Stomatal response to air humidity and its relation to stomatal density in a wide range of warm climate species

The gas exchange of 19 widely different warm climate species was observed at different leaf to air vapour pressure deficits (VPD). In all species stomata tended to close as VPD increased resulting in a decrease in net photosynthesis. The absolute reduction in leaf conductance per unit increase in VPD was greatest in those species which had a large leaf conductance at low VPDs. This would be expected even if stomata of all species were equally sensitive. However the percentage reduction in net photosynthesis (used as a measure of the relative sensitivity of stomata of the different species) was also closely related to the maximal conductance at low VPD. Similarily the relative sensitivity of stomata to changes in VPD was closely related to the weighted stomatal density or crowding index.The hypothesis is presented that stomatal closure at different VPDs is related to peristomatal evaporation coupled with a high resistance between the epidermis and the mesophyll and low resistance between the stomatal apparatus and the epidermal cells. This hypothesis is consistent with the greater relative sensitivity of stomata on leaves with a high crowding index.The results and the hypothesis are discussed in the light of selection, for optimal productivity under differing conditions of relative humidity and soil water availablility, by observation of stomatal density and distribution on the two sides of the leaf.Visiting scientist, plant physiologist and research assitant of the Cassava Program     

Redox interconversion of Escherichia coli glutathione reductase. A study with permeabilized and intact cells

Summary The redox interconversion of Escherichia coli glutathione reductase has been studied both in situ, with permeabilized cells treated with different reductants, and in vivo, with intact cells incubated with compounds known to alter their intracellular redox state.The enzyme from toulene-permeabilized cells was inactivated in situ by NADPH, NADH, dithionite, dithiothreitol, or GSH. The enzyme remained, however, fully active upon incubation with the oxidized forms of such compounds. The inactivation was time-, temperature-, and concentration-dependent; a 50% inactivation was promoted by just 2 M NADPH, while 700 M NADH was required for a similar effect. The enzyme from permeabilized cells was completely protected against redox inactivation by GSSG, and to a lesser extent by dithiothreitol, GSH, and NAD(P)⁺. The inactive enzyme was efficiently reactivated in situ by physiological GSSG concentrations. A significant reactivation was promoted also by GSH, although at concentrations two orders of magnitude below its physiological concentrations. The glutathione reductase from intact E. coli cells was inactivated in vivo by incubation with DL-malate, DL-isocitrate, or higher L-lactate concentrations. The enzyme was protected against redox inactivation and fully reactivated by diamide in a concentration-dependent fashion. Diamide reactivation was not dependent on the synthesis of new protein, thus suggesting that the effect was really a true reactivation and not due to de novo synthesis of active enzyme. The glutathione reductase activity increased significantly after incubation of intact cells with tert-butyl or cumene hydroperoxides, suggesting that the enzyme was partially inactive within such cells. In conclusion, the above results show that both in situ and in vivo the glutathione reductase of Escherichia coli is subjected to a redox interconversion mechanism probably controlled by the intracellular NADPH and GSSG concentrations.     

Further segregation analysis of the fragile X syndrome with special reference to transmitting males

Summary A new series of 96 pedigrees with the fra(X) syndrome was analysed using complex segregation analysis with pointers, defining affection as any degree of mental impairment. These families were found to exhibit the same segregation pattern as the first series of 110 pedigrees (Sherman et al. 1984). The best estimate for penetrance of mental impairment in males was 79% and in females was 35% for the combined data. Again, there was little evidence for sporadic cases among affected males.Many more intellectually normal transmitting males have been observed since the existence of such males and the concomitant need to investigate the paternal side of pedigrees was recognized. On further investigation of all 206 pedigrees from the old and new data sets, the sibships of nonexpressing males appeared to be different from those of expressing males. Our analysis, using mental impairment as the phenotype, suggested that obligate carrier mothers and daughters of intellectually normal transmitting males are rarely, if ever, mentally impaired and that the sibs of transmitting males are much less likely to be retarded than the sibs of mentally impaired males. Though mothers and daughters of transmitting males are similar in phenotype, the expression of the gene in their offspring appears to be different: the penetrance of mental impairment is higher in offspring of intellectually normal daughters of transmitting males than in offspring of intellectually normal mothers of transmitting males. The implications of these observations for genetic counseling and for genetic models of the fra(X) syndrome are discussed.     

Chromosome numbers of goldenrods,Euthamia and Solidago (Compositae: Astereae). II. Additional counts with comments on cytogeography

Chromosome number determinations were made from 407 wild or transplanted individuals and seedlings representing 65 taxa and hybrids inEuthamia andSolidago. The following are first reports:Euthamia remota, 2n=9II;Solidago leavenworthii, 2n=54;S. mollis, 2n=36;S. mollis var.angustata, 2n=36;S. rigida var.glabrata, 2n=9II;S. sempervirens var.azorica, 2n=9II; andS. sparsiflora, 2n=54. Most species have been sampled only a few times or are consistently of one cytotype. Sufficient counts have been made to indicate some general patterns of cytotype distribution in the following species complexes:S. gigantea, S. canadensis, S. flexicaulis, S. rugosa, andS. uliginosa.     

