Investigating and modeling the combined effects of pH and osmotic pressure on seed germination for use in phytoactivity and allelopathic research

Phytoactivity and allelopathic studies are heavily dependent on germination bioassays of water solutions of allelochemical(s), which necessarily imply that pH and osmotic pressure vary among treatments and between treatments and controls and are therefore a confounding factor in the assessment of seed germination responses to allelochemical(s). When the contribution of pH and osmotic pressure to seed germination responses is considered in experimental designs their effects are almost without exceptions examined separately being assumed, without any evidences, that pH and osmotic pressure act independently on seed germination responses. The objectives of this work were to examine experimentally such assumption using wheat, lettuce, and subterranean clover cultivars to evaluate and model the combined effects on germination of pH and osmotic pressure in the range between 3.0–6.0 and 0–100 mOsmol kg^?1, respectively. Empirical equations are fitted, discussed, and the need to consider the simultaneous effects of pH and osmotic pressure firmly established. Finally, the use of the equations fitted and its impact on conclusions is exemplified in a dose-response bioassay of water extracts of Cistus ladanifer on seed germination using subterranean clover as target species where hormesis was found before allelochemical effects were corrected for pH and osmotic pressure values of control and extracts.     

Uptake and translocation of phytochemical 2-benzoxazolinone (BOA) in radish seeds and seedlings

The molecular aspects of phytochemical interactions between plants, especially the process of phytochemical translocation by the target plant, remain challenging for those studying allelopathy. 2-Benzoxazolinone (BOA) is a natural chemical produced by rye (Secale cereale) and is known to have phytotoxic effects on weed seeds and seedlings. The translocation of BOA into target plants has been poorly investigated. Therefore, the total absorption of [ring U 14C] BOA was estimated by oxidizing whole seedlings of Raphanus sativus cv. for 8 days and quantifying the radioactivity. Non-radiolabelled BOA in seedlings was also estimated by HPLC. BOA applied at 10(-3) M was readily taken up by germinated radish at a rate of 1556 nmol g(-1) FW. At these same concentrations, BOA reduced radish germination by 50% and caused a delay in radicle elongation. Exogenous BOA was responsible for the observed germination inhibition. At a concentration of 10(-5) M, BOA was taken up by germinated seeds (31 nmol g(-1) FW), but this quantity did not affect radish germination. Labelled BOA was not mineralized in the culture medium during seedling growth as no 14CO2 was recovered. Both 10(-3) and 10(-5) M BOA were translocated into radish organs, mainly into roots and cotyledons. These organs were then identified as potential physiological target sites. Cotyledons remained the target sink (44% of the total radioactivity). The kinetics of BOA uptake at 10(-3) and 10(-5) M in radish seedlings was identical: BOA accumulation was proportional to its initial concentration. A comparison between radioactivity and HPLC quantification for 10(-3) M BOA indicated that BOA (along with some metabolites) could effectively be recovered in radish organs using chromatography.     

Differential Inactivation of Seed Exudate Stimulation of Pythium ultimum Sporangium Germination by Enterobacter cloacae Influences Biological Control Efficacy on Different Plant Species

This study was initiated to understand whether differential biological control efficacy of Enterobacter cloacae on various plant species is due to differences in the ability of E. cloacae to inactivate the stimulatory activity of seed exudates to Pythium ultimum sporangium germination. In biological control assays, E. cloacae was effective in controlling Pythium damping-off when placed on the seeds of carrot, cotton, cucumber, lettuce, radish, tomato, and wheat but failed to protect corn and pea from damping-off. Seeds from plants such as corn and pea had high rates of exudation, whereas cotton and cucumber seeds had much lower rates of exudation. Patterns of seed exudation and the release of P. ultimum sporangium germination stimulants varied among the plants tested. Seed exudates of plants such as carrot, corn, lettuce, pea, radish, and wheat were generally more stimulatory to P. ultimum than were the exudates of cotton, cucumber, sunflower, and tomato. However, this was not directly related to the ability of E. cloacae to inactivate the stimulatory activity of the exudate and reduce P. ultimum sporangium germination. In the spermosphere, E. cloacae readily reduced the stimulatory activity of seed exudates from all plant species except corn and pea. Our data have shown that the inability of E. cloacae to protect corn and pea seeds from Pythium damping-off is directly related to its ability to inactivate the stimulatory activity of seed exudates. On all other plants tested, E. cloacae was effective in suppressing damping-off and inactivating the stimulatory activity of seed exudates.     

