Nitric oxide enhances desiccation tolerance of recalcitrant Antiaris toxicaria seeds via protein S-nitrosylation and carbonylation

The viability of recalcitrant seeds is lost following stress from either drying or freezing. Reactive oxygen species (ROS) resulting from uncontrolled metabolic activity are likely responsible for seed sensitivity to drying. Nitric oxide (NO) and the ascorbate-glutathione cycle can be used for the detoxification of ROS, but their roles in the seed response to desiccation remain poorly understood. Here, we report that desiccation induces rapid accumulation of H(2)O(2), which blocks recalcitrant Antiaris toxicaria seed germination; however, pretreatment with NO increases the activity of antioxidant ascorbate-glutathione pathway enzymes and metabolites, diminishes H(2)O(2) production and assuages the inhibitory effects of desiccation on seed germination. Desiccation increases the protein carbonylation levels and reduces protein S-nitrosylation of these antioxidant enzymes; these effects can be reversed with NO treatment. Antioxidant protein S-nitrosylation levels can be further increased by the application of S-nitrosoglutathione reductase inhibitors, which further enhances NO-induced seed germination rates after desiccation and reduces desiccation-induced H(2)O(2) accumulation. These findings suggest that NO reinforces recalcitrant seed desiccation tolerance by regulating antioxidant enzyme activities to stabilize H(2)O(2) accumulation at an appropriate concentration. During this process, protein carbonylation and S-nitrosylation patterns are used as a specific molecular switch to control antioxidant enzyme activities.     

ROS production and antioxidative system activity in embryonic axes of <Emphasis Type="Italic">Quercus robur</Emphasis> seeds under different desiccation rate conditions

The seeds of pedunculate oak (Quercus robur L.) were subjected to slow (S) and rapid (R) desiccation at desiccation rates of 0.16 and 0.39% H₂O per hour, respectively. Till ca. 40% water content (WC) the germination capacity of seeds in the S and R variants was high (ca. 100%). Between 40 and 28% WC, germination capacity declined to 20 and 50% in S and R variants, respectively. The decrease in seed viability was accompanied by a significant increase of electrolyte leakage from embryonic axes (28% for S and 15% for R variants). In the embryonic axes of seeds subjected to slow desiccation, malondialdehyde (MDA) and free fatty acid (FFA) contents were significantly higher than those in R variants, indicating greater membrane damage due to lipid peroxidation. The production of ROS (H₂O₂ and O₂^·−) was significantly higher in S than in R variants. The low molecular weight antioxidants α-tocopherol, ascorbic acid (ASA), and phenolic compounds indicated different reactions in response to desiccation stress. ASA levels decreased during desiccation to a similar degree in both the S and R variants. A significant decrease of total phenols was observed in R variant, which coincided with a significant increase of guaiacol peroxidase (POX) activity. α-Tocopherol content was significantly higher in the embryonic axes of seeds subjected to rapid drying. The activities of the enzymatic scavengers APX and GR had similar runs and were slightly higher in R variant. The activities of POX and SOD were significantly higher in the embryonic axes of seeds subjected to rapid drying. These results show that rapid dehydration of Q. robur seeds leads to the greater mobilization of antioxidant system in embryonic axes, particularly increased levels of α-tocopherol and POX and SOD activities, in the first stages of water loss. This mobilization has a greater impact on maintenance of higher viability of seeds after drying to lower level of WC.     

Reactive oxygen species,ABA and nitric oxide interactions on the germination of warm-season C<Subscript>4</Subscript>-grasses

Hydrogen peroxide (H₂O₂) as a source of reactive oxygen species (ROS) significantly stimulated germination of switchgrass (Panicum virgatum L.) seeds with an optimal concentration of 20 mM at both 25 and 35°C. For non-dormant switchgrass seeds exhibiting different levels of germination, treatment with H₂O₂ resulted in rapid germination (<3 days) of all germinable seeds as compared to seeds placed on water. Exposure to 20 mM H₂O₂ elicited simultaneous growth of the root and shoot system, resulting in more uniform seedling development. Seeds of big bluestem (Andropogon gerardii Vitman) and indiangrass [Sorghastrum nutans (L.) Nash] also responded positively to H₂O₂ treatment, indicating the universality of the effect of H₂O₂ on seed germination in warm-season prairie grasses. For switchgrass seeds, abscisic acid (ABA) and the NADPH-oxidase inhibitor, diphenyleneiodonium (DPI) at 20 μM retarded germination (radicle emergence), stunted root growth and partially inhibited NADPH-oxidase activity in seeds. H₂O₂ reversed the inhibitory effects of DPI and ABA on germination and coleoptile elongation, but did not overcome DPI inhibition of root elongation. Treatment with H₂O₂ appeared to enhance endogenous production of nitric oxide, and a scavenger of nitric oxide abolished the peroxide-responsive stimulation of switchgrass seed germination. The activities and levels of several proteins changed earlier in seeds imbibed on H₂O₂ as compared to seeds maintained on water or on ABA. These data demonstrate that seed germination of warm-season grasses is significantly responsive to oxidative conditions and highlights the complex interplay between seed redox status, ABA, ROS and NO in this system.     

