Reaction of Germinating Maize Pollen to <i>Helminthosporium maydis</i> Pathotoxins<sup>1</sup>

Laughnan, John R.; Gabay, Sabit

doi:10.2135/cropsci1973.0011183x001300060028x

Cited by 49 publications

(12 citation statements)

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“…It had been suggested (13), but later modified (2), that the primary effect may lie in a disturbance of mitochondrial oxidation. A mitochondrial target site would be consistent with increased leakage of ions (6,7) and inhibition of root growth and pollen tube elongation (11) of corn susceptible to the toxin. In addition to these effects, a drop in transpiration and photosynthetic rates caused by toxin was ascribed to stomatal closure induced by alteration of K+ flux in guard and subsidiary cells (1).…”

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confidence: 85%

Inhibition of Dark CO₂ Fixation and Photosynthesis in Leaf Discs of Corn Susceptible to the Host-specific Toxin Produced by Helminthosporium maydis, Race T

Bhullar¹,

Daly²,

Rehfeld³

1975

Plant Physiol.

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The host-specific toxin produced by Helminthosporium maydis, race T, causes 50% inhibition of dark fixation of "4CO2 by leaf discs of susceptible (Texas male sterile) corn when it is diluted to approximately 1/10,000 of the volume of the original fungus culture filtrate. Dilutions of 1/10 or less are required for equivalent inhibition of discs prepared from resistant (N) corn. Root growth and photosynthesis were considerably less sensitive (dilution values 1/3000 and 1/1200, respectively), as was leakage of "C induced by toxin from preloaded discs. ions induced by most of these toxins has centered attention on host membranes as a site of action (5,19,21,22). A major problem in the identification of a primary site for race T toxin is the considerable variation in toxin dosage and time of exposure that has been reported for each effect. In this laboratory, for example, 50% inhibition of susceptible corn root growth can be achieved with 1/3000 dilution of race T toxin, whereas dilutions of 1/ 10 to 1 / 100 apparently are required for rapid induction of ion leakage (6, 7) or inhibition of mitochondrial oxidation (9, 13, 16).At present, it is impossible to decide whether the variations arise from differences in toxin potency, the nature of the assay systems employed, or fundamental differences in the innate sensitivity of the processes under examination. It seems reasonable that the primary site would show the greatest sensitivity; that is, would require the least amount of toxin for a response.As a first approach to the problem, a quantitative bioassay for standardizing activity of toxin from various sources becomes essential. Inhibition of root growth has been used for other host specific toxins. Although usable for race T toxin, we have found this method time-consuming, tedious, and unreliable because of variations in seed germination and seedling vigor. During studies of the effect of T toxin on several physiological and biochemical processes of corn leaves, we observed significant reduction in dark fixation of CO2. In addition to its intrinsic interest in connection with a mode of action, we also have found the phenomenon to be useful as a reliable, sensitive, and rapid bioassay. MATERIALS AND METHODS

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confidence: 85%

Inhibition of Dark CO₂ Fixation and Photosynthesis in Leaf Discs of Corn Susceptible to the Host-specific Toxin Produced by Helminthosporium maydis, Race T

Bhullar¹,

Daly²,

Rehfeld³

1975

Plant Physiol.

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“…During the development of the augmented K+ uptake capacity in either N or T roots, the sensitivity to the toxin did not change; uptake in N roots was inhibited by 10 to 25% and uptake in T roots was inhibited by 70 to 80%. The difference in toxin sensitivity of K+ uptake between N and T roots may be due to N possessing a protective mechanism which is deficient in T.The extreme susceptibility of Texas cytoplasmic male-sterile (T) maize to Southern Corn Leaf Blight is cytoplasmically conditioned and inherited in association with the non-Mendelian determinant of male sterility (12,18). T versions of a given maize inbred are more susceptible to Helminthosporium maydis, race T than normal cytoplasmic (N) versions (7, 10).…”

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confidence: 99%

Influence of Helminthosporium maydis, Race T, Toxin on Potassium Uptake in Maize Roots

Frick¹,

Nicholson²,

Hodges³

et al. 1976

Plant Physiol.

