Phosphorus deficiency induced by nitrogen input in Douglas fir in the Netherlands

Summary A re-examination of earlier NPK fertilization experiments in Douglas fir stands on sandy soils shows the effects of high nitrogen input by air pollution during the last 10–15 years on plant nutrition at these sites. In 1960, experimental plots showed a positive growth reaction to nitrogen, phosphorus, and potassium fertilization. All suffered from severe phosphorus deficiency in 1984, low phosphorus in the needles was invariably accompanied by a high nitrogen content, with all N/P ratios between 20 and 30. The same conclusion emerges from an independent investigation of nutrient status of a selection of Douglas fir stands. Hence, if stand productivity and a balanced nutrient status of the trees is to be maintained, the increase in atmospheric input of nitrogen calls for supplementary fertilization. Given the current N/P ratios in the needles, a positive growth response to phosphorus fertilization is to be expected.     

Siderophores and outer membrane proteins of antagonistic, plant-growth-stimulating, root-colonizing Pseudomonas spp

As an approach to understanding the molecular basis of the reduction in plant yield depression by root-colonizing Pseudomonas spp. and especially of the role of the bacterial cell surfaces in this process, we characterized 30 plant-root-colonizing Pseudomonas spp. with respect to siderophore production, antagonistic activity, plasmid content, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis patterns of their cell envelope proteins. The results showed that all strains produce hydroxamate-type siderophores which, because of the correlation with Fe3+ limitation, are thought to be the major factor responsible for antagonistic activity. Siderophore-negative mutants of two strains had a strongly decreased antagonistic activity. Five strains maintained their antagonistic activity under conditions of iron excess. Analysis of cell envelope protein patterns of cells grown in excess Fe3+ showed that most strains differed from each other, although two classes of similar or identical strains were found. In one case such a class was subdivided on the basis of the patterns of proteins derepressed by iron limitation. Small plasmids were not detected in any of the strains, and only one of the four tested strains contained a large plasmid. Therefore, it is unlikely that the Fe3+ uptake system of the antagonistic strains is usually plasmid encoded.     

Resistance of citrus fruit to mass transport of water vapor and other gases

The resistance of oranges (Citrus sinensis L. Osbeck) and grapefruit (Citrus paradisi Macf.) to ethylene, O₂, CO₂, and H₂O mass transport was investigated anatomically with scanning electron microscope and physiologically by gas exchange measurements at steady state. The resistance of untreated fruit to water vapor is far less than to ethylene, CO₂ and O₂. Waxing partially or completely plugs stomatal pores and forms an intermittent cracked layer over the surface of fruit, restricting transport of ethylene, O₂, and CO₂, but not of water; whereas individual sealing of fruit with high density polyethylene films reduces water transport by 90% without substantially inhibiting gas exchange.

Stomata of harvested citrus fruits are essentially closed. However, ethylene, O₂ and CO₂ still diffuse mainly through the residual stomatal opening where the relative transport resistance (approximately 6,000 seconds per centimeter) depends on the relative diffusivity of each gas in air. Water moves preferentially by a different pathway, probably through a liquid aqueous phase in the cuticle where water conductance is 60-fold greater. Other gases are constrained from using this pathway because their diffusivity in liquid water is 10⁴-fold less than in air.

     

Osmotic regulation of aldose reductase protein synthesis in renal medullary cells

Renal medullary cells are normally exposed to high extracellular NaCl as part of the urinary concentrating mechanism. They react to this stress by accumulating sorbitol and other organic osmolytes. PAP-HT25, a line of epithelial cells derived from rabbit renal inner medulla, expresses this response. In hypertonic medium, these cells accumulate large amounts of sorbitol. There is a large increase in the amount of aldose reductase, which catalyzes production of sorbitol from glucose. The purpose of the present study was to investigate whether the aldose reductase protein increases because of faster synthesis or slower degradation. We measured the rate of synthesis and degradation of aldose reductase protein by pulse-chase with [35S]methionine, followed by immunoprecipitation with specific antiserum and autoradiography. The protein synthesis rate was 6 times greater in cells grown in hypertonic (500 mosmol/kg) medium, than in those grown in normal (300 mosmol/kg) medium. When control cells were switched to hypertonic medium, the synthesis rate increased 15-fold by 24 h, then decreased to 11-fold after 48 h. In contrast, synthesis rate continued to increase past 24 h when accumulation of sorbitol was prevented by inhibiting aldose reductase activity with Tolrestat. Thus, there is a feedback mechanism by which cellular sorbitol accumulation inhibits aldose reductase protein synthesis. Degradation of aldose reductase protein was slow (only about 25% in 3 days) and was not affected by osmolality. Thus, the osmoregulatory increase in aldose reductase protein is due to an increase in its synthesis rate and not to any change in its degradation.     

Chaetomella acutiseta produces chaetomellic acids A and B which are reversible inhibitors of farnesyl-protien transferase

Chaetomellic acids A and B, isolated from Chaetomella acutiseta, are specific inhibitors of farnesyl-protein transferase that do not inhibit geranylgeranyl transferase type 1 or squalene synthase. Chaetomellic acids A and B are reversible inhibitors, resemble farnesyl diphosphate and probably inhibit FPTase by substituting for farnesyl diphosphate. Chaetomellic acid production appears to be widespread within the genus Chaetomella. Correspondence to: R. B. Lingham