a1_The halophytic C4 grass, Aeluropus littoralis, was cultivated under low (50 mM) and high (200 mM) NaCl salinity and inoculated with the arbuscular mycorrhizal fungi (AMF) Claroideoglomus etunicatum in a sand culture medium for 20 weeks. Shoot and root dry mass increased under salinity conditions up to 24 and 86%, respectively. Although the root colonization rate significantly decreased in the presence of salt, AMF-colonized (+AMF) plants had higher biomass compared with plants without AMF colonization (-AMF) only under saline conditions. Net CO2 assimilation rate increased significantly by both salinity levels despite stable stomatal opening. In contrast, AMF-mediated elevation of the net CO2 assimilation rate was associated with a higher stomatal conductance. Unexpectedly, leaf activity of phosphoenolpyruvate carboxylase decreased by salinity and AMF colonization. Transpiration rate was not affected by treatments resulting in higher water-use efficiency under salinity and AMF conditions. Concentrations of soluble sugars and free α-amino acids increased by both salinity and AMF treatments in the shoot but not in the roots. Proline concentration in the leaves was higher in the salt-treated plants, but AMF colonization did not affect it significantly. Leaf activity of nitrate reductase increased by both salinity and AMF treatments. Mycorrhizal plants had significantly higher Na+ and K+ uptake, while Ca2+ uptake was not affected by salt or AMF colonization. The ratio of K+/Na+ increased by AMF in the shoot while it decreased in the roots. Leaf osmotic potential was lowered under salinity in both +AMF and -AMF plants. Our results indicated that higher dry matter production in the presence of salt and AMF could be attributed to higher CO2 and nitrate assimilation rates in the leaves., a2_Higher leaf accumulation of soluble sugars and α-amino acids but not proline and elevated water-use efficiency were associated with the improved growth of A. littoralis inoculated with AMF., R. Hajiboland, F. Dashtebani, N. Aliasgharzad., and Obsahuje seznam literatury
The review is done to summarise the history of the discoveries of the many anatomical, agronomical, and physiological aspects of C4 photosynthesis (where the first chemical products of CO2 fixation in illuminated leaves are four-carbon dicarboxylic acids) and to document correctly the scientists at the University of Arizona and the University of California, Davis, who made these early discoveries. The findings were milestones in plant science that occurred shortly after the biochemical pathway of C3 photosynthesis in green algae (where the first chemical product is a three-carbon compound) was elucidated at the University of California, Berkeley, and earned a Nobel Prize in chemistry. These remarkable achievements were the result of ground-breaking pioneering research efforts carried out by many agronomists, plant physiologists and biochemists in several laboratories, particularly in the USA. Numerous reviews and books written in the past four decades on the history of C4 photosynthesis have focused on the biochemical aspects and give an unbalanced history of the multidisciplinary/multinstitutional nature of the achievements made by agronomists, who published much of their work in Crop Science. Most notable among the characteristics of the C4 species that differentiated them from the C3 ones are: (I) high optimum temperature and high irradiance saturation for maximum leaf photosynthetic rates; (II) apparent lack of CO2 release in a rapid stream of CO2-free air in illuminated leaves in varying temperatures and high irradiances; (III) a very low CO2 compensation point; (IV) lower mesophyll resistances to CO2 diffusion coupled with higher stomatal resistances, and, hence, higher instantaneous leaf water use efficiency; (V) the existence of the so-called "Kranz leaf anatomy" and the higher internal exposed mesophyll surface area per cell volume; and (VI) the ability to recycle respiratory CO2 by illuminated leaves.
In individual leaves, the photon-saturated photosynthetic activity (Psat, expressed on a dry mass basis) was closely related to the nitrogen content (Nc) as follows: Psat = Cf Nc + Psat0, where Cf and Psat0 are constants. On a whole plant basis, the relative growth rate (RGR) was closely related to Nc in canopy leaf as follows: RGR = DMf Nc + RGR0, where DMf and RGR0 are constants. However, the coefficients Cf and DMf were markedly different among plant species. To explain these differences, it is suggested that carbon assimilation (or dry matter production) is controlled by both the Nc in a leaf (or leaves) and by the net N translocation from leaves. This is supported by the finding that Psat is related to the rate of 35S-methionine translocation from leaves. We propose another estimation method for the net N translocation rate (NFR) from leaves: Nc, after full leafing, is expressed as a function of time: Nc = (Nc0 - Ncd) exp(-Nft) + Ncd, where Nf is a coefficient, t is the number of days after leaf emergence, Nc0 is the initial value of Nc, and Ncd is the Nc of the dead leaf. The NFR is then calculated as NFR = ΔNc/Δt = -Nf (Nc - Ncd). Thus Nf is the coefficient for the NFR per unit Nc. NFR is a good indicator of net N translocation from leaves because NFR is closely related to the rate of 35S-methionine translocation from leaves. Since Psat is related to the 14C-photosynthate translocation rate, Cf (or DMf) corresponds to the coefficient of saccharide translocation rate per unit amount of Nc. Cf (or DMf) is closely related to the Nf of individual leaves (or the Nf of canopy leaf). This indicates that C assimilation and C translocation from leaves are related to Nc and N translocation from leaves (net translocation of N). Cf and Nf are negatively correlated with leaf longevity, which is important because a high or low CO2 assimilation rate in leaves is accompanied by a correspondingly high or low N translocation in leaf, and the degree of N translocation in leaves decreases or increases leaf longevity. Thus, since a relatively high Psat (or RGR) is accompanied by a rapid Nc decrease in leaves, it is difficult to maintain a high Psat (or RGR) for a sustained time period. and M. Osaki, T. Shinano.
