Protoplasts to plants of Gentianaceae. Regeneration of lisianthus (Eustoma grandiflorum) is affected by calcium ion preconditioning,osmolality and pH of the culture media

A reliable method has been developed for regeneration of whole plants from isolated protoplasts of five cultivars of lisianthus,Eustoma grandiflorum (Griseb.) Schinners (Gentianaceae). Protoplasts were isolated from either cotyledons or leaves and cultured in agarose beads surrounded by liquid V-KM media containing 5.37 µM 1-naphthyleneacetic acid (NAA) and 2.28 µM zeatin. When microcalli were approximately 1 mm in diameter, the agarose beads were transferred to shoot regeneration media containing 0.1 µM indolebutyric acid (IBA) and 4.44 µM 6-benzylaminopurine (BAP). Shoots were produced from the calli during several sub-culture periods. Protoplast viability and the subsequent regeneration of plants were dependent on calcium levels and growth regulator presence in thein vitro seed germination media, on the osmolality of the protoplast purification solution, and osmolality increase and pH of the culture media. Shoots were rooted in Murashige & Skoog (1962) media containing 5.71 µM indole-3-acetic acid (IAA). Plantlets derived from protoplasts of five lisianthus cultivars (Fresh White, Hakusen, Miss Lilac, Fresh Purple and Doremi Wine Red) have been successfully transferred to the glasshouse.     

Development of ABA Antagonists to Overcome ABA- and Low Temperature-Induced Inhibition of Seed Germination in Canola,Lentil, and Soybean

ABA antagonists have potential application as growth regulators to improve germination and seedling growth at low temperatures for oilseeds and pulses grown in regions with short seasons such as those in western Canada. Towards development of practical ABA antagonists, a series of 3′-substituted ABA analogs were synthesized and screened in seed germination assays in canola (Brassica napus), lentil (Lens culinaris), and soybean (Glycine max) at low temperature and in overcoming exogenous ABA. The most promising analog, ABA 1009, was selected for further germination testing of dose responses in canola, lentil, and soybean. Analog ABA 1009 at 100 µM was effective in overcoming ABA (10 µM)-induced inhibition for canola, lentil, and soybean germination at ambient temperature, and also promoted germination at low temperature for canola (5 °C).

     

Membrane potential changes during pollen germination and tube growth

Using methods of quantitative fluorescent microscopy, we studied membrane potential changes during pollen germination and in growing pollen tubes. Two voltage-sensitive dyes were used, i.e., DiBAC₄(3), to determine the mean membrane potential values in pollen grains and isolated protoplasts, and Di-4-ANEPPS, to map the membrane potential distribution on the surfaces of the pollen protoplast and pollen tube. We have shown that the activation of the tobacco pollen grain is accompanied by the hyperpolarization of the vegetative cell plasma membrane by about 8 mV. Lily pollen protoplasts were significantly hyperpolarized (−108 mV) with respect to the pollen grains (−23 mV) from which they were isolated. We have found the polar distribution of the membrane potential along the protoplast surface and the longitudinal potential gradient along the pollen tube. In the presence of plasma membrane H⁺-ATPase inhibitor sodium orthovanadate (1 mM) or its activator fusicoccin (1 μM), the longitudinal voltage gradient was modified, but did not disappear. Anion channel blocker NPPB (40 μM) fully discarded the gradient in pollen tubes. The obtained results indicate the hyperpolarization of the plasma membrane during pollen germination and uneven potential distribution on the pollen grain and tube surfaces. An inhibitory analysis of the distribution of the potential in the tube has revealed the involvement of the plasma membrane H⁺-ATPase and anion channels in the regulation of its value.     

Characterization of multisporic and monosporic isolates of Lecanicillium (= Verticillium) lecanii for the management of Toxoptera aurantii in cocoa

