Low Gs Research Articles

FUNCTIONING AND ROLE OF STOMATA IN MANGO LEAVES

Understanding stomatal functioning and its role is important since stomata control both photosynthesis, i.e. the production potential, and transpiration, which in turn influences irrigation management. Moreover, it is well known that stressing conditions which induce stomatal closure are needed for flowering in mango. The first striking feature is that mango seems to be well protected against excessive losses of water through transpiration. Stomatal frequency is high but stomata are small, which allows for quick responses to relevant stimuli. Transpiration curves show that a loss of less than 2% of water can lead to complete stomatal closure. Stomatal conductance, g,, is also very sensitive to the ambient concentration of CO 2 of the air. This is consistent with the close linear relationship we observed between g s and net photosynthesis, A net , all year round. High water availability and humidity of the air, plus the presence of an intense sink activity are needed to achieve the highest g s values. Interestingly measurements of chlorophyll fluorescence did not reveal any photoinhibition in high photosynthetically photon flux density and low gs conditions. The practical consequences of these observations are discussed.

Effects of water vapour pressure deficit and stomatal conductance on photosynthesis, internal pressurization and convective flow in three emergent wetland plants

Internal pressurization and convective gas flow in emergent wetland plants is a function of the water vapour pressure deficit (WPD) and stomatal conductance (Gs) separating the external atmosphere from the internal aerenchyma. We have compared the effects of WPD and Gs under a range of light intensities on static pressures and convective flows in Phragmites australis, Typha orientalis and Baumea articulata. The capacity of the three species to generate flows per unit leaf area differed, being greatest in P. australisand lowest in B. articulata. In all three species, decreasing light intensity from full sunlight (2200 μmol m−2 s−1 photosynthetically active photon flux density (PPFD)) to < 200 and < 10 μmol m−2 s−1PPFD caused immediate decreases in photosynthetic assimilation, followed by more gradual decreases in transpiration and Gs. However, internal pressures and flows in the two low light intensities remained similar to values recorded in full sunlight. WPD was more significantly related to pressures and flows in P. australis and T. orientalis than Gs. In B. articulata, pressures increased at low Gs values but flow rates were unaffected, as predicted by earlier models describing pore size effects on pressures and flows. The data suggest that emergent macrophytes can maintain significant internal convection even at low light intensities, and this may be beneficial for nocturnal aeration, particularly in arid climates where the atmospheric humidity at night is low.

Strategy shifts in leaf physiology, structure and nutrient content between species of high‐ and low‐rainfall and high‐ and low‐nutrient habitats

Summary Relationships were examined among photosynthetic capacity (Amass and Aarea), foliar dark respiration rate (Rd‐mass and Rd‐area), stomatal conductance to water (Gs), specific leaf area (SLA), and leaf nitrogen (N) and phosphorus (P) across 79 perennial species occurring at four sites with contrasting rainfall levels and soil nutrients in eastern Australia. We hypothesized that the slope of log–log ‘scaling’ relationships between these traits would be positive and would not differ between sites, although slope elevations might shift between habitat types. Amass, Rd‐mass, SLA, Nmass and Pmass were positively associated in common slopes fitted across sites or rainfall zones, although rather weakly within individual sites in some cases. The relationships between Amass (and Rd‐mass) with each of Nmass and SLA were partially independent of each other, with Amass (or Rd‐mass) increasing with SLA at a given Nmass, or with Nmass at a given SLA (only weakly in the case of Amass). These results improve the quantification and extend the generalization of reported patterns to floras largely unlike those studied previously, with the additional contribution of including phosphorus data. Species from drier sites differed in several important respects. They had (i) higher leaf N and P (per dry mass or area); (ii) lower photosynthetic capacity at a given leaf N or P; (iii) higher Rd‐mass at a given SLA or Amass; and (iv) lower Gs at a given Aarea (implying lower internal CO2 concentration). These trends can be interpreted as part of a previously undocumented water conservation strategy in species from dry habitats. By investing heavily in photosynthetic enzymes, a larger drawdown of internal CO2 concentration is achieved, and a given photosynthetic rate is possible at a lower stomatal conductance. Transpirational water use is similar, however, due to the lower‐humidity air in dry sites. The benefit of the strategy is that dry‐site species reduce water loss at a given Aarea, down to levels similar to wet‐site species, despite occurring in lower‐humidity environments. The cost of high leaf N is reflected in higher dark respiration rates and, presumably, additional costs incurred by N acquisition and increased herbivory risk.

