Krisztina Balla

Effect of heat and drought stress on the structure and composition of arabinoxylan and β-glucan in wheat grain

The effects of heat (H), drought (D) and H+D (from 12th day after heading for 15 days) on the dietary fiber content and composition (arabinoxylan (AX) and β-glucan) of three winter wheat varieties (Plainsman V, Mv Magma and Fatima 2) were determined. Results showed that H and D stress decreased the TKW, the β-glucan contents of the seeds and the quantity of the DP3+DP4 units, while the protein and AX contents increased. The highest amounts of AX and proteins were in the H+D stressed samples with heat stress also increasing the water extractability (WE) of the AX. However, while the content of AX content was generally increased by all stresses, drought stress had negative effect on the AX content of the drought tolerant Plainsman V. Fatima 2 behaved similarly to Plainsman V as regards to its drought tolerance, but was very sensitive to heat stress, while Mv Magma was the most resistant to heat stress.

Drought tolerance in cereals in terms of water retention, photosynthesis and antioxidant enzyme activities

Experiments were carried out on three bread wheat varieties, one barley and one durum wheat variety grown in pots in the phytotron and subjected to water withdrawal for 7 days during grain-filling. Leaf water loss, net assimilation rate and transpiration showed marked differences, allowing the genotypes to be ranked. Although the most resistant variety had the highest activity for ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR) and glutathione-S-transferase (GST), which did not rise further in response to drought and the most susceptible variety had the lowest values, which increased to the greatest extent under drought, the level of sensitivity could not be predicted for all the genotypes from the enzyme activity values alone. The largest increases were recorded for the APX, CAT and GR activities. In most genotypes the GR activity was correlated with that of GST, CAT and APX. Changes in the enzyme activities were observed after a decline in transpiration and photosynthesis. The range of soil moisture values over which the antioxidant enzyme activity levels remained relatively unchanged was a better indication of tolerance to drought than either basic or stress-induced activity levels.

Heat stress induced changes in the activity of antioxidant enzymes in wheat

Introduction The cellular changes induced by temperature stress result in the over-accumulation of toxic components in the cells. These extremely toxic compounds include reactive oxygen species (ROS), which are present to some extent in all plants as the product of the aerobic metabolism. Stress tolerance is thus based on antioxidant compounds and antioxidant enzyme systems which, when activated, are capable of neutralising the reactive oxygen species continuously produced in response to stress factors (Daood et al., 2006; El-Tayeb, 2006; Misan et al., 2006). If not removed, these compounds damage the cell tissues, eventually resulting in cell death (Bencze and Veisz, 2005). It was proved by Mittler (2002) that stress increases the production of ROS, the accumulation of which causes typical symptoms in stressed plants. High temperature also has a destructive effect on major physiological processes. The ROS accumulated as the result of heat stress lead to mitochondrial dysfunction, an increase in lipid peroxidation and the oxidative destruction of cell components (Fridovich, 1978). Many data have been presented proving the role of antioxidant enzymes (e.g. catalase, peroxidases, the enzymes of the ascorbate-glutathione cycle, etc.) and radical scavengers (e.g. glutathione, ascorbic acid, etc.) in the defence against various stress effects. A number of authors have reported a rise in the activity of the antioxidant enzymes responsible for eliminating ROS in the course of heat stress (Rainwater et al., 1996; Jiang and Huang, 2001; Vacca et al., 2004). Two antioxidant enzymes were examined in the present experiments: glutathione reductase (GR) and ascorbate peroxidase (APx).

Physiological response of wheat varieties to elevated atmospheric CO2 and low water supply levels

In the phytotron experiment, the effect of elevated atmospheric CO2 (EC, 750 μmol mol−1) on the drought tolerance was studied in two winter varieties (Mv Mambo, tolerant; Mv Regiment, moderately tolerant) and in one spring variety of wheat (Lona, sensitive to drought). Changes in net photosynthetic rate (PN), stomatal conductance, transpiration, wateruse efficiency, effective quantum yield of photosystem II, and activities of glutathione reductase (GR), glutathione-Stransferase (GST), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were monitored during water withdrawal. Drought caused a faster decline of PN at EC, leading to the lower assimilation rates under severe drought compared with ambient CO2 (NC). In the sensitive variety, PN remained high for a longer period at EC. The growth at EC resulted in a more relaxed activation level of the antioxidant enzyme system in all three varieties, with very low activities of GR, GST, APX, and POD. The similar, low values were due to decreases in the varieties which had higher ambient values. A parallel increase of CAT was, however, recorded in two varieties. As the decline in PN was faster at EC under drought but there was no change in the rate of electron transport compared to NC values, a higher level of oxidative stress was induced. This triggered a more pronounced, general response in the antioxidant enzyme system at EC, leading to very high activities of APX, CAT, and GST in all three varieties. The results indicated that EC had generally favourable effects on the development and stress tolerance of plants, although bigger foliage made the plants more prone to the water loss. The relaxation of the defence mechanisms increased potentially the risk of damage due to the higher level of oxidative stress at EC under severe drought compared with NC.

