Leaf water relations characteristics of differently potassium fertilized and watered field grown barley plants

Seasonal leaf water relations characteristics were studied in fully irrigated spring barley (Hordeum distichum L. cv. Gunnar) fertilized at low (50 kg K ha⁻¹) or high (200 kg K ha⁻¹) levels of potassium applied as KCl. The investigation was undertaken from about 14 days before anthesis until the milk ripe stage in leaves of different position and age. Additionally, the effects of severe water stress on leaf water relations were studied in the middle of the grain filling period in spring barley (cv. Alis). The leaf water relations characteristics were determined by the pressure volume (PV) technique. Water relations of fully irrigated plants were compared in leaf No 7 with the water relations of slowly droughted plants (cv. Alis). Leaf osmotic potential at full turgor (ψ _π ¹⁰⁰ ) decreased 0.1 to 0.3 MPa in droughted leaves indicating a limited osmotic adjustment due to solute accumulation. The leaf osmotic potential at zero turgor (ψ _π ⁰ ) was about −2.2 MPa in fully irrigated plants and −2.6 MPa in droughted plants. The relative water content at zero turgor (R⁰) decreased 0.1 unit in severely droughted leaves. The ratio of turgid leaf weight to dry weight (TW/DW) tended to be increased by drought. The tissue modulus of elasticity (ε) decreased in droughted plants and together with osmotic adjustment mediated turgor maintenance during drought. A similar response to drought was found in low and high K plants except that the R⁰ and ε values tended to be higher in the high K plants. Conclusively, during drought limited osmotic adjustment and increase in elasticity of the leaf tissue mediated turgor maintenance. These effects were only slightly modified by high potassium application. The seasonal analysis in fully irrigated plants (cv. Gunnar) showed that within about 14 days from leaf emergence ψ _π ¹⁰⁰ decreased from about −0.9 to −1.6 MPa in leaf No 7 (counting the first leaf to emerge as number one) and from about −1.1 to −1.9 MPa in leaf No 8 (the flag leaf) due to solute accumulation. A similar decrease took place in ψ _π ⁰ except that the level of ψ _π ⁰ was displaced to a lower level of about 0.2 to 0.3 MPa. Both ψ _π ¹⁰⁰ and ψ _π ⁰ tended to be 0.05 to 0.10 MPa lower in high K than in low K plants. R⁰ was about 0.8 to 0.9 and was independent of leaf position and age, but tended to be highest in high K plants. The TW/DW ratio decreased from about 5.5 in leaf No 6 to 4.5 in leaf No 7 and 3.8 in leaf No 8. The TW/DW ratio was 4 to 10% higher in high K than in low K plants indicating larger leaf cell size in the former. The apoplastic water content (V_a) at full turgor constituted about 15% in leaf No 7. ε was maximum at full turgor and varied from about 11 to 34 MPa. ε tended to be higher in high K plants. Conclusively, in fully watered plants an ontogenetically determined accumulation of solutes (probably organic as discussed) occurred in the leaves independent of K application. The main effect of high K application on water relations was an increase in leaf water content and a slight decrease in leaf ψ_π. The effect of K status on growth and drought resistance is discussed.     

Flagella of a chrysophycean alga play an active role in prey capture and selection

Summary The flagella of the pigmented algaEpipyxis pulchra (Chrysophyceae) were observed with image enhanced video microscopy to play an active role in gathering, physically seizing and selecting prey prior to phagocytosis. Vegetative unicells of this sessile, freshwater species possess two structurally and functionally distinct flagella, both active in feeding. During prey gathering the long flagellum, which is adorned with stiff hairs, beats rapidly to direct a strong water current towards the cell while the short, smooth flagellum moves very little. When a potential food particle is drawn by the current to contact the flagellar surfaces, the long flagellum stops beating and positions itself, in concert with the short flagellum, to seize the prey between them. Both flagella then briefly rotate the prey before selecting or rejecting it. If rejected, the particle is discarded by the coordinated activity of both flagella. If selected as food, the prey is held in place until a complex collecting cup emanates out from a position near the basal bodies and engulfs it. The cup plus enclosed food particle, now a food vacuole, is then retracted back to the cell proper.     

Induction of beta-1,3-glucanase in barley in response to infection by fungal pathogens.

The sequence of a partial cDNA clone corresponding to an mRNA induced in leaves of barley (Hordeum vulgare) by infection with fungal pathogens matched almost perfectly with that of a cDNA clone coding for beta-1,-3-glucanase isolated from the scutellum of barley. Western blot analysis of intercellular proteins from near-isogenic barley lines inoculated with the powdery mildew fungus (Erysiphe graminis f. sp. hordei) showed a strong induction of glucanase in all inoculated lines but was most pronounced in two resistant lines. These data were confirmed by beta-1,3-glucanase assays. The barley cDNA was used as a hybridization probe to detect mRNAs in barley, wheat (Triticum aestivum), rice (oryza sativus), and sorghum (Sorghum bicolor), which are induced by infection with the necrotrophic pathogen Bipolaris sorokiniana. These results demonstrate that activation of beta-1,3-glucanase genes may be a general response of cereals to infection by fungal pathogens.     