Seven multisporic isolates, two from Cuba, four from the Southeastern State ofTabasco and two from Central Mexico, weremorphologically and physiologically comparedwith 28 monosporic isolates (four permultisporic isolate) of the fungus Lecanicillium (= Verticillium) lecanii.Mycelium type and colony appearance wereassociated with specific conidial length,conidial production and germination speed. Ingeneral, isolates with a cottony-likeappearance of the mycelium and without anystriations had small conidia and a highconidial production; the opposite was found forisolates with sparse mycelium and striatedcolonies. There was an inverse correlationbetween germination time of 50% of theconidia (GT₅₀) and their length (r =–0.72, P = 0.01). Three conidia length groupswere determined: small (2.9–3.9 µm),intermediate (4.6–5.8 µm), and large(6.5–8.8 µm). Based on shape, five groups of conidia were distinguished:cylindrical with half constriction and roundedends; crescent-shape, curved with both endsacute; conidia with one end somewhat moredistinctly narrowed; lanceolate form; andovoid to ellipsoidal shape. Differenceswere found between monosporic cultures andmultisporic isolates, particularly withGTM₅₀ and conidial production where severalmonosporic cultures exceeded their multisporicisolates. Results of analyses with singlecharacteristics were also confirmed withmultivariate analysis helping to identify thatthe four Tabasco groups were morphologicallyand physiologically more variable. Based onthese results it is possible to improve thecontrol potential of isolates of L. lecaniiby making monosporic cultures.     

Isolation of Allium pollen protoplasts

Studies on protoplasts isolation were carried out with mature pollen grains of 29 samples of species of Allium aflatunense, A. cepa, A. fistulosum, A. karataviense, A. longicuspis, A. nutans, A. odorum, A. sativum and A. schoenoprasum. Surface sterilized pollen grains drifted from crushed anthers were incubated in an enzyme solution containing 1% (w/v) cellulase Onozuka R-10, 1% (w/v) Macerozyme R-10, 0,5 mol l^-1 sucrose and the basal salts of Nitsch medium. Protoplasts were released within 3 to 120 min, either from the pollen grain, through a slightly disturbed germination pore (narrow aperture), or through a wider aperture, when the exine surrounding the germination pore was disturbed. For the first time, protoplasts were obtained from 13 genotypes of 6 Allium species, at a rate of 1 to 30% of the digested intact pollen grains, depending on the genotype.     

Targeted destruction of fungal structures of Erysiphe trifoliorum on flat leaf surfaces of Marchantia polymorpha

In this study, we observed the germination behaviour of airborne conidia from powdery mildews that settle on thalloid surfaces. We inoculated thalli (flat, sheet‐like leaf tissues) and gemmae (small, flat, sheet‐like leaf tissues that propagate asexually via bud‐like structures) of the common liverwort (Marchantia polymorpha) with conidia from tomato powdery mildew (Oidium neolycopersici; KTP‐02) and red clover powdery mildew (Erysiphe trifoliorum; KRCP‐4N) and examined their germination and subsequent appressorium formation under a high‐fidelity digital microscope. Conidial bodies and germ tubes of the inoculated KRCP‐4N conidia were destroyed on both the thalli and gemmae. The destruction of these fungal structures was observed only for KRCP‐4N conidia inoculated onto M. polymorpha on both leaf surfaces. No differences in destruction of the KRCP‐4N fungal structures between thalli and gemmae were observed. At 4 h post‐inoculation, destruction of the germ tube tip was observed when it reached the gemmae leaf surface. At 6 h post‐inoculation, the conidial bodies and germ tubes were destroyed. In contrast, KTP‐02 conidia were not destroyed and formed normal, well‐lobed appressoria on the surface of M. polymorpha gemmae.     

Swelling of penicillium digitatum conidia by a fusarium acuminatum NRRL 6227 metabolite

Fusarium acuminatum NRRL 6227 produces an antifungal metabolite that causes incubating conidia of several Penicillium species to swell 5–10 diameters while inhibiting germination. The swollen conidia are spherical, translucent, nonviable and easily shattered with a slight physical pressure; however, they remain resistant to osmotic shock. This antibiotic has been identified as a cyclic peptide composed of alanine, glutamic acid, leucine, threonine and tyrosine.     

Gene transfer between canola (Brassica napus L. and B. campestris L.) and related weed species

