Photosystem II Regulation and Dynamics of the Chloroplast D1 Protein in Arabidopsis Leaves during Photosynthesis and Photoinhibition.

Arabidopsis thaliana leaves were examined in short-term (1 h) and long-term (10 h) irradiance experiments involving growth, saturating and excess light. Changes in photosynthetic and chlorophyll fluorescence parameters and in populations of functional photosystem II (PSII) centers were independently measured. Xanthophyll pigments, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-binding sites, the amounts of D1 protein, and the rates of D1 protein synthesis were determined. These comprehensive studies revealed that under growth or light-saturating conditions, photosynthetic parameters remained largely unaltered. Photoprotection occurred at light saturation indicated by a dark-reversible increase in non-photochemical quenching accompanied by a 5-fold increase in antheraxanthin and zeaxanthin. No consistent change in the concentrations of functional PSII centers, DCMU-binding sites, or D1 protein pool size occurred. D1 protein synthesis was rapid. In excess irradiance, quantum yield of O2 evolution and the efficiency of PSII were reduced, associated with a 15- to 20-fold increase in antheraxanthin and zeaxanthin and a sustained increase in nonphotochemical quenching. A decrease in functional PSII center concentration occurred, followed by a decline in the concentration of D1 protein; the latter, however, was not matched by a decrease in DCMU-binding sites. In the most extreme treatments, DCMU-binding site concentration remained 2 times greater than the concentration of D1 protein recognized by antibodies. D1 protein synthesis rates remained unaltered at excess irradiances.

Response of Tradescantia albiflora to growth irradiance: Change versus changeability.

Most chloroplasts undergo changes in composition, function and structure in response to growth irradiance. However, Tradescantia albiflora, a facultative shade plant, is unable to modulate its light-harvesting components and has the same Chl a/Chl b ratios and number of functional PS II and PS I reaction centres on a Chl basis at all growth irradiances. With increasing growth irradiance, Tradescantia leaves have the same relative amount of chlorophyll-proteins of PS II and PS I, but increased xanthophyll cycle components and more zeaxanthin formation under high light. Despite high-light leaves having enhanced xanthophyll cycle content, all Tradescantia leaves acclimated to varying growth irradiances have similar non-photochemical quenching. These data strongly suggest that not all of the zeaxanthin formed under high light is necessarily non-covalently bound to major and minor light-harvesting proteins of both photosystems, but free zeaxanthin may be associated with LHC II and LHC I or located in the lipid bilayer. Under the unusual circumstances in light-acclimated Tradescantia where the numbers of functional PS II and PS I reaction centres and their antenna size are unaltered during growth under different irradiances, the extents of PS II photoinactivation by high irradiances are comparable. This is due to the extent of PS II photoinactivation being a light dosage effect that depends on the input (photon exposure, antenna size) and output (photosynthetic capacity, non-radiative dissipation) parameters, which in Tradescantia are not greatly varied by changes in growth irradiance.

Effect of vanadate on reproductive efficiency in normal and streptozocin-treated diabetic rats.

The effects of oral vanadate treatment on the reproductive efficiency of normal and diabetic female rats were studied. Vanadate treatment in a dose-dependent manner reduced both the conception rate and the ability to carry pregnancy to term compared with a control group. These effects were more severe in diabetic groups as compared with nondiabetic groups. At the 0.25 mg/mL vanadate dose, the conception rate was reduced by 13% and 33% for the nondiabetic group and the diabetic group, respectively. At the 0.50 mg/mL dose, this rate decreased by 20% and 47% for the nondiabetic and diabetic groups, respectively. With an identical oral vanadate regimen of 0.25 mg/mL, the ability to sustain pregnancy to term was reduced by 30% and 90% for the nondiabetic and diabetic groups, respectively, and by 84% and 100% for these groups at a dose of 0.50 mg/mL. Although the blood vanadate concentrations were an order of magnitude higher in diabetic animals treated with vanadate than in nondiabetic animals under an identical vanadate treatment, oral vanadate treatments had no measurable effects in ameliorating hyperglycemia in these diabetic pregnant animals. In conclusion, vanadate is ineffective in normalizing blood glucose in pregnant diabetic rats, and it impairs reproductive capacity and the ability to sustain pregnancy to term in both nondiabetic and diabetic animals.

