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1.
Iodine deficiency (ID) and related disorders are still major, yet unresolved health concerns. Recently, in a systematic survey
of schoolage children (SAC), we reported severe to moderate ID, in Ankara and three cities from Black Sea region of Turkey.
The current study attempted to evaluate selenium (Se) status, thiocyanate (SCN−) overload, and their possible contribution to the goiter endemics and thyroid hormone profile observed in these cities. Thyroid
ultrasonography was performed and serum Se, SCN−, thyroid hormones, sensitive TSH (sTSH) levels, and urinary iodine concentrations (UICs) were determined from 251 SAC (9–11
yr old).
Thyroid volumes (TVs) exceeding recommended upper normal limits and median UIC indicated goitre endemics and moderate to severe
ID in the areas studied. Mean serum SCN− concentrations were found to be greater than the controls from the literature. The UIC/SCN− ratio was found to be lowest in Bayburt and Trabzon denoting that SCN− overload may contribute to the goiter endemics. Serum Se concentrations represent a marginal deficiency in the four areas
studied. No significant correlations between serum Se concentrations and the other parameters studied (i.e., TV, SCN−, thyroid hormones, sTSH, UIC) was detected.
In conclusion, this study showed that selenium is also marginally deficient in the iodine-deficient endemic areas studied,
but this has little or no impact on the thyroid hormone profile and the goiter endemics. SCN− overload may contribute to the endemics, especially for the areas where iodine is severely deficient. An effective iodine
supplementation program will not only resolve the goiter endemics but also the consequence of SCN− overload as well in the endemic goiter areas studied. 相似文献
2.
Selenoenzyme activities in selenium- and iodine-deficient sheep 总被引:3,自引:0,他引:3
Voudouri AE Chadio SE Menegatos JG Zervas GP Nicol F Arthur JR 《Biological trace element research》2003,94(3):213-224
This study was conducted to evaluate the effects of single and combined deficiencies of selenium and iodine on selenoenzyme
activities in sheep. Twenty-four male lambs were assigned to one of four semisynthetic diets: combined deficient A (Se−I), Se-deficient B (Se−I+), I-deficient C (Se+I−), and basal diet D (Se+I+). Thyroid hormones (T3, T4), thyroid stimulating hormone (TSH), and inorganic iodine (PII) were determined in plasma. Selenium and glutathione peroxidase
activity (GSH-Px) were determined in erythrocytes, and tissue samples, including the thyroid, liver, kidney, and brain, were
taken for selenoenzyme analysis. Plasma T3, T4, and TSH concentrations were similar in all groups. Type I deiodinase (ID-I) activity in liver and kidney remained unchanged
in Se or I deficiency. In contrast, hepatic ID-I activity was increased by 70% in combined Se-I deficiency. Thyroidal cystolic
GSH-Px (c-GSH-Px) and phospholipid GSH-Px (ph-GSH-Px) activities remained constant in both Se-deficient groups, whereas thyroidal
c-GSH-Px activity increased (57%) in I deficiency. Type II deiodinase (ID-II) activity was not detectable in the cerebrum
and cerebellum, whereas cerebellum Type III deiodinase (ID-III) activity was decreased in I deficiency and combined Se-I deficiencies.
The results of the present study support a sensitive interaction between Se and I deficiencies in sheep thyroid and brain.
Furthermore, the lack of thyroidal ID-I activity, the presservation of the thyroidal antioxidant enzymes, and the increases
in hepatic ID-I indicate that a compensatory mechanism(s) works toward retaining plasma T3 levels, mostly by de novo synthesis of T3 and peripheral deiodination of T4 in Se- and I-deficient sheep. 相似文献
3.
Begoña Blasco Juan J. Rios Luis M. Cervilla Eva Sánchez-Rodríguez María M. Rubio-Wilhelmi Miguel A. Rosales Juan M. Ruiz Luis Romero 《Journal of Plant Growth Regulation》2010,29(4):477-486
Iodine is vital to human health, and iodine biofortification programs help improve human intake through plant consumption.