Brassica species are particularly receptive to gene transformation techniques. There now exists canola genotypes with transgenic herbicide resistance for glyphosate, imidazolinone, sulfonylurea and glufosinate herbicides. The main concern of introducing such herbicide resistance into commercial agriculture is the introgression of the engineered gene to related weed species. The potential of gene transfer between canola (Brassica napus and B. campestris) and related weed species was determined by hand pollination under controlled greenhouse conditions. Canola was used as both male and female parent in crosses to the related weed species collected in the Inland Northwest region of the United States. Weed species used included: field mustard (B. rapa), wild mustard (S. arvensis) and black mustard (B. nigra). Biological and cytological aspects necessary for successful hybrid seed production were investigated including: pollen germination on the stigma; pollen tube growth down the style; attraction of pollen tubes to the ovule; ovule fertilisation; embryo and endosperm developmental stages. Pollen germination was observed in all 25 hybrid combinations. Pollen tubes were found in the ovary of over 80% of combinations. About 30% of the hybrid combinations developed to the heart stage of embryo development or further. In an additional study involving transgenic glufosinate herbicide resistant B. napus and field mustard it was found that hybrids occurred with relatively high frequency, hybrids exhibited glufosinate herbicide resistance and a small proportion of hybrids produced self fertile seeds. These fertile plants were found to backcross to either canola or weed parent.     

In vitro germination and growth of lily pollen tubes is affected by calcium inhibitor with reference to calcium distribution

The calcium inhibitors A23187, EGTA and La³⁺ inhibit pollen grain germination and growth of pollen tubes of Lilium davidii var. unicolor at different concentrations. Treatment with 10⁻⁴ or 10⁻⁵ M ionophores A23187 reduced germination rate and resulted in distortion of pollen tube. Addition of 2 or 10 mM of the chelator EGTA disturbed the direction of pollen tube growth and extended the diameter of pollen tube as observed by light and confocal microscopy. The Ca²⁺-channel blocker lanthanum chloride (La³⁺) restrained germination or markedly caused transformation of pollen tube. Furthermore, all treatments led to disappearance of any calcium gradient. Calcium distribution in pollen grain and pollen tube was altered as shown by confocal microscopy for each treatment. This indicates that the inhibitors influence pollen development by affecting the calcium gradient which may play a critical role in germination and tube growth. Fourier transform infrared (FTIR) spectra indicated slight increases in contents of amide I and a substantial decrease in the content of aliphatic esters and saturated esters in treated pollen tubes compared with normal pollen tubes. The FTIR analysis confirmed that EGTA and La³⁺ weakened the accumulation of ester in pollen tubes, which may be associated with an increased content of amide I.     

Morphological Alterations of Metarhizium anisopliae During Penetration of Boophilus microplus Ticks

Chronological histological alterations of Metarhizium anisopliae during interaction with the cattle tick Boophilus microplus were investigated by light and scanning electron microscopy. M. anisopliae invades B. microplus by a process which involves adhesion of conidia to the cuticle, conidia germination, formation of appressoria and penetration through the cuticle. Twenty-four hours post-infection conidia are adhered and germination starts on the surface of the tick. At this time, the conidia differentiate to form appressoria exerting mechanical pressure and trigger hydrolytic enzyme secretion leading to penetration. Massive penetration is observed 72 h post-inoculation, and after 96 h, the hyphae start to emerge from the cuticle surface to form conidia. The intense invasion of adjacent tissues by hyphae was observed by light microscopy, confirming the ability of M. anisopliae to produce significant morphological alterations in the cuticle, and its infective effectiveness in B. microplus.     

The effect of cherry leaf roll virus infection on the performance of birch pollen and studies on virus replication in germinating pollen

The rates of germ tube elongation in vitro of pollen from cherry leaf roll virus (CLRV)-infected birch (Betula pendula) did not differ significantly from those of pollen from virus-free trees. Differences in percentage germination of pollen collected from trees at different sites were significant but percentages of germination of pollen from virus-infected and virus-free trees did not differ greatly from one another. In vivo, pollen from infected trees germinated on healthy and CLRV-infected stigmas and callose plugs formed in both types of tissues. However, the extent of callose plug formation was greater in the pollen tubes of virus-free grains germinating in infected stigmas than in reciprocal crosses. CLRV coat antigen was detected by ELISA in stigmatic tissue, from healthy trees, on which virus-carrying pollen grains had germinated. Using fluorescein isothiocyanate conjugated to CLRV-specific γ-globulin, viral coat antigen was detected throughout germ tubes from virus-carrying but not virus-free pollen germinating in vitro. Protoplasts released following Driselase digestion of pollen germ tubes from virus-infected trees contained CLRV antigen detectable by ELISA. During germination of virus-infected pollen there was little synthesis of viral coat protein or nucleic acid but, following inoculation with purified virus particles, protoplasts made from healthy germinating pollen produced increasing amounts of CLRV-specific antigen implying that CLRV replicated in this system.     

