Changes in chloroplastidic pigments, gas exchange and carbohydrate concentrations were assessed during the rapid initial expansion of C. guianensis leaflet. Leaves at metaphyll stage were tagged and assessments were carried out 14, 17, 20, 23, 27, and 31 days later. Pigments synthesis, distribution and accumulation were uniform among leaflet sections (basal, median and apical). Chlorophyll (Chl) a, Chl b, Chl (a+b), and total carotenoids (Car) concentrations were significantly increased after 27 days from metaphyll, and the most expressive increases were parallel to lower specific leaflet area. Chl a/b was lower on day 14 and it was increased on subsequent days. Negative net photosynthesis rate (PN), and the lowest stomatal conductance (gs) and transpiration (E) were registered on day 14, following significant increases on subsequent days. The Chl (a+b) and Chl a effects on PN were more expressive until day 20. Intercellular to ambient CO2 concentration ratio (Ci/Ca) was higher on day 14 and lower on subsequent days, and no stomatal limitation to CO2 influx inside leaflets was observed. Leaflet temperature was almost constant (ca. 35°C) during leaflet development. Sucrose and starch concentrations were increased in parallel to increases in PN. Altogether, these results highlight the main physiological changes during C. guianensis leaflet expansion and they should be considered in future experiments focusing on factors affecting PN in this species. and F. K. C. Moraes ... [et al.].
Článek přestavuje taxonomicky problematický rod chrpa z čeledi Asteraceae. Jsou diskutovány současné pohledy na vymezení a vnitřní členění rodu založené na molekulárních znacích. Dále je popsána problematika hybridizace, která je v rodu velmi častá, a její souvislost s polyploidií (druhy stejné ploidie se často kříží za vzniku rozsáhlých a variabilních hybridních rojů, zatímco mezi ploidiemi je silná reprodukční bariéra)., Centaurea is a taxonomically critical genus from the Asteraceae family. Current delimitation of the genus and its internal classification based on molecular data are discussed. Hybridization and polyploidy are common in Centaurea. The frequency of hybridization depends on ploidy levels of the taxa (homoploid taxa usually hybridize easily and form extensive and variable hybrid swarms, while heteroploid taxa are reproductively strongly isolated)., and Petr Koutecký.
Most organisms inhabiting earth feed directly or indirectly on the products synthesized by the reaction of photosynthesis, which at the current atmospheric CO2 levels operates only at two thirds of its peak efficiency. Restricting the photorespiratory loss of carbon and thereby improving the efficiency of photosynthesis is seen by many as a good option to enhance productivity of food crops. Research during last half a century has shown that several plant species developed CO2-concentrating mechanism (CCM) to restrict photorespiration under lower concentration of available CO2. CCMs are now known to be operative in several terrestrial and aquatic plants, ranging from most advanced higher plants to algae, cyanobacteria and diatoms. Plants with C4 pathway of photosynthesis (where four-carbon compound is the first product of photosynthesis) or crassulacean acid metabolism (CAM) may consistently operate CCM. Some plants however can undergo a shift in photosynthetic metabolism only with change in environmental variables. More recently, a shift in plant photosynthetic metabolism is reported at high altitude where improved efficiency of CO2 uptake is related to the recapture of photorespiratory loss of carbon. Of the divergent CO2 assimilation strategies operative in different oraganisms, the capacity to recapture photorespiratory CO2 could be an important approach to develop plants with efficient photosynthetic capacity. and S. K. Vats, S. Kumar, P. S. Ahuja
Geitlerinema amphibium (BA-13), mat-forming cyanobacterium from the southern Baltic Sea, was grown at three irradiances [5, 65, and 125 μmol(photon) m-2 s-1] and three temperatures (15, 22.5, and 30°C). To determine the effect of the investigated factors and their interaction on culture concentration, pigment content, and photosynthetic parameters of cyanobacterium, factorial experiments and two-way analysis of variance (ANOVA) were carried out. Both chlorophyll (Chl) a and phycobilins (PB) were influenced by the irradiance and temperature, but stronger effect was noted in the case of the former one. Chl a and PB concentration per 100 μm of filament dropped above 4-fold with the increasing irradiance. The ratios between individual carotenoids [β-carotene, zeaxanthin, and myxoxanthophyll (Myx)] and Chl a increased significantly with an increase in the irradiance. The greatest fluctuations were observed in the ratio of Myx to Chl a (above 10-fold). Thus, Myx was suggested as the main photoprotective carotenoid in G. amphibium. Based on photosynthetic light response (PI) curves, two mechanisms of photoacclimation in G. amphibium were recognized: a change of photosynthetic units (PSU) number and a change of PSU size. These two mechanisms constituted the base of significant changes in photosynthetic rate and its parameters, such as the compensation point (PC), the initial slope of photosynthetic curve (α), saturation irradiance (EK), maximal photosynthetic rate (Pmax), and dark respiration rate (RD). The greatest changes were observed in PC values (about 15-fold within the range of the factors tested). Studied parameters showed a wide range of changes, which might indicate G. amphibium ability to acclimatize well to irradiance and temperature, and indirectly might explain the successful growth of cyanobacterium in dynamically changing environmental conditions., S. Jodłowska, A. Latała., and Obsahuje bibliografii
