American Journal of Botany, 48, 6, July, 1961

Abstract: Wheat grains given 800 kr of Co⁶⁰ gamma radiation before moistening ean germinate and grow into small seedlings without cell division or desoxyribonucleic acid (DNA) synthesis. This growth is sustained by metabolism and is not merely water uptake. The growing seedlings increase in dry matter, protein, and ribonucleic acid (RNA). They can perform photosynthesis by fixing carbon from CO₂ into sugar phosphates, sucrose, amino acids, and organic acids. These results suggest that such irradiated cereals may be used for certain physiological and anatomical studies of germination and development in an intact growing organism in the absence of DNA synthesis, mitosis, and cell division.

Abstract: A morphological and histological study has been made of wheat seedlings growing without desoxyribonucleic acid (DNA) synthesis, mitosis, and cell division after gamma-irradiation of the grain. The development of these seedlings parallels the normal development of unirradiated wheat in correlative growth of primordia and organs and in the production of highly differentiated cell and tissue types (e.g., trichoblasts, vascular elements, chlorenchymatous mesophyll, and cortical parenchyma). The absence of cell division makes these seedlings differ from unirradiated plants in several respects: no initiation of new organs; abnormal maturation of regions corresponding to the meristems; greater cell lengths. Guard cells, subsidiaries, and hair-bearing cells are lacking, except in the apical 2-3 millimeters of the first leaf. Anatomic similarities of these plants to those treated with maleic hydrazide, including maturation to the tip of the roots, are discussed. The central cylinder of the upper pair of lateral seminal root primordia becomes highly differentiated with negligible elongation of the primordia. The occurrence of a high degree of differentiation after doses of radiation that produce extensive chromosome breakage indicates that in the absence of mitosis the chromosomes need not remain intact for the cells to continue differentiation. These studies show that such seedlings can be used to indicate the capacities of the cells in the embryo for differentiation without DNA synthesis, mitosis, and cell division.

Abstract: A study was made, using C¹⁴O₂, of the host-parasite relationship of dwarfmistletoe (Arceuthobium americanum Nutt.) growing on lodgepole pine (Pinus contorta Dougl.) seedlings. The translocation patterns of radioactive photosynthate were outlined to determine the feasibility of using a systemic selective herbicide for dwarfmistletoe control. Selective administration of the C¹⁴O₂ for 24-hr experimental periods in a controlled-environment chamber demonstrated that dwarfmistletoe carried on photosynthesis and that a significant portion of the photosynthate (largely sucrose) was translocated into the pine. Photosynthate produced in a terminal needle cluster of the pine was translocated basipetally to the roots, but also was accumulated in intercepting dwarfmistletoe plants. Both glucose and fructose as well as sucrose were found in large amounts in pine-produced photosynthate, but primarily sucrose was translocated, as demonstrated by paper chromatography. The principal damaging effect of the dwarfmistletoe appeared to be the cutting off of photosynthate translocation to the roots. The dwarfmistletoe acts as a biological girdle resulting in an accumulation of photosynthate above the site of infection. Presumably carbohydrates can be withheld from the roots in quantities sufficient to cause the characteristic decline of the tree that is associated with severe attack by dwarfmistletoe.

Abstract: The genus Ascoidea Bref. & Lindau in Brefeld (1891) belongs to the family Ascoideaceae (Endomycetales, Hemiascomycetidae). Ascoidea differs from all other ascomycetes by its possession of characteristic multispored asci which proliferate, the newer asci being formed through the collar-like wall remnants of older asci. Ascogenous hyphae are absent. The present fungus differs in many ways from the type and the only species of the genus, A. rubescens Bref. & Lindau. Ascoidea hylecoeti reproduces asexually by chlamydospores. The asci are conical and many spored. They are aggregated in thick clusters of 50-200 individual asci. The number of ascospores per ascus is much larger than that of A. rubescens and their size is much smaller. Ascoidea hylecoeti is known to occur only in association with the genus Hylecoetus, one of the ambrosia beetles.

