Stem diameter in relation to plant water status

An instrument containing a linear variable differential transformer was constructed to obtain continuous, nondestructive measurements of both short term changes in stem diameter and long term growth. In cotton plants, stem diameter, leaf water potential, and leaf relative water content are all closely related to net radiation at the top of the canopy. Leaves from the east and west sides of a plant show slight, but consistent differences in diurnal water potential patterns.     

Leaf water balance during oscillation of stomatal aperture

Continuous transpiration and β-guage measurements were made on cotton plants, the stomatal apertures of which had been induced to oscillate, thus allowing a water balance to be made, and leaf potential to be measured as functions of time.     

The occurrence of nitrate reductase in apple leaves

Nitrate reductase utilizing NADH or reduced flavin mononucleotide (FMNH₂) as electron donor was extracted from the leaves, stems and petioles, and roots of apple seedlings. Successful extraction was made possible by the use of insoluble polyvinylpyrrolidone (Polyclar AT) which forms insoluble complexes with polyphenols and tannins. The level of nitrate reductase per gram fresh weight was highest in the leaf tissue although the nitrate content of the roots was much higher than that of the leaves. Nitrite reductase activity was detected only in leaf extracts and was 4 times higher than nitrate reductase activity. Nitrate was found in all parts of young apple trees and trace amounts were also detected in mature leaves from mature trees. Nitrate reductase was induced in young leaves of apple seedlings and in mature leaves from 3 fruit-bearing varieties. An inhibitor of polyphenoloxidase, 2-mercaptobenzothiazole was used in both the inducing medium and the extracting medium in concentrations from 10⁻³ to 10⁻⁵m with no effect upon nitrate reductase activity.     

Comparison between NO(x) Evolution Mechanisms of Wild-Type and nr(1) Mutant Soybean Leaves

The nr₁ soybean (Glycine max [L.] Merr.) mutant does not contain the two constitutive nitrate reductases, one of which is responsible for enzymic conversion of nitrite to NO_x (NO + NO₂). It was tested for possible nonenzymic NO_x formation and evolution because of known chemical reactions between NO₂⁻ and plant metabolites and the instability of nitrous acid. It did not evolve NO_x during the in vivo NR assay, but intact leaves did evolve small amounts of NO_x under dark, anaerobic conditions. Experiments were conducted to compare NO₃⁻ reduction, NO₂⁻ accumulation, and the NO_x evolution processes of the wild type (cv Williams) and the nr₁ mutant. In vivo NR assays showed that wild-type leaves had three times more NO₃⁻ reducing capacity than the nr₁ mutant. NO_x evolution from intact, anerobic nr₁ leaves was approximately 10 to 20% that from wild-type leaves. Nitrite content of the nr₁ mutant leaves was usually higher than wild type due to low NO_x evolution. Lag times and threshold NO₂⁻ concentrations for NO_x evolution were similar for the two genotypes. While only 1 to 2% of NO_x from wild type is NO₂, the nr₁ mutant evolved 15 to 30% NO₂. The kinetic patterns of NO_x evolution with time weré completely different for the mutant and wild type. Comparisons of light and heat treatments also gave very different results. It is generally accepted that the NO_x evolution by wild type is primarily an enzymic conversion of NO₂⁻ to NO. However, this report concludes that NO_x evolution by the nr₁ mutant was due to nonenzymic, chemical reactions between plant metabolites and accumulated NO₂⁻ and/or decomposition of nitrous acid. Nonenzymic NO_x evolution probably also occurs in wild type to a degree but could be easily masked by high rates of the enzymic process.     

Cellular events during the primary immune response in the spleen

Summary The cellular events during the primary immune response in T and B cell compartments in the splenic white pulp were analysed in germfree mice immunized with sheep erythrocytes. Light, fluorescence and electronmicroscopic studies revealed that the initial formation of lymphoid blast cells occurs in the thymus-dependent area, i.e. the central periarteriolar lymphatic sheath (central PALS), 2 days after immunization. Lymphoblasts were found in close relation with erythrocyte-containing macrophages and with interdigitating cells. With fluorescence microscopy these blast cells were Ig negative. Lymphoblasts in the central PALS showed many polyribosomes in the cytoplasm, but were virtually devoid of endoplasmic reticulum. The ultrastructure of lymphoblasts in the central PALS, and their relation with interdigitating cells, suggests that these cells are the progeny of antigen-activated T cells.Cells with a positive cytoplasmic fluorescence, plasmablasts, appeared 3 days after immunization in the peripheral part of the PALS. During the progress of the immune response these cells accumulated around branches of the central arteriole, and moved along marginal zone bridging channels towards the red pulp. In the electron microscope plasmablasts showed many polyribosomes, short strands of rough endoplasmic reticulum close to mitochondria, and a few electron-dense bodies. The cell organelles of plasmablasts were frequently gathered in a so called uropod, which is a morphological sign of active cell movement.Germinal center formation started within primary follicles, 4 days after immunization. Blast cells in germinal centers did not show cytoplasmic fluorescence. During the course of the immune response, germinal centers extended in diameter, and fluorescent dendritic cells appeared at the periphery of the germinal center.From the present observations we conclude that: (1) cellular cooperation between different lymphoid and non-lymphoid cell types during the immune response against SRBC takes place in the PALS, (2) the cellular cooperation in the PALS results in the differentiation of B cells into immunoglobulin-producing plasmablasts, (3) the cellular cooperation in the PALS preceeds the formation of germinal centers in primary follicles, hence germinal centers are not involved in early T-B cell cooperation.     