There is no research on whether iodine biofortification influences basic plant physiological processes. Because nitrogen (N)
uptake, utilization, and accumulation are determining factors in crop yield, the aim of this work was to establish the effect
of the application of different doses (20, 40, and 80 μM) and forms of iodine (iodate [IO3
−] vs. Iodide [I−]) on N metabolism and photorespiration. For this study we analyzed shoot biomass and the activities of nitrate reductase
(NR), nitrite reductase (NiR), glutamine synthetase (GS), glutamate synthase (GOGAT), aspartate aminotransferase (AAT), glutamate
dehydrogenase (GDH), glycolate oxidase (GO), glutamate:glyoxylate aminotransferase (GGAT), serine:glyoxylate aminotransferase
(SGAT), hydroxypyruvate reductase (HR) and catalase (CAT), nitrate (NO3
−), ammonium (NH4
+), organic and total N, amino acids, proteins, serine (ser), malate, and α-ketoglutaric acid in edible lettuce leaves. Application
of I− at doses of at least 40 μM reduced the foliar concentration of NO3
− with no decrease in biomass production, which may improve the nutritional quality of lettuce plants. In contrast, the application
of 80 μM of I− is phytotoxic for lettuce plants, reducing the biomass, foliar concentration of organic N and NO3
−, and NR and GDH activities. HR activity is significantly inhibited with all doses of I−; the least inhibition was at 80 μM. This may involve a decrease in the incorporation of carbonated skeletons from photorespiration
into the Calvin cycle, which may be partially associated with the biomass decrease. Finally, the application of IO3
− increases biomass production, stimulates NO3
− reduction and NH4
+ incorporation (GS/GOGAT), and optimizes the photorespiratory process. Hence, this appears to be the most appropriate form
of iodine from an agronomic standpoint. 相似文献
4.
Adsorption–desorption of iodine in two forms, viz., iodide (I−) and iodate (IO3−), in three types of soil were investigated. The soils were: red soil developed on Quaternary red earths (REQ)— clayey, kaolintic
thermic plinthite Aquult, Inceptisol soil (IS) and alluvial soil (AS)—Fluvio-marine yellow loamy soil. The isothermal curves
of iodine adsorption on soils were described by Langmuir and Freundlich equation, and the maximum adsorption values (y
m) were obtained from the simple Langmuir model. As compared with the iodide, the iodate was adsorbed in higher amounts by
the soils tested. Among three soils, the REQ soil adsorbed more iodine (I− and IO3−) than the IS and AS. The distribution coefficient (K
d) of iodine in the soils decreased exponentially with increasing iodine loading concentration. Desorption of iodine in soil
was increased correspondingly with increasing adsorption values. The REQ soil had a greater affinity for iodine than the IS
and AS at the same iodine loadings. In the pot experiment cultivated with pakchoi (Brassica chinensis L.) and added with two exogenous iodine sources, the iodide form was quickly taken up by pakchoi and caused more toxicity
to the vegetable. The rate of iodine loss from soil was higher for iodide form as compared with the iodate. The iodine bioavailability
was the highest but the persistence was the weakest in AS among the three soils tested, and the REQ soil showed just the opposite
trend to that of the AS soil. This study is of theoretical importance to understand the relationship between iodine adsorption–desorption
characteristics and their bioavailability in different soils and it also has practical implications for seeking effective
alternatives of iodine biofortification to prevent iodine deficiency disorders. 相似文献
5.
Weng HX Hong CL Yan AL Pan LH Qin YC Bao LT Xie LL 《Biological trace element research》2008,125(1):59-71
Iodine-enhanced vegetable has been proven to be an effective way to reduce iodine deficiency disorders in many regions. However,
the knowledge about what mechanisms control plant uptake of iodine and where iodine is stored in plants is still very limited.
