Molecular genetic characterization of rice seed lipoxygenase 3 and assessment of its effects on seed longevity

Lipoxygenases (LOXs) are enzymes involved in lipid peroxidation. Here we reported the identification, molecular and functional characterization of the gene encoding rice (Oryza sativa L.) seed LOX3 (sLOX3). Via a map-based cloning strategy we identified Os03g0700400 as the candidate gene encoding sLOX3. Further functional complementary test and biochemical characterization of the recombinant Os03g0700400 protein verified the identification. The sLOX3 gene was highly expressed in roots, moderately in embryos and very weakly in leaves, leaf sheaths and stems. Transient expression experiment (in rice protoplasts) and subsequent laser confocal microscopic analysis demonstrated that the sLOX3 protein was localized into the cytosol. We next showed that overexpression of sLOX3 in a japonica sLOX3-normal rice cultivar, Wuyunjing 7 accelerated the decrease of seed germination ability when the seeds were routinely stored, which demonstrated that sLOX3 had a negative effect on seed longevity (storability). Meanwhile, an increased occurrence of embryo decay was observed in the same transgenic seeds, suggesting that sLOX3 might negatively affect seed longevity by facilitating colonization of particular seed pathogens. Our result forwarded the understanding of the effects of 9-LOX on rice seed longevity.     

Association analysis of seed longevity in rice under conventional and high-temperature germination conditions

Seed longevity varies considerably in cultivated rice, but the underlying mechanism of longevity is not well understood. To measure seed longevity, we performed an aging treatment at 45 °C on seeds maintained at 14 % moisture content for 14 days. We measured the percentage germination of both treated and normal seeds at 25 °C as a control of seed longevity using four replications over 2 years. In total, 140 accessions from a core collection with diverse origins were genotyped using 204 SSR markers, which distributed into 12 chromosomes, to identify marker–trait associations with seed longevity. An analysis of the population structure revealed four subgroups. The r ² values ranged from 0.0 to 0.8901 for all intrachromosomal loci pairs, with an average of 0.0773. Linkage disequilibrium (LD) between linked markers decreased with distance and displayed a substantial drop in LD decay values between 20 and 50 cM. Marker–trait associations were investigated using a mixed linear model approach, considering both population structure (Q) and kinship (K). Twelve marker–trait associations (P < 0.01) were common between the two germination treatments and over the 2-year study, explaining more than 10 % of the total variation. These ten different markers were distributed on five chromosomes. The significant associated SSR markers identified will be useful to seed-bank managers to ensure collections are maintained at high levels of viability to avoid loss of genotypes from the population and for marker-assisted selection.     

1,2,4-三氯苯对水稻种子萌发及幼苗生长的毒性机理

以水稻为试材,采用水培方法研究了1,2,4-三氯苯(1,2,4-TCB)对水稻种子萌发、幼苗生长、叶绿素含量、蛋白质含量、脯氨酸含量、细胞膜通透性的影响.结果表明,水稻种子的萌发率和活力指数随1,2,4-TCB处理浓度的升高而逐渐降低,呈现一定的浓度-效应关系,高浓度(80和100 mg·L^-1) 1,2,4-TCB处理组水稻种子的活力指数仅为对照组的7. 89％和1.92％,水稻幼苗的株高和根长均受到抑制,表现出一定的浓度-效应和时间-效应关系.水稻叶片的叶绿素a、叶绿素b、总叶绿素和蛋白质含量均随1,2,4-TCB浓度的升高而降低.水稻叶片游离脯氨酸含量和细胞膜的通透性随处理浓度的升高而增加.当1,2,4-TCB处理浓度＞15 mg·L^-1时,游离脯氨酸含量和叶片细胞膜的通透性急剧增加,与对照组相比各组差异均显著(P＜0.01).这表明1,2,4-TCB对水稻幼苗的损伤是一个复杂的过程,其机理可能与1,2,4-TCB使植物细胞膜、细胞内蛋白质和细胞器结构和功能损伤有关.     

