VARIATION IN ALCOHOL DEHYDROGENASE ACTIVITY AND FLOOD TOLERANCE IN WHITE CLOVER,TRIFOLIUM REPENS

Flooding results in induction of anaerobic metabolism in many higher plants. As an important component of anaerobic energy production, alcohol dehydrogenase (ADH) activity increases markedly in response to flooding in white clover, Trifolium repens. Significant inter-individual variation in flood-induced ADH activity exists in natural populations of T. repens. The genetic basis of this variation was analyzed by offspring-midparent regression of data from 75 greenhouse reared families; the estimated heritability of flood-induced ADH activity was 0.55 (±0.13). Genetic variation in flood-induced ADH activity has pronounced effects on physiological response and flood tolerance in this species. ADH activity is positively correlated with the rate of ethanol production, indicating that observed in vitro activity differences are manifested in in vivo physiological function. T. repens plants with higher ADH activities during flooding have greater flood tolerance (measured as growth rate when flooded/unflooded growth rate). Variation in ADH activity during flooding accounts for more than 79% of the variance in flood tolerance. On the basis of a limited field survey of populations occupying three sites differing in exposure to flooding conditions, individuals from site C, the most frequently flooded site, expressed significantly higher average ADH activity when flooded than individuals from site A, a site with no history of flooding. Since ADH activity levels are not correlated with electrophoretic mobility variation in T. repens, this work supports previous suggestions that regulatory variation in enzyme activity may play a central role in biochemical adaptations to environmental stress.     

GENESIS OF THE APYRENE PARASPERM IN THE APPLE SNAIL POMACEA CANALICULATA (GASTROPODA: AMPULLARIIDAE): AN ULTRASTRUCTURAL STUDY

The apyrene paraspermatogenesis in the freshwater gastropod Pomaceacanaliculata has been studied with electron microscopy. Matureapyrene parasperm result from a cytodifferentiation processwithout maturation division. The atypical condition is recognizedearly. Paraspermatogonia are characterized by voluminous nucleiwith irregular clusters of heterochromatin, numerous dilated cisternaeof the rough endoplasmic reticulum and small electron-dense granulesspread through the cytoplasm. As this process advances, the nucleibecome lobed and chromatin degenerates. The remnant chromatin condensesto form dense bodies which are finally excreted from the cells.At the cytoplasmic level a centriolar multiplication with the consequentflagellogenesis takes place. The axonemal microtubules run alongthe entire length of the cell and emerge from the posteriorend forming a tuft of three or more free flagella. The roughendoplasmic reticulum and the Golgi complex are involved inthe production of secretory granules, some of which are laterreleased by exocytosis. At the end of paraspermatogenesis matureapyrene parasperm are fusiform-shaped anuclear ciliated cells. (Received 20 January 2000; accepted 18 July 2000)     

Exopolysaccharide-producing strains of thermophilic lactic acid bacteria cluster into groups according to their EPS structure

AIMS: To compare galactose-negative strains of Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus isolated from fermented milk products and known to produce exopolysaccharides (EPSs). METHODS AND RESULTS: The structures of the EPSs were determined using nuclear magnetic resonance (NMR) and their genetic relationships determined using restriction endonuclease analysis (REA) and random amplification of polymorphic DNA (RAPD). Similar groupings were apparent by REA and RAPD, and each group produced an EPS with a particular subunit structure. CONCLUSION: Although none of the strains assimilated galactose, all inserted a high proportion of galactose into their EPS when grown in skimmed milk, and fell into three distinct groups. Significance and Impact of the Study: This information should help in an understanding of genetic exchanges in lactic acid bacteria.     

Iron plaque enhances phosphorus uptake by rice (Oryza sativa) growing under varying phosphorus and iron concentrations

Both solution culture and pot experiments were performed to investigate (a) the effects of external Fe (II) concentrations and forms on the formation of iron plaque on the roots of rice (Oryza sativa) and subsequent P adsorption on iron plaque and shoot P concentrations and (b) the effects of soil moisture regimes on the formation of iron plaque and P adsorption on root surfaces and P accumulation in shoots. The results showed that iron plaque was significantly increased with increasing Fe²⁺ concentrations in the solution culture. The amounts of P adsorbed on the iron plaque were increased significantly with external Fe²⁺ concentrations. Although shoot P concentration was not significantly affected by Fe²⁺ treatment after incubation for 2 days, it was significantly increased in the Fe‐treated plants compared with Fe‐deprived ones after incubation for 4 days. Soil culture experiment showed that the formation of iron plaque on root surfaces was promoted by exogenous iron, with greater amount of iron plaque being formed by addition of ferric hydroxide than of ferric oxide. Phosphorus adsorption on iron plaque also increased with the addition of iron oxides, and increasing soil P increased the amounts of P associated with the iron plaque and shoot P concentration. The amounts of iron plaque were almost sixfold higher under flooding condition than under field capacity condition. Plants pretreated under flooding condition generally had higher shoot P concentrations when they were transplanted to solutions with varying P levels, and this was most pronounced in the treatment with highest solution P concentration. The results suggest that iron plaque acts as a nutrient reservoir for phosphorus in the rhizosphere and helps enhance P acquisition by rice.     

Phytotoxicity of pheromonal chemicals to fruit tree foliage: chemical and physiological characterization.

Some recent high-load, low-density pheromone-release devices emit an ethanolic blend of pheromone directly onto crop foliage to control insect pests by mating disruption. This study characterized the phytotoxicity associated with deposition of some pheromonal compounds in concentrated drops on the foliage of trees bearing aerosol release devices. The relative toxicity of straight-chained alkanes, alcohols, aldehydes, and acetates with chain lengths varying from C-2 to approximately C-20 was quantified in the laboratory by the severity of necrotic lesions. The order of severity for phytotoxicity caused by pheromonal compounds was alkanes < acetates = aldehydes < or = alcohols. Within compound classes tested, pheromones with chain lengths of 6-13 carbons were the most phytotoxic. Phytotoxicity was not detectable at dosages <1 mg administered in 10 microl of ethanol. Phytotoxicity of pheromones was highly correlated with presence of both a hydrophilic and lipophilic molecular domain. We postulate nonspecific membrane disruption as a likely mode of action for pheromonal phytotoxicity. Limited attempts to remediate this effect by changing carrier solvents or adding surfactants, spreaders, or nonvolatile diluents were not successful. Because the toxic action of pheromones upon plant tissues appears relatively benign, and growers have not been adverse to localized phytotoxicity to foliage and fruits on two trees per 0.4 ha, we propose that limited phytotoxicity associated with first-generation aerosol dispenser technology can be viewed as non-threatening.