A series of controlled experiments, including solution culture, pot planting, and field experiments were carried out to investigate
the uptake mechanism of iodine in different forms. A new methodology for observing the iodine distribution within the plant
tissues, based on AgI precipitation reaction and transmission electron microscope techniques, has been developed and successfully
applied to Chinese cabbage. Results show that iodine uptake by Chinese cabbage was more effective when iodine was in the form
of IO3
− than in the form of I− if the concentration was low (<0.5 mg L−1), but the trend was opposite if iodine concentration was 0.5 mg L−1 or higher. The uptake was more sensitive to metabolism inhibitor in lower concentration of iodine, which implies that the
uptake mechanism transits from active to passive as the iodine concentration increases, especially when the iodine is in the
form of IO3
−. The inorganic iodine fertilizer provided a quicker supply for plant uptake, but the higher level of iodine was toxic to
plant growth. The organic iodine fertilizer (seaweed composite) provided a more sustainable iodine supply for plants. Most
of the iodine uptake by the cabbage is intercepted and stored in the fibrins in the root while the iodine that is transported
to the above-ground portion (shoots and leaves) is selectively stored in the chloroplasts. 相似文献
6.
Changes in the conformation of spinach thylakoid membranes were monitored in 5-doxyl stearic acid (SAL)-treated thylakoid
membranes in the presence of various anions (Cl−, Br−, I−, NO2
−, SO4
2−, PO4
3−). The presence of anions made the thylakoid membrane more fluid. The extent of change in membrane fluidity differed with
different anion and was reversible. 相似文献
7.
B. Blasco J. J. Rios R. Leyva R. Melgarejo C. Constán-Aguilar E. Sánchez-Rodríguez M. M. Rubio-Wilhelmi L. Romero J. M. Ruiz 《Plant Growth Regulation》2011,65(1):137-143
Iodine, essential to human life, is in part ingested through vegetable consumption, explaining the current application of
this element in biofortification programs. Few data are available on the effects of iodine on main plant metabolisms such
as carbon metabolism. The objective of this study was to determine the effect of the application of different doses (20, 40
and 80 μM) and forms of iodine (iodate [IO3
−] and iodide [I−]) on photosynthesis and carbohydrate metabolism in lettuce plants. None of these treatments exerted significant effects on
the synthesis pathway or on sucrose degradation. Application of 80 μM of I− reduced the photosynthesis rate, which may be associated with the reduction found in biomass and photosynthetic parameters
(stomatic conductance and transpiration). This finding confirms that the application of high doses of I− has a phytotoxic effect on plant physiology. In contrast, all IO3
− treatments increased the biomass of the plants which showed an elevated photosynthetic rate, stomatic conductance, and transpiration
(vs. controls). The differential crop behavior observed with the two forms of this trace element suggests that IO3
− should be selected for future biofortification programs. 相似文献
8.
I. E. Papadakis A. Giannakoula C. P. Antonopoulou M. Moustakas E. Avramaki I. N. Therios 《Photosynthetica》2007,45(2):208-213
Citrus volkameriana (L.) plants were grown for 43 d in nutrient solutions containing 0, 2, 14, 98, or 686 μM Mn (Mn0, Mn2, Mn14, Mn98, and Mn686, respectively). To adequately investigate the combined effects of Mn nutrition and irradiance on photosystem 2 (PS2) activity,
irradiance response curves for electron transport rate (ETR), nonphotochemical quenching (qN), photochemical quenching (qP), and real photochemical efficiency of PS2 (ΦPS2) were recorded under 10 different irradiances (66, 96, 136, 226, 336, 536, 811, 1 211, 1 911, and 3 111 μmol m−2 s−1, I66 to I3111, respectively) generated with the PAM-2000 fluorometer. Leaf chlorophyll content was significantly lower under Mn excess (Mn686) compared to Mn0; its highest values were recorded in the treatments Mn2-Mn98. However, ETR and ΦPS2 values were significantly lower under Mn0 compared to the other Mn treatments, when plants were exposed to irradiances ≥96 μmol m−2 s−1. Furthermore, Mn0 plants had significantly higher values of qN and lower values of qP at irradiances ≤226 and ≥336 μmol m−2 s−1, respectively, than those grown under Mn2-Mn686. Irrespective of Mn treatment, the values of ΦPS2 and qN decreased, while those of qP increased progressively by increasing irradiance from I136 to I3111. Finally, Mn2-Mn98 plants were less sensitive to photoinhibition of photosynthesis (≥811 μmol m−2 s−1) than the Mn686 (≥536 μmol m−2 s−1) and Mn0 (≥336 μmol m−2 s−1) ones. 相似文献
9.