Proanthocyanidins accelerate the germination of cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) seeds

Proanthocyanidins (PAs) are the end products of the flavonoid biosynthetic pathway in many seeds, but their biological function is rarely unknown during seed germination. In the present study, we observed that PAs pretreatment accelerated cucumber seeds germination with maximum efficiency at 0.15% by measuring germination percentage and radical length. Using inhibitors of abscisic acid (ABA), gibberellins (GA) and alternative oxidase (AOX) and H₂O₂ scavenger pretreatment and gene expression analysis, we found that the accelerated effect of 0.15% PAs on seed germination was due to the decreased ABA biogenesis and enhanced GA production. ROS are induced by PAs pretreatment. Then, the enhanced ROS contributed to GA and ethylene accumulation and ABA decrease in seeds. Moreover, the improvement of GA was involved in the further induction of antioxidant enzymes activities. Therefore, our findings uncover a novel role of PAs in seed germination and clarify the relationships between ROS, ABA, GA and ethylene during seed germination.     

Antioxidative response of ascorbate-glutathione pathway enzymes and metabolites to desiccation of recalcitrant Acer saccharinum seeds

Ascorbate–glutathione systems were studied during desiccation of recalcitrant seeds of the silver maple (Acer saccharinum L.). The desiccated seeds gradually lost their germination capacity and this was strongly correlated with an increase in electrolyte leakage from seeds. Simultaneously the increase of reactive oxygen species (ROS) (superoxide radical – O₂⁻ and hydrogen peroxide – H₂O₂) production was observed. The results indicate that remarkable changes in the concentrations and redox status of ascorbate and glutathione occur in embryo axes and cotyledons. After shedding, concentrations of ascorbic acid (ASA) and the reduced form of glutathione (GSH) are higher in embryo axes than in cotyledons and their redox status is high in both embryo parts. Cotyledons in freshly shed seeds are devoid of GSH. At the first stages of desiccation, up to a level of 43% of moisture content, ASA content in embryo axes and GSH content in cotyledons increased. Below this level of moisture content, the antioxidant contents as well as their redox status rapidly decreased. The enzymes of the ascorbate–glutathione pathway: ascorbate peroxidase (APX) (EC 1.11.1.11), monodehydroascorbate reductase (MR) (EC 1.6.5.4), dehydroascorbate reductase (DHAR) (EC 1.8.5.1) and glutathione reductase (GR) (EC 1.6.4.2) increased their activity during desiccation, but mainly in embryonic axes. The changes are probably required for counteracting the production of ROS during desiccation. The relationship between ascorbate and glutathione metabolism and their relevance during desiccation of recalcitrant Acer saccharinum seeds is discussed.     

Ce^3+和La^3+对人工老化沙葱种子活力及生理特性的影响

以未老化和人工老化后的沙葱(Allium mongolicum Regel.)种子为材料,采用氯化铈(Ce3+)和氯化镧(La3+)浸种,测定种子萌发和生理指标,探讨Ce3+和La3+浸种对种子萌发、老化种子活力和生理特性的影响。结果显示:(1)在老化0~5 h时,Ce3+和La3+处理可显著促进沙葱种子萌发,提高种子活力;在老化5 h后,Ce3+和La3+处理对种子萌发无明显促进作用。(2)在老化0~15 h时,Ce3+和La3+处理的沙葱种子中抗氧化酶活性和抗坏血酸(AsA)含量提高,其超氧阴离子自由基(O2-·)产生速率、过氧化氢(H2O2)含量和丙二醛(MDA)含量显著降低;在老化15 h后,Ce3+和La3+处理的种子抗氧化酶活性提高、AsA含量降低,O2-·产生速率和MDA含量提高。(3)在老化5 h时,沙葱种子呼吸速率发生跃变达到最大,Ce3+和La3+处理显著降低了种子呼吸速率。(4)Ce3+和La3+处理在老化0~5 h时提高了沙葱种子超弱发光(UWL)强度,但在老化5 h后沙葱种子的UWL强度降低。研究认为,在沙葱种子人工老化初期,Ce3+和La3+浸种处理可以诱导增强种子抗氧化酶活性和提高AsA含量,有效清除因老化产生积累的过量活性氧(ROS),减轻过氧化伤害,提高种子活力;种子老化中后期,其内部ROS产生与清除系统发生紊乱,加剧了ROS对种子结构的损伤,Ce3+和La3+浸种处理的缓解效应丧失。     