Influence of nutrient versus water supply on hydraulic architecture and water balance in Pinus taeda

ABSTRACTWe investigated the hydraulic consequences of a major decrease in root‐to‐leaf area ratio (AR:AL) caused by nutrient amendments to 15‐year‐old Pinus taeda L. stands on sandy soil. In theory, such a reduction in AR:AL should compromise the trees’ ability to extract water from drying sand. Under equally high soil moisture, canopy stomatal conductance (GS) of fertilized trees (F) was 50% that of irrigated/fertilized trees (IF), irrigated trees (I), and untreated control trees (C). As predicted from theory, F trees also decreased their stomatal sensitivity to vapour pressure deficit by 50%. The lower GS in F was associated with 50% reduction in leaf‐specific hydraulic conductance (KL) compared with other treatments. The lower KL in F was in turn a result of a higher leaf area per sapwood area and a lower specific conductivity (conducting efficiency) of the plant and its root xylem. The root xylem of F trees was also 50% more resistant to cavitation than the other treatments. A transport model predicted that the lower AR:AL in IF trees resulted in a considerably restricted ability to extract water during drought. However, this deficiency was not exposed because irrigation minimized drought. In contrast, the lower AR:AL in F trees caused only a limited restriction in water extraction during drought owing to the more cavitation resistant root xylem in this treatment. In both fertilized treatments, approximate safety margins from predicted hydraulic failure were minimal suggesting increased vulnerability to drought‐induced dieback compared with non‐fertilized trees. However, IF trees are likely to be so affected even under a mild drought if irrigation is withheld.

Leaf Water Relation Parameters in Almond Compared to Hazelnut Trees during a Deficit Irrigation Period

The influence of deficit irrigation on predawn leaf water potential (Ψpd) and leaf gas-exchange parameters was analyzed in almond [Prunus dulcis (Mill.) D.A. Webb] and compared to hazelnut (Corylus avellana L.). Both species were planted in adjacent plots in which four irrigation treatments were applied: T-100%, T-130%, and T-70%, which were irrigated at full crop evapotranspiration (ETc), 1.3 × ETc, and 0.7 × ETc, respectively, and a regulated deficit irrigation (RDI) treatment, which consisted of full irrigation for the full season, except from middle June to late August when 0.2 × ETc was applied. Under nonstressful conditions, hazelnut had a lower net CO2 assimilation rate (A) (12.2 μmol·m-2·s-1) than almond (15.5 μmol·m-2·s-1). Reductions in net CO2 assimilation rate (A) induced by decreases in Ψpd were higher in hazelnut than in almond. Gas-exchange activity from early morning to midday decreased in hazelnut for all irrigation treatments, but in almond increased in the well-watered treatments and decreased slightly or remained constant in the RDI. Hazelnut had a higher A sensitivity to variations in stomatal conductance (gs) than almond, especially at low gs values. The Ψpd values in almond and hazelnut of the T-100% and T-130% treatments were affected by decreasing values in midsummer, but in hazelnut Ψpd was probably also affected by sink kernel filling. These facts indicate that hazelnut RDI management could be more problematic than in almond.

Expression of functional stimulatory guanine nucleotide binding protein in nonfunctioning thyroid adenomas is not correlated to adenylate cyclase activity and growth of these tumors.

In thyroid cells, the alpha-subunit of the stimulatory guanine nucleotide binding protein (Gs alpha) acts as signal transducer between the TSH receptor and the adenylate cyclase (AC), and it regulates both growth and function. In order to analyze Gs alpha expression by both Western blot analysis and in situ, we generated an antibody raised against a recombinant human Gs alpha protein. With this antibody, a strong cytoplasmic Gs alpha-immunostaining was detectable in cultured human thyroid cells and in TSH-stimulated rat thyroids, in contrast to normal human thyroids and to T4-treated rat thyroids, which showed only weak immunoreactivity. We obtained the following results by immunohistochemistry and Western blot analysis of 32 actively growing human thyroid adenomas: 1) strong Gs alpha expression in 11 adenomas, including 4 hyperfunctioning nodules, 1 of these with a point mutation in codon 201 of the Gs alpha gene; 2) no expression or only weak Gs alpha expression in 13 adenomas; and 3) a pattern of Gs alpha-positive and Gs alpha-negative cells in the remaining 8 adenomas. In addition, we analyzed ADP-ribosylation of Gs alpha and AC activity in 9 nonfunctioning adenomas and found a significant correlation between Gs alpha immunoreactivity and ADP-ribosylation and no correlation of both with basal and TSH-stimulated AC activity. In both types of adenomas, i.e. those with high as well as low Gs alpha, an indistinguishably high fraction of proliferating cells was detectable. We conclude that expression of functional Gs alpha protein in nonfunctioning thyroid adenomas is neither correlated to the basal or TSH-stimulated AC activity nor to the proliferation rate of these tumors.

