Inhibition of seed germination by extracts of bitter Hawkesbury watermelon containing cucurbitacin, a feeding stimulant for corn rootworm (Coleoptera: Chrysomelidae)

Cucurbitacins are feeding stimulants for corn rootworm used in baits to control the adults of this insect pest. Corn rootworm larvae also feed compulsively on cucurbitacins. Cucurbitacins are reported to be gibberellin antagonists that may preclude their use as seed treatments for these soil-dwelling insects. The crude extract of a bitter Hawkesbury watermelon containing cucurbitacin E-glycoside significantly inhibited germination of watermelon, squash, and tomato seeds. Although the germination of corn seed was not significantly inhibited, root elongation was inhibited by crude extracts, but not by high-performance liquid chromatography-purified cucurbitacin E-glycoside. Therefore, the effects of the major components in the bitter watermelon extract (e.g., sugars) on seed germination and root elongation were determined. Pure sugars (glucose and fructose), at concentrations found in watermelon extract, mimicked the inhibition of seed germination and root elongation seen with the crude bitter Hawkesbury watermelon extract. Removal of these sugars may be necessary to use this extract as a bait for corn rootworm larvae as a seed or root treatment.     

Inhibition of Lettuce Seed Germination and Root Elongation by Derivatives of Auxin and Reversal by Derivatives of Cycocel

Lettuce seed germination or lettuce root elongation after germination in water was inhibited by 5.7 × 10^-6M indoleacetic acid (IAA) and designated other IAA derivatives. These IAA-inhibited growth responses were reversed by 10^-5 to 10^-6M Cycocel, (2-chloroethyl) trimethylammonium chloride, which alone was without effect. Only those Cycocel analogs, which have previously been shown to be active as plant growth retardants, were effective in reversing IAA inhibition of germination or root elongation. These results are consistent with the concept that Cycocel at low concentrations acts as an auxin antagonist. However. Cycocel did not reverse the inhibitory effects from indole-3-propionic acid or indole-3-butyric acid.     

不同工艺阶段味精废水对作物种子发芽和根伸长的毒性效应

为了对味精废水的污染进行全面的评价,针对不同工艺阶段排放的味精废水,采用小麦、白菜和西红柿等作物种子,以污水为环境介质,进行了种子发芽和根伸长的污染暴露实验,并结合污染现场,进行了相应的定量分析.结果表明,在高浓度原味精废母液中, 小麦种子的发芽抑制率和根伸长的抑制率与废水的浓度呈显著正相关.味精废水对3种作物种子的发芽和根伸长的毒性强弱顺序为：西红柿＞白菜＞小麦西红柿对味精废水毒性响应最为敏感,可以认为是一种较为理想的生物毒性指示作物.味精生产不同工艺阶段所排放的污水对这3种作物种子的发芽半抑制浓度(IC₅₀)为22.0～32432 mg·L^-1,对根伸长的半抑制浓度(IC₅₀)为17.3～3320 mg·L^-1.     

重金属对土壤中萝卜种子发芽与根伸长抑制的生态毒性

高等植物是生态系统中的基本组成部分。一个平衡、稳定的生态系统生产健康、优良的高等植物。反之 ,一个不稳定或受到外来污染的生态系统 ,对高等植物的生长可带来不利和可见的负面影响。因此 ,利用高等植物的生长状况监测土壤污染程度 ,是从生态学角度衡量土壤健康状况 ,评价土壤质量的重要方法之一[4 ,6] 1) 。土壤生态毒理学评价方法是对化学分析方法的重要补充。目前已建立的高等植物毒理试验有三种方法 ,即 1根伸长试验 ;2种子发芽试验 ;3早期植物幼苗生长试验[3 ,5,6,10 ] 。最初 ,这类试验主要用于纯化学品的毒性检验 ,但随着对土壤…     

Pre-germination effects on mechanically impeded root growth of barley (Hordeum vulgare L)

