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Seed germination is crucial for the life cycle of plants and maximum crop production. This critical developmental step is regulated by diverse endogenous [hormones, reactive oxygen species (ROS)] and exogenous (light, temperature) factors. Reactive oxygen species promote the release of seed dormancy by biomolecules oxidation, testa weakening and endosperm decay. Reactive oxygen species modulate metabolic and hormone signaling pathways that induce and maintain seed dormancy and germination. Endosperm provides nutrients and senses environmental signals to regulate the growth of the embryo by secreting timely signals. The growing energy demand of the developing embryo and endosperm is fulfilled by functional mitochondria. Mitochondrial matrix-localized heat shock protein GhHSP24.7 controls seed germination in a temperature-dependent manner. In this review, we summarize comprehensive view of biochemical and molecular mechanisms, which coordinately control seed germination. We also discuss that the accurate and optimized coordination of ROS, mitochondria, heat shock proteins is required to permit testa rupture and subsequent germination.

The increasing global phenomenon of soil salinization has prompted heightened interest in the physiological ecology of plant salt and alkali tolerance. Halostachys caspica  belonging to Amaranthaceae, an exceptionally salt-tolerant halophyte, is widely distributed in the arid and saline-alkali regions of Xinjiang, in Northwest China. Soil salinization and alkalinization frequently co-occur in nature, but very few studies focus on the interactive effects of various salt and alkali stress on plants. In this study, the impacts on the  H. caspica  seed germination, germination recovery and seedling growth were investigated under the salt and alkali stress. The results showed that the seed germination percentage was not significantly reduced at low salinity at pH 5.30–9.60, but decreased with elevated salt concentration and pH. Immediately after, salt was removed, ungerminated seeds under high salt concentration treatment exhibited a higher recovery germination percentage, indicating seed germination of  H. caspica was inhibited under the condition of high salt-alkali stress. Stepwise regression analysis indicated that, at the same salt concentrations, alkaline salts exerted a more severe inhibition on seed germination, compared to neutral salts. The detrimental effects of salinity or high pH alone were less serious than their combination. Salt concentration, pH value, and their interactions had inhibitory effects on seed germination, with salinity being the decisive factor, while pH played a secondary role in salt-alkali mixed stress.

Growth of plants, apart from being complex and highly dynamic, is directly dependent on the environmental conditions, particularly the quality of soil for terrestrial plants and the water quality for aquatic plants. Presence of microplastics in the environment may affect the plant growth in numerous ways depending on the contents of the growing medium. However, increasing presence of microplastics at an alarming rate due to its pervasive usage and mismanagement of plastics have led to significant environmental problems. Several research studies have been conducted as well as reviewed to investigate the toxic effects of microplastics on aquatic systems, but studies that investigate the toxic effect of microplastics on the terrestrial systems are limited. Hence, in this review the individual and the combined effects of microplastics on the growth of plants and seed germination in both aquatic and terrestrial ecosystems are concisely discussed. At the beginning accumulation of microplastics on aquatic and terrestrial ecosystem is discussed and the reasonable solutions are highlighted that can mitigate the effects from the widespread increase of the plastic debris. Thereafter, the individual and combined effect of microplastics on seed germination and plant growth is reviewed separately while summarizing the important aspects and future perspectives. This review will provide an insight into the existing gap in the current research works and thus could offer possible implications on the effect of microplastics on plant growth and seed germination in aquatic and terrestrial ecosystem.

Drylands are predicted to become more arid and saline due to increasing global temperature and drought. Although species from the Caatinga, a Brazilian tropical dry forest, are tolerant to these conditions, the capacity for germination to withstand extreme soil temperature and water deficit associated with climate change remains to be quantified. We aimed to evaluate how germination will be affected under future climate change scenarios of limited water and increased temperature. Seeds of three species were germinated at different temperatures and osmotic potentials. Thermal time and hydrotime model parameters were established and thresholds for germination calculated. Germination performance in 2055 was predicted, by combining temperature and osmotic/salt stress thresholds, considering soil temperature and moisture following rainfall events. The most pessimistic climate scenario predicts an increase of 3.9 °C in soil temperature and 30% decrease in rainfall. Under this scenario, soil temperature is never lower than the minimum and seldomly higher than maximum temperature thresholds for germination. As long as the soil moisture (0.139 cm³ cm³) requirements are met, germination can be achieved in 1 day. According to the base water potential and soil characteristics, the minimum weekly rainfall for germination is estimated to be 17.5 mm. Currently, the required minimum rainfall occurs in 14 weeks of the year but will be reduced to 4 weeks by 2055. This may not be sufficient for seedling recruitment of some species in the natural environment. Thus, in future climate scenarios, rainfall rather than temperature will be extremely limiting for seed germination.