Permanent plastid-nuclear complexes (PNCs) exist in tobacco cells from their mitosis up to programmed cell death (PCD). PNCs in senescing cells of tobacco leaves were typical by enclosure of peroxisomes and mitochondria among chloroplasts which were in contact with nucleus. Such a complex position provides simultaneous interaction of these organelles and direct regulation of metabolism and PCD avoiding the cytosol. and T. Selga, M. Selga, A. Ozoliņa.
The aim of our study was to answer whether any positive correlation exists between K+ uptake and salt tolerance in wheat. We carried out a sand-culture experiment with salt-tolerant, DK961 (ST), and salt-sensitive, JN17 (SS), wheat cultivars, where photosynthesis, the K+/Na+ ratio, growth, and the biomass yield were examined. The seeds were exposed for four weeks to six NaCl concentrations (50, 100, 150, 200, 250, and 300 mM), which were embodied in the Hoagland solution. Salinity-induced decrease of K+ or increase in the Na+ content was much smaller in ST than that in SS. The reductions in the light-saturated photosynthetic rate (P Nmax) and chlorophyll content caused by salinity were smaller in the ST compared to SS. Stomatal conductance decreased in both cultivars under saline conditions; nevertheless, it was lower in SS than in ST. The antioxidative capacity was higher in ST than that in SS under saline conditions. Significant positive correlations were observed in both cultivars between K+ contents and P Nmax/biomass yields. We suggest that higher-affinity K+ uptake might play a key role in higher salt tolerance and it might be a reliable indicator for breeding new species of salt-tolerant wheat., D. Cheng, G. Wu, Y. Zheng., and Obsahuje seznam literatury
Watermelon [Citrullus lanatus (Thunb.) Mansfeld] is a photophilic plant, whose net photosynthetic rate was significantly decreased when seedlings were grown under low light condition. However, treatment with 100 mg kg-1 5-aminolevulinic acid (ALA) could significantly restore the photosynthetic ability under the environmental stress. The parameters of leaf gas exchange, chlorophyll modulated fluorescence and fast induction fluorescence of the ALA-treated plants were higher than that of the control. Additionally, ALA treatment increased the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX). Nevertheless, the treatment of diethyldithiocarbamate (DDC), an inhibitor of SOD activity, dramatically depressed photosynthesis of watermelon leaves, while ALA could reverse the inhibition of DDC. Therefore, it can be deduced that ALA promotion on photosynthesis of watermelon leaves under low light stress is attributed to its promotion on antioxidant enzyme activities, and the increased activities of the enzymes, which are mainly located near the reaction centers of PSI, can scavenge superoxide anions, leading to an increase of apparent electron transport rate and an alleviation of photosynthetic photoinhibition under the stressed environment. and Y.-P. Sun, Z.-P. Zhang, L.-J. Wang.
Productivity of most improved major food crops showed stagnation in the past decades. As human population is projected to reach 9-10 billion by the end of the 21st century, agricultural productivity must be increased to ensure their demands. Photosynthetic capacity is the basic process underlying primary biological productivity in green plants and enhancing it might lead to increasing potential of the crop yields. Several approaches may improve the photosynthetic capacity, including integrated systems management, in order to close wide gaps between actual farmer’s and the optimum obtainable yield. Conventional and molecular genetic improvement to increase leaf net photosynthesis (P N) are viable approaches, which have been recently shown in few crops. Bioengineering the more efficient CC4 into C3 system is another ambitious approach that is currently being applied to the C3 rice crop. Two under-researched, yet old important crops native to the tropic Americas (i.e., the CC4 amaranths and the C3-CC4 intermediate cassava), have shown high potential P N, high productivity, high water use efficiency, and tolerance to heat and drought stresses. These physiological traits make them suitable for future agricultural systems, particularly in a globally warming climate. Work on crop canopy photosynthesis included that on flowering genes, which control formation and decline of the canopy photosynthetic activity, have contributed to the climate change research effort. The plant breeders need to select for higher P N to enhance the yield and crop tolerance to environmental stresses. The plant science instructors, and researchers, for various reasons, need to focus more on tropical species and to use the research, highlighted here, as an example of how to increase their yields., M. A. El-Sharkawy., and Obsahuje seznam literatury
Seedlings of winter rape were cultured in vitro on media containing 24-epibrassinolide, EBR (100 nM) and cadmium (300 µM). After 14 d of growth, fast fluorescence kinetics of chlorophyll (Chl) a and contents of photosynthetic pigments and Cd in cotyledons were measured. Cd was strongly accumulated but its content in cotyledons was 14.7 % smaller in the presence of EBR. Neither Cd nor EBR influenced the contents of Chl a and b and carotenoids. Cd lowered the specific energy fluxes per excited cross section (CS) of cotyledon. The number of active reaction centres (RC) of photosystem 2 (RC/CS) decreased by about 21.0 % and the transport of photosynthetic electrons (ET0/CS) by about 17.1 %. Simultaneously, under the influence of Cd, the activity of O2 evolving centres (OEC) diminished by about 19.5 % and energy dissipation (DI0/CS) increased by about 14.6 %. In the cotyledons of seedlings grown on media without Cd, EBR induced only a small increase in the activity of most photochemical reactions per CS. However, EBR strongly affected seedlings cultured with cadmium. Specific energy fluxes TR0/CS and ET0/CS of the cotyledons of plants Cd+EBR media were about 10.9 and 20.9 % higher, respectively, than values obtained for plants grown with Cd only. EBR also limited the increase of DI0/CS induced by Cd and simultaneously protected the complex of OEC against a decrease of activity. Hence EBR reduces the toxic effect of Cd on photochemical processes by diminishing the damage of photochemical RCs and OECs as well as maintaining efficient photosynthetic electron transport. and A. Janeczko ... [et al.].