Abstract: A significant effect of decreasing population size on pollen germination in vitro was observed in 8 angiosperm genera. Reduction of pollen germination percentages (Y) occurred linearly in Petunia inflata, with decrease of population size (X) below 200 grains per 0.01-ml drop, and differences from linear regression of Y = 1.43 + 0.39X were not significant. Water extracts of pollen and other plant parts contained a factor or factors which could overcome fully the population effect. The pollen growth factor was dialyzable, insoluble in ether, relatively heat-stable, and was not replaceable by kinetin or auxin. Cultural requirements of petunia pollen were studied in detail and linear growth rates in vitro of 122 µ/hr and in situ of 900 µ/hr were recorded. Growth in hanging drops tapered off in ca. 6 hr, at about the time of second mitosis. Pollen tube inhibition by incompatibility (S) alleles in situ also was observed after about 6 hr. The inhibition of pollen-tube growth by stylar extracts was investigated by in-vitro matings of 6 S allele genotypes. Highly significant differences in 5 hr growth were observed in a study of 4200 tubes; incompatible matings averaged 342 µ, semi-compatible (e.g., S₁₁ x S₁S₂) averaged 434 µ, and compatible averaged 516 µ. In semi-vitro studies of stylar segments which were pollinated and placed on agar, incompatibility was consistently and clearly evident. It is proposed that the pollen growth factor or factors ("PGF") may be consumed during growth and that incompatibility inhibits the production or utilization by, or transfer to the pollen tube of PGF. Assuming that second mitosis involves extraordinary demands for PGF, the differences between bi-nucleate and tri-nucleate pollen grains in vitro and in incompatibile matings thus might be satisfactorily resolved.

Abstract: Callus derived from seedlings of Norway spruce has been cultured for 3 1/2 yr on a medium supplemented with malt extract. The responses of the callus to auxin, kinetin, light intensity, and pH were determined. The malt extract employed was fractionated by various methods, and it was shown that the active fractions were generally ninhydrin positive. The free amino acid composition of the extract was determined. Malt extract could be replaced completely by casein hydrolysate. Arginine, glutamine, or urea, although less effective, also supported continuous growth of the callus. In contrast, NH₄NO₃ as a sole source of nitrogen failed to support growth. The same compounds that supported growth of the established strain of callus also stimulated initial formation of callus from seedlings. Inositol was the only vitamin that could be shown to stimulate callus growth. A synthetic medium has been developed for the cultures; it includes inorganic nutrients, naphthal-eneacetic acid, kinetin, myo-inositol, and either arginine or urea. Thiamin, choline chloride, and cystein are also added to the medium, although a requirement for the latter 2 of these 3 compounds has not been demonstrated.

Abstract: Although several critical studies of Psilophyton princeps have limited its range to Lower and Middle Devonian, the writers have been able to identify plant remains from the Upper Devonian as P. princeps. Specimens prepared by maceration and transfer techniques demonstrate positive agreement of characteristics of the spines, cuticle and vasculature with P. princeps from Canada and Scotland.

Abstract: The vascular cambium of pear is continually undergoing changes in composition and dimension. Circumferential growth occurs through oblique, anticlinal divisions of fusiform initials, followed by apical, intrusive growth. The production of new fusiform initials proceeds at rates which result in numbers of cells far in excess of those required for adequate circumferential expansion. Many of these cells are lost from the cambium, and others are transformed to ray initials. Consequently, a relatively low proportion of the new initials survive to repeat the cycle of elongation and division. New ray initials arise from existing ray initials and from fusiform initials. Although the immediate environment has a profound effect upon the fate of each cambial cell, over-all cambial changes are obviously synchronized.