Influence of the testa on seed dormancy, germination, and longevity in Arabidopsis

The testa of higher plant seeds protects the embryo against adverse environmental conditions. Its role is assumed mainly by controlling germination through dormancy imposition and by limiting the detrimental activity of physical and biological agents during seed storage. To analyze the function of the testa in the model plant Arabidopsis, we compared mutants affected in testa pigmentation and/or structure for dormancy, germination, and storability. The seeds of most mutants exhibited reduced dormancy. Moreover, unlike wild-type testas, mutant testas were permeable to tetrazolium salts. These altered dormancy and tetrazolium uptake properties were related to defects in the pigmentation of the endothelium and its neighboring crushed parenchymatic layers, as determined by vanillin staining and microscopic observations. Structural aberrations such as missing layers or a modified epidermal layer in specific mutants also affected dormancy levels and permeability to tetrazolium. Both structural and pigmentation mutants deteriorated faster than the wild types during natural aging at room temperature, with structural mutants being the most strongly affected.     

镉对水稻种子萌发的影响

以不同类型的319个水稻品种为研究对象,研究了10 mg·L^-1 Cd²⁺处理对水稻种子萌发的影响.结果表明:Cd²⁺对种子发芽率影响较小,对根系生长的影响显著,且大于对芽生长的影响;不同类型水稻种子萌发对Cd的响应差异较大,敏感顺序为粳稻>籼稻>杂交稻;两系不育系根系长度和根系数量受Cd的抑制程度显著高于三系.应用快速聚类方法,可以将参试品种划分为耐受型、中间型和敏感型3种不同的敏感类型.     

Study on the mechanism of cerium nitrate effects on germination of aged rice seed

Attempts were made to promote germination of naturally and artificially aged rice seeds by treating them with cerium nitrate. The germination rate, germination index, and vigor index of aged rice seed were significantly increased by cerium. It was because the treatments of aged rice seed with cerium nitrate enhanced respiratory rate and activities of superoxide dismutase, catalase, and peroxidase, and decreased superoxide O₂ ⁻ and malondialdehyde contents that plasma membrane permeability was reduced. It was suggested that cerium be used for the seed treatment before sowing.     

Study of lanthanum on seed germination and growth of rice

A study of lanthanum nitrate on the seed germination and the growth of rice was conducted. The results of this experiment indicate that soaking in a proper concentration of La(NO3)3 could accelerate the germination of the rice seeds, significantly increase seed vigor and chlorophyll contents, and improve root growth. Because during the soaking stage with La(NO3)3 the absorbed water and imbibition process of the rice seeds was quickened, the plasma membrane permeability of the seeds was increased, O2 and H2O were easier to get into the cell, and the respiratory rate was enhanced. During the germination stage, La(NO3)3 could enhance the activities of alpha-amylase, proteinase, lipase, and other hydrolytic enzymes and the contents of plant hormones, such as IAA, GAs, CTK, and so forth, except ABA contents, changed little.     

Effect of lanthanum on aged seed germination of rice

Attempts were made to promote germination of natural aged rice seeds by treating them with lanthanum nitrate. In tests to measure the germination rate, germination index, and vigor index of natural aged rice seeds were found to be significantly increased by lanthanum. It is treating aged rice seed with lanthanum nitrate that enhanced the respiratory rate and activities of superoxide dismutase, catalase, and peroxidase, and decreased superoxide and malondidehyde contents, and therefore reduced plasma membrane permeability. It suggests that lanthanum may be used to pretreat seed before sowing.     

酸雨胁迫对水稻萌发过程中生理代谢影响的初探

为了探索酸雨对水稻种子萌发时能量代谢的动态影响,以pH 2.5、4.0的模拟酸雨处理水稻(宁粳1号)种子,研究酸雨胁迫对水稻种子呼吸速率,CAT(过氧化氢酶)活性,线粒体蛋白与ATP含量及能荷(EC)的动态影响.结果 显示酸雨持续胁迫7 d,随时间延长,酸雨胁迫下各指标均发生变化:种子呼吸作用先升后降,在第4天达到呼吸顶峰;CAT活性和线粒体蛋白含量均呈上升趋势最后趋于平稳;ATP含量及EC水平先急剧上升,第5天达到最高值后有所下降.     