J. A. Marchese R. S. Mattana L. C. Ming F. Broetto P. F. Vendramini R. M. Moraes 《Photosynthetica》2008,46(4):501-505
We evaluated the growth and development of the medicinal species Pothomorphe umbellata (L.) Miq. under different shade levels (full sun and 30, 50, and 70 % shade, marked as I100, I70, I50, and I30, respectively) and their effects on gas exchange and activities of antioxidant enzymes. Photosynthetically active radiation
varied from 1 254 μmol m−2 s−1 at I100 to 285 μmol m−2 s−1 at I30. Stomatal conductance, net photosynthetic rate, and relative chlorophyll (Chl) content were maximal in I70 plants. Plants grown under I100 produced leaves with lower Chl content and signs of chlorosis and necrosis. These symptoms indicated Chl degradation induced
by the generation of reactive oxygen species. Stress related antioxidant enzyme activities (Mn-SOD, Fe-SOD, and Cu/Zn-SOD)
were highest in I100 plants, whereas catalase activity was the lowest. Hence P. umbellata is a shade species (sciophyte), a feature that should be considered in reforestation programs or in field plantings for production
of medicinal constituents. 相似文献
10.
Both native Trametes hirsuta laccase and the same laccase modified with palmytic chains to turn it more hydrophobic were prepared and studied with cyclic
voltammetry and Raman spectroscopy. Native laccase immobilized in the monoolein cubic phase was characterized with resonance
Raman spectroscopy, which demonstrated that the structure at the “blue” copper site of the protein remained intact. The diamond-type
monoolein cubic phase prevents denaturation of enzymes on the electrode surface and provides contact of the enzyme with the
electrode either directly or through the mediation by electroactive probes. Direct electron transfer for both laccases incorporated
into a lyotropic liquid crystal was obtained under anaerobic conditions, whereas bioelectrocatalytic activity was shown only
for the native enzyme. The differences in electrochemical behavior of native and hydrophobic laccase as well as possible mechanisms
of direct and mediated electron transfers are discussed. The Michaelis constant for 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate)
diammonium salt (ABTS2−), K
Mapp, and the maximal current, I
max, for the native enzyme immobilized onto the electrode were estimated to be 0.24 mM, and 5.3 μA, respectively. The maximal
current density and the efficiency of the catalysis, I
max/K
Mapp, were found to be 73 μA cm−2 and 208.2 μA cm−2 mM−1, respectively, and indicated a high efficiency of oxygen electroreduction by the enzyme in the presence of ABTS2− in the cubic-phase environment. Rate constants were calculated to be 7.5 × 104 and 3.6 × 104 M−1 s−1 for native and hydrophobic laccase, respectively. 相似文献
11.
Aqueous iodine (I2(aq)) is a potent disinfectant that is being evaluated as a soil sanitizer for agricultural fields and a water purification treatment
for the International Space Station. Rice (Oryza sativa L.) plants were grown in solution culture containing different I compounds at approximately 0, 18, or 30 μM total I [I2(aq) + iodide (I−)] consisting of 0, 6, and 20 μM I as I2(aq), respectively. In addition, humic acid (HA) was added to half the treatments. Most I2(aq) was electrochemically reduced to the endpoint metabolite I− within 24 h with HA promoting the response. Plants receiving the highest dose of I2(aq), particularly those in treatments without HA, had the least growth and the greatest biomass I concentrations. Roots from
both I2(aq) treatments without HA were periodically sampled for bacteria. Viable and direct caints of bacterial cell density declined
with increasing I2(aq) concentrations within the first hour after treatment application. However, cell densities recovered within 96 hours and eventually
surpassed the control treatment cell density. Additionally, the resulting high viable: direct count density ratio suggests
that opportunistic species likely dominated the post I2(aq) environment. 相似文献
12.