The effects of conditions pre-dating germination on growth rate of impeded barley cv. Harrington roots were measured using an agar-capillary tube technique. Seedling root tips were directed into glass capillary tubes twothirds filled with agar at eight concentrations ranging from 1.6 to 9.6%, equivalent to penetrometer resistances of 25 to 1240 kPa. The rate of unrestricted root elongation (growth in air) of seed stored for 13 months (old seed), and of seed grown for a second generation without subsequent storage (new seed) was compared with growth in agar over a 24-hour interval. Root elongation rate of old and new seed was identical in the absence of resistance. At low to intermediate agar concentrations, elongation was significantly slower in roots from old, compared with new seed. At high agar concentrations root growth of old and new seed was the same. In both old and new seed, root growth through agar was greater in seed that germinated after 24, compared with 48 h. Differences in impeded root growth between old and new seed were lost in progeny of the test seed. Environmental factors that pre-date germination are an important influence on the ability of seedling roots to elongate through soil.LRS Contribution no. 3879349LRS Contribution no. 3879349     

Dependence of Lettuce Seed Germination on Actinomycin D-resistant RNA Synthesis

The response of Grand Rapids lettuce half seed and intact seed to different nucleic acid and protein synthesis inhibitors was studied. 6-azauracil, 2-thiouracil and cycloheximide were strong inhibitors of germination of intact seed as well as of radicle elongation of half seed. Inhibition by 6-azauracil and 2-thiouracil was reversed by uracil but not by orotic acid, thymine or deoxycytidine. Actinomycin D and puromycin were ineffective suggesting that actinomycin D-resistant RNA synthesis possibly controls both germination of intact seed and radicle elongation of half seed. The requirements of RNA synthesis for the elongation of radicle in half seed in light and in the presence of gibberellic acid was the same. Such was not the case in the germination of intact seed which had different requirements of RNA synthesis in light and in presence of gibberellic acid. It is concluded that the mechanism of gibberellic acid and light in the intact seed germination, in so far as it involves the regulation of RNA synthesis, depends on the integrity of the seed coats.     

Reduced de-etiolation of hypocotyl growth in a tomato mutant is associated with hypersensitivity to, and high endogenous levels of, abscisic acid.

A recessive single gene mutant, 7B-1, in tomato was originally selected for its photoperiod-dependent male sterility. The 7B-1 mutant also has some pleiotropic effects including reduced light-induced inhibition, i.e. de-etiolation, of the hypocotyl in long days (LD), increased seed size and weight, and reduced transpiration rate. These traits led us to investigate the sensitivity of 7B-1 to exogenous hormones and the interaction of these responses with daylength. In LD, but not in short days (SD), 7B-1 was more sensitive than wild-type (WT) to exogenous abscisic acid (ABA) for inhibition of seed germination, root elongation and transpiration rate. 7B-1 mutant also exhibited reduced responses to exogenous gibberellin (GA(3)) for hypocotyl elongation, and to inhibitors of GA biosynthesis for seed germination and root and hypocotyl elongation. 7B-1 hypocotyls contained a higher level of endogenous ABA than WT in both photoperiods, although ABA levels were higher in LD than in SD. In contrast, growth-active GAs, i.e. GA(1), GA(3) and GA(4), and IAA were low in the mutant hypocotyls. The 7B-1 mutant appears to be an ABA-overproducer, and the photoperiod-regulated ABA levels may be responsible for the hypersensitivity of the mutant to exogenous ABA.     

Phytotoxicity of iron in relation to its solubility conditions and the effect of ionic strength

The effect of iron on root elongation and seed germination of Lactuca sativa was investigated within the limits of the plant's sensitivity to an acidic environment and iron solubility under experimental conditions. Because ionic strength was found to have phytotoxic effects, the same pH and ionic strength conditions were kept constant over the entire iron concentration range, so as to evaluate solely the effect of iron. 0.14 mM Fe³⁺ was found to be the lowest effective concentration inhibiting root elongation. The low solubility of iron at a pH of 3 (the lowest value which could be applied for root elongation) excluded the testing of higher iron concentrations. Due to the lower sensitivity of seed germination to acidity, a pH of 2.6 could be applied in this case. The lowest effective iron concentration (the lowest applied concentration causing a significant decrease in germination as compared to the control, P < 0.05), EC50 (the concentration at which germination was 50% of that of the control specimens) and the completely effective iron concentration (the concentration that completely inhibited seed germination) were 0.6, 0.92 and 2.0 mM, respectively.     