Plasmid-encoded protein: the principal factor in the "metabolic burden" associated with recombinant bacteria

Experimental elucidation of the metabolic load placed on bacteria by the expression of foreign protein is presented. The host/vector system is Escherichia coli RR1/pBR329 (amp(r), cam(r), and let(r)). Plasmid content results, which indicate that the plasmid copy number monotonically increases with decreasing growth rate, are consistent with the literature on ColE1-like plasmids. More significantly, we have experimentally quantified the reduction in growth rate brought about by the expression of chloramphenicol-acetyl-transferase (CAT) and beta-lactamase. Results indicate a nearly linear decrease in growth rate with increasing foreign protein content. Also, the change in growth rate due to foreign protein expression depends on the growth rate of the cells. The observed linear relationship is media independent and, to our knowledge, previously undocumented. Furthermore, the induction of CAT, mediated by the presence of chloramphenicol, is shown to occur only at low growth rates, which further increases the metabolic load.Results are vdelineated with the aid of a structured kinetic model representing the metabolism of recombinant E. coli. In this article, several previous hypotheses and model predictions are justified and validated. This work provides an important step in the development of comprehensive, methabolically-structured, kinetic models capable of prediciting optimal conditions for maximizing product yield.     

metabolism of prostaglandins of the A-type

, originally introduced as an inadvertent contaminant in solutions used for evaluating the stability of prostaglandins, proved to lead to the rapid disappearance of the cyclopentenone unit of PGA₂ (as monitored by circular dichroic spectroscopy). The cyclopentenone unit is converted, in various metabolites, to a 9-keto, 9α or 9β-hydroxy group lacking the ring unsaturation. The major EtoAc-soluble 9-hydroxy metabolite (Compound-I) was shown to be 9α, 15α-dihydroxy-2,3,4,5-tetranor-13- -prostenoic acid. Similar tetranor 9-hydroxy metabolites with one additional degree of unsaturation, and with a 9β-hydroxy group, also occur but these have not been fully characterized. Only two of the wide range of 9-keto metabolites are fully characterized by mass spectral (MS) data: 9,15-oxo-2,3,4,5-tetranorprostanoic acid and 9,15-oxo-2,3,4,5-tetranor-13- -prostenoic acid. The water soluble metabolites have not been characterized further.The fully characterized metabolites together with MS data from mixtures of minor metabolites indicate that can perform the following transformations: β-oxidation, dehydrogenation at C-15, reduction of the enone carbon-carbon double bonds (both Δ^10,11 and Δ^13,14), reduction of the 9-ketone, and possibly migration of the cyclopentyl double bond (Δ^10,11 → Δ^11,12). metabolizes 15-epimeric PGA₂ equally readily with the production of similar products. PGA₁ affords less 9-keto metabolites with compound I constituting 33% of the product by HPLC analysis. displays some enantioselectivity, PGA₂ and 15-epi-PGA₂ are each metabolized more rapidly than their enantiomers. Other prostaglandins appear to be less readily metabolized.     

Enkephalin and substance P effects related to trigeminal pain

Iontophoretic applications of enkephalin (20-150 nA) reduced the spontaneous firing frequency of nociceptive neurons in the trigeminal nucleus caudalis of decerebrated cats. The response evoked by noxious stimulation (tooth pulp) was gradually inhibited during the 1st minute of application of the opioid and generally remained depressed for 5 min after the current was turned off. These effects of enkephalin were blocked by intravenously or iontophoretically administered naloxone. Nonnociceptive neurons or nociceptive neurons responding to nonnoxious inputs were less frequently inhibited by enkephalin. When tested on nonnociceptive cells, similar applications of substance P usually had little effect. Nociceptive neurons, however, were strongly excited by substance P. This action was not constant and was interrupted by periods of inactivation. Both types of peptide action were similar in temporal aspects. The results suggest a functional interrelationship between enkephalin and substance P in a trigeminal system mediating nociception.     

Temperature-sensitive deoxyribonucleic acid replication in a dnaC mutant of Bacillus subtilis.

A temperature-sensitive mutant of Bacillus subtilis is defective in deoxyribonucleic acid (DNA) synthesis, contains a lesion in the dnaC locus, and is not primarily an initiation mutant. The amount of DNA synthesized by this mutant at temperatures above 40 C decreases with increasing temperature. DNA synthesis resumes within 20 min after the temperature is lowered to 30 C. In the presence of chloramphenical, DNA synthesis begins at a reduced rate after the temperature is lowered to 30 C. Spores germinated at 46 C cannot initiate DNA replication. The capacity for residual DNA synthesis is stable at the restrictive temperature during inhibition of DNA synthesis. When the temperature is lowered to 30 C after a period of incubation at 43 C, DNA synthesis starts at the origin of the chromosome as well as at preexisting growing points. Similar DNA synthesis patterns are found in mutant cells in vivo and after toluene treatment.