Seed germination is a crucial plant-life process whose success depends largely on the seed's ability to germinate under favourable environmental conditions. Through molecular signalling, a seed is able to perceive environmental information, assimilate it, and transmit signals that determine its destiny. Reactive Oxygen and Nitrogen Species (RONS) function as signalling molecules that influence multiple phases of plant development. In the process of seed germination, their presence generally promotes germination completion, though not to the same extent in all species and environments. As signalling molecules, they participate in the sensing of light and temperature fluctuations as favourable germination cues, but they also play a role in inhibiting germination when temperatures exceed the optimal range, preventing seedling exposure to heat. Depending on environmental conditions, RONS set up crosstalk with the major phytohormones involved in germination, ABA, GA, and even auxin, regulating their biosynthesis and signalling. Here, we show relevant studies on how RONS exert seed germination control on multiple levels, such as through protein oxidation, epigenetic control, promotion of phytohormone key-metabolism genes expression, post-translational protein modifications, and redox interactions with DOG1. This review summarises the current understanding of the role of RONS in the seed, from its maturation to the transduction of environmental conditions. Special consideration is given to the RONS-mediated germination response to favourable stimuli, such as light or temperature fluctuations, and to conditions that inhibit germination, such as high temperatures.

Background Seed germination is a crucial process, which determines the initiation of seed plant life cycle. The early events during this important life cycle transition that called early seed germination is defined as initially water uptake plus radicle growing out of the covering seed layers. However, a specific genome-wide analysis of early seed germination in rice is still obscure. Results In this study, the physiological characteristics of rice seed during seed germination are determined to define key points of early seed germination. Transcriptome analyses of early phase of seed germination provided deeper insight into the genetic regulation landscape. Many genes involved in starch-to-sucrose transition were differentially expressed, especially alpha-amylase 1b and beta-amylase 2, which were predominantly expressed. Differential exon usage (DEU) genes were identified, which were significantly enriched in the pathway of starch and sucrose metabolism, indicating that DEU events were critical for starch-to-sucrose transition at early seed germination. Transcription factors (TFs) were also dramatic expressed, including the abscisic acid (ABA) responsive gene, OsABI5, and gibberellic acid (GA) responsive genes, GAI . Moreover, GAI transactivated GA responsive gene, GAMYB in vivo, indicating a potential pathway involved in early seed germination process. In addition, CBL-interacting protein kinase (CIPK) genes, such as CIPK13, CIPK14 and CIPK17 were potentially interacted with other proteins, indicating its pivotal role at early seed germination. Conclusion Taken together, gene regulation of early seed germination in rice was complex and protein-to-gene or protein-to-protein interactions were indispensable.

Germination of seeds of some summer annuals in Kentucky (eastern USA) in late-winter lead to the hypothesis that under present climate conditions the whole length of the winter cold stratification (CS) period is not required for dormancy-break of seeds of summer annuals with physiological dormancy (PD). We evaluated our data from germination phenology studies of 45 species (69 datasets) and buried-seed studies of 33 species (44 datasets). We determined time and temperature of germination after CS and percentage of the total number of hours of CS during winter (% of winter CS) seeds received prior to start of germination. In the phenology studies, mean temperature during the week of first germination for C3 and C4 species was 11.1 and 14.4°C, respectively, and % of winter CS was 80.8 and 87.4, respectively. In the buried-seed studies, % of CS for C3 and C4 species was 40.8 and 48.1, respectively, when they germinated to 25% at 20/10°C. For 32 of 33 species in the buried-seed studies, the minimum temperature at which seeds germinated decreased with increased CS; thus, seeds had Type 2 non-deep PD. The time of germination is controlled by a number of hours of CS, a decrease in minimum temperature at which seeds can germinate and a temperature increase in early spring. Seeds can germinate at relatively high temperatures as early as December and January, but they continue to be CS until spring. Temperature increases in eastern North America due to global warming are not likely to inhibit the germination of summer annuals with PD in spring.