The role of selenium in thyroid hormone metabolism and effects of selenium deficiency on thyroid hormone and iodine metabolism 总被引:1,自引:0,他引:1
John R. Arthur Fergus Nicol Geoffrey J. Beckett 《Biological trace element research》1992,34(3):321-325
Selenium deficiency impairs thyroid hormone metabolism by inhibiting the synthesis and activity of the iodothyronine deiodinases,
which convert thyroxine (T4) to the more metabolically active 3,3′–5 triiodothyronine (T3). Hepatic type I iodothyronine deiodinase, identified in partially purified cell fractions using affinity labeling with [125I]N-bromoacetyl reverse triiodothyronine, is also labeled with75Se by in vivo treatment of rats with75Se−Na2SeO3. Thus, the type I iodothyronine 5′-deiodinase is a selenoenzyme. In rats, concurrent selenium and iodine deficiency produces
greater increases in thyroid weight and plasma thyrotrophin than iodine deficiency alone. These results indicate that a concurrent
selenium deficiency could be a major determinant of the severity of iodine deficiency. 相似文献
13.
In the Xinjiang province of western China, conventional methods of iodine (I) supplementation (i.e, goiter pills and iodinated
salt) used to mitigate I deficiencies were ineffectual. However, the recent addition of KIO3 to irrigation waters has proven effective. This study was conducted to determine the effects of I form and concentration
on rice (Oryza sativa L.) growth, I partitioning within the plant, and ultimately to assist in establishing guidelines for
incorporating I into the human food chain. We compared IO3
− vs. I− in order to determine how these chemical species differ in their biological effects. Rice was grown in 48 L aerated tubs
containing nutrient solution and IO3
− or I− at 0, 1, 10, or 100 μM concentrations (approximately 0, 0.1, 1, and 10 mg kg−1 I). The IO3
− at 1 and 10 μM had no effect on biomass yields, and the 100 μM treatment had a small negative effect. The I− at 10 and 100 μM was detrimental to biomass yields. The IO3
− treatments had more I partitioning to the roots (56%) on average than did the I− treatments (36%), suggesting differences in uptake or translocation between I forms. The data support the theory that IO3
− is electrochemically or biologically reduced to I− prior to plant uptake. None of the treatments provided sufficient I in the seed to meet human dietary requirements. The I
concentration found in straw at 100 μM IO3
− was several times greater than seed, and could provide an indirect source of dietary I via livestock feeding on the straw.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
Many of the structural domains involved in Ca2+ channel (CACN) inactivation are also involved in determining their sensitivity to antagonist inhibition. We hypothesize that
differences in inactivation properties and their structural determinants may suggest candidate domains as targets for the
development of novel, selective antagonists. The characteristics of Ca2+ current (ICa) inactivation, steady-state inactivation (SSIN), and recovery from inactivation were studied in freshly dispersed smooth
muscle cells from rabbit portal vein (RPV) using whole-cell, voltage-clamp methods. The time course of inactivation could
be represented by two time constants. Increasing ICa by increasing [Ca2+]o or with more negative holding potentials decreased both time constants. With Sr2+, Ba2+, or Na+ as the charge carrier, ICa inactivation was also represented by two time constants, both of which were larger than those found with Ca2+. With Ca2+, Sr2+, or Ba2+ as the charge carrier, both time constants had minimum values near the voltage associated with maximum current. When Na+ (140 mM) was the charge carrier, voltages for Imax (−20 mV) or τmin (o mV) did not correspond. SSIN of ICa had a half-maximum voltage of −32±4 mV for Ca2+, −43 mV±5 mV for Sr2+, −41±5 mV for Ba2+, and −68±6 mV for Na+. The slope factor for SSIN per e-fold voltage change was 6.5±0.2 mV for Ca2+, 6.8±0.3 for Sr2+, and 6.6±0.2 for Ba2+, representing four equivalent charges. When Na+ or Li+ was the charge carrier, the slope factor was 13.5±0.7 mV, representing two equivalent charges. For ICa in rat left ventricular (rLV) myocytes, there was no difference in the slope factor of SSIN for Ca2+ and Na+. The rate of recovery of ICa from inactivation varied inversely with recovery voltage and was independent of the charge carrier. These results suggest
that inactivation of ICa in PV myocytes possess an intrinsic voltage dependence that is modified by Ca2+. For RPV but not rLV ICa, the charge of the permeating ion confers the voltage-dependency of SSIN. 相似文献
15.