Hydrogen peroxide scavenging regulates germination ability during wheat (Triticum aestivum L.) seed maturation

Hydrogen peroxide (H₂O₂) promotes seed germination of cereal plants and ascorbic acid which acts as antioxidant suppresses the germination of wheat seeds, but the role of H₂O₂ scavenging on germination during seed maturation has not been demonstrated. We investigated relationship of germination, ascorbate, H₂O₂ scavenging enzymes and sensitivity to ascorbic acid (AsA) maturing seeds of two typical wheat (Triticum aestivum L.) cultivars, cvs. Shirogane-Komugi and Norin61. Shirogane-Komugi had marked high germination ability than Norin61 during seed maturation. Although the H₂O₂ content had no difference in the two culti-vars, sensitivity to AsA of Norin61 seeds was higher than that of Shirogane-Komugi seeds during seed maturation. The sensitivity to AsA closely correlated with germination characteristic in the two cultivars. Especially, at 28 days after pollination (DAP), sensitivity to AsA in Norin61 seeds was remarkably high. At that stage, no significant differences were observed in endogenous AsA level, ascorbate peroxidase (APX, EC 1.11.1.11) and dehydroascorbate reductase (DHAR, EC 1.8.5.1) activities in the two cultivars. However, catalase (CAT, EC 1.11.1.6) activity and CAT mRNA in Norin61 were remarkably higher than in Shirogane-Komugi. Sensitivity to AsA at 35 and 42 DAPs kept high levels in Norin61, and endogenous AsA and CAT activity in the seeds were significantly higher than in Shirogane-Komugi. These results revealed a direct correlation between germination and antioxidant sensitivity during the developmental stages of wheat seeds.Key words: ascorbic acid, germination, hydorogen peroxide, maturation, wheat seed     

Active oxygen species metabolism in neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) seeds exposed to natural ageing and controlled deterioration

Success of ex situ storage of germplasm for trade and conservation essentially depends upon the precision of the protocol employed for the assessment of germination potential. Active oxygen species and antioxidative enzymes during natural ageing (NA) and controlled deterioration (CD) was monitored during the loss of seed vigour and germination potential in neem seeds showing intermediate seed storage behaviour. Higher levels of SOD, CAT and APX were strongly and positively associated with germination and vigour. The loss of CAT and APX activity estimated quantitatively and number of isoenzymes were closely accompanied with the simultaneous increase in the amounts of H₂O₂ and OH-radical. The decline in germination and vigour was negatively related with the levels of H₂O₂ and OH-radical and enhanced electrolyte leakage. The amounts of OH-radical were positively correlated with the decline in DNA content and DNA damage. The levels of SOD isoenzymes initially increased as the germination index of seeds declined from 5250 to 762 and 882 under NA and CD conditions, respectively. Increasing activity of SOD in the ageing seeds were associated with the accumulation of H₂O₂. The role of antioxidative enzymes in maintaining signalling and damaging amounts of AOS as well as revelations of different pathways of ageing during NA and CD in the ageing neem seeds were discussed.     

