V. Hejnák

The effect of abscisic acid on rate of photosynthesis and transpiration in six barley genotypes under water stress

For six barley genotypes evaluated from various climatic areas mild water stress resulted in reduced gas exchange parameters (P N a E). For all (except the Mexican Namoi) there was a fall in the water use efficiency (WUE). The largest fall was recorded for the French genotype Adagio. Treating the plants with abscisic acid under a mild water stress resulted in all genotypes showing further, statistically significant reductions in P N (except for the wild W 154) and E in comparison with untreated plants. ABA under mild water stress supported the plant’s water conservation and in a number of cases also improved the WUE (for the Czech genotype Maridol, the English Braemar, the French Adagio, the Israeli wild W 154 and partially in the Yugoslavian Novosadski).

Growth and photosynthesis of Upland and Pima cotton: response to drought and heat stress

The effects of drought and heat stress on physiology of two common cotton species, Gossypium hirsutum L. (Upland) and G. barbadense L. (Pima) were investigated in this study. Four consecutive 28-day pot experiments were carried out in a fully controlled growth chamber under four temperatures (25, 30, 35 and 40°C), while two water treatments (well-watered and drought) were imposed for 10 days to both cotton species. Growth according to dry matter accumulation of G. barbadense was more limited by sole drought conditions (50%), whereas heat stress was more remarkable on growth of G. hirsutum (64%). Chlorophyll (Chl) a and b content were more temperature-sensitive in G. hirsutum than G. barbadense under well-watered conditions. The most noticeable decrease in droughtinduced rates of photosynthesis rate (P n ), transpiration rate (E) and stomatal conductance (g s ) were recorded under 35°C, although genotypic variation was found under 25°C. Higher water use efficiency was associated with higher temperature. Relative decrease in Chl a content, g s and maximal quantum efficiency of PSII exhibited by both spe cies were distinctive physiological traits for heat and drought tolerance.

The Effect of Abscisic Acid and Benzylaminopurine on Photosynthesis and Transpiration Rates of Maize (Zea mays L.) under Water Stress and Subsequent Rehydration

The young plants of maize were cultivated as sand culture under controlled conditions in a greenhouse. The water stress caused by interruption of irrigation for a period of 8 days had the effect of statistically significant decrease of the photosynthesis rate (P N) and the transpiration rate (E) as compared with plants under no stress. When the plants were treated with a 100 μM abscisic acid (ABA) solution before the interruption of irrigation, this had the effect of further decrease of the levels of P N and E during the first period of measurement (3 to 4 days after interruption of irrigation) and the effect of slowing down the development of water stress in the following period (7 to 8 days after interruption of irrigation). ABA applied through irrigation was more effective than the one applied by sprinkling because it significantly increased the water use efficiency (WUE) in the treated plants. Benzylaminopurine (BAP) used as a 10 μM solution brought about an increase of P N and E in comparison with the plants under stress, not treated phytohormones. The result of the combined application of both growth regulators were steady levels of P N during the entire eight-day evaluation of water stress imposed on maize plants. However, during the second period of measuring, the higher levels of E were reflected in a decrease of the WUE level. Two days after irrigation was resumed, the subsequent saturation of plants with water was manifested by an increase of P N in all groups of plants under stress. However, the fairly steady levels remained below the level of P N measured in the control sample under no stress. Rehydration had various effects on E. The level of E increased the most in the case where ABA was used as irrigation. It also increased moderately in the case where ABA was applied by sprinkling and in the case of the plants under stress, not treated phytohormones. On the contrary, E stagnated in the cases with BAP and decreased in the cases where ABA and BAP were applied together.