Differential acute effects of oxovanadiums and insulin on glucose and lactate metabolism under in vivo and in vitro conditions.

Oxovanadium compounds such as vanadate and peroxovanadiums have been shown to have insulin-mimetic effects on various metabolic pathways, including glucose metabolism. A differential effect of various oxovanadium species on glucose metabolism in different tissues has been reported. The results from our present in vivo studies using rats show that peroxovanadiums and insulin have similar acute effects on decreasing blood glucose levels, but dissimilar effects on blood lactate levels. Furthermore, when bisperoxovanadate (BPV) was administered acutely to intact animals immediately before a bolus insulin challenge, it blunted the effectiveness of insulin in decreasing the blood lactate level, but at the same time demonstrated a synergistic effect on the hypoglycemic action of insulin. It was also observed in in vitro studies using normal 3T3-L1 adipocytes (not serum-deprived) that 1,10-phenanthroline bisperoxovanadate (PHEN-BPV) attenuates the incorporation of carbon from lactate but not from glucose, into lipid in both the absence and presence of insulin. Additionally, it was observed that PHEN-BPV had no effect on lactate dehydrogenase (LDH) activity. Thus, one may speculate that PHEN-BPV interferes with carrier-mediated lactate transport. These observations demonstrate that insulin and oxovanadiums differ in the handling of different metabolic substrates. Thus, even though oxovanadiums mimic many of the metabolic actions of insulin, their metabolic effects are by no means identical. Moreover, since vanadate had no acute effect on glucose metabolism under in vivo conditions, this may suggest that to be effective as a hypoglycemic agent vanadate needs to be converted to some other biologically active oxovanadium species. Finally, the observed interference by PHEN-BPV in the metabolism of lactate may predispose subjects using oral vanadate, as a part of the therapeutic regimen for management of diabetic hyperglycemia, to lactic acidosis.

Effects of maternal vanadate treatment of fetal development.

Oral vanadate treatment is effective in normalizing blood glucose in both Type I and Type II diabetics. Using Sprague Dawley rats we examined the effectiveness of such treatment in amelioration of hyperglycemia in diabetic pregnancy and its effect on fetal growth in both normal and diabetic pregnant dams. Initiation of vanadate treatment to diabetic and normal pregnant dams increased blood vanadium levels in both groups, but this concentration in the diabetic pregnant group reached approximately twice the value present in the normal group. Despite this high blood vanadium level in the diabetic pregnant dams, oral vanadate treatment was not effective in normalizing blood sugar in this group. Additionally, vanadate treatment was found to be toxic during diabetic pregnancy, causing death to 45% of the test animals. Maternal blood vanadium had a negative effect on fetal development, markedly reducing the number of live fetuses per pregnancy. In summary, oral vanadate treatment is toxic and ineffective during diabetic pregnancies and interferes with fetal growth and development in both normal and diabetic pregnancy.

A comparison of flat and shallow conical tips for cervical cryotherapy.

BACKGROUND: Although two types of cervical cryotherapy tips are widely used, there have been no randomized prospective comparison studies reported in the medical literature. Shallow conical tip proponents theorize that a greater depth of freeze near the os yields better treatment of cervical intraepithelial neoplasia (CIN) without elevating the squamocolumnar junction into the cervical canal. Flat tip proponents theorize an equally effective CIN treatment with lower incidence of posttreatment squamocolumnar junction location in the cervical canal. METHODS: A comparative descriptive study was performed to evaluate 117 cryotherapy candidates with biopsy-proved CIN who were classified by location of their squamocolumnar junctions (ectocervix, at the os, or in the canal). They were then randomized to receive double-freeze cervical cryotherapy with either a flat or shallow conical tip. Four or more months later, repeated colposcopy and Papanicolaou smears were performed to assess resolution of CIN and posttreatment location of the squamocolumnar junction. RESULTS: Eighty-four patients (71%) completed the study. Analysis indicated no important difference between the two tips in eliminating CIN. The squamocolumnar junction was colposcopically visualized at all posttreatment examinations. When the pretreatment squamocolumnar junction location was on the ectocervix, data analysis indicated that squamocolumnar junction movement was greater with the shallow conical tip (P = .037), particularly into the canal, where it is clinically more difficult to visualize (P = .019). There were no significant differences in movement of the squamocolumnar junction when it was originally at the os or in the canal. CONCLUSIONS: This study found no significant difference in effectiveness of the two types of tips in eliminating CIN and supports the practice of using one type--either flat or shallow conical tips--to treat all candidates for cervical cryotherapy. Using the flat tip when the pretreatment squamocolumnar junction is on the ectocervix will allow easier posttreatment visualization of the squamocolumnar junction. Further studies with a greater number of subjects are indicated.