Dormancy removal of apple seeds by cold stratification is associated with fluctuation in H2O2, NO production and protein carbonylation level

Reactive oxygen (ROS) and nitrogen (RNS) species play a signaling role in seed dormancy alleviation and germination. Their action may be described by the oxidative/nitrosative “window/door”. ROS accumulation in embryos could lead to oxidative modification of protein through carbonylation. Mature apple (Malus domestica Borkh.) seeds are dormant and do not germinate. Their dormancy may be overcome by 70–90 days long cold stratification. The aim of this work was to analyze the relationship between germinability of embryos isolated from cold (5 °C) or warm (25 °C) stratified apple seeds and ROS or nitric oxide (NO) production and accumulation of protein carbonyl groups. A biphasic pattern of variation in H₂O₂ concentration in the embryos during cold stratification was detected. H₂O₂ content increased markedly after 7 days of seeds imbibition at 5 °C. After an additional two months of cold stratification, the H₂O₂ concentration in embryos reached the maximum. NO production by the embryos was low during entire period of stratification, but increased significantly in germination sensu stricto (i.e. phase II of the germination process). The highest content of protein carbonyl groups was detected after 6 weeks of cold stratification treatment. Fluctuation of H₂O₂ and protein carbonylation seems to play a pivotal role in seed dormancy alleviation by cold stratification, while NO appears to be necessary for seed germination.     

Dynamics of Water and Abscisic Acid During Embryogeny and Embryo Drying in the Recalcitrant Seeds of Vateria indica L.

Vateria indica L. is a critically endangered tree species in South-Western Ghats of India, commercially exploited for its valuable resins. Seed recalcitrance is a major problem hindering the natural regeneration of this species and it poses a great challenge in seed storage and conservation. There was a continuous import of water from the maternal tissues to seed tissues till maturity and the seeds were released in a fully hydrated state. Differential accumulation of water has been noticed in the cotyledons and embryonal axis. There was a positive correlation between seed moisture content and rate of germination which is a character of recalcitrant seeds. The critical moisture content was found to be 40% in the axis and 23.5% in the cotyledons, below which the embryo will not germinate. Loss of germination ability as a result of desiccation was attributed to the cell membrane damage, expressed as the electrolyte leakage exceeding 0.79 μS/cm. ABA peaked in the mid embryogenesis, then dropped drastically and maintained a lower level till seed maturity. On desiccation, ABA started to increase but gradually dropped down. Both cotyledons and embryonal axis had differential ABA content but exhibited a general pattern of ABA level during embryogeny. Due to the thin seed coat/embryo ratio and low investment in the seed coat, this recalcitrant seed could not hold water as efficient as orthodox seeds. Thus, it germinated as soon as it was shed from the mother plant. On desiccation, ABA shot up and moisture content decreased along with electrolyte leakage and cell membrane damage. All these hindered germination of the seed. Thus, we can see a clear interplay between moisture content and ABA levels during embryogeny and desiccation. Since the seed biology of this species has not been well documented, the present work is mainly intended to study the dynamics of water and ABA during embryogeny and embryo drying. This study can surely contribute to the long-term storage and conservation of recalcitrant seeds which is a less explored area.

     

Investigating seed dormancy in cotton (Gossypium hirsutum L.): understanding the physiological changes in embryo during after‐ripening and germination

• The dormancy of seeds of upland cotton can be broken during dry after‐ripening, but the mechanism of its dormancy release remains unclear.
• Freshly harvested cotton seeds were subjected to after‐ripening for 180 days. Cotton seeds from different days of after‐ripening (DAR) were sampled for dynamic physiological determination and germination tests. The intact seeds and isolated embryos were germinated to assess effects of the seed coat on embryo germination. Content of H₂O₂ and phytohormones and activities of antioxidant enzymes and glucose‐6‐phosphate dehydrogenase were measured during after‐ripening and germination.
• Germination of intact seeds increased from 7% upon harvest to 96% at 30 DAR, while embryo germination improved from an initial rate of 82% to 100% after 14 DAR. Based on T₅₀ (time when 50% of seeds germinate) and germination index, the intact seed and isolated embryo needed 30 and 21 DAR, respectively, to acquire relatively stable germination. The content of H₂O₂ increased during after‐ripening and continued to increase within the first few hours of imbibition, along with a decrease in abscisic acid (ABA) content. A noticeable increase was observed in gibberellic acid content during germination when ABA content decreased to a lower level. Coat removal treatment accelerated embryo absorption of water, which further improved the accumulation of H₂O₂ and changed peroxidase content during germination.
• For cotton seed, the alleviation of coat‐imposed dormancy required 30 days of after‐ripening, accompanied by rapid dormancy release (within 21 DAR) in naked embryos. H₂O₂ acted as a core link between the response to environmental changes and induction of other physiological changes for breaking seed dormancy.