A comparative study on the transformation of Aspergillus nidulans by microprojectile bombardment of conidia and a more conventional procedure using protoplasts treated with polyethyleneglycol

 An Aspergillus nidulans strain, auxotrophic for pyrimidine, was transformed to prototrophy by means of microprojectile bombardment. The transformation frequency was somewhat lower than conventional polyethyleneglycol-mediated transformation of protoplasts. However, the percentage of stable transformants was considerably higher with the biolistic approach. Typically, integrations of several copies of the plasmid introduced into chromosomal DNA were observed. The effect of several parameters, like the concentration of conidia, chamber pressure during bombardment and size of microprojectiles, on transformation frequencies were investigated and compared to previously published data on microprojectile bombardment of fungal conidia. Optimum results (6 transformants/μg plasmid DNA) were obtained when 10⁸ conidia were bombarded with a helium pressure of 5.5–8.3 MPa (800–1200 lb/in²). M5, M10 and M17 tungsten particles were equally efficient. Received: 9 August 1995/Received revision: 27 September 1995/Accepted: 4 October 1995     

Impact of culture age on conidial germination,desiccation and UV tolerance of entomopathogenic fungi

The impact of culture age on conidial yields, germination and tolerance to UV exposure of freshly harvested and dry conidia produced by five entomopathogenic fungal (EPF) isolates was studied. Beauveria bassiana, Metarhizium anisopliae, Lecanicillium lecanii and Lecanicillium muscarium were grown on potato dextrose agar (PDA) medium for 7 or 14 days at 25°C. While the age of cultures had a significant impact on the germination rate of conidia produced by isolates L. lecanii CBS 122.175 and B. bassiana LMSA 1.01.093, other EPF isolates germinated at the same rate regardless of the culture age. When exposed to UV radiation, conidia produced by all isolates germinated at a lower rate compared to the non-irradiated conidia, although this decrease in germination (20–80% decrease) was unaffected by the culture age. Air-drying had only a slight impact on conidial germination (0–60% decrease). Under the conditions of this study, the stability of irradiated conidia produced by M. anisopliae LMSA 1.01.197 and B. bassiana CBS 110.25 was significantly increased when conidia were dried prior to UV exposure. This increase in tolerance to stress of dried conidia might be caused, at least partially, by the low metabolic activity associated with dehydration.     

Susceptibility of Larvae of Galleria mellonella to Infection by Aspergillus fumigatus is Dependent upon Stage of Conidial Germination

The ability of conidia of the human pathogenic fungus Aspergillus fumigatus to kill larvae of the insect Galleria mellonella was investigated. Conidia at different stages of the germination process displayed variations in their virulence as measured using the Galleria infection model. Non-germinating (‘resting’) conidia were avirulent except when an inoculation density of 1 × 10⁷ conidia per insect was used. Conidia that had been induced to commence the germination process by pre-culturing in growth medium for 3 h were capable of killing larvae at densities of 1 × 10⁶ and 1 × 10⁷ per insect. An inoculation density of 1 × 10⁵ conidia per insect remained avirulent. Conidia in the outgrowth phase of germination (characterised as the formation of a germ tube) were the most virulent and were capable of killing 100% of larvae after 5 or 24 h when 1 × 10⁷ or 1 × 10⁶ conidia, that had been allowed to germinate for 24 h, were used. Examination of the response of insect haemocytes to conidia at different stages of the germination process established that haemocytes could engulf non-germinating conidia and those in the early stages of the germination process but that conidia, which had reached the outgrowth stages of germination were not phagocytosed. The results presented here indicate that haemocytes of G. mellonella are capable of phagocytosing A. fumigatus conidia less than 3.0 μm in diameter but that conidia greater than this are too large to be engulfed. The virulence of A. fumigatus in G. mellonella larvae can be ascertained within 60–90 h if infection densities of 1 × 10⁶ or 1 × 10⁷ activated conidia (pre-incubated for 2–3 h) per insect are employed.     

