Effects of supplemental UV-B radiation on growth and leaf photosynthetic reactions of soybean (Glycine max)

Experiments were conducted under greenhouse conditions to investigate the effects of enhanced UV-B radiation (280 to 320 nm) on height, fresh and dry weights, leaf chlorophyll and carotenoids, CO₂ uptake rates, and Hill activity in soybean ( Glycine max L. cv. Bragg). Plants were exposed for 6 h continuously from midmorning to midafternoon each day to UV-B radiation which was provided by Westinghouse FS-40 sun lamps filtered with 0.127-mm cellulose acetate film (UV-B enhanced) or 0.127-mm Mylar S film (UV-B Mylar control). Three different UV-B enhanced radiation levels were tested: 1.09 (treatment T₁), 1.36 (treatment T₂), and 1.83 (treatment T₃) UV-B sun equivalent units (UV-B_sec) where 1 UV-B_sec= 15.98 mW·m⁻² of solar UV-B obtained by applying EXP -[(α-265)/21]², a weighting function that simulates the DNA absorption spectrum, to the UV-B lamp systems. These UV-B levels correspond to a calculated decrease in stratospheric ozone content of 6%, 21%, and 36% for treatment T₁, T₂, and T₃, respectively.
Daily exposure of soybean plants to UV-B radiation significantly decreased height, fresh and dry weights, leaf chlorophyll and carotenoid contents, and CO₂ uptake rates. Leaf pigment extracted in 80% acetone from UV-B-treated soybean plants showed considerable increase in absorption in the wavelength region of 330 to 400 nm with increased UV-B radiation levels. Chloroplast preparations from leaves of T₂ and T₃ plants showed significant reductions in Hill reaction measurements.     

Investigations on Myelination In Vitro: Regulation of 2',3'-Cyclic Nucleotide 3'-Phosphohydrolase by Thyroid Hormone in Cultures of Dissociated Brain Cells from Embryonic Mice

Abstract: The direct influence of l -3,3',5-triiodothyronine (T₃) on the development of 2',3'-cyclic nucleotide 3'-phosphohydrolase (EC 3.1.4.37, CNPase) is demonstrated by using an in vitro culture system of dissociated embryonic mouse brain cells. Serum from a thyroidectomized calf, which contained low levels of T₃ (31 ng/100 ml), and thyroxine, T₄ (<1 μg/ml), was used in the culture medium in place of normal calf serum (T₃, 103 ng/100 ml; T₄, 5.7 μg/ml) to render the culture responsive to exogenously added T₃. The lower levels of enzyme activity observed in the presence of such a deficient medium could be restored to normal values by T₃ supplementation. Half-maximal effect was obtained with 2.5 ± 10⁻⁹ m -T₃. Three days of hormone treatment resulted in the maximal stimulation of CNPase. T₄ was less effective in inducing CNPase activity and the inactive analog of the hormone, reverse T₃ (3,3',5'-T₃) was ineffective. The morphological appearance of the cells was characterized by deformed (smaller size and less in number) reaggregates in the cultures, lacking hormone.     

Characterization of the Thyroid Hormone Transport System of Cerebrocortical Rat Neurons in Primary Culture

Abstract: The uptake of 3',3,5-triiodo- l -thyronine (T₃) and l -thyroxine (T₄) by primary cultures derived from rat brain hemispheres was studied under initial velocity conditions, at 25°C. Uptake of both hormones was carrier mediated and obeyed simple Michaelis-Menten kinetics. The K _m of T₃ uptake was very similar to that of T₄, and did not vary significantly from day 1 to 4 in culture (310–400 n M ). The maximal velocity ( V _max) of T₃ uptake nearly doubled between day 1 and 4 of culture (41 ± 3 vs. 70 ± 5 pmol/min/mg of DNA, respectively). The V _max of T₄ uptake did not change (28 ± 8 and 31 ± 4 pmol/min/mg of DNA on days 1 and 4, respectively). The rank order of unlabeled thyroid hormone analogues to compete with labeled T₃ or T₄ uptakes were the same (T₃ > T₄ > 3',5',3-triiodo- l -thyronine > 3',3,5-triiodo- d -thyronine > triiodothyroacetic acid), indicating that the transport system is stereospecific. Unlabeled T₄ was a stronger competitor of labeled T₄ uptake than of labeled T₃ uptake, whereas unlabeled T₃ had the same potency for both processes. These results suggest that T₃ and T₄ are transported either by two distinct carriers or by the same carrier bearing separate binding sites for each hormone. They also indicate that the efficiency of T₃ uptake increases during neuronal maturation.     