     

Ecological significance of seed desiccation sensitivity in Quercus ilex

Background and Aims

Several widespread tree species of temperate forests, such as species of the genus Quercus, produce recalcitrant (desiccation-sensitive) seeds. However, the ecological significance of seed desiccation sensitivity in temperate regions is largely unknown. Do seeds of such species suffer from drying during the period when they remain on the soil, between shedding in autumn and the return of conditions required for germination in spring?

Methods

To test this hypothesis, the Mediterranean holm oak (Quercus ilex) forest was used as a model system. The relationships between the climate in winter, the characteristics of microhabitats, acorn morphological traits, and the water status and viability of seeds after winter were then investigated in 42 woodlands sampled over the entire French distribution of the species.

Key Results

The percentages of germination and normal seedling development were tightly linked to the water content of seeds after the winter period, revealing that in situ desiccation is a major cause of mortality. The homogeneity of seed response to drying suggests that neither intraspecific genetic variation nor environmental conditions had a significant impact on the level of desiccation sensitivity of seeds. In contrast, the water and viability status of seeds at the time of collection were dramatically influenced by cumulative rainfall and maximum temperatures during winter. A significant effect of shade and of the type of soil cover was also evidenced.

Conclusions

The findings establish that seed desiccation sensitivity is a key functional trait which may influence the success of recruitment in temperate recalcitrant seed species. Considering that most models of climate change predict changes in rainfall and temperature in the Mediterranean basin, the present work could help foresee changes in the distribution of Q. ilex and other oak species, and hence plant community alterations.     

Homeohydrous (Recalcitrant) Seeds: Dehydration, the State of Water and Viability Characteristics in Landolphia kirkii

Differential scanning calorimetry was used to study the relationships among drying rate, desiccation sensitivity, and the properties of water in homeohydrous (recalcitrant) seeds of Landolphia kirkii. Slow drying of intact seeds to axis moisture contents of approximately 0.9 to 0.7 gram/gram caused lethal damage, whereas very rapid (flash) drying of excised embryonic axes permitted removal of water to approximately 0.3 gram/gram. The amount of nonfreezable water in embryonic axes (0.28 gram H₂O/gram dry mass) did not change with drying rate and was similar to that of desiccation-tolerant seeds. These results suggest that the amount of nonfreezable water per se is not an important factor in desiccation sensitivity. However, flash drying that removed all freezable water damaged embryonic axes. Differences between desiccation-sensitive and -tolerant seeds occur at two levels: (a) tolerant seeds naturally lose freezable water, and sensitive seeds can lose this water without obvious damage only if it is removed very rapidly; (b) tolerant seeds can withstand the loss of a substantial proportion of nonfreezable water, whereas sensitive seeds are damaged if nonfreezable water is removed.     

Desiccation sensitivity and successful cryopreservation of oil seeds of European hazelnut (Corylus avellana)

The sensitivity of a Polish provenance of dormant Corylus avellana seeds to extreme desiccation and cryopreservation in liquid nitrogen (LN, ?196°C) was investigated. No sensitivity to desiccation was observed as seeds readily germinated and exhibited seedling emergence, even when the critical water content (WC) of seeds (nuts devoid of pericarp) was reduced to 0.027 g H₂O/g dry mass, g g^?1 by drying. Results of germination and seedling emergence tests indicated that seeds tolerated cooling in LN when desiccated to a WC in the range of 0.05–0.10 and 0.08–0.10 g g^?1, respectively. The results of this study demonstrate the feasibility of long‐term cryopreservation of European hazelnut seeds. As the seeds of this species have been classified in several different categories (orthodox, suborthodox and recalcitrant), based on their response to desiccation and low temperature, the assignment of the seeds of hazelnut to a specific category is provided and discussed.     

外源H2O2对盐胁迫下小白菜种子萌发和幼苗生理特性的影响

以小白菜"甜脆青"为试材,研究不同浓度（5、10、25、50和100 mmol/L）过氧化氢（H₂O₂）浸种处理对100 mmol/L NaCl胁迫下小白菜（Brassica chinensis L.）种子萌发、幼苗生长及生理特性的影响。结果表明：100 mmol/L NaCl胁迫明显抑制小白菜种子的萌发状况和幼苗生长,发芽势、发芽指数、活力指数及幼苗根和芽长度和鲜重均明显降低,根和芽中CAT的活性及K⁺含量明显受到抑制,渗透调节物质、活性氧和MDA含量显著增加。不同浓度H₂O₂浸种处理提高了NaCl胁迫下小白菜种子发芽势、发芽指数和活力指数,促进小白菜根和芽的生长,增强了NaCl胁迫下根和芽中SOD、CAT和APX的活性及K⁺含量,降低O₂^-·产生速率及H₂O₂和MDA含量,进一步促进脯氨酸和可溶性糖含量的增加,降低体内Na⁺含量。其中以10 mmol/L H₂O₂处理缓解盐胁迫效果最好,明显缓解NaCl胁迫对小白菜种子萌发和幼苗生长的抑制。     