Two components of onset and recovery during photoinhibition of Ulva rotundata.

Short-term (up to 5 h) transfers of shade-adapted (100 µmol · m(-2) · s(-1)) clonal tissue of the marine macroalga Ulva rotundata Blid. (Chlorophyta) to higher irradiances (1700, 850, and 350 µmol · m(-2) · s(-1)) led to photoinhibition of room-temperature chlorophyll fluorescence and O2 evolution. The ratio of variable to maximum (Fv/Fm) and variable (Fv) fluorescence, and quantum yield (ϕ) declined with increasing irradiance and duration of exposure. This decline could be resolved into two components, consistent with the separation of photoinhibition into energy-dissipative processes (photoprotection) and damage to photosystem II (PSII) by excess excitation. The first component, a rapid decrease in Fv/Fm and in Fv, corresponds to an increase in initial (Fo) fluorescence and is highly sensitive to 1 mM chloramphenicol. This component is rapidly reversible under dim (40 µmol · m(-2) · s(-1)) light, but is less reversible with increasing duration of exposure, and may reflect damage to PSII. The second (after 1 h exposure) component, a slower decline in Fv/Fm and Fv with declining Fo, appears to be associated with the photoprotective interconversion of violaxanthin to zeaxanthin and is sensitive to dithiothreitol. The accumulation of zeaxanthin in U. rotundata is very slow, and may account for the predominance of increases in Fo at high irradiances.

Photoacclimation and photoinhibition in Ulva rotundata as influenced by nitrogen availability.

Clonal tissue of the marine chlorophyte macroalga, Ulva rotundata Blid., was transferred from 100 to 1700 µmol photons · m(-2) · s(-1) under limiting (1.5 µM NH 4 (+) maximum, N/P=2) and sufficient (15 µM NH 4 (+) maximum, N/P=20) nitrogen supply at 18° C and 11 h light-13 h darkness daily. Photoinhibition was assayed by light-response curves (photosynthetic O2 exchange), and chlorophyll fluorescence at 77 K and room temperature. Daily surface-area growth rate (µSA) in N-sufficient plants increased sixfold over 3 d and was sustained at that level. During this period, respiration (R d) doubled and light-saturated net photosynthesis capacity (P m) increased by nearly 50%, indicating acclimation to high light. Quantum yield (ϕ) decreased by 25% on the first day, but recovered completely within one week. The ratio of variable to maximum fluorescence (F v/F m) also decreased markedly on the first day, because of an increase in initial fluorescence (F o) and a decrease in F m, and partially recovered over several days. Under the added stress of N deficiency, µSA accelerated fivefold over 4 d, despite chronic photoinhibition, then declined along with tissue-N. Respiration doubled, but P m decreased by 50% over one week, indicating inability to acclimate to high light. Both ϕ and F v/F m decreased markedly on the first day and did not significantly recover. Changes in F o, F m and xanthophyll-cycle components indicate concurrent photodamage to photosystem II (PSII) and photoprotection by thermal deexcitation in the antenna pigments. Increasing µSA coincided with photoinhibition of PSII. Insufficient diel-carbon balance because of elevated R d and declining P m and tissue-N, rather than photochemical damage per se, was the apparent proximate cause of decelerating growth rate and subsequent tissue degeneration under N deficiency in U. rotundata.