Physiological response of Pinus halepensis needles under ozone and water stress conditions

The aim of this study was to evaluate how physiological processes of potted Pinus halepensis plants, grown under controlled conditions, were affected by ozone (O₃) and/or water stress, integrating the gas exchange and biochemical data with fluorescence OJIP polyphasic transient data. Plants submitted to only water stress (T₁) and with ozone (T₃) showed a strong decrease in stomatal conductance and gas exchange, coinciding with a reduction of maximum yield of photochemistry ( φ _po) and very negative values of leaf water potential. Simultaneously, a great increase of both PSII antenna size, indicated by absorption per reaction centre, and electron transport per reaction centre were found. The reduction of photosynthesis in the O₃-treated plants (T₂) by a slowing down of the Calvin cycle was supported by the increase of related fluorescence parameters such as relative variable fluorescence, heat de-excitation constant, energy de-excitation by spillover, and the decrease of φ _po. We suggest an antagonistic effect between the two stresses to explain the delayed ozone-induced decrease of stomatal conductance values for T₃ with respect to T₁ plants, by an alteration of the physiological mechanisms of stomatal opening, which involve the increase of intra-cellular free-calcium induced by ABA under co-occurring water shortage. We emphasise the importance of considering the intensity of the individual stress factor in studies concerning the interaction of stresses.     

Changes in thyroid function and gonadotrophin activity during sexual development in ducks Anas sp. (Aves: Anatidae)

Age-related changes in plasma iodohormone concentrations in male and female Aylesbury and Khaki Campbell ducklings were determined between the second week after hatching and sexual maturity.
In both sexes and strains the concentration of total thyroxine (T₄) and the free thyroxine index (FT₄1) were low during the first 6–8 weeks after hatching. A marked increase in the T₄ and FT₄1 occurred when the ducklings were nine weeks old; T₄ progressively increased over the following four weeks and remained high thereafter. The T₄ concentration in both sexes was directly related to age.
Concentrations of total tri-iodothyronine (T₃) were more variable than T₄ but were highest before sexual maturation and inversely age-related. An age-related decline in free tri-iodothyronine index (FT₃1) was observed during the first nine weeks.
The possibility that these maturational changes in thyroid function may reflect changes in gonadal activity was assessed by measuring the concentration of luteinizing hormone (LH) in the same plasma samples. Although plasma LH increased with age, in all cases the increase occurred after changes in the thyroid hormones were observed. Moreover, the maturational pattern of LH was related to sex and strain whereas thyroid function was unaffected by sex or strain.
These results demonstrate reciprocal changes in plasma T₃ and T₄ levels in ducks during sexual development, although the stimuli responsible and physiological significance are uncertain.     

Seasonal changes of thyroid hormones in field-collected Atlantic cod in relation to condition indices, water temperature and photoperiod

Serum T₄ and T₃ in wild Atlantic cod Gadus morhua ranged from 1 to 12 ng ml⁻¹ and from 2 to 27 ng ml⁻¹ respectively over a 3-year period. In general, the concentrations increased from summer (T₃) or early autumn (T₄) to maxima in mid-winter and declined abruptly during spring. The T₄/T₃ monthly means were lowest in summer and highest in winter. The seasonal patterns of thyroid hormones were weakly correlated with changes in water temperature. However, both T₄ and T₃ co-varied simultaneously with photoperiod. In addition, T₃ was correlated with the hepatosomatic index and condition factor during summer and autumn. It is suggested that the seasonal changes in the release of T₄ from the thyroid were photoperioddriven, and that the course of T3 was regulated by the metabolic state of the fish during the somatic growth period.     

Maize streak virus-resistant transgenic maize: a first for Africa

In this article, we report transgene-derived resistance in maize to the severe pathogen maize streak virus (MSV). The mutated MSV replication-associated protein gene that was used to transform maize showed stable expression to the fourth generation. Transgenic T₂ and T₃ plants displayed a significant delay in symptom development, a decrease in symptom severity and higher survival rates than non-transgenic plants after MSV challenge, as did a transgenic hybrid made by crossing T₂ Hi-II with the widely grown, commercial, highly MSV-susceptible, white maize genotype WM3. To the best of our knowledge, this is the first maize to be developed with transgenic MSV resistance and the first all-African-produced genetically modified crop plant.     