Responses to drought and flooding in tropical forage grasses

Long dry seasons or permanent flooding, typical of tropical savannas, severely limit the growth of pasture plants. This study compares the responses of water relations, carbon assimilation and alcohol dehydrogenase (ADH) activity to drought and flooding in four perennial Ca grasses: the tufted or caespitose Hyparrhenia rufa and Andropogon gayanus (CIAT 621) and the stoloniferous Brachiaria mutica and Echinochloa polystachya. Plants of the four species were subjected to medium term flooding (20-25 days) and moderate drought in a greenhouse. Leaf water potential (W), stomatal conductance (Gs) and photosynthesis rate (Pn) were measured throughout the experiment and ADH activity was measured in flooded and control plants. Moderate drought produced similar effects in all grasses reducing Gs which caused reduced Pn. Net photosynthesis compensation point was reached at the lowest W in A. gayanus which was considered as the most drought tolerant. The responses to flooding varied across species. Andropogon gayanus and H. rufa showed early stomatal closure without concurrent decrease in W and leaf turgor. This low Gs was responsible of reduced Pn and growth rate. There was a slight increase of Gs in the middle of the flooding period and both grasses recovered pre-stress Gs and Pn after drainage. ADH activity increased markedly only in A. gayanus under flooding suggesting that this grass was the most flood-sensitive. Stomatal aperture, Pn and ADH activity in B. mutica and E. polystachya were not affected by flooding. The higher flood-tolerance in these grasses might be attributed to enhanced oxygen diffusion to the roots through the hollow stolons, development of adventitious rootlets and large aerenchyma in the roots which compensate for the reduction of soil oxygen and permit the maintenance of root activity.

Effects of transforming growth factor beta 1 on the adenylyl cyclase-cAMP pathway in prostate cancer.

We reported previously that MATLyLu rat prostate cancer cells engineered to overproduce transforming growth factor beta 1 (TGF beta 1) produce larger, more metastatic tumors in vivo. We recognized that this ability of TGF beta 1 to act as a positive modulator of prostate tumor behavior might be due to effects of TGF beta 1 on the host and/or on the tumor cells. In this study we demonstrated that the cells themselves respond to endogenously produced TGF beta 1, and that the adenylyl cyclase (AC)-cAMP pathway is affected. TGF beta 1-overproducing cells had lower membrane AC activity, lower intracellular cAMP content, and a lower Gs alpha protein level than did control cells. Prostate cancer cells were growth inhibited by 8-bromo-cAMP or forskolin, agents that elevate intracellular cAMP. Thus, TGF beta 1 overproduction affects the phenotype of the tumor cells, deliberate activation of endogenously produced latent TGF beta 1 is not required (indicating that the cells themselves are capable of activating latent TGF beta 1), and TGF beta 1 overproduction lowers the cellular concentration of the growth inhibitor cAMP. Therefore, TGF beta 1 overproduction could affect tumor behavior in vivo in part via a direct effect on the tumor cells.

Location and characterization of autonomously replicating sequences from chromosome VI of Saccharomyces cerevisiae.

We have reported the isolation of linking clones of HindIII and EcoRI fragments, altogether spanning a 230-kb continuous stretch of chromosome VI. The presence or absence of autonomously replicating sequence (ARS) activities in all of these fragments has been determined by using ARS searching vectors containing CEN4. Nine ARS fragments were identified, and their positions were mapped on the chromosome. Structures essential for and/or stimulative to ARS activity were determined for the ARS fragments by deletions and mutations. The organization of functional elements composed of core and stimulative sequences was found to be variable. Single core sequences were identified in eight of nine ARSs. The remaining ARS (ARS603) essential element is composed of two core-like sequences. The lengths of 3'- and 5'-flanking stimulative sequences required for the full activity of ARSs varied from ARS to ARS. Five ARSs required more than 100 bp of the 3'-flanking sequence as stimulative sequences, while not more than 79 bp of the 3' sequence was required by the other three ARSs. In addition, five ARSs had stimulative sequences varying from 127 to 312 bp in the 5'-flanking region of the core sequence. In general, these stimulative activities were correlated with low local delta Gs of unwinding, suggesting that the low local delta G of an ARS is an important element for determining the efficiency of initiation of replication of ARS plasmids.