A greenhouse pot experiment was carried out to investigate the availability of iodide and iodate to soil-grown spinach (Spinacia oleracea L.) in relation to total iodine concentration in soil solution. Four iodine concentrations (0, 0.5, 1, 2 mg kg−1) for iodide (I−) and iodate (IO3−) were used. Results showed that the biomass productions of spinach were not significantly affected by the addition of iodate and iodide to the soil, and that iodine concentrations in spinach plants on the basis of fresh weights increased with increasing addition of iodine. Iodine concentrations in tissues were much greater for plants grown with iodate than with iodide. In contrast to the iodide treatments, in iodate treatment leaves accounted for a larger fraction of the total plant iodine. The soil-to-leaf transfer factors (TFleaf) for plants grown with iodate were about tenfold higher than those grown with iodide. Iodine concentrations in soil solution increased with increasing iodine additions to the soil irrespective of iodine species. However, total iodine in soil solution was generally higher for iodate treatments than iodide both in pots with and without spinach. According to these results, iodate can be considered as potential iodine fertilizer to increase iodine content in vegetables. 相似文献
16.
Pan Yuerong 《Human Evolution》1990,5(3):239-240
The paper deals with a new form ofSinoadapis from the Lufeng hominoid Locality, assigned toSinoadapis shihuibaensis sp. nov. Holotype PA 882 A fragment of right mandible with C,−M3. Other materials. PA 903 A fragment of left maxilla with P3−M3. PA 959 Left lower tooth row with I1−P2, P4. PA 902 Right upper tooth row with C′−P3. PA 964 An isolated left I1. PA 907 An isolated right I3. PA 972 An isolated right M3. 相似文献
17.
α-Proteobacteria that can oxidize iodide (I−) to molecular iodine (I2) have only been isolated from iodide-rich natural and artificial environments, i.e., natural gas brine waters and seawaters
supplemented with iodide, respectively. To understand the growth characteristics of such iodide-oxidizing bacteria (IOB) under
iodide-rich environments, microcosms comprising natural seawater and 1 mM iodide were prepared, and the succession of microbial
communities was monitored by culture-independent techniques. PCR-denaturing gradient gel electrophoresis and 16S rRNA gene
sequence analysis showed that bacteria closely related with known IOB were predominant in the microcosms after several weeks
of incubation. Quantitative PCR analysis targeting specific 16S rRNA gene regions of IOB showed that the relative abundance
of IOB in the microcosms was 6–76% of the total bacterial population, whereas that in natural seawater was less than 1%. When
103 cells mL−1 of IOB were inoculated into natural seawater supplemented with 0.1–1 mM iodide, significant growth (cell densities, 105–106 cells mL−1) and I2 production (6–32 μM) were observed. Interestingly, similar growth stimulation occurred when 12–44 μM of I2 was added to seawater, instead of iodide. IOB were found to be more I2 tolerant than the other heterotrophic bacteria in seawater. These results suggest that I2 plays a key role in the growth stimulation of IOB in seawater. IOB could potentially attack other bacteria with I2 to occupy their ecological niche in iodide-rich environments. 相似文献
18.