Gas exchange and Triticum sp. with different ploidy in relation to irradiance

Different species of Triticum were grown during a greenhouse experiment, including T. monococcum L., T. dicoccum Schrank, T. durum Desf., T. spelta L. and T. aestivum cv. Vanek. The goal was to establish the influence of irradiance on the parameters of photosynthetic performance in relation to their ploidy. Photosynthetic rate (Pn), transpiration (E) and stomatal conductance (gs) were measured at irradiance ranging from 217–1305 μmol/m2/s. In all monitored species, saturation irradiance for photosynthesis at the level of 609 μmol/m2/s was reached. The highest average Pn was measured in the diploid T. monococcum (32.5 μmol CO2/ m2/s) while the lowest Pn occurred in the hexaploid T. spelta (22.0 μmol CO2/m 2/s). The Pn in hexaploid T. aestivum (29.6 μmol CO2/m 2/s) was comparable with the tetraploid T. durum. Similarly, E also decreased with the increase of ploidy. The highest gs was measured in T. durum (1.03 mol CO2/m 2/s) and T. aestivum (0.99 mol CO2/ m2/s). In all monitored species a close linear dependency was recorded between Pn and gs. Species with lower ploidy reach maximum values of Pn with lower gs. Hexaploid T. aestivum and tetraploid T. durum, require higher gs in order to achieve higher Pn and yet they do not reach the Pn values of species with lower ploidy.

Use of combustion methods for calorimetry in the applied physiology of plants

As a thermodynamics method, combustion calorimetry has a wide spectrum of uses in the applied physiology of plants. During evaluations, it suitably combines its physical relations with properties of living organisms, thus providing a solid overview concerning the exchange of energy between a plant and its environment. Measuring photosynthetic rate, expressed through changes of energy content, is comparable with gasometric methods, because the course of photosynthesis and the energy content in leaves dependent on their ontogenetic development is similar. Combustion calorimetry enables monitoring the changes of accumulation of assimilated nutrients and their translocation between the individual organs of the plant. The close relation between the creation of dry matter and the accumulation of energy-rich substances into the plant body is apparent from the acquired experimental data. Based on the methods of combustion calorimetry, it is possible to determine the relationship between the source and the sink. It is further possible to use this method as one of the detection methods to determine changes in metabolism and the degree of resistance of plants, as well as ecosystems, under stress conditions.

The effect of the aridisation of a habitat on the accumulation capability of sink in selected varieties of spring barley

One of the ways of reducing energy-intensive inputs to agricultural systems is to replace the less performing cultivars with more productive ones and to cultivate varieties with sufficient accumulation capabilities of sink even under worse environmental conditions, for example, in the event of aridisation of the environment. The cultivation process is managed in such a way so that the largest share of the total production of all the plant biomass is represented by the organs providing the actual economic yield. From the results there is a clear difference between the Czech variety Malz and the Dutch Jersey in the formation of spike under the effect of water stress. For the Malz variety the number of grains in the spike dropped by 17.5% compensated for by their increased weight. For the Jersey variety there was a 16.7% fall in the number of grains in the spike, but no compensation in the increased weight of the grains was observed.

Physiological responses as influenced by night freeze stress at the beginning of vegetative growth of sunflower

Physiological changes on leaves of young sunflower plants (genotypes C120, C124, C148 and PAC2) were evaluated in a growth chamber after exposure to night frost of -3 and -5°C for a period of 12 h. Net CO2 assimilation rate (PN), potential photochemical efficiency of electron transport PS2 (FV/FM), relative electrolyte leakage (REL%) and osmotic potential (ψπ) were monitored in the plants. Stressed plants were evaluated immediately (2 h) after the effect of the freezing temperature (var. S1), after 2-day recovery (var. S2) and after 6-day recovery (var. S3). The PN was determined as the most sensitive of the evaluated parameters of the sunflower. In genotypes C120, C148 and PAC2, a statistically evident decrease of PN in all variants S1-S3 was found during a temperature of -3°C. To the contrary, the results have proved minor sensitivity or, more precisely, a high stability of FV/FM, ψπ a REL% at the freezing temperature of -3°C. The results showed that physiological parameters were more sensitive to a freeze temperature at −5°C. It was also possible to determine the differences between genotypes. Statistically evident changes were found there in comparison to control plants: decrease of PN in genotypes C120 and C148 in all variants S1-S3, in genotype C124 in variant S1 and in genotype PAC2 in variant S3. There was also the decrease of FV/FM in genotypes C120, C124 and C148 in variant S1; increased REL% in genotype C120 in variants S1 and S3 and in genotypes C124 and C148 in variant S1; decreased ψπ in genotype C124 in variants S1-S3 and in genotypes C120 and C148 in variant S2. As apparent from the above, the PAC2 genotype may be considered relatively resistant to freeze stress, while genotypes C120, C124 and C148 rather sensitive to freeze stress.