2-3H-Benzoxazolinone (BOA) induces loss of salt tolerance in salt-adapted plants

In order to test the stress hypothesis of allelopathy of Reigosa et al. (1999, 2002) , the combined action of a well-established allelochemical compound (2-3 H -benzoxazolinone, BOA) and a common abiotic stress (salt stress) were investigated in lettuce ( Lactuca sativa L.). In a previous study ( Baerson et al. 2005 ), we demonstrated that the primary effects of BOA are related to the expression of genes involved in detoxification and stress responses, which might serve to simultaneously alleviate biotic and abiotic stresses. Through analysis of the same physiological and biochemical parameters previously studied for BOA alone ( Sánchez-Moreiras & Reigosa 2005 ), we observed specific effects of salt stress alone, as well as for the two stresses together (BOA and salt). This paper demonstrates that plants showing tolerance to salt stress (reduced stomatal density, increased proline content, higher K⁺ concentration, etc .) become salt sensitive (markedly low Ψw values, high putrescine content, increased lipid peroxidation, etc .) when simultaneously treated with the allelochemical BOA. We also report additional information on the mechanisms of action of BOA, and general stress responses in this plant species.     

Seed dynamics of an endemic palm in a Northwestern Mexican tropical dry forest: implications for population spatial structure

Seed dynamics are an important part of the life history of plants and may have strong implications on abundance and spatial distribution of populations. In this study, we explored how seed dynamics (removal, predation, germination) interact with micro-environmental conditions to affect the spatial structure of populations of Brahea aculeata (Arecaceae) in a tropical dry forest. B. aculeata is distributed throughout arroyo basins and attains its highest densities near to arroyos/rivers. We hypothesized that: (i) seed removal, predation and germination vary across topographic positions resulting in greater palm abundances adjacent to arroyos and (ii) seed removers/predators respond to both a seed density-dependent effect and a microclimate effect. To test this, in six arroyos basins, seeds were sown across three topographic positions (stream, mid and top of basins) with two seed abundances (1 and 10), protected and non-protected from potential predators. Predation, removal and germination were then followed. After 107 days, 100 % of the exposed seeds were removed/predated and none germinated. For seed removal, we found differences among topographic positions and seed densities with higher removal (up to 80 %) and lower predation rates for grouped seeds. Germination was only observed for protected seeds with higher germination rates in single (17 % ± 9) than in grouped seeds (4 % ± 1). The highest germination and establishment rates were adjacent to the streams; areas which had the lowest light intensity (mean ± SE = 883 ± 160 lm/ft²) and temperatures (mean ± SE = 20.1 ± 0.6 °C), and highest humidity (mean ± SE = 50.8 ± 1.8 %), especially during the rainy season. Differential seedling establishment rates across the landscape due to spatial patterns of seed predation/removal as well as micro-environmental variables appear to have implications for shaping the spatial structure of B. aculeata population at Sierra de Álamos, Mexico.     

Germination biology and seedling growth of Clusia hilariana Schltdl., a dominant CAM-tree of drought-prone sandy coastal plains

The spatial and temporal fluctuations of water availability can be an obstacle for recruitment of many species in the restinga and might restrict seed germination and seedling growth in specific regeneration safe-sites. Clusia hilariana is one of the most dominant species of Restinga de Jurubatiba. This species has a high proportion of seedling establishment occurring inside the tanks of soil bromeliads underneath vegetation patches. Given the thin seed coats, the fast germination time and seed dispersal of C. hilariana during the dry season, we hypothesized that their major regeneration niche (the tanks of soil bromeliads) is related to susceptibility of seed germination and also seedling growth to low water availability. To test this hypothesis, seeds were germinated under decreasing water potentials using PEG 6000 solutions and seedlings were grown under varying water regimes. The percentage of seed germination progressively decreased at lower water potentials. After 38 days in ?1.0 MPa no seeds germinated. However, approximately 90% of seeds germinated when transferred to Ψ = 0 MPa. The relative growth rates of seedlings of C. hilariana did not differ between water treatments. Thus, the major regeneration niche of C. hilariana is not a consequence of a high sensitivity of seeds and seedlings to water shortage. Nonetheless, C. hilariana showed an array of seed and seedling traits that may help to overcome establishment constraints of the harsh environment of restingas.     