Seed storage in polyethylene bags of a recalcitrant species (Quercus ilex): analysis of some bio-energetic and oxidative parameters

Some technological and physiological aspects were analysed during seed storage of holm oak (Quercus ilex L.), a typical Mediterranean recalcitrant species. Considering the mild dormancy and desiccation sensitivity of these seeds, the influence of the storage environment on viability was examined. Acorns were maintained at low temperature and at high moisture content either inside thin polyethylene bags or mixed with peat in a bin. Storage in polyethylene bags, if compared with peat treatment, maintained optimal seed quality parameters. The effects of the two treatments on some physiological parameters were analysed during 1-year seed storage. Acorns stored in a bin with peat started to germinate early and exhibited a more rapid seed deterioration caused by metabolism-linked oxidative damage. The latter phenomenon was linked to a higher respiration and H₂O₂ level, induction of catalase activity, as well as lowered glutathione pool and ATP content. In addition, a more oxidized redox poise was observed. On the contrary, the plastic film of polyethylene, limiting gaseous exchanges, maintained acorn metabolic activity at low levels and allowed the accumulation of ethylene inside the storage atmosphere. These factors, inducing a dormant-like state, could have played a crucial role in prolonging seed storage.     

Storage elicits a fast antioxidant enzyme activity in <Emphasis Type="Italic">Araucaria angustifolia</Emphasis> embryos

Storage of recalcitrant seeds leads to the initiation of subcellular damage or to the initiation of germination process, and both may result in viability loss. This study aimed to elucidate the biochemical basis of embryos survival of Araucaria angustifolia recalcitrant seeds during storage. After harvesting, seeds were stored at ambient conditions (without temperature and humidity control) and in a cold chamber (temperature of 10 ± 3 °C, and relative humidity of 45 ± 5 %). Moisture content, viability, H₂O₂ content, lipid peroxidation, protein content, and activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), at 0, 15, 45 and 90 days of storage, were evaluated. Seed viability reduced about 40 % during the storage period accompanied by a reduction in soluble protein (about 64 % of reduction) in both storage conditions, and increased lipid peroxidation (about 115 % and 66 % for ambient and cold chamber conditions, respectively). H₂O₂ content used as a marker of oxidative stress was reduced during the period, possibly controlled by the action of CAT and APX, for which increased activities were observed. The results allowed the identification of seven SOD isoenzymes (one Mn-SOD, five Fe-SOD and one Cu/Zn-SOD), whose activities also increased in response to storage. Some biochemical damage resulting from storage was observed, but viability reduction was not due to failure of enzymatic protection mechanisms.     

GABA Enhances Thermotolerance of Seeds Germination by Attenuating the ROS Damage in Arabidopsis

Seeds germination is strictly controlled by environment factor such as high temperature (HT) through altering the balance between gibberellin acid (GA) and abscisic acid (ABA). Gama-aminobutyric acid (GABA) is a small molecule with four-carbon amino acid, which plays a crucial role during plant physiological process associated with pollination, wounding or abiotic stress, but its role in seeds germination under HT remains elusive. In this study we found that HT induced the overaccumulation of ROS, mainly H₂O₂ and O₂^- , to suppress seeds germination, meanwhile, HT also activated the enzyme activity of GAD for the rapid accumulation of GABA, hinting the regulatory function of GABA in controlling seeds germination against HT stress. Applying GABA directly attenuated HT-induced ROS accumulation, upregulated GA biosynthesis and downregulated ABA biosynthesis, ultimately enhanced seeds germination. Consistently, genetic analysis using the gad1/2 mutant defective in GABA biosynthesis, or pop2-5 mutant with high endogenous GABA content supported the potential function of GABA in improving seeds germination tolerance to HT through scavenging ROS overaccumulation. Based on these data, we propose that GABA acts as a novel signal to enhance thermotolerance of seeds germination through alleviating the ROS damage to seeds viability.