Robert D. Powell

Opening of the hypocotyl hook in seedlings as influenced by light and adjacent tissues

The influence of the cotyledons and apical bud and the root system on the light-induced opening of the hypocotyl hook of etiolated seedlings of Gossypium hirsutum L., Phaseolus vulgaris L., Helianthus annuus L., Ipomoea alla L., Ipomoea sp., Cucumis sativus L., Linum usitatissimum L., Hibiscus esculentus L., and Raphanus sativus L. was studied. Light stimulated the opening of hypocotyl hook in all cases, but the cotyledons and roots had different effects in different plants. Generally, the presence of cotyledons and the remainder of the shoot apical to the hook inhibited light-mediated opening, but in Gossypium the organs stimulated light-mediated opening. Presence of roots either promoted opening, had no effect, or had an effect only when the cotyledons were present. In the dark the adjacent organs had a reduced effect over that shown in the light, but one cultivar of cotton, Acala SJ1, opened the hook in the dark without cotyledons as much as under any condition in the light. The variation between species in hook opening may related to the need of that process for a proper hormonal balance, as affected by light, which must be obtained from adjacent tissues.

Specificity and Prevalence of Natural Bovine Anti-Alpha Galactosyl (Galα1-6Glc or Galα1-6Gal) Antibodies

ABSTRACT Immunity against the carbohydrate components of microorganisms mediated by antibodies is an important part of host defenses. Humans and closely related primates, but not other mammals, possess natural anti-Galα1-3Gal antibodies which also, although less avidly, react with melibiose (Galα1-6Glc). Using an enzyme-linked immunosorbent assay (ELISA) with melibiose-bovine serum albumin as an antigen, we analyzed bovine anti-alpha galactosyl antibodies with respect to specificity and distribution in individual animals. Inhibition assays showed that melibiose was the strongest inhibitor, followed equally by stachyose (Galα1-6Galα1-6Glcβ1-2Fru) and raffinose (Galα1-6Glcβ1-2Fru) and then by Galβ1-6Gal, Gal, and Galα1-2Gal. Others, including Galα1-3Gal and Galα1-4Gal, only exhibited minor inhibition. Thus, these bovine anti-alpha galactosyl antibodies appeared to preferentially react with Galα1-6Glc or Galα1-6Gal. The distinction of this specificity from that (Galα1-3Gal) of human antibodies was further demonstrated by the poor reaction of bovine serum to the Galα1-3Gal antigen in comparison to human serum. All 27 healthy bovine serum samples of the three age groups (newborn, calf, and adult) tested contained such antibodies with titers increasing with age. The antibodies purified by affinity chromatography using a melibiose-agarose column were mainly of the immunoglobulin G (IgG) isotype with a concentration of >23 μg/ml in most samples. IgG1 was found to be the primary antimelibiose IgG isotype in all age groups by isotype-specific ELISA, but a significant increase in IgG2, an isotype more related to innate immunity, was observed in calves and adults, compared to newborns. The purified antibodies reacted with the type II bovine strain ofStreptococcus agalactiae, a common pathogen of bovine mastitis. Thus, these anti-Galα1-6Glc or Galα1-6Gal antibodies in cattle might be involved in defense against microbes bearing this or the related epitopes.

Structure and Properties of Cotton Fibers from Controlled Growth Environments

The influences of growth environment on gross and fine structures, mechanical properties, and responses to chemical treatments were determined from cotton fibers of Rex and Texas Marker-1 varieties grown under ranges of controlled environment. Cell walls of fibers composed of cellulose deposited at constant and varying temperatures were found to differ in many of their properties. The cell wall thickens more slowly at lower than at higher temperatures and the walls are thinner even though the wall development periods are longer. Properties of fibers indicate that cellulose from the low-temperature environment is less compact and more responsive to chemical reagents than from the high temperatures. The fibers from low temperatures are weaker and more extensible. Relationships between cell wall thickness, fine structure, mechanical properties and chemical reactivities are illustrated.

Chilling injury in okra (Hibiscus esculentus L.) in relation to plant development and nitrogen metabolism

SummaryOkra plants were exposed to chilling temperatures of 5° or 10°C for various periods up to 144 hours in a controlled environment room. Controls were maintained in a similar room at 25°C. Seedling plants which had developed five true leaves and plants in a preflowering condition with well developed buds were used. Results showed that injury occurred at both 5° and 10°C in plants at both growth stages. Seedling plants exposed at 5°C for 144 hours were killed while the older ones died back to the lower nodes. Eventually growth occurred from the buds at these nodes. In cases where the plants survived there was a delay in flowering and a decrease in the total number of flowers. Increased cold exposure resulted in an increased percentage dry matter. It appeared that increased dessication contributed to injury, but that atmospheric humidity itself had little relationship to injury. The insoluble nitrogen fraction did not show any great change. There was an increase in some amino acids, and it was noted that these were the same as those derived from pyruvate. The soluble protein fraction did not change. It was suggested that this lack of change might be a manifestation of the difference between plants that can be hardened and those that cannot.