Agrobacterium tumefaciens-mediated barley transformation

Genetically transformed barley was produced by eco-cultivating immature embryo explants with Agrobacterium tumefaciens carrying a binary vector coding for chimaeric bacterial genes, bar and gus , and selecting for bialaphos-resistant cultures from which plants were regenerated. Integration of both genes was confirmed by gel blot hybridization analysis of DNA from the transformed plants and their progenies. From 1282 embryos, plants were recovered for 54 independently transformed lines, giving a transformation efficiency of 4.2%. Transgene numbers in the different lines ranged from single copy insertion to at least ten copies. Sixteen out of 18 plants grown to maturity were fully fertile. Both marker genes, bar and gus , were expressed and co-segregated in the T₁ progeny plants. In the majority of cases, the genes showed Mendelian segregation predicted for transgene insertion at a single locus. In one family with multiple transgene insertions, molecular analysis of T₁ and T₂ plants suggested that the T-DNA had inserted at two unlinked loci.     

Dose-related effects of 17βoestradiol (E2) on liver weight, plasma E2, protein, calcium and thyroid hormone levels, and measurement of the binding of thyroid hormones to vitellogenin in rainbow trout, Salmo gairdneri Richardson

Administration of 17β-oestradiol (E₂) to rainbow trout, in the form of hydrogenated coconut oil implants produced a stable, long-term elevation in plasma E₂ levels. The elevation was doserelated (over the range 1–10mg kg-¹ body weight) both 4 and 8 weeks after implantation. Dose-related increases were also observed with respect to liver weight-body weight ratios and plasma protein levels. Plasma T₃ and total calcium levels were depressed and elevated, respectively, by E₂ treatment but the responses were not linearly related to the dose of E₂ administered; there was no significant effect of E₂ on plasma T₄ levels.
E₂ induced a shift in the binding of T₃ to plasma proteins, with T₃ binding to smaller molecular weight proteins; neither T₄ nor T₃ bound to vitellogenin which was present at high levels in the plasma of E₂-treated fish.     

Triiodothyronine Is a High-Affinity Inhibitor of Amino Acid Transport System L1 in Cultured Astrocytes

Abstract: The relationship between the transport of thyroid hormones and that of amino acids was examined by measuring the uptake of amino acids that are characteristic substrates of systems L, A, and N, and the effect of 3,3',5-triiodo-L-thyronine (T₃) on this uptake, in cultured astrocytes. Tryptophan and leucine uptakes were rapid, Na⁺-independent, and efficiently inhibited by T₃ (half-inhibition at ∼ 2 μ M ). Two Na⁺-independent L-like systems (L₁ and L₂), common to leucine and aromatic amino acids, were characterized kinetically. System L₂ had a low affinity for leucine and tryptophan ( K _m= 0.3–0.9 m M ). The high-affinity system L₁ ( K _m∼ 10 μ M for both amino acids) was competitively inhibited by T₃ with a K _i of 2–3 μ M (close to the T₃ transport K _m). Several T₃ analogues inhibited system L₁ and the T₃ transport system similarly. Glutamine uptake and α-(methylamino)isobutyric acid uptake were, respectively, two and 200 times lower than tryptophan and leucine uptakes. T₃ had little effect on the uptakes of glutamine and α-(methylamino)isobutyric acid. The results indicate that the T₃ transport system and system L₁ are related.     

'GM-gene-deletor': fused loxP-FRT recognition sequences dramatically improve the efficiency of FLP or CRE recombinase on transgene excision from pollen and seed of tobacco plants

Pollen- and seed-mediated transgene flow is a concern in plant biotechnology. We report here a highly efficient 'genetically modified (GM)-gene-deletor' system to remove all functional transgenes from pollen, seed or both. With the three pollen- and/or seed-specific gene promoters tested, the phage CRE/ loxP or yeast FLP/ FRT system alone was inefficient in excising transgenes from tobacco pollen and/or seed, with no transgenic event having 100% efficiency. When loxP-FRT fusion sequences were used as recognition sites, simultaneous expression of both FLP and CRE reduced the average excision efficiency, but the expression of FLP or CRE alone increased the average excision efficiency, with many transgenic events being 100% efficient based on more than 25 000 T₁ progeny examined per event. The 'GM-gene-deletor' reported here may be used to produce 'non-transgenic' pollen and/or seed from transgenic plants and to provide a bioconfinement tool for transgenic crops and perennials, with special applicability towards vegetatively propagated plants and trees.     