Responses of Cereal Plants to Environmental and Climate Changes – A Review

The projections of the global climate changes on the Earth expect a rise in the concentration of greenhouse gases, increase in temperature and aridisation of the environment. By the middle of the twenty-first century, the concentration of CO2 will probably rise up to 500 μl l−1 of air. Already now, 61% of the area of land on the Earth has precipitation lower than 500 mm. One-sixth of the world’s population can be affected by an acute shortage of water. A total of 35–50% of inhabitants of the Earth are struggling with salinity of soil. All this currently has and will have consequences for the agricultural production. The areas between 15° and 30° of the north and south longitude and the deep inland areas are endangered the most. Cereals are major crops with respect to human nutrition. In order to ensure permanently sustainable production of cereals, it is important to study the diversity of their production under the influence of natural and climate changes. Based on this analysis, it is necessary to design measures to stabilise yields. This is the purpose of this chapter. Based on the study of a number of literature sources, we presume that the increased concentration of CO2 will only partly compensate for the losses of the yields of cereals resulting from the increase in temperature and aridisation of the environment taking place on a global scale. However, cereals have a number of adaptation mechanisms to maintain turgor and to improve water management in dry and salinised habitats. With a view of ensuring permanent sustainability of agricultural production under the changing natural and climatic conditions, we present two options of using the diversity of adaptation mechanisms: (1) to adapt the composition of the cereals grown to changing conditions; (2) to breed varieties more resistant to changing conditions. Breeding resistant genotypes is the least costly solution to ensure sustainable development of agriculture in arid areas. We believe that the choice of suitable selection criteria is most important. For the screening of genotypes resistant to drought and salinisation, it is important to use more parameters: physiological and biochemical indicators at the cellular level and the genes of resistance to drought and salinisation. The suitable selection criteria and the important features of drought and salinisation resistance are a high level of osmotic adjustment, low stomatal conductivity and good growth of roots. Breeding aimed at achieving a higher degree of drought resistance should be focused on (1) improvement of the availability of water through the root system; (2) the limitation of water loss through transpiration and higher water use efficiency for production of biomass; (3) prolongation of the activity and increase of the power of the sink. In the selection of the genetic sources of resistance to abiotic stresses, we recommend paying an even greater attention to wild species and region-specific and primitive varieties of cereals, originating from worse natural and climatic areas. Another promising path is to use gene transfers to improve the photosynthetic and growth capacity of cereals during the presence of stress factors. In order to improve the water management in cereals under dry conditions, we also suggest using growth regulators to a greater extent. Abscisic acid applied on plants can serve as an antitranspirant. It can increase water use efficiency.

The impacts of the aridisation of a habitat on the photosynthetic fixation of energy in spring barley ( Hordeum vulgare L.)

Aridisation of a habitat is expressed by a reduced photosynthetic fixation of energy in the plants especially in the photosynthetic organs — the leaves. The quantity of energy fixed by plants can be increased by additional intensification methods such as nitrogen fertilisation. However, this places very high demands on additional inputted energy and involves gradual exhaustion of non-renewable resources. These intensification methods also have a negative effect on the environment.

Isoflavones Production and Possible Mechanism of Their Exudation in Genista tinctoria L. Suspension Culture after Treatment with Vanadium Compounds

The family Fabaceae traditionally serves as a food and herbal remedies source. Certain plants serve for treatment of menopausal symptoms based on a presence of typical secondary metabolites, isoflavones. Beside soybean and clovers, other plants or cultures in vitro can produce these molecules. A cultivation in vitro can be enhanced by elicitation that stimulates metabolites biosynthesis via stress reaction. Vanadium compounds have been already described as potential elicitors, and the aim of this study was to determine the impact of NH4VO3 and VOSO4 solutions on isoflavones production in Genista tinctoria L. cell cultures. The significant increase of isoflavones content, such as genistin, genistein, or formononetin, was measured in a nutrient medium or dry mass after NH4VO3 treatment for 24 or 48 h. The possible transport mechanism of isoflavones release as a result of elicitation was further evaluated. An incubation with different transport inhibitors prior to elicitation took effect on isoflavones content in the medium. However, there was a non-ended result for particular metabolites such as genistein and daidzein, where ATP-binding cassette (ABC) or, alternatively, multidrug and toxin extrusion (MATE) proteins can participate. Possible elicitation by some inhibitors was discussed as a result of their pleiotropic effect. Despite this outcome, the determination of the transport mechanism is an important step for identification of the specific transporter.