Defective Glucose Transport Across Brain Tissue Barriers: A Newly Recognized Neurological Syndrome

Impaired glucose transport across brain tissue barriers causes infantile seizures, developmental delay and acquired microcephaly. Since the first report in 1991 (De Vivo et al, NEJM, 1991) 17 patients have been identified with the glucose transporter protein syndrome (GTPS). The diagnostic feature of the syndrome is an unexplained hypoglycorrhachia in the clinical setting of an infantile epileptic encephalopathy. We review our clinical experience by highlighting one illustrative case: a 6-year old girl who presented at age 2 months with infantile seizures and hypoglycorrhachia. The CSF/blood glucose ratio was 0.33. DNA sequencing identified a missense mutation in exon 7 (C1108T). Erythrocyte GLUT1 immunoreactivity was normal. The time course of 3-0-methyl-glucose (3OMG) uptake by erythrocytes of the patient was 46% that of mother and father. The apparent K_m was similar in all cases (2–4 mmol/L), but the apparent V_max in the patient was only 28% that of the parents (500 versus 1,766 fmol/s/10⁶RBC; p < 0.004). In addition, a 3-month trial of oral thioctic acid also benefited the patient and increased the V_max to 935 fmol/s/10⁶ RBC (p < 3 × 10^–7). Uptake of dehydroascorbic acid by erythrocytes of the patient was impaired to the same degree as that of 3OMG (V_max was 38% of that of the mother's), which supports previous observations of GLUT1 being multifunctional. These studies confirm the molecular basis of the GTPS and the multifunctional role of GLUT1. The need for more effective treatment is compelling.     

Cyclic Variations in Plant Properties under Constant Environmental Conditions

Cyclic fluctuations in stomatal aperture, transpiration rate and leaf water potential under constant environmental conditions have been investigated in intact plants of cotton, pepper, and sunflower. Stomatal aperture and transpiration rate were least when leaf water potential was high and were greatest when leaf water potential was low. Lowest leaf water potential values lagged behind the occurrence of highest transpiration rates, and high overall resistance to water flow occurred in cycling plants. Both of these are considered essential for the occurrence of persistent cyclic behaviour. Hydropassive opening of stomates as the leaves wilted facilitated cycling in cotton and pepper, but not in sunflower, where hydropassive opening did not occur. The roots were identified as the site of the major resistance to water flow in the plant and further experiments directly showed the importance of this root resistance in initiating cycling by causing water stress in the leaves as the stomates opened. Root resistance varied diurnally, becoming increasingly important at night. Root resistance naturally rose to high levels in cotton. High levels were induced in pepper or sunflower by having the roots in deionized water for several days or by anoxia. Quantitative measurements of overall plant resistance were made from leaf water potential and transpiration rate data. The results are discussed and it suggested that plant resistance may indirectly be of importance in the movement of water from the plant to the air.     

Temperature effects on radial propagation of water potential in cotton stem bark

Low temperature affects the lateral movement of water across the xylem-phloem boundary in intact cotton stems. There is a reduction in the effective diffusion coefficient relating free energy flux to water potential gradients with an associated increase in resistance to water flow. Detached phloem and excised leaves do not show this effect of low temperature. Experiments on stem section halves indicate that the effect is probably associated with the cambial region.     

Rehydration versus Growth-induced Water Uptake in Plant Tissues

Experiments show that the rate of water uptake by living tissues external to mature xylem of cotton stems (Gossypium hirsutum L. Auburn 7-683) is very similar to the corresponding curves for leaf tissue. In both cases one obtains a two-phase curve with phase I corresponding to passive rehydration and phase II pertaining to active growth.