Seasonal changes in thyroidal status in the plaice, Pleuronectes platessa L.

A chemically specific analysis for plasma thyroid hormones has been used to disclose a seasonal bimodality in the concentrations of thyroxine (T₄) and triiodothyronine (T₃) in the plaice; maxima in both hormone levels occur in winter and in summer. The ratio of T₄ concentrations to T₃ varies seasonally being at a minimum in summer. A highly significant correlation of T₄ plasma levels with the landings per unit fishing effort for the same area has been observed.     

A 10-kDa acyl-CoA-binding protein (ACBP) from Brassica napus enhances acyl exchange between acyl-CoA and phosphatidylcholine

The gene encoding a 10-kDa acyl-CoA-binding protein (ACBP) from Brassica napus was over-expressed in developing seeds of Arabidopsis thaliana . Biochemical analysis of T₂ and T₃ A. thaliana seeds revealed a significant increase in polyunsaturated fatty acids (FAs) (18:2 ^{cis Δ9,12} and 18:3 ^{cis Δ9,12,15}) at the expense of very long monounsaturated FA (20:1 ^{cis Δ11}) and saturated FAs. In vitro assays demonstrated that recombinant B. napus ACBP (rBnACBP) strongly increases the formation of phosphatidylcholine (PC) in the absence of added lysophosphatidylcholine in microsomes from ΔYOR175c yeast expressing A. thaliana lysophosphatidylcholine acyltransferase ( AthLPCAT ) cDNA or in microsomes from microspore-derived cell suspension cultures of B. napus L. cv. Jet Neuf. rBnACBP or bovine serum albumin (BSA) were also shown to be crucial for AthLPCAT to catalyse the transfer of acyl group from PC into acyl-CoA in vitro . These data suggest that the cytosolic 10-kDa ACBP has an effect on the equilibrium between metabolically active acyl pools (acyl-CoA and phospholipid pools) involved in FA modifications and triacylglycerol bioassembly in plants. Over-expression of ACBP during seed development may represent a useful biotechnological approach for altering the FA composition of seed oil.     

INHIBITION OF THYROXINE-INDUCED RESORPTION OF TADPOLE TAIL BY ADENOSINE 3', 5'-CYCLIC MONOPHOSPHATE

Small segments of tail of Bufo bufo japonicus tadpoles were cultured in medium containing thyroxine (T₄) and dibutyryl cyclic AMP (dbcAMP). Like prolactin, the cyclic nucleotide blocked T₄-induced shrinkage or tail pieces. Histological study of the segments after 4-days culture revealed that dbcAMP suppressed degenerative changes induced by T₄. The inhibitory effect of prolactin on T₄-induced tail regression was promoted by caffeine, an inhibitor of adenosine 3', 5'-cyclic monophosphate (cyclic AMP)-phosphodiesterase.
The effect of prolactin on the level of cyclic AMP in the tail was also studied in vivo . Sixty min after prolactin injection, the cyclic AMP level was 2–3 times the control value. Possible involvement of cyclic AMP in the action of prolactin, which blocks tail resorption induced by T₄, was discussed.     

Seasonal and diurnal rhythms of thyroidal status in the rainbow trout, Salmo gairdneri Richardson

The concentrations of thyroxine (T₄) and triiodothyronine (T₃) in the blood plasma of rainbow trout ( Salmo gairdneri Richardson) at intervals throughout the year have been measured by a chemically specific gas-liquid chromatographic (GLC) method. Mean hormone levels showed a seasonal variation, maximal levels of both hormones occurring in winter and minimal concentrations in mid summer. An apparent secondary maximum in mean T₄ and T₃ concentrations was observed in spring. (T₄)/(T₃) ratios have been found to be highest in winter and lowest in summer. A radioimmunoassay procedure, validated by GLC analyses, revealed the presence of a diurnal rhythm in serum T₄ levels of trout sampled in September and in April.     