In vitro allelopathic properties of wild rocket (Diplotaxis tenuifolia DC) extract and of its potential allelochemical S-glucopyranosyl thiohydroximate

Abstract

An aqueous extract of wild rocket (Diplotaxis tenuifolia DC) was tested for its allelopathic activity in vitro on radish germination and seedling growth in light and darkness. The extract caused a delay in the onset and a significant decrease in the rate of germination (40%) in the light. The photo-inhibition was accompanied by an inhibition of water uptake into the seed, and a decrease of protein content as well as an increase of peroxidase activity into the seedlings. Microscopic observations suggest that the extract markedly changes radish radicle development inducing a decreased imbibition and distension of seed cells. Consistent results were obtained with some species such as purslane, lambsquarter and tree of heaven present in the cultivated wild rocket field and with cultivated lettuce and barley. Finally, a potential allelochemical, biologically active, was isolated from the extract: S-glucopyranosyl thiohydroximate at concentration of 6.3×10^?4 M.     

Water Content and Phytochrome-induced Potential Germination Responses in Lettuce Seeds

Grand Rapids lettuce seeds (Lactuca sativa L.) with 6 to 8% water content show no light-induced germination responses, whereas in seeds with 15% or more water content, germination is promoted or retarded by red and far red light respectively. By adjusting seed water content, persistent potentiated responses to light are induced in the seeds at seed water levels much below that required for germination itself. Alternate moistening and drying of seeds in conjunction with red and far red irradiations show that potentiated responses may be phototransformed only with sufficient seed water. However, the process of drying and remoistening has no effect on potentiated responses.     

Differential inactivation of seed exudate stimulation of Pythium ultimum sporangium germination by Enterobacter cloacae influences biological control efficacy on different plant species

This study was initiated to understand whether differential biological control efficacy of Enterobacter cloacae on various plant species is due to differences in the ability of E. cloacae to inactivate the stimulatory activity of seed exudates to Pythium ultimum sporangium germination. In biological control assays, E. cloacae was effective in controlling Pythium damping-off when placed on the seeds of carrot, cotton, cucumber, lettuce, radish, tomato, and wheat but failed to protect corn and pea from damping-off. Seeds from plants such as corn and pea had high rates of exudation, whereas cotton and cucumber seeds had much lower rates of exudation. Patterns of seed exudation and the release of P. ultimum sporangium germination stimulants varied among the plants tested. Seed exudates of plants such as carrot, corn, lettuce, pea, radish, and wheat were generally more stimulatory to P. ultimum than were the exudates of cotton, cucumber, sunflower, and tomato. However, this was not directly related to the ability of E. cloacae to inactivate the stimulatory activity of the exudate and reduce P. ultimum sporangium germination. In the spermosphere, E. cloacae readily reduced the stimulatory activity of seed exudates from all plant species except corn and pea. Our data have shown that the inability of E. cloacae to protect corn and pea seeds from Pythium damping-off is directly related to its ability to inactivate the stimulatory activity of seed exudates. On all other plants tested, E. cloacae was effective in suppressing damping-off and inactivating the stimulatory activity of seed exudates.     

Influence of post-flowering temperature on seed development, and subsequent performance of crisp lettuce

Crisp lettuce plants cv. Saladin were grown from the time they started flowering, at 20/10°C (16 h day, 8 h night), 25/15°C and 30/20°C in glasshouses on two occasions in 1985. Yields of seed increased from, on average, 15 g to 27 g and then fell to 20 g per plant with progressive increases in temperature. The number of mature florets per plant increased with temperature but the number of seeds per mature floret was lower at 20/10°C and 30/20°C than at 25/15°C. An increase in temperature reduced mean seed weight by up to 45%, seed volume by 15%, cell numerical volume density (N_v) by 27% and the number of cells per seed by 39%. Percentage seed germination reached a maximum early in seed development at the stage when the pappus appeared through the involucral bracts. Differences in percentage germination and vigour of seeds (slope test) from different temperatures were accounted for largely by the effects on mean seed weight. However, when germinated at 30°C seeds produced at 30/20°C germinated more readily than those produced at 25/15°C or 20/10°C. Seed vigour gradually increased with an increase in the length of storage after harvest, reaching a maximum after 260 days. In general, seeds produced at 25/15°C exhibited a greater variation in numbers of seeds per floret, N_v, seed weight, times of seedling emergence, seedling and mature head weight than seeds produced at lower or higher temperatures.     