Priming of field-sown rice seed enhances germination, seedling establishment, allometry and yield

Poor seedling establishment is a major deterrent in adopting direct seeding of rice. Seed priming to obtain better crop stand could be an attractive approach. The objective of this study was to determine the effectiveness of seed priming strategies on the improved agronomic characters of direct-sown rice. Seed priming strategies were: hydropriming for 48 h, osmohardening with KCl or CaCl₂ for 24 h, ascorbate priming for 48 h and seed hardening for 24 h, pre-germination (traditional soaking for nursery raising) and untreated control. Seed priming improved germination and emergence, allometry, kernel yield, and its quality, whilst pre-germination displayed poor and erratic emergence of seedling followed by poor plant performance. Faster and uniform emergence was due to improved α-amylase activity, which increased the level of soluble sugars in the primed kernels. Osmohardening with KCl gave greater kernel and straw yield and harvest index, followed by that of CaCl₂, hardening and ascorbate priming. Improved yield was attributed principally to number of fertile tillers and 1000 kernel weight. A positive correlation between mean emergence time and days to heading, while a negative one between kernel yield and harvest index suggested long-term effects of seed priming on plant growth and development. The results suggest that physiological changes produced by osmohardening enhanced the starch hydrolysis and made more sugars available for embryo growth, vigorous seedling production and, later on, improved allometric, kernel yield and quality attributes.     

镧浸种对水稻种子萌发及幼苗生长的影响

以水稻种子为材料,研究了稀土元素镧对水稻种子活力和幼苗生长的影响。结果表明,1~20mg.L-1La3+处理能提高水稻种子的活力,提高蛋白酶、淀粉酶和脂肪酶的活性,并能促进水稻茎、叶和根系的生长,其中10mg.L-1La3+处理效果最佳。当浓度超过30mg.L-1时,水稻种子萌发和幼苗生长受到抑制。此外,镧对水稻植株地下部分(根系)生长的影响比地上部分(茎叶)生长的影响要明显。镧对水稻种子萌发期间3种酶活性的影响程度表现为蛋白酶>脂肪酶>淀粉酶。     

Light, salinity, and temperature effects on the seed germination of perennial grasses

The germination requirements of four perennial halophytic grasses, Aeluropus lagopoides, Halopyrum mucronatum, Sporobolus ioclados, and Urochondra setulosa, were studied under control conditions in the laboratory. Treatments included two light levels (12?:?12 h light?:?dark period and 24-h dark environment), six salinity concentrations (0, 100, 200, 300, 400, and 500 mmol/L NaCl), and four temperature regimes (fluctuating day?:?night temperature regimes of 10°?:?20°, 15°?:?25°, 20°?:?30° and 25°?:?35°C), using a completely randomized block design. Best seed germination of all grasses was obtained in a distilled water control. Increase in salinity progressively inhibited germination of all species. For example, few seeds of H. mucronatum germinated above 300 mmol/L NaCl, while seeds of the other grasses germinated in up to 500 mmol/L NaCl. Optimal temperature regime for germination for all species was 20°?:?30°C both for light- and dark-germinated seeds. At higher temperatures differences between light and dark treatments were not significant. Absence of light had no effect on the seed germination of U. setulosa and H. mucronatum; however, germination was lower in all salinity treatments. In the case of A. lagopoides, absence of light substantially inhibited the germination both in control and saline conditions. The light effect was marked in the case of S. ioclados, which showed very low germination in the absence of light both under saline and nonsaline conditions.     