Effect of malformin on phytochrome- and Ethrel-mediated responses

On etiolated cuttings of Phaseolus vulgaris malformin inhibitedseveral phytochromemediated responses. This included hypocotylhook-opening, leaf expansion, and inhibition of stem elongation.Malformin also inhibited anthocyanin synthesis by sorghum, buthad no effect upon lettuce seed germination in the light ordark. Malformin alleviated Ethrel-induced hook-retention, inhibitionof stem elongation, and root curvatures, but not Ethrel-inducedstimulation of lettuce seed germination in the dark. (Received February 19, 1975; )     

Allelopathic Inhibitors in Seeds of Hevacleum laciniatum

Biological inhibitors present in the dry seeds of Heracleum laciniatum Horn have been studied by means of thin layer chromatography and various bioassays. The ethylacetate fraction of methanol extracts contained three main groups of inhibitors having the following R values when chromatographed on silica gel with chloroform: (1) 0.60–0.80; (2) 0.20–0.40; (3) 0.0–0.10. The group (1) inhibited lettuce seed germination and root growth, elongation of Avena first internode segments, growth of the fungus Cladosporium cucumerinum, and it caused leakage of betacyanin from red beet tuber slices. The groups (2) and (3) had no activity in red beet betacyanin leakage test, but they were inhibitory in the other bioassays used. The group (3) were generally less active than the group (2). The group (2) contained the furanocoumarins pimpinellin, bergapten, isobergapten and angelicin. Inhibitors present in the groups (1) and (3) have not been identified. Effects of five synthetic furanocoumarins (pimpinellin, bergapten, isobergapten, isopimpinellin, sphondin) on lettuce seed germination and Cladosporium growth were investigated. Pimpinellin was inhibitory to Cladosporium growth, and lettuce seed germination was inhibited by pimpinellin and sphondin.     

Inhibition of seedling survival under Rhododendron maximum (Ericaceae): could allelopathy be a cause?

In the southern Appalachian mountains a subcanopy species, Rhododendron maximum, inhibits the establishment and survival of canopy tree seedlings. One of the mechanisms by which seedlings could be inhibited is an allelopathic effect of decomposing litter or leachate from the canopy of R. maximum (R.m.) on seed germination, root elongation, or mycorrhizal colonization. The potential for allelopathy by R.m. was tested with two bioassay species (lettuce and cress), with seeds from four native tree species, and with three ectomycorrhizal fungi. Inhibitory influences of throughfall, fresh litter, and decomposed litter (organic layer) from forest with R.m. (+R.m. sites) were compared to similar extractions made from forest without R.m. (-R.m. sites). Throughfall and leachates of the organic layer from both +R.m. and -R.m. sites stimulated germination of the bioassay species above that of the distilled water control, to a similar extent. There was an inhibitory effect of leachates of litter from +R.m. sites on seed germination and root elongation rate of both bioassay species compared with that of litter from -R.m. sites. Native tree seed stratified in forest floor material from both forest types had a slightly higher seed germination rate compared with the control. A 2-yr study of seed germination and seedling mortality of two tree species, Quercus rubra and Prunus serotina, in field plots showed no significant influence of litter or organic layer from either forest type. Incorporating R.m. leaf material into the growth medium in vitro depressed growth of one ectomycorrhizal species but did not affect two other species. Leaf material from other deciduous tree species depressed ectomycorrhizal growth to a similar or greater extent as leaf material from R.m. In conclusion, R.m. litter can have an allelopathic effect on seed germination and root elongation of bioassay species as well as some ectomycorrhizal species. However, this allelopathic affect is not manifest in field sites and is not likely to be an important cause for the inhibition of seedling survival within thickets of R.m.     

Light-controlled Cycocel Reversal of Coumarin Inhibition of Lettuce Seed Germination and Root Growth

Lettuce seed germination or lettuce root elongation after germination in water was inhibited by coumarin and these inhibitions were reversed by Cycocel. 2.53 × 10³ M Cycocel reversed the inhibition of seed germination by 6.8 × 10⁴ M coumarin. and 6.32 × lO^?4 M Cycocel reversed the inhibition of root elongation by 3.4 × 10³ M coumarin. No other analogs of Cycocel reversed these coumarin induced inhibitions of growth. Cycocel reversal of coumarin inhibition of lettuce seed germination occurred in red light but not in far-red light or darkness. The red-far-red system was photoreversible. Cycocel and kinetin appear to act similarly in reversing coumarin inhibition of germination. Gibberellin A₃ and IAA were unable to reverse these coumarin induced inhibitions. A common mechanism is suggested for Cycocel reversal of coumarin and lAA inhibition of growth.     