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The effect of a toxin extract of Helminthosporium maydis, race T on K + (86Rb) uptake by excised root segments of normal (N) and Texas cytoplasmic male-sterile (T) versions of corn inbred W64A was investigated. The uptake of K+ was inhibited in both N and T roots by the toxin. This was true for both basal (freshly excised) and augmented (pretreated with aeration) K+ uptake. Augmented uptake was more toxin-sensitive than basal uptake (irrespective of cytoplasm type), and the augmented uptake in T roots was seven to eight times more toxin-sensitive than in N roots.Specific zones of roots differed in their basal and augmented K+ uptake rates as well as their toxin sensitivities. The root apex of T was more sensitive to toxin than the apex of N roots when basal K+ uptake was measured. In mature zones of the root, T was more sensitive than N when augmented rates were measured. During the development of the augmented K+ uptake capacity in either N or T roots, the sensitivity to the toxin did not change; uptake in N roots was inhibited by 10 to 25% and uptake in T roots was inhibited by 70 to 80%. The difference in toxin sensitivity of K+ uptake between N and T roots may be due to N possessing a protective mechanism which is deficient in T.The extreme susceptibility of Texas cytoplasmic male-sterile (T) maize to Southern Corn Leaf Blight is cytoplasmically conditioned and inherited in association with the non-Mendelian determinant of male sterility (12,18). T versions of a given maize inbred are more susceptible to Helminthosporium maydis, race T than normal cytoplasmic (N) versions (7, 10). The fungal pathogen synthesizes a toxin complex which accounts for this difference in levels of susceptibility of the host cytoplasmic types (7,8 Table I and Figure 1, the absorption period was 60 min during which time some augmentation occurred. The segments were exposed to label and toxin simultaneously. Labeled segments were washed for 20 min in 40 ml of cold I mM CaSO4, weighed, and assayed for " Rb content by liquid scintillation spectrometry. Transfer of segments between solutions was by filtration on a Buchner funnel. Influx of K+ and 86Rb were taken to be equivalent using tissue grown in the absence of exogenous K+ (17).Basal rates of K+ uptake were measured in freshly cut root segments, whereas augmented rates were measured after aeration of segments in distilled H20. This augmented uptake potential has been referred to as in "induced" ion uptake (19), or as "aging" (1, 16) and may be an important feature of the transport process.Helminthosporium maydis Nisikado and Miyake, race T, was grown for 8 to 10 days in shake culture (100 rpm, 24 C) on Fries medium (26), without micronutrients. The culture fluid was filtered through cheesecloth, concentrated to one-tenth volume by flash evaporation at 45 C, and precipitated (12 hr, 4 C) with two volumes of cold methyl alcohol. The precipitate was removed by centrifugation and the methyl alcohol was removed from the aqueous-methyl alcohol phase by flash evaporation. The rema...

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“…It has been shown that a toxin from Drechslera maydis prevented germination of pollen from maize plants susceptible to the disease but not of pollen from resistant plants (30), and compounds present in Alternaria brassicicola culture filtrates inhibited Brassica pollen germination (6). In very few cases (5,30) has it been possible to make pollinations with selected pollen. Success has previously been limited because the selection procedure killed the pollen-producing plants (but not in ref.…”

Section: Discussionmentioning

confidence: 99%

Pollen selection: a transgenic reconstruction approach.

Touraev

Fink²,

Stöger³

et al. 1995

Proc. Natl. Acad. Sci. U.S.A.

