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Growth parameters and carbohydrate contents were determined for Fraxinus pennsylvanica Marsh. seedlings inoculated with Glomus macrocarpum Tul. and Tul. or Glomus fasciculatum (Thaxt.) Gerd. and Trappe, and for uninoculated controls that were grown in a greenhouse for 16 weeks at root temperatures of 15, 25 or 35 °C. Seedling growth responded rapidly to mycorrhizal inoculation when root temperatures were 25 or 35 °C. Response to inoculation at 15 °C was delayed but seedlings at this temperature finally attained the size of those grown at 25 and 35 °C. Growth of noninoculated plants was best at 15 and 25 °C. Inoculation with mycorrhizal fungi moderated the adverse effect of higher root temperature. Infection of roots by both fungal species was greater at 25 °C than at 15 or 35 °C. Sugar content increased as root temperature increased whereas starch content was inversely related. Both soluble sugar and starch content were less in mycorrhizal than in nonmycorrhizal seedlings. [ABSTRACT FROM AUTHOR]

Green ash (Fraxinus pennsylvanica Marsh.) was either inoculated or not with Glomus etunicatum Becker and Gerd. and grown for 37 d to permit root colonization. Root hydraulic conductivity (Lp) per unit length was measured on excised root systems to examine the influence of vesicular-arbuscular (VA) mycorrhiza inoculation, seedling size, phosphorus (P) nutrition, and biomass distribution. Fertilization with P eliminated significant differences in seedling size and dry matter distribution between mycorrhizal (M) and non-mycorrhizal (NM) seedlings, but VA mycorrhizas increased root and leaf P concentration. Root Lp was similar in M and NM seedlings of similar size, and was lower in M seedlings for a given root P concentration. Root Lp decreased with age and weight, and increased as the proportion of dry weight in the leaves increased in both M and NM seedlings. Mycorrhizal colonization had no significant effect on root Lp in the absence of a significant growth response. [ABSTRACT FROM AUTHOR]

Inoculation of seedlings of green ash (Fraxinus pennsylvanica Marsh.) with vesicular-arbuscular (VA) mycorrhizal fungi, significantly increased seedling heights, root collar diameters, dry matter accumulations and phosphorus (P) nutrition relative to control seedlings. The ability of these VA mycorrhizal fungis, which were isolated form low P forest soils (5-7 mg kg-1), to enhance seedling growth in a high-P (148 mg kg-1) nursery soil provides evidence for the occurrence of VA mycorrhizal fungi which may be effective under both high and low soil P conditions. There was a significant positive correlation between foliar P concentration and percentage infection. Despite significant differences in tissue P concentrations among seedlings receiving different inoculum treatments, the degree of growth enhancement was the same. Growth increase due to enhanced P nutrition in seedlings with higher concentration of foliar P may have been offset by an increased drain on host photosynthate via production and maintenance of greater amounts of fungal biomass, or may have been limited by the low K fertility of the nursery soil. Colonization percentages in roots of seedlings of green ash were high despite high soil P concentrations. The pattern of infection development was unique for each VA mycorrhizal fungal species. A modification of the gridline intercept technique was used to assess intensity of infection. Infection for all endophytes during the period of most rapid vegetative host growth was predominantly arbuscular. However, arbuscular intensity fluctuated during this period. Vesicles increased in number with time but always made up a small percentage of total infection. [ABSTRACT FROM AUTHOR]

The effects of Glomus macrocarpum and a high rate of nutrient addition upon growth, root carbohydrate and P content, and mycorrhizal development in green ash (Fraxinus pennsylvanica) seedlings were studied over two growing seasons. Mycorrhizal and similarly growing non-mycorrhizal seedlings had similar seasonal patterns in growth and in root carbohydrate and P content. No clear difference in mycorrhizal development as as result of nutrient treatment occurred until the middle of the second growing season when the percent root infection of seedlings that received low nutrient increased and that of seedlings that received high nutrient decreased. A seasonal cycle with two phases in the interaction of the VA mycorrhiza and host growth, root: shoot ratios, root infection, root content of soluble sugars, starch and P, arbuscule and vesicle numbers, and spore population is proposed. [ABSTRACT FROM AUTHOR]