Toxic effects of nanoparticles on bioluminescence activity,seed germination,and gene mutation

The potential environmental toxicities of several metal oxide nanoparticles (NPs; CuO, TiO₂, NiO, Fe₂O₃, ZnO, and Co₃O₄) were evaluated in the context of bioluminescence activity, seed germination, and bacterial gene mutation. The bioassays exhibited different sensitivities, i.e., each kind of NP exhibited a different level of toxicity in each of the bioassays. However, with a few exceptions, CuO and ZnO NPs had most toxic for germination of Lactuca seed (EC₅₀ 0.46 mg CuO/l) and bioluminescence (EC₅₀ 1.05 mg ZnO/l). Three NPs (Co₃O₄, TiO₂, and Fe₂O₃) among all tested concentrations (max. 1,000 mg/l) showed no inhibitory effects on the tested organisms, except for Co₃O₄ NPs on bioluminescence activity (EC₅₀ 62.04 mg/l). The sensitivity of Lactuca seeds was greater than that of Raphanus seeds (EC₅₀ 0.46 mg CuO/l versus 26.84 mg CuO /l ). The ranking of metal toxicity levels on bioluminescence was in the order of ZnO?>?CuO?>?Co₃O₄?>?NiO?>?Fe₂O₃, TiO₂, while CuO?>?ZnO?>?NiO?>?Co₃O₄, Fe₂O₃, TiO₂ on germination. No revertant mutagenic ratio (greater than 2.0) of Salmonella typhimurium TA 98 was observed under any tested condition. These findings demonstrate that several bioassays, as opposed to any single one, are needed for the accurate assessment of NP toxicity on ecosystems.     

Influence and interaction of iron and lead on seed germination in upland rice

Plant and Soil - This study investigated whether soil chemistry act as abiotic drivers of Myrtaceae assemblages, and also investigated the occurrence of indicator species. We first characterize the...     

Inhibitory effects of monoterpenes on seed germination and seedling growth

Monoterpenes, the chemical constituents of essential oils found in plants, are known biologically active compounds. The present study was conducted to investigate the inhibitory effects of 30 monoterpenes including monoterpene hydrocarbons and oxygenated monoterpenes on seed germination and seedling growth of Amaranthus retroflexus, Chenopodium album and Rumex crispus under laboratory conditions. The monoterpenes were applied at contents of 10 and 20 microl for liquid compounds and 10 and 20 microg for solid compounds. The results show that most of the monoterpenes significantly inhibited seed germination and seedling growth of the tested plants. Oxygenated monoterpenes including beta-citronellol, nerol and terpinen-4-ol completely inhibited seed germination and seedling growth of all tested plants. Their inhibitory effects were also stronger than that of the herbicide 2,4-D. In general, monoterpenes were less effective against seed germination and seedling growth of C. album as compared with R. crispus and A. retroflexus. Phytotoxic effects of monoterpene hydrocarbons were found to be lower than those of oxygenated monoterpenes. The alcohol derivatives of oxygenated monoterpenes were also found to be more phytotoxic as compared with their acetate derivatives. Based on the present results, it can be concluded that the oxygenated monoterpenes can be used as potential bio-herbicides.     

Vitamin E is essential for seed longevity and for preventing lipid peroxidation during germination

Tocopherols (vitamin E) are lipophilic antioxidants synthesized by all plants and are particularly abundant in seeds. Despite cloning of the complete suite of tocopherol biosynthetic enzymes and successful engineering of the tocopherol content and composition of Arabidopsis thaliana leaves and seeds, the functions of tocopherols in plants have remained elusive. To address this issue, we have isolated and characterized two VITAMIN E loci (VTE1 and VTE2) in Arabidopsis that when mutated result in tocopherol deficiency in all tissues. vte1 disrupts tocopherol cyclase activity and accumulates a redox-active biosynthetic intermediate, whereas vte2 disrupts homogentisate phytyl transferase activity and does not accumulate pathway intermediates. Mutations at either locus cause significantly reduced seed longevity compared with the wild type, indicating a critical role for tocopherols in maintaining viability during quiescence. However, only vte2 mutants exhibited severe seedling growth defects during germination and contained levels of lipid hydroperoxides and hydroxy fatty acids elevated up to 4- and 100-fold, respectively, relative to the wild type. These data demonstrate that a primary function of tocopherols in plants is to limit nonenzymatic lipid oxidation during seed storage, germination, and early seedling development. The vte mutant phenotypes also explain the strong selection for retention of tocopherol biosynthesis during the evolution of seed-bearing plants.