Location and characterization of autonomously replicating sequences from chromosome VI of Saccharomyces cerevisiae.

We have reported the isolation of linking clones of HindIII and EcoRI fragments, altogether spanning a 230-kb continuous stretch of chromosome VI. The presence or absence of autonomously replicating sequence (ARS) activities in all of these fragments has been determined by using ARS searching vectors containing CEN4. Nine ARS fragments were identified, and their positions were mapped on the chromosome. Structures essential for and/or stimulative to ARS activity were determined for the ARS fragments by deletions and mutations. The organization of functional elements composed of core and stimulative sequences was found to be variable. Single core sequences were identified in eight of nine ARSs. The remaining ARS (ARS603) essential element is composed of two core-like sequences. The lengths of 3'- and 5'-flanking stimulative sequences required for the full activity of ARSs varied from ARS to ARS. Five ARSs required more than 100 bp of the 3'-flanking sequence as stimulative sequences, while not more than 79 bp of the 3' sequence was required by the other three ARSs. In addition, five ARSs had stimulative sequences varying from 127 to 312 bp in the 5'-flanking region of the core sequence. In general, these stimulative activities were correlated with low local delta Gs of unwinding, suggesting that the low local delta G of an ARS is an important element for determining the efficiency of initiation of replication of ARS plasmids.

Pion double-charge-exchange on calcium isotopes

The authors examine the contributions of the conventional sequential mechanism and the pion absorption-emission mechanism for the double charge exchange (DCX) on calcium isotopes. It is shown that by combining these two mechanisms the experimental data for the double isobaric analogue transitions can be reproduced quite well. The predictions for the low energy GS to GS DCX on calcium isotopes are presented.

Glycogen synthase turnover and phosphorylation in rat H4IIE hepatoma cells

Glycogen synthase was isolated from rat H4IIE hepatoma cells by the use of specific antibodies. Immunoprecipitates from cells grown in the presence of [ 35S]methionine contained two 35S-labeled polypeptides, designated GS 1 and GS 2, separable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Labeling of both species was half-maximal after 3 h and remained constant up to 48 h. When cells were incubated with [ 32P]-phosphate, 32P was incorporated into both species with similar kinetics, half-maximal labeling occurring after 2–3 h. The steady-state ratio 32 P 35 S was significantly higher for the lower mobility GS 2 polypeptide. Pulse-chase experiments showed that the two subunits followed similar kinetics with respect to 35S-labeling. However, the turnover of 32P on the GS 2 subunit was significantly faster ( t 1 2 ~ 30 min ) than that on the GS 1 subunit ( t 1 2 ~ 2 h ). We suggest that the two polypeptides represent different phosphorylation states of the glycogen synthase subunit and are rapidly interconverted.

Glutamine Synthetase of Streptomyces cattleya: Purification and Regulation of Synthesis

Glutamine synthetase (GS; EC 6.3.1.2) from Streptomyces cattleya was purified using a single affinity-gel chromatography step, and some of its properties were determined. Levels of GS in S. cattleya cells varied by a factor of 8 depending upon the source of nitrogen in the growth medium. Of 24 nitrogen sources examined only glutamine or NH4Cl utilization resulted in very low GS activity. Addition of NH4Cl to a culture with high GS levels appeared to stop further synthesis and resulted in a progressive decrease in the specific activity of the enzyme. The GS inhibitor methionine sulphoximine (MSX) inhibited GS activity but had no effect on exponentially growing cells. The presence of MSX either lengthened or shortened the period between spore inoculation and initiation of exponential growth, depending on the source of nitrogen. In glutamine minimal medium MSX produced earlier and more efficient spore germination while in glutamate or nitrate minimal medium germination was delayed by its presence.

ACTIVITY OF GLUTAMINE SYNTHETASE AND GLUTAMATE DEHYDROGENASE IN TRIFOLIUM SUBTERRANEUM L. AND ALLIUM CEPA L: EFFECTS OF MYCORRHIZAL INFECTION AND PHOSPHATE NUTRITION