Diaspore dispersal season influences root growth and seed traits,but not germination responses,of sympatric Piper species in a seasonal forest

• Seeds may differ in terms of dormancy, longevity, sensitivity to desiccation and dry mass, according to the timing (dry season/rainy season) of diaspore dispersal. In addition, seasonal variations in temperature and water availability can act as signals of the season during seed development, influencing germination responses and root growth. We evaluated the effects of temperature variations and water availability on germination parameters, root growth and seed traits of four coexisting Piper species in seasonal vegetation that differed in diaspore dispersal timing.
• Eight temperature treatments (15, 20, 23, 25, 28, 30, 35 °C, and alternate 30 °C–20 °C) and four induced water potentials (0, −0.3, −0.6 and −1.2 MPa) were used. The parameters germination onset, germination percentage (G%), mean germination time (MGT), root elongation, seed longevity during ex situ storage and dry mass of seeds were evaluated.
• Germination responses observed were independent of the diaspore dispersal timing, such as variations in germination onset, G% and MGT, both in temperature and water availability treatments. In contrast, root elongation, longevity and dry mass of seeds varied according to the time of diaspore dispersal.
• Our results corroborate the hypothesis that the timing of diaspore dispersal is an important factor in controlling the initial development of seedlings in seasonal vegetation, but not in germination responses. The predominance of negative effects of temperature increases and water deficit on root growth shows that the initial stages of plant development can be strongly impacted by these environmental factors.

     

A mechanism for promoting the germination of Zinnia elegans seeds by hydrogen peroxide

H(2)O(2) promotes seed germination of cereal plants such as barley, wheat and rice, and several mechanisms have been proposed for its action [Naredo et al. (1998) Seed Sci. Technol. 26: 675-689]. We investigated the role of H(2)O(2) in the germination of Zinnia elegans seeds. H(2)O(2) promoted seed germination in a dose-dependent manner as did respiratory inhibitors, indicating that H(2)O(2) itself possibly promotes seed germination rather than O(2). Seed germination was promoted by removal of pericarp from seeds or by removal of ethanol-soluble compounds from the seeds with pericarp. The ethanol-soluble compounds suppressed the germination of seeds having no pericarp, and this effect was reversed by H(2)O(2). These findings indicate that oxidation of the germination inhibitor(s) present in the pericarp by H(2)O(2) promotes seed germination. Antioxidants which are derivatives of well-known germination inhibitors suppressed seed germination in a dose-dependent manner, suggesting that, to initiate seed germination, a germination inhibitor(s) should be decomposed by an oxidant such as H(2)O(2).     

Nitric oxide accelerates seed germination in warm-season grasses

The nitric oxide (NO) donor sodium nitroprusside (SNP) significantly promoted germination of switchgrass (Panicum virgatum L. cv Kanlow) in the light and in the dark at 25°C, across a broad range of concentrations. SNP also promoted seed germination in two other warm-season grasses. A chemical scavenger of NO inhibited germination and blocked SNP stimulation of seed germination. The phenolic (+)-catechin acted synergistically with SNP and nitrite in promoting seed germination. Acidified nitrite, an alternate NO donor also significantly stimulated seed germination. Interestingly, sodium cyanide, potassium ferricyanide and potassium ferrocyanide at 200 μM strongly enhanced seed germination as well, whereas potassium chloride was without effect. Ferrocyanide and cyanide stimulation of seed germination was blocked by an NO scavenger. Incubation of seeds with a fluorescent NO-specific probe provided evidence for NO production in germinating switchgrass seeds. Abscisic acid (ABA) at 10 μM depressed germination, inhibited root elongation and essentially abolished coleoptile emergence. SNP partially overcame ABA effects on radicle emergence but did not overcome the effects of ABA on coleoptile elongation. Light microscopy indicated extension of the radicle and coleoptiles in seeds maintained on water or on SNP after 2 days. In contrast, there was minimal growth of the radicle and coleoptile in ABA-treated seeds even after 3–4 days. These data indicate that seed germination of warm-season grasses is significantly influenced by NO signaling pathways and document that NO could be an endogenous trigger for release from dormancy in these species.     