The present piece of work highlights the comparative effects of two active forms of brassinosteroids (BRs), 28-homobrassinolide (HBL) and 24-epibrassinolide (EBL), on growth parameters, carbonic anhydrase activity and photosynthetic parameters in Lycopersicon esculentum (cv. K-21) sampled at 45 (24 h after spray) and 60 days after sowing, under natural conditions. Out of the two active forms of BR, EBL proved better than HBL in improving the above parameters, when applied as foliar spray. Of the three concentrations (10-6 M, 10-8 M or 10-10 M) of HBL and EBL, 10-8M proved best in both cases. and S. Hayat ... [et al.].
In this study, cotton seedlings were subjected to osmotic-, salt- and alkali stresses. The growth, photosynthesis, inorganic ions, and organic acids in the stressed seedlings were measured, to compare the mechanisms by which plants adapt to these stresses and attempt to probe the mechanisms by which plants adapt to high pH stress. Our results indicated that, at high stress intensity, both osmotic and alkali stresses showed a stronger injurious effect on growth and photosynthesis than salt stress. Cotton accumulated large amount of Na+ under salt and alkali stresses, but not under osmotic stress. In addition, the reductions of K+, NO3 -, and H2PO4 - under osmotic stress were much greater than those under salt stress with increasing stress intensity. The lack of inorganic ions limited water uptake and was the main reason for the higher injury from osmotic-compared to salt stress on cotton. Compared with salt- and alkali stresses, the most dramatic response to osmotic stress was the accumulation of soluble sugars as the main organic osmolytes. In addition, we found that organic acid metabolism adjustment may play different roles under different types of stress. Under alkali stress, organic acids might play an important role in maintaining ion balance of cotton; however, under osmotic stress, malate might play an important osmotic role. and W. Chen ... [et al.].
Field trials under rain-fed conditions at the International Center for Tropical Agriculture (CIAT) in Colombia were conducted to study the comparative leaf photosynthesis, growth, yield, and nutrient use efficiency in two groups of cassava cultivars representing tall (large leaf canopy and shoot biomass) and short (small leaf canopy and shoot biomass) plant types. Using the standard plant density (10,000 plants ha-1), tall cultivars produced higher shoot biomass, larger seasonal leaf area indices (LAIs) and greater final storage root yields than the short cultivars. At six months after planting, yields were similar in both plant types with the short ones tending to form and fill storage roots at a much earlier time in their growth stage. Root yield, shoot and total biomass in all cultivars were significantly correlated with seasonal average LAI. Short cultivars maintained lower than optimal LAI for yield. Seasonal PN, across cultivars, was 12% greater in short types, with maximum values obtained in Brazilian genotypes. This difference in PN was attributed to nonstomatal factors (i.e., anatomical/biochemical mesophyll characteristics). Compared with tall cultivars, short ones had 14 to 24 % greater nutrient use efficiency (NUE) in terms of storage root production. The lesser NUE in tall plants was attributed mainly to more total nutrient uptake than in short cultivars. It was concluded that short-stemmed cultivars are superior in producing dry matter in their storage roots per unit nutrient absorbed, making them advantageous for soil fertility conservation while their yields approach those in tall types. It was recommended that breeding programs should focus on selection for more efficient short- to medium-stemmed genotypes since resource-limited cassava farmers rarely apply agrochemicals nor recycle residual parts of the crop back to the soil. Such improved short types were expected to surpass tall types in yields when grown at higher than standard plant population densities (>10,000 plants ha-1) in order to maximize irradiance interception. Below a certain population density (<10,000 plants ha-1), tall cultivars should be planted. Findings were discussed in relation to cultivation and cropping systems strategies for water and nutrient conservation and use efficiencies under stressful environments as well as under predicted water deficits in the tropics caused by trends in global climate change. Cassava is expected to play a major role in food and biofuel production due to its high photosynthetic capacity and its ability to conserve water as compared to major cereal grain crops. The interdisciplinary/interinstitutions research reported here, including, an associated release of a drought-tolerant, short-stem cultivar that was eagerly accepted by cassava farmers, reflects well on the productivity of the CIAT international research in Cali, Colombia., and M. A. El-Sharkawy, S. M. de Tafur
The effects of potassium (K) deficiency on chlorophyll (Chl) content, photosynthetic gas exchange, and photosystem II (PSII) photochemistry during the seedling stage were investigated in two soybean [Glycine max (L.) Merr.] cultivars, low-K sensitive Tiefeng31 and low-K tolerant Shennong6. The cultivars were grown hydroponically in K-sufficient (KS) and K-deficient (KD) solutions. Photosynthetic gas exchange and Chl content in Tiefeng31 were severely affected by the low K condition, but were almost unaffected in Shennong6. This difference is in accordance with the PSII photochemistry in the plants, indicating that the photosynthetic apparatus of Shennong6 is more tolerant to low-K stress than that of Tiefeng31. and X.-T. Li ... [et al.].
