The model couples stomatal conductance (gs) and net photosynthetic rate (PN) describing not only part of the curve up to and including saturation irradiance (Imax), but also the range above the saturation irradiance. Maximum stomatal conductance (gsmax) and Imax can be calculated by the coupled model. For winter wheat (Triticum aestivum) the fitted results showed that maximum PN
(Pmax) at 600 µmol mol-1 was more than at 350 µmol mol-1 under the same leaf temperature, which can not be explained by the stomatal closure at high CO2 concentration because gsmax at 600 µmol mol-1 was less than at 350 µmol mol-1. The irradiance-response curves for winter wheat had similar tendency, e.g. at 25 °C and 350 µmol mol-1 both PN and gs almost synchronously reached the maximum values at about 1 600 µmol m-2 s-1. At 25 °C and 600 µmol mol-1 the Imax corresponding to Pmax and
gsmax was 2 080 and 1 575 µmol m-2 s-1, respectively. and Z.-P. Ye, Q. Yu.
In CO2-free air, the CO2 postirradiation burst (PIB) in wheat leaves was measured with an IRGA in an open gas exchange system to ascertain its potential role in alleviating photoinhibition of photorespiratory carbon oxidation (PCO) under a CO2 deficiency. A pre-photosynthesized leaf having been transferred into CO2-free air exhibited a typical CO2 PIB following darkening which could last, with a rate substantially higher than that of dark respiration, over a long time period (at least more than 2 h) of continuously alternate irradiation (2 min)-dark (2 min)-light transitions. The rate and the time of PIB maintenance, although unaffected by the exogenous dark respiration inhibitor iodoacetic acid, were stimulated largely by increasing irradiance and O2 level, and suppressed by DCMU and N-ethyl-maleimide (NEM). They also showed a large photosynthates-loading dependence. In a darkened leaf, the irradiation-induced PIB in the CO2-free air was clearly revealed and it was characterized by an initial net uptake of respiratory CO2. The light-induced PIB was accelerated by increasing irradiance, and delayed by prolonging the period of darkening the leaves. Hence, the origin of carbon needed for a long-term CO2 evolution in the CO2-free air might not only be derived directly from the pool of intermediates in the Calvin cycle, but it might also arise indirectly from a remotely fixed reserve of photosynthates in the leaf via a PCO-mediated, yet to be further clarified, mobilization process. Such mobilization of photosynthates probably exerted an important role in coordination of photochemical reactions and carbon assimilation during photosynthesis in C3 plants under the photoinhibitory conditions. and Fusheng Xiong, Yuzhu Gao, Ping Song.
The effects of NaCl treatment on the photosynthetic machinery in wheat (Triticum aestivum L.) cultivars differing in salt tolerance were investigated by comparison with iso-osmotic PEG treatment. Both cultivars similarly reduced the photosystem 2 (PS2) energy conversion efficiency (ΦPS2) rapidly when plants were exposed to a 100 mM NaCl solution, though no decline was detected under the iso-osmotic PEG treatment. There was no correlation between the reduction of the leaf relative water content (RWC) and the ΦPS2 in the two iso-osmotic stress treatments. In contrast, a decline of ΦPS2 along with the increase of the leaf sodium content above 4 % dry matter was detected under the NaCl treatment, while no such correlation was detected with other cations. The recovery of ΦPS2 after photoinhibitory irradiation was repressed by the NaCl treatment as the increase of the duration of the treatment. Norin 61 subjected to the 100 mM NaCl treatment for 10 d showed a decline of the ΦPS2 after 1 h moderate irradiation of 400 μmol m-2 s-1 PPFD. Thus the concentrated Na+ within a leaf under salinity treatments may decrease the stability of PS2 functions and lead to photochemical inactivation. and S. Muranaka, K. Shimizu, M. Kato.
Twenty-five genotypes of early CIMMYT hexaploid wheat were screened for salt tolerance in a glasshouse experiment using photosynthetic capacity and water relation parameters as selection criteria. Under salt stress (150 mM NaCl) the genotypes Frontana, Norin-10, Mayo-54, Noreste-66, and Yaktana-54 excelled all other lines in shoot dry mass, and Na(20)TPP, Penjamo-62, Inia-66, Frontana, Siete Cerros, and Jaral-66 in grain yield per plant in both absolute and relative (percent of control) terms. Although net photosynthetic rate (PN) declined in all genotypes due to salt stress, it was not helpful in discriminating among genotypes according to salt tolerance. Similarly, no positive relationships of salt tolerance of the genotypes with stomatal conductance, leaf water potential, or turgor pressure were found. Every genotype used its own specific mechanism to tolerate salt stress. However, a large amount of variation in salt tolerance observed in 25 early CIMMYT wheat genotypes can be of considerable practical value for improving salt tolerance in the existing commercial hexaploid wheats. and M. Ashraf, M. Shahbaz.