In situ seed baiting to isolate germination-enhancing fungi for an epiphytic orchid,Dendrobium aphyllum (Orchidaceae)

Orchid conservation efforts, using seeds and species-specific fungi that support seed germination, require the isolation, identification, and germination enhancement testing of symbiotic fungi. However, few studies have focused on developing such techniques for the epiphytes that constitute the majority of orchids. In this study, conducted in Xishuangbanna Tropical Botanical Garden, Yunnan, China, we used seeds of Dendrobium aphyllum, a locally endangered and medicinally valuable epiphytic orchid, to attract germination promoting fungi. Of the two fungi isolated from seed baiting, Tulasnella spp. and Trichoderma spp., Tulasnella, enhanced seed germination by 13.6 %, protocorm formation by 85.7 %, and seedling development by 45.2 % (all P?Epulorhiza, another seed germination promoting fungi isolated from Cymbidium mannii, also enhanced seed germination (6.5 %; P?P?Trichoderma suppressed seed germination by 26.4 % (P?Tulasnella was the only treatment that produced seedlings. Light increased seed imbibition, protocorm formation, and two-leaved seed development of Tulasnella inoculated seeds (P?Tulasnella be introduced for facilitating D. aphyllum seed germination at the protocorm formation stage and that light be provided for increasing germination as well as further seedling development. Our findings suggest that in situ seed baiting can be used to isolate seed germination-enhancing fungi for the development of seedling production for conservation and reintroduction efforts of epiphytic orchids such as D. aphyllum.     

Allelopathy in Heracleum laciniatum: Inhibition of Lettuce Seed Germination and Root Growth

Both dark and red light germination of lettuce seeds (cv. “Maikönig”) as well as their root and hypocotol elongation were inhibited when the seeds were sown in petri dishes together with a few seeds of Heracleum laciniatum Horn. This inhibition was not significantly counteracted by the presence of gibberellic acid (GA₃) or/and 6-benzylaminopurine (BA). However, a large proportion of the lettuce seeds germinated abnormally (only cotyledons emerged) when treated with BA in the presence of Heracleum seeds. GA₃ had alone no significant effect on abnormal germination, but it counteracted the effect of BA to some extent. The inhibitory effect of Heracleum seeds gradually disappeared during a moist incubation period of one to seven days in darkness at 25°C. When lettuce seeds were pre-incubated together with Heracleum seeds for one to five days the remaining, non-germinated lettuce seeds had lost their ability for subsequent germination in darkness in distilled water. This induced dark dormancy was to a great extent broken by red light, but not by GA₃ or/and BA. H. laciniatum seeds inhibited the germination of Salix pentandra seeds and to some extent also the germination of radish but had no effect on the germination of spruce.     

Effect of cold stratification on seed germination in <Emphasis Type="Italic">Solidago</Emphasis> × <Emphasis Type="Italic">niederederi</Emphasis> (<Emphasis Type="Italic">Asteraceae</Emphasis>) and its parental species

In this study, we investigated the influence of cold stratification on seed germination in S. × niederederi, a hybrid between the North American S. canadensis and the European S. virgaurea, using fruit samples collected in 2016 in Poland. We aimed to test the hypothesis that the low temperature exposure decreases the final percentage and speed of seed germination in the hybrid and its parental species. For each species, sets of 100 achenes in three replications were mixed with dry sand and stored in Petri dishes in darkness for 12 weeks, at ?18 °C and?+?4 °C, and?+?25 °C. The seeds were incubated for 21 d at room temperature (+25 °C), under the 12 h photoperiod (630 lx). We showed a lack of significant differences in: (i) the final percentage of germinated seeds of studied species stored at the same conditions, (ii) the final percentage of germinated seeds between the applied stratification conditions in the hybrid and its parental species, and (iii) the mean values of Timson’s index, mean germination time, and coefficient of velocity of germination between the stratification conditions in each species. The statistically significant inter-specific differences in the mean germination time parameter after the +25 °C treatment suggest that the seeds of S. × niederederi are able to germinate faster than the seeds of its parental species. However, to improve our knowledge of naturalization and invasion abilities of S. × niederederi by sexual reproduction, the seed germination and seedling survival of the hybrid should be tested in the field.     