The parameters estimated from traditional A/Ci curve analysis are dependent upon some underlying assumptions that substomatal CO2 concentration (Ci) equals the chloroplast CO2 concentration (Cc) and the Ci value at which the A/Ci curve switches between Rubisco- and electron transport-limited portions of the curve (Ci-t) is set to a constant. However, the assumptions reduced the accuracy of parameter estimation significantly without taking the influence of Ci-t value and mesophyll conductance (gm) on parameters into account. Based on the analysis of Larix gmelinii's A/Ci curves, it showed the Ci-t value varied significantly, ranging from 24 Pa to 72 Pa and averaging 38 Pa. t-test demonstrated there were significant differences in parameters respectively estimated from A/Ci and A/Cc curve analysis (p<0.01). Compared with the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), the maximum electron transport rate (Jmax) and Jmax/Vcmax estimated from A/Cc curve analysis which considers the effects of gm limit and simultaneously fits parameters with the whole A/Cc curve, mean Vcmax estimated from A/Ci curve analysis (Vcmax-Ci) was underestimated by 37.49%; mean Jmax estimated from A/Ci curve analysis (Jmax-Ci) was overestimated by 17.8% and (Jmax-Ci)/(Vcmax-Ci) was overestimated by 24.2%. However, there was a significant linear relationship between Vcmax estimated from A/Ci curve analysis and Vcmax estimated from A/Cc curve analysis, so was it Jmax (p<0.05). and W. Zeng ... [et al.].
a1_Photosynthetic gas exchange, dry mass production, water relations and inducibility of crassulacean acid metabolism (CAM) pathway as well as antioxidative protection during the C3-CAM shift were investigated in Sedum album and Sedum stoloniferum from Crassulaceae under water stress for 20 days. Leaf relative water content (RWC), leaf osmotic and water potential decreased with increasing water stress in both studied species. Significant reduction in dry matter production and leaf thickness was detected only in S. stoloniferum after 20-d water stress. Δtitratable acidity and phosphoenolpyruvate carboxylase (PEPC) activity in S. album responded to drought at early stages of stress treatment, continued to increase throughout the entire stress period and reached levels 15 times higher than those in well-watered plants. In S. stoloniferum, however, both parameters responded later and after a transient increase declined again. In S. stoloniferum, in spite of increase by drought stress, net night-time CO2 assimilation was negative resembling a C3-like pattern of gas exchange. Catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) activities increased in plants subjected to mild water stress while declined as the stress became severe. Although malondialdehyde (MDA) content was higher in drought-stressed S. stoloniferum, the increase in the concentration of hydrogen peroxide (H2O2) that may act as a signal for C3-CAM transition was higher in S. album compared with S. stoloniferum. In drought-stressed plants, SOD activity showed a clear diurnal fluctuation that was more steadily expressed in S. album. In addition, such pattern was observed for CAT only in S. album. We concluded that temporal and diurnal fluctuation patterns in the activity of antioxidant enzymes depended on duration of drought stress and was related to the mode of photosynthesis and degree of CAM induction., a2_According to our results, S. stoloniferum developed a low degree of CAM activity, e.g. CAM-cycling metabolism, under drought conditions., G. Habibi, R. Hajiboland., and Obsahuje bibliografii