SummaryActivities of glutamate dehydrogenase and glutamine synthetase were determined using crude extracts of roots and shoots of mycorrhizal and non‐mycorrhizal plants of Trifolium subterraneum L. and Allium cepa L., grown at different levels of fertilizer phosphate.Glutamate dehydrogenase activity was low in all tissues [0.1 to 1.6 μmol NAD(P)H oxidized min−1 gFW−1 tissue] and there was no consistent effect of mycorrhizal infection or phosphate nutrition on this activity.Glutamine synthetase (GS) activity (assayed by the transferase method) was in the range 1 to 40/iimol γ‐glutamyl hydroxamate produced min−1 gFW−1. In general, activity of this enzyme was low in phosphate‐deficient plants and was increased both by mycorrhizal infection and by improved phosphate supply. In T. subterraneum routine assays of GS were done on roots only. The effects of mycorrhizal infection in increasing enzyme activity in roots were similar whether natural soil inoculum (containing a mixture of several mycorrhizal fungi) or inoculum of Glomus mosseae Nichol. &amp; Gerd. was used. Both increased phosphate supply and mycorrhizal infection increased nodulation of clover plants as well as GS activity, so that it was difficult to relate changes in GS activity to the interacting effects of mycorrhizal infection and phosphate nutrition.Onions had low GS activity in uninfected roots, compared with shoots. Again improved phosphate supply resulted in increased enzyme activity in both roots and shoots. However, the patterns of interaction between phosphate supply, P concentration in tissues, mycorrhizal infection and enzyme activity were different in the two tissues. In shoots, as expected, the effects were consistent with an indirect effect of mycorrhizal infection on enzyme activity, via improved P nutrition. In roots there appeared to be a ‘fungal effect’ superimposed on the phosphate effect. This was investigated by manipulating the amount of fungal tissue in mycorrhizal roots via differences in propagule density of G. mosseae in soil. Results were again consistent with the hypothesis that the mycorrhizal fungi contributed GS activity to the symbiotic root system. Fungal structures were separated from roots following digestion in cellulase and pectinase. GS activity was high in fungal tissue from young roots (29 to 31 d), but low in older infections (55 d). The high activity could not have been caused by contamination of fungal tissue by root cells. The digestion technique reduced GS activity in uninfected and infected root segments, so that results obtained with separated fungi are not quantitatively comparable with those obtained from extracts of fresh tissues.We conclude that vesicular‐arbuscular mycorrhizal fungi are able to assimilate ammonium via GS. This ability would be important in increased uptake of nitrogen which is an inevitable prerequisite for increased growth following relief of phosphate stress. It is also consistent with the recent findings by others that hyphae of G. mosseae can absorb and translocate 15NH+4

Randomized response estimates of problem use of alcohol among employed females.

As part of the evaluation of an alcoholism orientation program conducted in 12 federal agencies, 378 female employees were asked to provide personal information about problems associated with their use of alcohol. The optimized form of the unrelated question randomized response technique (RRT) was used to provide for a comparison of estimates of frequency of problem drinking obtained with guaranteed confidentiality of response versus estimates obtained using a conventional anonymous questionnaire. The estimated proportion of alcoholics or possible alcoholics among participants in the orientation program was 34.3% (+/- 4.9) by the RRT and 21.9% (+/- 3.6) by direct response. Significant underreporting of alcoholism was found among older respondents (greater than or equal to 36 years), lower GS level respondents (less than grade 6), those with low seniority (less than 8 years), and those never married. Further, significant underreporting was found among those who claimed they were told they had to attend the program versus others, and among those who claimed they were not curious about the topic of alcoholism versus others. The RRT is recommended for use in experimental situations where answers to sensitive questions are needed to evaluate program success. The necessity for caution in interpretation of apparent differences in respondent characteristics with respect to problems with alcohol use is discussed. Finally, the findings indicate the importance of providing avenues by which confidential treatment for alcoholism can be obtained.

The solar radial gradient of galactic cosmic rays

The radial gradient of cosmic rays in the interplanetary region has been investigated taking into account convection, diffusion, energy losses, and differential streaming S. At high energies the analysis given here shows that S can be neglected and the radial gradient written C(r, T)Gs(r, T), where Gs(r, T) is the gradient given by the convection–diffusion theory and C(r, T) is an energy-dependent correction factor which can be computed from the observed differential intensity spectrum. During 1964–65 this result can probably be used for protons and helium nuclei down to a few hundred MeV/nucleon, with, at that time, [Formula: see text]. At lower energies Gs will be quite inaccurate as an estimate of the radial gradient unless changes in C are offset by streaming. Combining observations with this analysis it is shown that the radial anisotropy of protons (ξ) is: (i) positive but small (&lt; 0.02%) at kinetic energies [Formula: see text]; (ii) negative in the range 40–600 MeV with ξmax = −0.75% (which should be observable); (iii) positive for energies less than about 40 MeV.