Abstract: The effect of carbon dioxide on radiation-induced chromosome aberrations has been investigated to determine the relation of this agent to dose rate and the efficacy of a pretreatment followed by X-irradiation in nitrogen or in vacuo. Carbon dioxide and air, present during the radiation treatment, significantly increase the frequency of chromosome aberrations induced by 300 r of X rays through a 46-fold difference in dose rate. Pretreatment with CO₂ and air also increases the aberration frequency if the radiation occurs in air. Pretreatment is completely ineffective when the inflorescences are irradiated in vacuo or in nitrogen. Thus it appears that CO₂ acts synergistically with oxygen in increasing the frequency of chromosome aberrations induced by X rays.

Abstract: Cultures of the red algae, Halosaccion glandiforme (Gmelin) Ruprecht, Rhodymenia palmata f. mollis Setchell et Gardner, Fauchea laciniata J. G. Agardh, and F. fryeana Setchell were started from spores and in some instances maintained for about 2 1/2 yr. Culture methods are described and the plants obtained in culture compared to those in nature. Of the plants cultured, only some of F. laciniata became fertile. The use of spores undergoing their first division in germination for observation of mitotic divisions is reported.

Abstract: Normal cultures of Candida albicans give rise to a small-colony variant similar in many respects to the "petite" of Saccharomyces cerevisiae. The difference in colony size is due to a difference in the rate of cell division. They arise spontaneously from the wild-type at a frequency of from 1-3%, and the individual cells of both types are the same size. However, unlike the "petite," they contain the enzymes cytochrome oxidase, cytochrome b, and succinic dehydrogenase, and they respire normally.

Abstract: Etiolated pea stem segments were used to study the red, far-red reversible photoinhibition of stem growth. The growth of immature, apical tissue was insensitive to light after excision from the seedling, unless a growth-promoting sugar (sucrose, glucose, fructose) was included in the medium. Red light specifically inhibited the growth caused by the sugars. Growth promotions of the same magnitude caused by indoleacetic acid or gibberellic acid were not reduced by irradiation of the tissue. The effects of various other sugars were tested. Arabinose and galactose, which do not promote growth, did not cause photosensitive growth in the isolated tissue. Mannose and xylose promoted growth at low concentrations, and this small promotion was inhibited by irradiation. Photoinhibition occurred even at inhibitory concentrations of mannose and xylose. The distinctness of light-sensitive growth is discussed, and the photoinhibition of a growth process which is limited by availability of sugars is suggested.

Abstract: Seven biochemical mutants of Cladosporium fulvum Cke. were obtained by irradiating spores with ultraviolet light. Various combinations of 2 mutants failed to grow on minimal medium when the mixtures were made by shaking spore suspensions in deionized water. When the various combinations of 2 mutants were grown together on complete medium for one generation prior to transfer to minimal medium, 2 combinations were successful. The same 2 mutant pairs grew directly on minimal medium when spores and mycelium were mixed, centrifuged, and plated as pellets. These results suggest that heterocaryosis may occur in the tomato-leaf-mold organism. Diffusion tests performed with pairs of biochemical mutants showed that no cross-feeding between mutants occurred through the agar. Both parental types were reisolated from the presumed heterocaryon, 2 plus 6. The presence of anastomoses and occasional binucleate spores and mycelial cells was observed.

Abstract: The interactions between gibberellin and various environmental factors on stem elongation of greenhousegrown Phaseolus vulgaris have been studied in steady-state growth systems. The action of gibberellin was found to be independent of rate of accumulation of photosynthetic products, root activity, temperature, water availability and both ultraviolet and X-radiation. It was also shown that gibberellin interacts completely with red/far-red radiation given at the end of the daily light period. This interaction is complete even when maximum growth rates are experimentally reduced by limiting various independent factors. These results are interpreted as demonstrating that red/far-red radiation controls rate of stem elongation in greenhouse-grown plants through an effect on the endogenous gibberellin system of the plant. None of the other environmental factors studied seems to act through the gibberellin system.

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