The use of image analysis to monitor the germination of seeds of broccoli (Brassica oleracea) and radish (Raphanus sativus)

To study broccoli and radish seed germination under different temperature regimes the germination test has been used to assess final germination percentage, start and rate. This method has been integrated with a computer‐aided image analysis test which is more accurate in monitoring the extent of imbibition phases through the assessment of seed area increase and timing of radicle emergence detected on single seeds. In addition, seed area increase has been used also to establish a close relationship with radicle elongation rate in the time range when ‘visible germination’ is scored by a classical germination test. The results suggest that this image analysis parameter may be considered as a reliable seed imbibition marker to integrate the germination parameters obtained by a germination test.     

Environmental factors controlling seed germination and seedling recruitment of Stipa bungeana on the Loess Plateau of northwestern China

Germination studies are important for collecting information on field seedling recruitment, plant conservation and restoration. This study investigated the role of light, temperature, nitrogen, water stress and burial depth in controlling germination of Stipa bungeana seeds. S. bungeana seeds are photo-inhibited; light significantly decreased seed germination regardless of temperature and water conditions. Seeds germinated at 10–30° C, and the highest germination was 72 % and 88 % at 20° C in light and dark, respectively. Thermal model analysis showed that presence of light significantly increased average thermal requirement [θ _T (50)] from 105°Cd to 186°Cd at sub-optimal temperature, implying that light delays seed germination. Hydrotime model analysis showed that presence of light caused a shift in the median base water potential [Ψ _b(50)] from ?0.68 to ?0.26 MPa, which partly explains why light decreased both percentage and speed of germination, even at optimal conditions. As burial depth increased, seedling emergence initially increased and then decreased; the highest seedling emergence recruitment was 43 %, for seeds buried at a depth of 1 cm. Field observations showed that seedling emergence occurred primarily from July to September, and scarcely occurred from April to June. These results suggest that the light inhibitory effect is an adaptive mechanism that prevents S. bungeana seeds from germinating on the soil surface. To attain highest seedling establishment, seeds of S. bungeana should be sown at a soil depth of 1 cm prior to the rainy season, using seeds stored for 1 year.     

Positive responses of strawberry (<Emphasis Type="Italic">Fragaria</Emphasis> × <Emphasis Type="Italic">ananassa</Emphasis> Duch.) explants to salicylic and iron nanoparticle application under salinity conditions

Mucuna bracteata DC. ex Kurz is an important cover crop in plantations across the tropics. However, low germination rate and poor viability of Mucuna seeds pose significant challenges of using the seeds as starting material. To address these limitations, we have optimized seed germination conditions (such as scarification period, surface sterilization protocols and imbibition period) and in vitro propagation protocols for M. bracteata. We found that seeds treated with sulphuric acid for 30 min, imbibed for 6 h and incubated in dark conditions on a wet cotton roll (10 mL of sterile distilled water) supplemented with 0.1% activated charcoal produced the highest percentage of seed germination (44%) and seed vigor index. In vitro-derived cotyledonary nodes showed the highest number of shoots per explant (5.60) and rooting response (92.9%) when cultured on Murashige and Skoog medium containing 4.44 µM 6-benzylaminopurine and 10.7 µM 1-naphthaleneacetic acid, respectively. Of the 100 rooted plantlets acclimatized, 89.0% survived after 4 weeks of transplanting. Single sequence repeat and flow cytometry analysis were performed to confirm the genetic fidelity of the plants. Our protocol offers, for the first time, a simple and effective seed germination and scalable propagation procedures for M. bracteata. Furthermore, we have also estimated the genome size (1448?±?9 Mb) and DNA content (1.48?±?0.01 pg) for M. bracteata that can be used for future cytogenetic studies on genetic diversity and gene exchange.     

The novel ethylene antagonist, 3-cyclopropyl-1-enyl-propanoic acid sodium salt (CPAS), increases grain yield in wheat by delaying leaf senescence

Orchid is a major floral crop around the world and Dendrobium hybrids are considered to be one of the most popular orchids. In vitro germination of hybrid seeds is a common practice among orchid growers, however, in many cross pollinations the embryos may not develop to maturity, leading to poor seed germination. The effect of seed maturity and sucrose concentration were investigated via asymbiotic germination of nobile Dendrobium hybrids. Capsules were harvested from two hybrids (Den. Lucky Girl × Den. Second Love ‘Kirameki’ and Den. Lucky Girl × Den. Hamana Lake ‘Kumi’) and one selfing of Den. Second Love ‘Kirameki’ at 2, 3, 4, and 5 months after pollination and immature seeds were taken. Immature seeds from 3- to 5-month old capsules could be successfully germinated on Hyponex based medium. Immature seeds from 4-month old capsules showed greatest germination rate of tested treatments, whereas 3-month old immature seeds showed the least germination. After 6 weeks of in vitro culture, protocorms derived from embryos developed on every concentration of sucrose, but germination was greater at lower concentrations. Greater concentration of sucrose decreased normal-developed protocorms.     