Plasma and ovarian thyroxine levels in relation to sexual maturation and gestation in female Sebastes inermis

Plasma T₄ (L-thyroxine) concentrations in the viviparous rockfish Sebastes inermis showed a peak (119·3±27·8 ng ml⁻¹) during the development of embryos. Ovarian T₄ concentrations increased during vitellogenesis and final maturation and decreased during embryogenesis.However, total T₄ content within the ovary increased continuously up to the larval stages. Plasma oestradiol-17β, (E₂) concentrations peaked at the final maturation stage and then recovered to the level seen during the non-reproductive periods. Plasma testosterone (T) concentrations showed a peak (5·33±1·08 ng ml⁻¹) at the embryo stage and high levels were maintained throughout the gestation period. Plasma T₄ concentrations during the embryo stage and ovarian T₄ content during vitellogenesis were much higher than the levels reported in oviparous fishes. These data suggest that in viviparous rockfish, T₄ may be required for sustaining gestation or embryo development within the maternal body. In addition, the high content of total T₄ in the ovary implies that there probably does exist a maternal-embryo relationship during gestation as well as during vitellogenesis.     

Migration tendency in juvenile steelhead trout, Salmo gairdneri Richardson, injected with thyroxine and thiourea

Juvenile steelhead trout, Salmo gairdneri injected with thyroxine (T₄) near the time of seaward migration exhibited a significantly lower migration tendency than untreated controls of fish injected with saline, thiourea, or a combination of T₄ and thiourea. Fish injected with thiourea alone or in combination with T₄ prior to the time of maximum migration tendency showed enhanced migration over untreated and saline injected controls and those injected with T₄ alone. Injections of T₄ or a combination of T₄ and thiourea elevated plasma T₄ and tri-iodothyronine (T₃) concentrations, while injection of thiourea alone depressed thyroid hormone levels relative to saline-injected controls. Plasma concentrations of T₃ and T₄ returned to control levels within 10 days in all groups. We suggest that thyroid hormones are antagonistic to mechanisms underlying seaward migration of steelhead trout and that these antagonistic effects must be overcome before migration tendency is expressed.     

Evidence for Circadian Variations of Thyroid Hormone Concentrations and Type II 5'-Iodothyronine Deiodinase Activity in the Rat Central Nervous System

Abstract: The 24-h patterns of tissue thyroid hormone concentrations and type II 5'- and type III 5-iodothyronine deiodinase (5'D-II and 5D-III, respectively) activities were determined at 4-h intervals in different brain regions of male euthyroid rats entrained to a regular 12-h light/12-h dark cycle (lights on at 6:00 a.m.). Activity of 5'D-II, which catalyzes the intracellular conversion of thyroxine (T₄) to 3,3',5-triiodo- l -thyronine (T₃) in the CNS, and the tissue concentrations of both T₄ and T₃ exhibited significant daily variations in all brain regions examined. Periodic regression analysis revealed significant circadian rhythms with amplitudes ranging from 9 to 23% (for T₃) and from 15 to 40% (for T₄ and 5'D-II) of the daily mean value. 5'D-II activity showed a marked nocturnal increase (1.3–2.1-fold vs. daytime basal value), with a maximum at the end of the dark period and a minimum between noon and 4:00 p.m. 5D-III did not exhibit circadian patterns of variation in any of the brain tissues investigated. Our results disclose circadian rhythms of 5'D-II activity and thyroid hormone concentrations in discrete brain regions of rats entrained to a regular 12:12-h light-dark cycle and reveal that, in the rat CNS, T₃ biosynthesis is activated during the dark phase of the photoperiod. For all parameters under investigation, the patterns of variation observed were in part regionally specific, indicating that different regulatory mechanisms may be involved in generating the observed rhythms.     

Correlative Regulation of Nerve Growth Factor Level and Choline Acetyltransferase Activity by Thyroxine in Particular Regions of Infant Rat Brain

Abstract: Effects of thyroxine (T₄) on nerve growth factor (NGF) level and choline acetyltransferase (ChAT) activity of rat brains were investigated. Repetitive intraperitoneal administration of T₄ caused increases in both NGF level and ChAT activity in the frontal cortex, septum, hippocampus, and striatum and decreases in the cerebellum in 2-day-old rats. Only ChAT activity was elevated in the olfactory bulb, and the NGF level remained unchanged there. No changes were observed in the midbrain and pons/medulla. Furthermore, T₄ was effective on the post-natal rats only up to day 11. These results suggest that T₄ plays a role in the developmental regulation of NGF level and ChAT activity in rat brain in a region- and/or stage-specific manner. That (1) changes in NGF level and ChAT activity occurred in regions nearly identical to those that contained NGF-responding neurons, and (2) the change in NGF level in the hippocampus and frontal cortex was followed by the change of ChAT activity after a single injection of T₄ suggest that the effects of T₄ on cholinergic differentiation are, at least in part, mediated via NGF, which itself is quantitatively regulated by T₄.