Physiological effects of sublethal atrazine on barley chloroplast thylakoid membranes.

This study was conducted to more clearly define the physiological effects of PS II herbicides on chloroplast thylakoid membrane activity and composition. Barley (Hordeum vulgare L. cv Boone) was grown in hydroponic culture at 20°C in a growth chamber with a light intensity of 500 µmole photons m(-2) s(-1). Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), a Photosystem II herbicide, was supplied continuously via the roots to 7-day-old plants. Atrazine concentrations greater than 0.07 ppm (0.32 µM) were associated with decreased leaf chlorophyll (chl), lowered chl a/b ratio, inhibition of chloroplast electron transport, and plant death within 1 to 2 weeks. Atrazine at 0.07 ppm was defined as sublethal because no toxic effects were observed. Sublethal atrazine induced a decrease in chl a/b ratio with no effect on leaf chl content. Photosynthetic electron transport was either unaffected in fully expanded leaves or slightly stimulated in expanding leaves by treatment of intact plants with 0.07 ppm atrazine. The major effect of sublethal atrazine was on the chl-protein complex composition. Sublethal atrazine increased the level of the Photosystem II light-harvesting complex (LHC-II) and lowered the level of the CP1a Photosystem I complex relative to controls. The numbers of Photosystem II and Photosystem I reaction centers and cytochrome b 6/f complexes per unit chl were not affected by sublethal atrazine. The overall result was an atrazine-induced redistribution of light-harvesting chl from Photosystem I to Photosystem II with no effect on the number of thylakoid membrane-protein complexes associated with electron transport.

Acclimation of barley to changes in light intensity: chlorophyll organization.

Barley seedlings (Hordeum vulgare L. cv. Boone) were grown at 20°C with a 16h/8h light/dark cycle of either high (H) intensity (550 µmole m(-2) s(-1)) or low (L) intensity (55 µmole m(-2) s(-1)) white light. Plants were transferred from high to low (H → L) or low to high (L → H) light intensity at various times from 4 to 8 d after leaf emergence from the soil. Primary leaves were harvested at the beginning of the photoperiod and a 3 cm apical segment removed for analysis. H control plants had greater chlorophyll (Chl) per leaf area and higher Chl a/b ratios than L controls. Analysis of Chl-protein complexes revealed that H and L plants had the same percentage of total Chl (62-65%) associated with Photosystem II (PS II), but that the organization of Chl within PS II was different. H plants contained lower levels of light-harvesting complex (LHC-II) and higher levels of the PS II complex CPa compared with L plants. Leaf Chl content and Chl organization within PS II were sensitive to changes in light intensity. In H → L plants, leaf Chl content decreased, Chl a/b ratio decreased, and a redistribution of Chl from CPa to LHC-II occurred during acclimation to low light. Acclimation of L → H plants to high light involved an increase in leaf Chl content, an increase in Chl a/b ratio, and a decrease in LHC-II. In contrast, the level of photosystem I related Chl-protein complexes (CP1 + CP1a) was similar in all light treatments. The light acclimation process occurred slowly over a period of 6 to 8 d in H → L and L → H plants.

Acclimation of barley to changes in light intensity: photosynthetic electron transport activity and components.

Barley seedlings (Hordeum vulgare L. Boone) were grown at 20°C with 16 h/8 h light/dark cycle of either high (H) intensity (500 µmole m(-2) s(-1)) or low (L) intensity (55 µmole m(-2) s(-1)) white light. Plants were transferred from high to low (H → L) and low to high (L → H) light intensity at various times from 4 to 8 d after leaf emergence from the soil. Primary leaves were harvested at the beginning of the photoperiod. Thylakoid membranes were isolated from 3 cm apical segments and assayed for photosynthetic electron transport, Photosystem II (PS II) atrazine-binding sites (QB), cytochrome f(Cytf) and the P-700 reaction center of Photosystem I (PS I). Whole chain, PS I and PS II electron transport activities were higher in H than in L controls. QB and Cytf were elevated in H plants compared with L plants. The acclimation of H → L plants to low light occurred slowly over a period of 7 days and resulted in decreased whole chain and PS II electron transport with variable effects on PS I activity. The decrease in electron transport of H → L plants was associated with a decrease in both QB and Cytf. In L → H plants, acclimation to high light occurred slowly over a period of 7 days with increased whole chain, PS I and PS II activities. The increase in L → H electron transport was associated with increased levels of QB and Cytf. In contrast to the light intensity effects on QB levels, the P-700 content was similar in both control and transferred plants. Therefore, PS II/PS I ratios were dependent on light environment.

Does testosterone influence the post-stimulatory levels of calcitonin in normal men?

We have analysed the sex difference of calcitonin (CT) levels after combined stimulation with calcium and pentagastrin (Ca-PG) in the normal population, and the relationship of the post-stimulatory CT levels with free testosterone (FT). We have also studied the correlation between CT values and the anthropometric parameters, body mass index (BMI) and body surface area (BS), as well as the relationship between CT levels and calcium. A positive and statistically significant correlation was found between post-stimulatory CT and the increment over the base-line of CT and basal FT, and with the anthropometric parameters. However, the increment of CT and the peak values of CT did not have any significant correlation with the Ca levels (basal or post-stimulation). We conclude that the enhanced CT response found in normal men compared to normal women is at least partially determined by the higher testosterone levels found among normal men.

Plasma immunoreactive somatostatin is elevated in diabetic ketoacidosis and correlates with plasma non-esterified fatty acid concentration.

In experimental diabetes and after the administration of beta-hydroxybutyrate and non-esterified fatty acids (NEFA), an increase in circulating immunoreactive somatostatin (IRS) has been described. Both ketones and NEFA are raised in diabetic ketoacidosis. Therefore, we decided to investigate 10 patients in diabetic ketoacidosis by measuring, on admission and throughout the initial 24 hours of therapy, circulating levels of IRS, beta-hydroxybutyrate, acetoacetate, triglycerides, blood glucose, pH and NEFA. Fluids and insulin were administered IV following a previously established protocol. Nine patients showed abnormally high levels of circulating IRS. When compared with a group of controlled insulin-dependent diabetic patients, basal IRS was high (111 +/- 15 vs 28 +/- 3 pmol/l), and remained elevated for at least 24 h despite clear improvement of metabolic status. On admission we also found elevated levels of NEFA (1.04 +/- 0.2 mmol/l), triglycerides (4.7 +/- 1.1 mmol/l), beta-hydroxybutyrate (22.1 +/- 4mmol/l), and acetoacetate (4.8 +/- 1.1 mmol/l). A significant correlation was found initially between IRS and NEFA (p less than 0.01). We conclude that circulating IRS is high in most cases of diabetic ketoacidosis. The mechanism behind this hypersomatostatinaemia could be related to the abnormalities of lipid metabolism which occur in diabetic ketoacidosis.