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A transgenic reconstruction experiment has been performed to determine the feasibility of male gametophytic selection to enhance transmission of genes to the next sporophytic generation. For tobacco pollen from a transgenic plant containing a single hygromycin-resistance (hygromycin phosphotransferase, hpt-) gene under control of the dc3 promoter, which is active in both sporophytic and gametophytic tissues, 3 days of in vitro maturation in hygromycincontaining medium was sufficient to result in a 50% reduction of germinating pollen, as expected for meiotic segregation of a single locus insert. Pollination of wild-type plants with the selected pollen yielded 100%o transgenic offspring, as determined by the activity of the linked kanamycin-resistance gene-present within the same transferred T-DNA bordersunder control of the nos promoter. This is direct proof that selection acting on male gametophytes can be a means to alter the frequency of genes in the progeny.The plant life cycle consists of two distinct phases, the diploid sporophytic"and the haploid gametophytic phase. In angiosperms, the haploid phase is reduced, and the male and female gametophytes are enclosed in the respective sex organs of the sporophyte. Male and female gametophytes (i.e., pollen and embryo sacs) are formed from haploid spores, the direct products of meiosis, and the sporophytic phase starts again after the fusion of the two pollen-contained sperms with the egg and polar cells of the embryo sac in a double fertilization event. In spite of the large morphological and physiological differences, a large overlap of gene expression has been demonstrated between the sporophytic and gametophytic phase on the protein and mRNA level (for reviews, see refs. 1 and 2).These data provided the theoretical basis for the early pollen selection experiments (for review, see ref.2). The idea was that if such an overlap exists, it should be possible to exert selection pressures on pollen to increase the frequency of responsive genes in the subsequent sporophytic generation. Angiosperm pollen has some features that makes pollen selection a very attractive method of plant breeding: large population size, haploid nature of the cells, and independence from the maternal plant (3).A variety of selection pressures such as drugs, heat, water, cold temperature, and other stresses have been applied to mature pollen just before pollination, and nonstressed plants have been pollinated with the selected pollen in anticipation of obtaining progeny in which an increased frequency of resistant individuals can be found (for review, see ref. 4). Despite a few positive reports (5-9), the feasibility of pollen selection is still under question. This is mainly due to the problem of discriminating between gametophytic and sporophytic effects on pollen development (resulting from pollen-and antherexpressed genes, respectively; refs. 2 and 9) and a lack of appropriate selection schemes. The developmental windowThe publication costs of this article were defrayed in part by...

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Reaction of Germinating Maize Pollen to Helminthosporium maydis Pathotoxins¹

Cited by 49 publications

References 0 publications

Inhibition of Dark CO₂ Fixation and Photosynthesis in Leaf Discs of Corn Susceptible to the Host-specific Toxin Produced by Helminthosporium maydis, Race T

Inhibition of Dark CO₂ Fixation and Photosynthesis in Leaf Discs of Corn Susceptible to the Host-specific Toxin Produced by Helminthosporium maydis, Race T

Influence of Helminthosporium maydis, Race T, Toxin on Potassium Uptake in Maize Roots

Pollen selection: a transgenic reconstruction approach.

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Reaction of Germinating Maize Pollen to Helminthosporium maydis Pathotoxins1

Cited by 49 publications

References 0 publications

Inhibition of Dark CO2 Fixation and Photosynthesis in Leaf Discs of Corn Susceptible to the Host-specific Toxin Produced by Helminthosporium maydis, Race T

Inhibition of Dark CO2 Fixation and Photosynthesis in Leaf Discs of Corn Susceptible to the Host-specific Toxin Produced by Helminthosporium maydis, Race T

Influence of Helminthosporium maydis, Race T, Toxin on Potassium Uptake in Maize Roots

Pollen selection: a transgenic reconstruction approach.

Contact Info

Product

Resources

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Reaction of Germinating Maize Pollen to Helminthosporium maydis Pathotoxins¹

Inhibition of Dark CO₂ Fixation and Photosynthesis in Leaf Discs of Corn Susceptible to the Host-specific Toxin Produced by Helminthosporium maydis, Race T

Inhibition of Dark CO₂ Fixation and Photosynthesis in Leaf Discs of Corn Susceptible to the Host-specific Toxin Produced by Helminthosporium maydis, Race T