Celiakie je časté celoživotní autoimunitní onemocnění spuštěné konzumací lepku u geneticky predisponovaných jedinců. Chronické zánětlivé změny vedou k poškození sliznice tenkého střeva s následnou vilózní atrofií provázenou chronickou maldigescí a malabsorpcí. Neléčená celiakie je spojena s širokým spektrem střevních a mimostřevních obtíží a komplikací, z nichž nejzávažnější je lymfom tenkého střeva. Zlatým standardem diagnostiky je stanovení specifických autoprotilátek a průkaz vilózní atrofie v biopsii z duodenální sliznice. Kauzální a ve většině případů efektivní léčbou je celoživotní striktní bezlepková dieta, která vede k restituci sliznice tenkého střeva a snížení rizika závažných komplikací., Coeliac disease is a common lifelong autoimmune disorder triggered by gluten consumption in genetically predisposed patients. Chronic inflammatory response damages the mucosa of the small intestine resulting in villous atrophy with chronic maldigestion and malabsorption. Untreated coeliac disease may present with a variety of intestinal and extraintestinal symptoms and complications, the most serious of which is a small intestine lymphoma. The diagnosis is usually established by specific serology markers and villous atrophy in duodenal biopsy. The causal and, in most cases, effective treatment modality is a strict and life‑long gluten‑free diet that leads to regeneration of the intestinal mucosa and reduces the risk of serious complications., and Falt P., Fojtík P., Šmajstrla V.
The seedlings of wheat were treated by salt-stress (SS, molar ratio of NaCl: Na2SO4 = 1:1) and alkali-stress (AS, molar ratio of NaHCO3: Na2CO3 = 1:1). Relative growth rate (RGR), leaf area, and water content decreased with increasing salinity, and the extents of the reduction under AS were greater than those under SS. The contents of photosynthetic pigments did not decrease under SS, but increased at low salinity. On the contrary, the contents of photosynthetic pigments decreased sharply under AS with increasing salinity. Under SS, the changes of net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) were similar and all varied in a single-peak curve with increasing salinity, and they were lower than those of control only at salinity over 150 mM. Under AS, PN, gs, and E decreased sharply with rising salinity. The decrease of gs might cause the obvious decreases of E and intercellular CO2 concentration, and the increase of water use efficiency under both stresses. The Na+ content and Na+/K+ ratio in shoot increased and the K+ content in shoot decreased under both stresses, and the changing extents under AS were greater than those under SS. Thus SS and AS are two distinctive stresses with different characters; the destructive effects of AS on the growth and photosynthesis of wheat are more severe than those under SS. High pH is the key feature of the AS that is different from SS. The buffer capacity is essentially the measure of high pH action on plant. The deposition of mineral elements and the intracellular unbalance of Na+ and K+ caused by the high pH at AS might be the reason of the decrease of PN and gs and of the destruction of photosynthetic pigments. and C. W. Yang ... [et al.].
Activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) is an important parameter determining the rate of net photosynthesis (PN) in situ for which no information is available with reference to altitude. We analyzed activation state along with PN in three plant species and their cultivars grown at low (LA, 1 300 m) and high (HA, 4 200 m) altitudes. No significant change in PN and the initial activity of RuBPCO was obtained with reference to altitude. However, activation state of RuBPCO was reduced significantly in the HA plants as compared to the LA ones. Hence low partial pressure of CO2 prevailing at HA might be responsible for the lower activation state of RuBPCO. and Narinder Kumar, Sanjay Kumar, Paramvir Singh Ahuja.
The cadmium treatment of dark-grown leaves and isolated etioplast inner membranes of wheat resulted in a decrease of the amount of the 657 nm emitting (77 K fluorescence) protochlorophyllide (PChlide) form, a simultaneous increase of the 633 nm form and the appearance of a 641.5 nm emitting form. This effect did not occur if excess NADPH was added to the isolated membranes: these samples showed spectral properties identical to those of non-treated (control) samples. Inhibition of the PChlide phototransformation was observed in the cadmium-treated leaves and membranes, the irradiation resulted in the appearance of a smáli amount of chlorophyllide (Chlide) with characteristic emission band at 678 nm. If excess NADPH was added, the inhibition did not occur and flash irradiation resulted in formation of the 694 nm Chlide form similarly as in control plants.
Wheat (Triticum aestivum L.) genotypes K-65 (salt tolerant) and HD 2329 (salt sensitive) were grown in pots under natural conditions and irrigated with NaCl solutions of electrical conductivity (ECe) 4.0, 6.0, and 8.0 dS m-1. Control plants were irrigated without saline water. Observations were made on the top most fully expanded leaf at tillering, anthesis, and grain filling stages. The net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) were reduced with the addition of NaCl. The reduction was higher in HD 2329 than in K-65. Salinity enhanced leaf to air temperature gradient (ΔT) in both the genotypes. NaCl increased the activities of superoxide dismutase (SOD) and peroxidase (POX); the percent increment was higher in K-65. The sodium and potassium contents were higher in the roots and leaves of K-65 over HD 2329. Thus at cellular level K-65 has imparted salt tolerance by manipulating PN, E, gs, and K accumulation in leaves along with overproduction of antioxidative enzyme activities (SOD and POX). and N. Sharma ... [et al.].
With the increase in concentration of applied salicylic acid (SA), chlorophyll (Chl) content decreased significantly in both wheat and moong seedlings. Chl a/b ratio decreased significantly only in wheat and remained constant in moong. On the other hand, total carotenoid (Car) content, size of xanthophyll pool, and de-epoxidation rate increased significantly with an increase in SA concentration in both plant species. Hence SA treatment may induce Car biosynthesis in these plant species, but the increase in the xanthophyll pool and de-epoxidation rate indicates that SA may create oxidative stress the degree of which is different in various plants. and S. T. Moharekar ... [et al.].