The mechanism of the mycoinsecticide diluent on the efficacy of the oil formulation of insecticidal fungus

Adverse conditions, including low humidity, UV irradiation, and high temperature, appreciably affect the efficacy of mycoinsecticides. Oil formulation increased the virulence of Metarhizium anisopliae var. acridum (Ascomycota: Hypocreales) against locusts and grasshoppers by reducing the dependence on saturated water. A mycoinsecticide diluent (a water-in-oil emulsion) has been widely used to dilute the oil formulation of M. anisopliae in China. The aim of our study was to elucidate the mechanism by which the mycoinsecticide diluent improves the virulence of M. anisopliae. We investigated the effects of the mycoinsecticide diluent on the virulence, invasion speed, and viability of the conidia under various adverse conditions. The results demonstrated that the mycoinsecticide diluent significantly improved the virulence of conidia at low humidity (68, 75, and 84%). In particular, at an RH of 68%, the LT₅₀ for locusts treated with the emulsion was 5.4 days and was 31.6% lower than the value for locusts treated with an oil formulation. In addition, the concentration of the hyphal bodies found in the haemolymph of locusts treated with emulsion was about 27-fold higher than that in locusts treated with oil formulation four days after inoculation. This result was further confirmed by determining the concentration of M. anisopliae var. acridum DNA in locust haemolymph using quantitative PCR. The percentage germination of conidia in the emulsion was also significantly higher than that in oil at 68% RH. There was no significant difference in percentage germination between conidia treated with the emulsion and oil when exposed to irradiation with ultraviolet-B (UV-B) or high temperature. These results demonstrate that the mycoinsecticide diluent enhances the virulence of M. anisopliae formulated in oil at low humidity by providing adequate water for germination without interfering with the UV tolerance and thermotolerance of the conidia.     

A possible regulatory role for ethylene in the pollen-pistil interaction in a sporophytic self-incompatible system

The sporophytic type of self-incompatibility exhibited by Ipomoea cairica Sweet (Convolvulaceae) was partially overcome in vitro by treating the pollen and/or stigma with 10^–6 to 10^–1 M methionine, a precursor of ethylene. The implications of these observations are discussed in relation to other experiments involving use of the ethylene antagonist AgNO₃, individually and in combination with methionine and an optimum level of indole-3-acetic acid (10^–2 M). The results suggest a role for ethylene (which could also be IAA-induced) in regulating pollen germination and further tube growth in sporophytic self-incompatible systems. A hypothesis on the action of hormones in pollen germination and tube growth in a sporophytic self-incompatible (SSI) system is presented.     

In vitro maturation and germination of <Emphasis Type="Italic">Orychophragmus violaceus</Emphasis> microspores

Microspores cultured in vitro can be regarded as a system to study gene regulation, cell fate determination and cell differentiation during pollen development as well as an alternative method of genetic transformation in plants. In our study, pollen development and viability in Orychophragmus violaceus in vivo were determined and then pollen from the late unicellular stage was cultured in vitro. MS liquid medium + White vitamins + 2% (V/V) coconut milk + 0.5 M maltose, pH = 7.0 was the most appropriate for in vitro culture of Orychophragmus violaceus microspores. With this medium, the rates of in maturation and germination were 19.3% and 4.7%, respectively. Liquid medium with 0.6 M maltose + 1.6 mM boric acid + 2.9 mM Ca(NO₃)₂ + 29.6 μM vitamin B1, pH = 7.0 was optimal for germination of pollen matured in vivo. The rate of germination was 70.7%. Pollen matured in vitro cultured in similar medium exhibited a rate of germination of 62.7%. Hence, the experimental study showed that in vitro maturation of microspores is feasible and this experimental system can be applied to further theoretical and practical research.     

Reduction of the number of nuclei per cell ofHelminthosporium euphorbiae by protoplast isolation

Helminthosporium euphorbiae is a pathogen of the weedEuphorbia heterophylla, which causes severe losses in soybean (Glycine max) crops. The fungus causes leaf loss and affects germination, making it a promising biocontrol agent for this weed. In order to start a breeding program for this species, four isolates were examined for number of nuclei in the conidia and hyphae and nuclear behavior at different cultivation stages. The conidia were multinucleated with about 20 nuclei per conidium, and 5 to 7 nuclei were observed in the hyphae compartments. The high number of nuclei makes the genetic manipulation of this species diffucult, so the protoplast formation is an alternative for obtaining cells with a reduced number of nuclei. Thus the experimental conditions for the production and regeneration of protoplasts inH. euphorbiae were determined by assessing three enzymatic complexes and seven osmotic stabilizers. The efficiency of formation and regeneration frequency of the protoplasts varied depending on isolates, stabilizers and enzyme mixture used. The number of nuclei estimated per protoplast was reduced to 1 to 6, depending on the stage of mycelial growth during the protoplast formation process.