improve the seed germination potential associated with an improvement in seed energy levels due to increased activities of germination enzymes due to the speedy breakdown of seed reserves to simple metabolites as building blocks.

SEED RESERVE MOBILIZATION EVALUATION FOR SELECTION OF HIGH-VIGOR COMMON BEAN CULTIVARS

ABSTRACT The efficiency of seed reserve mobilization (SRM) can be affected by genotype characteristics and seed initial physiological quality, which are determinant for the choice of cultivars that present plants with high physiological performances. The objective of this study was to evaluate the SRM in different common bean cultivars with different vigor and determine the differences in this process between seed lots and cultivars. Six common bean cultivars were grown in the 2017-2018 and 2018-2019 crop seasons in Lages, Santa Catarina, Brazil. The physiological quality of the cultivars was defined by germination test, accelerated aging test, seedling length, and vigor index, establishing two vigor groups (high vigor and low vigor). SRM was evaluated based on seed and seedling dry weights, use of seed reserves, use rate of seed reserves, SRM rate to the seedling, and use efficiency of seed reserves. The high-vigor cultivars presented higher use rates of seed reserves, SRM rate to the seedling, and use efficiency of seed reserves, favoring the development of vigorous seedlings. The evaluation of SRM is an alternative to improve control of internal seed quality and selection of high-vigor common bean cultivars.

Plant and Seed Mortality of Fireweed Senecio madagascariensis Following Herbicide Application

Fireweed (Senecio madagascariensis Poir), is a weed of National significance and one of the worst weeds of coastal pastures in South Eastern Australia. Chemical control has been found to be effective in killing plants but there is no information on the effect of herbicides on the seeds that may be present on plants at the time of application. Consequently, a study was undertaken to determine the effect of five selective herbicides (1) on plant mortality at different life stages and (2) on the viability (as assessed by germination) of fireweeds seeds at different stages of maturity. Potted plants of the required growth stages were obtained through several collections of different sized seedlings from a field site near Brisbane. Before herbicide application, in the mature plant cohort the inflorescences were tagged according to their maturity as being either immature (IM) or intermediate (INT). Plants were sprayed with either fluroxypyr/aminopyralid (HotShot™) (A), bromoxynil (Bromicide® 200) (B), metsulfuron-methyl (Brush-Off®) (C), triclopyr/picloram/aminopyralid (Grazon™ extra) (D), triclopyr/picloram/aminopyralid (TordonTM regrowthMaster) (E) at the recommended rates with untreated control plants of the three growth stages also included for comparison. All herbicides killed fireweed seedlings and juvenile plants, but only treatments A, D and E gave high plant mortality (>80%) of mature plants. All herbicides also caused nil germination of seeds collected 30 days after spraying, except for a small percentage (8% germination) of mature seeds from Bromoxynil treated plants. These results have identified several herbicides capable of killing mature fireweed plants and minimizing replenishment of soil seed reserves.

Changes in hormonal balance as key to reserve degradation after dormancy overcoming in Annona macroprophyllata and Annona purpurea seeds

Studies on the effect of the applying of phytoregulators to overcome seed dormancy have been carried out in Annonaceae species, thus the endogenous relationship between abscisic acid and gibberellins after the application of phytoregulators needs to be known in these species. Considering the importance of hormonal balance in dormancy mechanisms, the aim of this research was to elucidate how endogenous ABA and GA concentrations change after the application of phytoregulators in seeds and how these changes affect reserve degradation during germination of Annona macroprophyllata and A. purpurea seeds. Seeds were submitted to three conditions: - no soaking, soaking-in-water and soaking-in-GA4+7+benzyladenine. ABA, GA, lipids, proteins, and total soluble sugars were quantified at 0, 2, 5, 10, and 15 days after the beginning of treatments. The application of phytoregulators led change of the hormonal balance inducing increase in endogenous GA and reduction in ABA levels since seed soaking. During imbibition, the degradation of seed reserves (breaks proteins first, and then soluble sugars and finally lipids) was observed and complete germination was obtained after 10 days, with primary root emission. In both species, dormancy can be broken soon after seed dispersal when the balance between GA and ABA is endogenously changed (by exogenous application of phytoregulators), leading to metabolic reserve degradation and germination.

Soil seed burial and competition with surrounding plants determine the emergence and development of seedling of an endangered species Horsfieldia hainanensis Merr. in China

Three well-conserved Horsfieldia hainanensis Merr. populations were used to investigate their soil seed bank and seedling regeneration characteristics and their relationship to environmental factors. The results showed that the seed reserves were low in the H. hainanensis soil seed bank (16.93~24.74 seed/m2). The distribution pattern for the seeds and seedlings in the H. hainanensis populations was aggregated, and they were mainly found around 2–3 m from the mother plant. The seeds in the litter layer and the 5–10 cm soil layer showed no vigor, and only 25.7%~33.3% of the total seeds in the 0–5 cm soil layer were viable affected by the high temperature and humidity, the animals’ eating and poisoning. Affected by the height and coverage of the surrounding herbaceous layer and shrub layer, the seedlings of H. hainanensis could not obtain enough light and nutrients in the competition, resulting in the survival competitiveness of 1- to 3-year-old (1–3a) seedlings in the habitat had been in a weak position and a large number of seedlings died. It would take at least four years for seedlings to develop under the current environmental constraints. It can be concluded that the low seed reserve in the soil seed bank and high mortality of seedlings of H. hainanensis lead to slow or even stagnation of population regeneration, which was an important reason for the endangered of H. hainanensis. Therefore, the next research focus is to explore the influence mechanism of environmental factors on seed germination and seedling growth of H. hainanensis.

Seed reserves reduction rate and reserves mobilization to the seedling explain the vigour of maize seeds

Understanding how the seed reserve dynamics occurs during germination and seedling formation is determinant for advancements on seed technology. The aims of this study were: to verify which accelerated ageing temperature is the most effective to separate the vigour levels of maize seeds and to evaluate the reserves dynamics during germination and seedling formation process. Seven maize cultivars were submitted to the germination rate, accelerated ageing, thousand seed weight, total seedling length, shoot and root length, dry matter of seed and seedling, remaining dry matter in the endosperm, seed reserves reduction rate, conversion efficiency of reserves, reserves mobilization rate to the seedling and energy expenditure using the completely randomized statistical design. The reserves dynamics and seedling formation depends on the genotype and the initial seed vigour. Accelerated ageing at 45 °C for 72 hours is the most efficient combination to segregate vigour levels. Genotypes with higher seed reserve utilisation efficiency have higher vigour, producing seedlings with higher dry matter, higher total, shoot and root length, regardless of seed weight. The two rates evaluated prompt us to conclude that they explain the maize seed vigour and can be used in quality control programs to select high physiological quality cultivars.