The eco-physiological responses of three nitrogen-fixing cyanobacteria (N-fixing cyanobacteria), Aphanizomenon gracile, Anabaena minderi, and Ana. torques-reginae, to light were assessed under nutrient saturation. The N-fixing cyanobacteria were isolated into monocultures from a natural
bloom in a shallow colored lake and their growth irradiance parameters and pigment composition were assessed. The different
ecological traits related to light use (μmax, α, I
k) suggest that these N-fixing cyanobacteria are well adapted to low light conditions at sufficient nutrients, yet interspecific
differences were observed. Aphanizomenon gracile and Anabaena minderi had high relative growth rates at low irradiances (ca. 70% of those in high light), low half saturation constant for light-limited
growth (I
k < 9.09 μmol photon m−2 s−1) and high efficiency (α < 0.11 day−1 μmol photon−1 m2 s). Conversely, Ana. torques-reginae showed poorer light competitiveness: low relative growth rates at low irradiances (ca. 40% of those in high light), low α
(0.009 day−1 μmol photon−1 m2 s) and higher I
k (35.5 μmol photon m−2 s−1). Final densities in Aphanizomenon gracile and Anabaena minderi reached bloom densities at irradiances above 30 μmol photon m−2 s−1 with different hierarchy depending on irradiance, whereas Ana. torques-reginae never achieved bloom densities. All species had very low densities at irradiances ≤17 μmol photon m−2 s−1, thus no N-fixing blooms would be expected at these irradiances. Also, under prolonged darkness and at lowest irradiance
(0 and 3 μmol photon m−2 s−1) akinetes were degraded, suggesting that in ecosystems with permanently dark sediments, the prevalence of N-fixing cyanobacteria
should not be favored. All species displayed peaks of phycocyanin, but no phycoeritrin, probably due to the prevailing red
light in the ecosystem from which they were isolated. 相似文献
19.
Z.-P. Ye 《Photosynthetica》2007,45(4):637-640
The calculated maximum net photosynthetic rate (P
N) at saturation irradiance (I
m) of 1 314.13 μmol m−2 s−1 was 25.49 μmol(CO2) m−2 s−1, and intrinsic quantum yield at zero irradiance was 0.103. The results fitted by nonrectangular hyperbolic model, rectangular
hyperbolic method, binomial regression method, and the new model were compared. The maximum P
N values calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were higher than the measured values,
and the I
m calculated by nonrectangular hyperbolic model and rectangular hyperbolic model were less than measured values. Results fitted
by new model showed that the response curve of P
N to I was nonlinear at low I for Oryza sativa, P
N increased nonlinearly with I below saturation value. Above this value, P
N decreased nonlinearly with I. 相似文献
20.
By simultaneously analyzing the chlorophyll a fluorescence transient and light absorbance at 820 nm as well as chlorophyll fluorescence quenching, we investigated the
effects of different photon flux densities (0, 15, 200 μmol m−2 s−1) with or without 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on the repair process of cucumber (Cucumis sativus L.) leaves after treatment with low temperature (6°C) combined with moderate photon flux density (200 μmol m−2 s−1) for 6 h. Both the maximal photochemical efficiency of Photosystem II (PSII) (F
v/F
m) and the content of active P700 (ΔI/I
o) significantly decreased after chilling treatment under 200 μmol m−2 s−1 light. After the leaves were transferred to 25°C, F
v/F
m recovered quickly under both 200 and 15 μmol m−2 s−1 light. ΔI/I
o recovered quickly under 15 μmol m−2 s−1 light, but the recovery rate of ΔI/I
o was slower than that of F
v/F
m. The cyclic electron transport was inhibited by chilling-light treatment obviously. The recovery of ΔI/I
o was severely suppressed by 200 μmol m−2 s−1 light, whereas a pretreatment with DCMU effectively relieved this suppression. The cyclic electron transport around PSI recovered
in a similar way as the active P700 content did, and the recovery of them was both accelerated by pretreatment with DCMU.
The results indicate that limiting electron transport from PSII to PSI protected PSI from further photoinhibition, accelerating
the recovery of PSI. Under a given photon flux density, faster recovery of PSII compared to PSI was detrimental to the recovery
of PSI or even to the whole photosystem. 相似文献