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seed germination

Seed germination is a transit process when an active plant with photosynthesis grows from a quiescent embryo, generated in the fertilized ovule. The process of seed germination includes the following five changes or steps: imbibition, respiration, effect of light on seed germination, mobilization of reserves during seed germination, and role of growth regulators and development of the embryo axis into a seedling. All five of these stages result from a interplay of several metabolic and cellular events, coordinated by a complex regulatory network that includes seed dormancy, an intrinsic ability to temporarily block radicle elongation to optimize the timing of germination. The primary plant hormones including abscisic acid (ABA) and gibberellin (GA) antagonistically regulate seed dormancy and germination [8–10] . ABA is synthesized during seed maturation and decreased before the onset of germination; it plays key roles in inhibiting germination and establishing and maintaining seed dormancy [11] . In contrast to ABA, GA significantly increases to promote germination by causing the secretion of hydrolytic enzymes that weaken the structure of the seed testa [12, 13] .

Seed germination is a crucial process that influences crop yield and quality. Therefore, understanding the molecular aspects of seed dormancy and germination is of a great significance for the improvement of crop yield and quality. Significant progress has been made in elucidating the molecular mechanisms underlying the roles of plant hormones, mainly ABA and GA, in the regulation of seed dormancy and germination in dicot species; however, this phenomenon is scarcely studied in cereals. Therefore, further study is required to identify the molecular features involved in the regulation of the metabolic and signaling aspects of different plant hormones, and therefore seed dormancy and germination in cereals. In addition, the roles of other regulatory factors, such as epigenetic and posttranscriptional regulations of gene expression in controlling dormancy and germination of cereal seeds remain to be clarified.

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Role of Engineered Zinc and Copper Oxide Nanoparticles in Promoting Plant Growth and Yield: Present Status and Future Prospects

How can we improve the speed of seed germination and seedling emergence? Is a higher rate of seed germination and seedling emergence directly correlated to the overall crop health?

Seed germination and seedling growth are preconditions for conservation of genetic resources and sustainable uses of different products of specific species which depends on perception of genetic inconsistency, evolutionary forces, and breeding system in tree improvement ( Azad et al., 2014 ). Tamarind is commonly grown from seeds. It can also be grown from vegetative propagation (macrovegetative propagation or micropropagation). Vegetative propagation is useful for conservation of different genotypes. Germination from seed is inexpensive and very important for rural tree breeders. It can be used as root stocks to produce large number of grafted ortet. Tamarind seed germination is influenced by different presowing treatments. Different researchers noticed various responses according to the different methods used. Seed germination required 7–20 days in controlled conditions ( Azad et al., 2013 ). It can vary by seed sources, climatic requirements, and cultivars as well. On an average, it starts to germinate from 13 days of seed sowing. Sometimes it may take 30 days to complete the germination process. El-Siddig et al. (2001) recommended 45 days to allow for maximum seed germination. Azad et al. (2013) noticed 58% seed germination in the control situation, and noticed that presowing significantly enhanced seed germination. They found almost 82% seed germination in cold water treatment (immersion in cold water for 24 h at 4°C) and scarification with sand paper. El-Siddig et al. (2001) noticed acid treatment (immersion of seeds in 97% sulfuric acid for 45 min at room temperature) is an effective method for rapid and synchronous germination of tamarind.

Praveen K. Kathare , Enamul Huq , in Reference Module in Life Sciences , 2020

Md. Salim Azad , in Exotic Fruits , 2018

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In some seeds (e.g., castor beans) absorption of nutrients from reserves is through the cotyledons, which later expand in the light to become the first organs active in photosynthesis. When the reserves are stored in the cotyledons themselves, these organs may shrink after germination and die or develop chlorophyll and become photosynthetic.

Seed dormancy

In many seeds the embryo cannot germinate even under suitable conditions until a certain period of time has lapsed. The time may be required for continued embryonic development in the seed or for some necessary finishing process—known as afterripening—the nature of which remains obscure.

The seeds of many species do not germinate immediately after exposure to conditions generally favourable for plant growth but require a “breaking” of dormancy, which may be associated with change in the seed coats or with the state of the embryo itself. Commonly, the embryo has no innate dormancy and will develop after the seed coat is removed or sufficiently damaged to allow water to enter. Germination in such cases depends upon rotting or abrasion of the seed coat in the gut of an animal or in the soil. Inhibitors of germination must be either leached away by water or the tissues containing them destroyed before germination can occur. Mechanical restriction of the growth of the embryo is common only in species that have thick, tough seed coats. Germination then depends upon weakening of the coat by abrasion or decomposition.

In the process of seed germination, water is absorbed by the embryo, which results in the rehydration and expansion of the cells. Shortly after the beginning of water uptake, or imbibition, the rate of respiration increases, and various metabolic processes, suspended or much reduced during dormancy, resume. These events are associated with structural changes in the organelles (membranous bodies concerned with metabolism), in the cells of the embryo.

The Australian Alps are located in southeast Australia and cover approximately 25000 km 2 . Seed collections were made at altitudes ranging from 1605 to 2212 m a.s.l. in the New South Wales portion of Kosciuszko National Park and including high elevation frost hollows as well as true alpine sites above treeline. Seeds were collected from herbfields and grasslands incorporating a range of bog and fen habitats and a mix of specialist and generalist species distributed along moisture gradients. More than half of Kosciuszko National Park's annual rainfall (1800–3100 mm) falls as winter snow and persists for at least 4 months. Data collected by the Bureau of Meteorology at Charlotte Pass (Kosciuszko Chalet; 36.43°S, 148.33°E, 1755 m a.s.l.) in Kosciuszko National Park between 1968 and 2014 indicate that air temperatures are commonly below zero during winter months and average between 15 and 20°C during summer (Bureau of Meteorology, 2010, http://www.bom.gov.au. Figure 1).

Australian alpine ecosystems, like alpine areas around the world, are under threat from climate change combined with changes in fire frequency, land use patterns, influx of invasive species, and the impacts of increased human visitation. Warming associated with climate change is occurring more rapidly above the treeline than at lower elevations, and alpine areas are predicted to continue to experience above average warming in the future (Kullman, 2004). The capacity for continued regeneration via seed under novel conditions is likely to play a significant role in the response of alpine plants to climate and associated changes. In addition, altered disturbance regimes are likely to require an increased role of restoration and rehabilitation in the region. The insights provided here are therefore crucial to conserving and managing alpine systems under change; they can help inform our predictions of how study species may be affected, form the basis of seed propagation plans for these species, and be used to guide future investigation into alpine seed germination strategies with identifiable conservation and management outcomes.

Introduction

Cochrane, A., Yates, C. J., Hoyle, G. L., and Nicotra, A. B, (2015). Will among-population variation in seed traits improve the chance of species persistence under climate change? Glob. Ecol. Biogeogr. 24, 12–24. doi: 10.1111/geb.12234

Seed mass declines with increasing latitude (Moles and Westoby, 2004) and has been shown to be correlated with a range of traits, including early seedling survival in low light, growth form, and dispersal syndrome (Leishman et al., 1995; Westoby et al., 1996; Moles et al., 2007). However, little is known about whether other reproductive traits, including germination strategies, correlate with other seed traits, with leaf or whole plant traits, or whether they might form another independent axis entirely.

Pauli, H., Gottfried, M., Lamprecht, A., Niessner, S., Rumpf, S., Winkler, M., et al. (2015). The GLORIA Field Manual – Standard Multi-Summit approach, Supplementary Methods and Extra Approaches. Vienna: GLORIA-Coordination, Austrian Academy of Sciences & University of Natural Resources and Life Sciences.