Analysis of diaspore morphology and seed germination in Bubon macedonicum L., a rare species in Italy

Bubon macedonicum L. is a chasmophytic species of south-eastern Europe. In Italy, it has been detected only in Rocca Monforte (Campobasso, central Italy). This rare species is included in the IUCN Red Lists of Critically Endangered Italian Flora, and there are no studies relating to B. macedonicum biology. The seed germination dynamics of this species was studied with the aim of building up an appropriate germination protocol to be used in ex situ conservation. On the basis of an ISTA protocol, about 3,000 seeds were collected from Rocca Monforte in August 2013. Fifty seeds were measured. The considered parameters were seed length, width, thickness, seed surface, volume, density, surface/mass ratio and eccentricity index. The morphometric parameters examined showed morphological dormancy, where a short warm period is necessary for embryo growth and seed germination. The results showed high germination percentages under the different conditions of temperature, pH, GA₃ and photoperiod. Only at 5 °C was there no germination. Finally, the seeds maintain high germination percentages from the seed storage process after 130 and 390 days. This factor can be considered of great importance for the conservation of B. macedonicum over the medium and long term.     

Seed storage at elevated partial pressure of oxygen, a fast method for analysing seed ageing under dry conditions

Background and Aims

Despite differences in physiology between dry and relative moist seeds, seed ageing tests most often use a temperature and seed moisture level that are higher than during dry storage used in commercial practice and gene banks. This study aimed to test whether seed ageing under dry conditions can be accelerated by storing under high-pressure oxygen.

Methods

Dry barley (Hordeum vulgare), cabbage (Brassica oleracea), lettuce (Lactuca sativa) and soybean (Glycine max) seeds were stored between 2 and 7 weeks in steel tanks under 18 MPa partial pressure of oxygen. Storage under high-pressure nitrogen gas or under ambient air pressure served as controls. The method was compared with storage at 45 °C after equilibration at 85 % relative humidity and long-term storage at the laboratory bench. Germination behaviour, seedling morphology and tocopherol levels were assessed.

Key Results

The ageing of the dry seeds was indeed accelerated by storing under high-pressure oxygen. The morphological ageing symptoms of the stored seeds resembled those observed after ageing under long-term dry storage conditions. Barley appeared more tolerant of this storage treatment compared with lettuce and soybean. Less-mature harvested cabbage seeds were more sensitive, as was the case for primed compared with non-primed lettuce seeds. Under high-pressure oxygen storage the tocopherol levels of dry seeds decreased, in a linear way with the decline in seed germination, but remained unchanged in seeds deteriorated during storage at 45 °C after equilibration at 85 % RH.

Conclusions

Seed storage under high-pressure oxygen offers a novel and relatively fast method to study the physiology and biochemistry of seed ageing at different seed moisture levels and temperatures, including those that are representative of the dry storage conditions as used in gene banks and commercial practice.     

Promoting Effect of Fusicoccin on Seed Germination

The effects of fusicoccin on the germination of dormant, light-requiring or abscisic acid-inhibited seeds has been investigated. (1) Fusicoccin (10^?6M) induces germination in dormant wheat seeds (Triticum durum cv. Cappelli; 1972 crop) and stimulates it in seeds already relieved from dormancy (1971 crop), with an effect similar to that of gibberellic acid. (2) Fusicoccin (1.5 × 10^?6M) is more active than the two phytohormones gibberellic acid and benzyladenine and than white light in stimulating light-requiring lettuce seeds (Lactuca sativa cv. Grand Rapids) to germinate. Germination of radish seeds (Raphanus sativus) is also accelerated by fusicoccin, while benzyladenine and gibberellic acid are less active in this material. (3) Fusicoccin (1.5 × 10^?5M) removes almost completely the inhibitory effect of abscisic acid on germination of radish and lettuce seeds, whereas benzyladenine (10^?4M) and gibberellic acid (3 × 10^?4M) remove the inhibition only partially. The possible relationship between these results and previous information on growth by cell enlargement is discussed in terms of the mechanism of action of fusicoccin as compared with natural hormones.