Germacranolides from Schkuhria anthemoidea

The isolation of eucannabinolide and three new sesquiterpene lactones from Schkuhria anthemoidea is reported. The structures and stereochemistries of the new compounds were established by chemical and spectroscopic means. The structure of santhemoidin B was confirmed by X-ray crystallography.     

Metabolism of leukotriene A4 by human erythrocytes. A novel cellular source of leukotriene B4

Human erythrocytes transformed leukotriene A4 into leukotriene B4. Metabolism was proportional to the erythrocyte concentration, even at subphysiological levels (0.08-4 X 10(9) erythrocytes/ml). Comparative metabolic studies excluded the possibility that leukotriene B4 originated from trace amounts of polymorphonuclear leukocytes or platelets present in the purified erythrocyte suspensions. For example, suspensions of isolated platelets (100-500 X 10(6) cells/ml) failed to convert leukotriene A4 into leukotriene B4; and conversion by suspensions of isolated polymorphonuclear neutrophils was insufficient to account for the amounts of leukotriene B4 formed by erythrocytes. Leukotriene B4 formation was maximal within 2 min and substrate concentration dependent. Enzymatic activity originated from a 56 degrees C labile nondialyzable (Mr greater than 30,000) soluble component in the 100,000 X g supernatant obtained from lysed erythrocytes. In contrast to the contemporary view, our results indicate that human erythrocytes are not metabolically inert in terms of eicosanoid biosynthesis. The role of human erythrocytes during inflammatory or pulmonary disorders deserves re-examination in this context.     

Right ventricular function in the hypoxaemic fetal sheep

Right ventricular function was investigated in seven fetal sheep (125-130 days gestation) hypoxaemic at a mean of 5 days postoperation, and were compared to nine normoxaemic fetal sheep of the same gestation. Arterial O2 and CO2 tensions, pH, and haematocrit values for the hypoxaemic and normoxaemic fetuses were 15.6 +/- 1.0 vs. 20.6 +/- 1.8 torr, 49.4 +/- 4.1 vs. 46.1 +/- 1.6 torr, 7.38 +/- 0.02 vs. 7.39 +/- 0.02, and 29 +/- 7.5 vs. 31 +/- 5.3%, respectively. Right ventricular output and stroke volume were similar in the two groups, 241 +/- 57 vs. 247 +/- 75 ml X min-1 X kg-1 and 1.5 +/- 0.4 vs. 1.5 +/- 0.4 ml X kg-1, respectively. Filling and afterload pressures were also similar in the hypoxaemic and normoxaemic fetuses with right atrial pressure of 3.0 +/- 1.0 vs. 3.7 +/- 1.2 mmHg, and arterial pressure of 42 +/- 5 vs. 43 +/- 4 mmHg, respectively. Ventricular function curves were produced by rapid withdrawal and re-infusion of fetal blood producing curves with a steep ascending limb and a plateau phase. The breakpoint joining the limbs of the control function curve for the hypoxaemic and normoxaemic fetuses were right atrial pressure 2.9 +/- 1.0 vs. 3.4 +/- 1.2 mmHg and a stroke volume of 1.5 +/- 0.5 vs. 1.5 +/- 0.4 ml X kg-1, respectively. Linear regression of stroke volume against arterial pressure from 30-90 mmHg during infusions of nitroprusside and phenylephrine at right atrial filling pressures greater than breakpoint was stroke volume = 0.018 ml X kg-1 X mmHg-1 arterial pressure +/- 2.25 ml X kg-1. This equation is not different from that calculated in normoxaemic fetuses, and demonstrates that the fetal right ventricle is quite sensitive to changes in arterial pressure. These data indicate that reduction in fetal oxygen content by an estimated 40% does not affect fetal right ventricular function.     

Isolation of yeast with killer activity and its breeding with an industrial baking strain by protoplast fusion

Summary Wild strains of Saccharomyces cerevisiae were isolated from dairy products, bakery goods, fresh fruit and vegetables, and tested for killer activity. Four isolates out of 238 strains possessed killer activity. The best of these was converted to the petite form and hybridized with an industrial strain of Saccharomyces cerevisiae by protoplast fusion. Thirty-eight out of 104 isolates had killer activity, and some of these had good dough-raising activity as well.     

Human genes for insulin-like growth factors I and II and epidermal growth factor are located on 12q22----q24.1, 11p15, and 4q25----q27, respectively

The genes coding for insulin-like growth factors I and II and epidermal growth factor have been localized to human chromosomes 12q22----q24.1, 11p15, and 4q25----q27, respectively.