The relationship between seed weight, embryo weight, ash content and maximum size attained by seedlings dependent on their own food reserves was investigated in 24 species of Compositae. The fraction of total seed weight contributed by the seed coat increased with seed weight from 15% in Erigeron canadensis to 61% in Tragopogon pratensis. Seedling weight was proportional to embryo weight raised to the power of ⅔. That is, the larger the embryo the less carbon it assimilated per unit weight of embryo. The relative growth rate of the seedlings during the first 3 weeks was inversely proportional to ln embryo weight. The root weight ratios of the seedlings were inversely proportional to ln embryo weight. The ash content of the seeds was negatively correlated with their weight but absolute mineral content per seed was directly proportional to maximum seedling size attained, regardless of seed size. It is postulated that the relatively larger seed coats of big seeds are a defence against increased risk of predation. The ash contents and root weight ratios of the seedlings suggest that the growth of small seedlings is limited by soil nutrients and that of large seedlings by light. [ABSTRACT FROM AUTHOR]

The relationship between the growth of the host, and development and morphology of a vesicular-arbuscular mycorrhizal fungus was studied in green ash (Fraxinus pennsylvanica Marsh.). A yearly cycle with three phases is suggested. Phase I is a period of fast shoot growth, slow root growth, rapid colonization of the root system by the mycorrhizal fungus and greater numbers of fungal arbuscles than vesicles. Phase II is a period of fast root growth and a decline in the percentage of root length infected. Phase III is. characterized by senescing leaves, infection percentages increasing to a static level, and greater numbers of vesicles than arbuscles. Mycorrhizal green ash seedlings generally had greater heights, weights and root collar diameters and lower root: shoot ratios than non-mycorrhizal seedlings. [ABSTRACT FROM AUTHOR]

Radioautographs by light and electron microscopy of callus cells of green ash (Fraxinus pennsylvanica Marsh.) that had been fed low levels of the growth factor [SUP3]H myo-inositol indicated an almost exclusive incorporation of the label into the cytoplasmic constituents. These results contrast with those from most other studies of incorporation in higher plants. The incorporation here of myo-inositol suggests that its prime function is the synthesis of cytoplasmic membrane systems of the cell rather than in the polysaccharide component of the primary wall. [ABSTRACT FROM AUTHOR]

In Fraxinus pennsylvanica seedlings which were injured by epidermal scraping, wound periderm was initiated before callus formation. Wound periderm was formed before normal periderm and stimulated formation of normal periderm in uninjured tissue near the wound. [ABSTRACT FROM AUTHOR]

Seedlings of Fraxinus pennsylvanica, Robinia pseudoacacia, and Ailanthus altissima were grown from seed for 30 days in different daylengths and used to investigate early periderm and xylem formation. Periderm and secondary xylem did not develop in dark-grown seedlings. Xylem increments of Fraxinus pennsylvanica and Robinia pseudoacacia seedlings increased significantly with each increase in daylength from 8 to 24 hours. Xylem increment in seedlings of Ailanthus altissima showed a slight but non-significant response to daylength. Phellogen formation and activity were stimulated in all three species as daylength was increased. Periderm was not present in 30-day-old Ailanthus altissima seedlings grown on 8-hour days, but phellem increased significantly as daylength was increased from 16 to 24 hours. In Fraxinus pennsylvanica seedlings periderm was formed earlier and phellem increment was greater in seedlings grown on 24-hour daylengths than in those grown on 16-hour daylengths. In the latter regime phellogen was formed sooner and was more active than in seedlings grown on 8-hour daylengths. Periderm increment in Robinia pseudoacacia seedlings could not be measured because of crushing of phellem, but it formed sooner and appeared to proliferate faster in seedlings grown on or 24 hour days than on shorter daylengths. Differences in time to formation of the vascular cambium and phellogen and in production of xylem and phellem indicated differences in physiological controls. [ABSTRACT FROM AUTHOR]

Seedlings of Fraxinus pennsylvanica were grown from seed and subjected to various treatments which removed leaves, cotyledons, stem apices or buds at periods up to 35 days after cotyledon emergence. In addition, portions of the stems of several seedlings were kept in darkness during the experiments. Periderm did not form in seedlings from which all foliage was removed as it emerged. Seedlings with any foliage developed periderm, but periderm-stimulatory substances were not released from foliage until it reached a certain stage of development. Both cotyledons and leaves exported periderm-stimulatory substances, but leaves appeared to export more. Substances produced in the apical meristem or actively growing buds had no effect on phellogen formation and activity, but appeared to regulate the kind of periderm cells produced, their differentiation, and their anticlinal divisions. The stimuli for periderm formation and subsequent development were strongly basipetal and only weakly acropetal. However, darkening the stem below the foliage appeared to moderate the polar transport of periderm-stimulatory substances. Foliar products increased wound-periderm formation and were essential for wound-stimulated formation of normal periderm. [ABSTRACT FROM AUTHOR]