Background Orchids require specific mycorrhizal associations for seed germination. During symbiotic germination, the seed coat is the first point of fungal attachment, and whether the seed coat plays a role in the identification of compatible and incompatible fungi is unclear. Here, we compared the effects of compatible and incompatible fungi on seed germination, protocorm formation, seedling development, and colonization patterns in Dendrobium officinale ; additionally, two experimental approaches, seeds pretreated with NaClO to change the permeability of the seed coat and fungi incubated with in vitro-produced protocorms, were used to assess the role of seed coat played during symbiotic seed germination. Results The two compatible fungi, Tulasnella sp. TPYD-2 and Serendipita indica PI could quickly promote D. officinale seed germination to the seedling stage. Sixty-two days after incubation, 67.8 ± 5.23% of seeds developed into seedlings with two leaves in the PI treatment, which was significantly higher than that in the TPYD-2 treatment (37.1 ± 3.55%), and massive pelotons formed inside the basal cells of the protocorm or seedlings in both compatible fungi treatments. In contrast, the incompatible fungus Tulasnella sp. FDd1 did not promote seed germination up to seedlings at 62 days after incubation, and only a few pelotons were occasionally observed inside the protocorms. NaClO seed pretreatment improved seed germination under all three fungal treatments but did not improve seed colonization or promote seedling formation by incompatible fungi. Without the seed coat barrier, the colonization of in vitro-produced protocorms by TPYD-2 and PI was slowed, postponing protocorm development and seedling formation compared to those in intact seeds incubated with the same fungi. Moreover, the incompatible fungus FDd1 was still unable to colonize in vitro-produced protocorms and promote seedling formation. Conclusions Compatible fungi could quickly promote seed germination up to the seedling stage accompanied by hyphal colonization of seeds and formation of many pelotons inside cells, while incompatible fungi could not continuously colonize seeds and form enough protocorms to support D. officinale seedling development. The improvement of seed germination by seed pretreatment may result from improving the seed coat hydrophilicity and permeability, but seed pretreatment cannot change the compatibility of a fungus with an orchid. Without a seed coat, the incompatible fungus FDd1 still cannot colonize in vitro-produced protocorms or support seedling development. These results suggest that seed coats are not involved in symbiotic germination in D. officinale .

Phytohormones and reactive oxygen species (ROS) are major determinants of the regulation of development and stress responses in plants. During life cycle of these organisms, signaling networks of plant growth regulators and ROS interact in order to render an appropriate developmental and environmental response. In plant's photosynthetic (e.g., leaves) and non-photosynthetic (e.g., seeds) tissues, enhanced and suboptimal ROS production is usually associated with stress, which in extreme cases can be lethal to cells, a whole organ or even an organism. However, controlled production of ROS is appreciated for cellular signaling. Despite the current progress that has been made in plant biology and increasing number of findings that have revealed roles of ROS and hormonal signaling in germination, some questions still arise, e.g., what are the downstream protein targets modified by ROS enabling stimulus-specific cellular responses of the seed? Or which molecular regulators allow ROS/phytohormones interactions and what is their function in seed life? In this particular review the role of some transcription factors, kinases and phosphatases is discussed, especially those which usually known to be involved in ROS and hormonal signal transduction under stress in plants, may also play a role in the regulation of processes occurring in seeds. The summarized recent findings regarding particular ROS- and phytohormones-related regulatory proteins, as well as their integration, allowed to propose a novel, possible model of action of LESION SIMULATING DISEASE 1, ENHANCED DISEASE SUSCEPTIBILITY 1, and PHYTOALEXIN DEFICIENT 4 functioning during seeds life.

Dry direct seeding of rice has emerged as an effective method for reducing the excessive water demand associated with conventional rice transplantation, presenting significant potential for enhancing sustainability. However, this cultivation method is hindered by high seed usage and often inconsistent and low seedling emergence. Seed priming, a pre-sowing treatment, has been employed to mitigate these issues, but the inconsistent effects of exogenous priming agents remain a concern. Currently, there is limited molecular-level information on the uneven seedling emergence and effective screening methods for priming agents. In this study, we employed a metabolomics approach using advanced chromatography and mass spectrometry technology to identify differential accumulation of metabolites (DAMs) in seeds with varying germination energies. The seed priming technique was also used to validate the identified DAMs. We investigated the proportion of different specific gravity seeds and the corresponding germination energy across 20 varieties and established a relationship between different specific gravity seeds and germination energy. Our results showed that seeds with high and low germination energy differed in several metabolites, including amino acids, organic acids, and others. We further confirmed the critical role of these DAMs in determining seed germination energy under dry direct seeding. This research provides valuable insights into the metabolic mechanisms associated with germination energy and offers a useful approach for screening effective endogenous seed priming agents.