Aluminum Tolerance in Moso Bamboo (<Emphasis Type="Italic">Phyllostachys pubescens</Emphasis>)

Moso bamboo (Phyllostachys pubescens) is widely distributed in the acid soil region of Southern China, where great potential of aluminum (Al) toxicity exists. To evaluate the Al tolerance of Moso bamboo, seed germination and root elongation were compared with two rice cultivars, and physical and physiological damages were examined under various levels of Al stress. Results showed that Moso bamboo seed germination was inhibited when Al concentration increased to 500 μM, and the median lethal concentration was 2,000 μM. Comparatively, the rice seed germination was not inhibited even at a concentration of 2,000 μM Al. Aluminum accumulated mainly in the cell wall of root apices, and entered into protoplasts as treating time prolonged and/or Al concentration increased, which resulted in apoptosis. The bamboo root epidermis degraded significantly in the presence of 2,000 μM Al. In conclusion, Moso bamboo is moderately weak in Al tolerance.     

Arabidopsis ROP9 and ROP10 GTPases differentially regulate auxin and ABA responses

Auxin and abscisic acid (ABA) are major plant hormones that act together to modulate numerous aspects of plant growth and development, including seed germination, primary root elongation, and lateral root formation. In this study, we analyzed the loss-of-function mutants of two closely related ROP (Rho of plants) GTPases, ROP9 and ROP10, and found that these ROP GTPases differentially regulate the auxin and ABA responses. rop9 and rop10 mutations enhanced the ABA-induced suppression of seed germination, primary root growth, and lateral root formation and the expression of ABA-responsive genes, whereas rop9 but not rop10 suppressed auxin-induced root phenotypes and auxin-responsive gene expression. These results suggest that both ROP9 and ROP10 function as negative regulators of ABA signaling, and that ROP9, but not ROP10, functions as a positive regulator of auxin signaling. Previously, ROPinteractive CRIB motif-containing protein 1 (RIC1) was reported to participate in auxin and ABA responses, and to have a similar effect as ROP9 and ROP10 on gene expression, root development, and seed germination. Because RIC proteins mediate ROP GTPase signaling, our results suggest that ROP9 and ROP10 GTPases function upstream of RIC1 in auxin- and ABA-regulated root development and seed germination.     

Effects of aqueous extract of rice plants (Oryza sativa L.) on seed germination and radicle elongation of Monochoria vaginalis var. plantaginea

Laboratory experiments were conducted to examine the allelopathic potentials of rice plants (Oryza sativa L.) on seed germination and radicle elongation of Monochoria vaginalis (Burm. f.) Presl var. plantaginea (Roxb.) Solms-Laubat. To compare the relative allelopathic potentials of rice plants at different growth stages, aqueous extracts of dried tissues were obtained from the seeds, husks, and seedlings harvested 10, 20, 40 and 120 days after seeding. When M. vaginalis seeds were incubated in solutions containing aqueous extracts, significant increases in the germination rate were observed for all the aqueous extracts except for the extract of 10 d-old shoots at higher dosages. When partitioned with ethyl acetate, the germination-promoter(s) in the aqueous extracts remained in the aqueous phase while some inhibitors were extracted with ethyl acetate. In contrast, aqueous shoot extracts added to the incubation media at the same dosage for promotion of seed germination inhibited radicle elongation of M. vaginalis, indicating that the sensitivity of the weed varies between these two growth stages.     

Allelopathic potential of Bothriochloa laguroides var. laguroides (DC.) Herter (Poaceae: Andropogoneae)

Bothriochloa laguroides var. laguroides (DC.) Herter, a native bluestem of America, has been shown to produce many biologically active compounds. The allelopathic potential of aqueous extracts from roots, stems and leaves was examined. Lettuce seeds (Lactuca sativa) and maize (Zea mays), the common allelopathy bioassay systems, as well as seeds from two native species, wintergreen paspalum (Paspalum guenoarum) and lovegrass (Eragrostis curvula), were germinated in the presence of aqueous extracts. Percent seed germination, root and shoot elongation were measured. After 4 and 7 days root, stem and leaf extracts caused inhibition of root and shoot elongation in all four species tested. Aqueous extracts were generally less inhibitory to seed germination. Aqueous extracts from different parts of B. laguroides var. laguroides show therefore allelopathic effects inhibiting, in particular, growth of competing plants.