Productivity of a doubled haploid winter wheat population under heat stress

Breeding of new winter wheat cultivars with good heat tolerance requires better understanding of the genetic background of heat tolerance. In the present work the effect of heat stress on the 6th day after heading was investigated in a doubled haploid (DH) population arising from a cross between heat-sensitive (Plainsman V) and heat-tolerant (Mv Magma) cultivars. Averaged over the population, heat stress was found to result in a significant reduction in biomass, grain yield and grain number per plant, and in thousand-kernel weight (TKW) and harvest index. High temperature had the greatest effect on the grain yield, with a drop of 36.2% compared with the control. This could be attributed jointly to significant reductions in the TKW of the main ear and in the grain number of the side tillers. The relationship between the yield parameters was confirmed by the positive correlations obtained for the lines in the population. The diverse levels of heat tolerance in the different lines were confirmed by the significant differences in the reduction in the chlorophyll content (SPAD index) of the flag-leaves and in yield parameters. The changes in yield components in stress condition, however, can be still the most effective tools for heat stress evaluation.

Response of wheat fungal diseases to elevated atmospheric CO2 level

Infection with fungal pathogens on wheat varieties with different levels of resistance was tested at ambient (NC, 390 ppm) and elevated (EC, 750 ppm) atmospheric CO2 levels in the phytotron. EC was found to affect many aspects of the plant-pathogen interaction. Infection with most fungal diseases was usually found to be promoted by elevated CO2 level in susceptible varieties. Powdery mildew, leaf rust and stem rust produced more severe symptoms on plants of susceptible varieties, while resistant varieties were not infected even at EC. The penetration of Fusarium head blight (FHB) into the spike was delayed by EC in Mv Mambo, while it was unaffected in Mv Regiment and stimulated in Mv Emma. EC increased the propagation of FHB in Mv Mambo and Mv Emma. Enhanced resistance to the spread of Fusarium within the plant was only found in Mv Regiment, which has good resistance to penetration but poor resistance to the spread of FHB at NC. FHB infection was more severe at EC in two varieties, while the plants of Mv ...

Change in water stress resistance of cereals due to atmospheric CO 2 enrichment

Oil rape is a valuable fodder because in early spring and late autumn it produces green forage used for the nutrition of domestic animals. It has been replacing sunflower and soy in colder and wetter regions. It is additionally advantageous because it leaves behind more nitrogen in soil, which is beneficial to other plants in plant rotation. There are some possible ways for the fixation of nitrogen in soil and they are as follows: by the means of oil rape straw ; by relatively long roots ; by the action of nitrogen bacteria, which perform the nitrogen synthesis within their root system, which is the case in some leguminous plants. Oil seed rape is expected to be wider used in crop rotation of West and Middle Europe, Croatia included. Due to this various sorts have been introduced and potential positive impacts have been studied in order to boost the process. This paper presents information on barley and wheat yield in case when they were sown after oil seed rape and corn. The aim of the research is to determine the presence of positive impacts upon the soil with special attention paid to a potential increase of nitrogen content after oil seed rape was grown. The preceding crops had statistically significant effect. Rape yield was significantly higher compared to the one with corn as preceding crops. Very similar results were obtained in 2007.The maize hybrids seed from three different FAO groups (FAO 400, FAO 500 and FAO 600) in four fractions (KO, KP, SO and SP) produced in two climatically different years (extremely dry 2000 and extremely wet 2001) had been different in quality and chemical composition. The effects of year, genetic specifity and seed fraction at the kernel mass, chemical composition (starch, proteins, cellulose, oil and moisture content) and seed vigour have been evaluated. The influence of agroecological conditions during two production years have been exposed at seed chemical composition and vigour indicators (cold test – CT and bulk seed electrical conductivity - EC). The genetic specificity and seed fraction had significant influence at all tested indices, with the exception of the influence of the fraction at the starch content

Effect of different sowing times on the plant developmental parameters of wheat (Triticum aestivum L.)

Studies on plant development phases and yield component patterns of wheat are essential for a better understanding of adaptation in wheat. Our main aim was to carry out detailed phenological analyses of 18 wheat genotypes in three sowing times for determining the effect of sowing date on individual phenophases, and yield components. Sowing date had the single greatest effect on the start of intensive stem elongation. The longer vegetation period had a favourable effect on main spike length and on the spikelet number per spike, but had no influence on thousand-kernel weight and grain number per spike. The time between the first node appearance and start of intensive stem elongation had a significant effect on the number of reproductive tillers. A close association (R2 = 0.191) was observed during the second phase of intensive stem elongation between the boot stage-to-heading interval and the number of spikelets per spike. Two-way analysis of variance on the yield components showed that the sowing date, as a main factor, had a weaker effect on the phenophases than on morphological and developmental parameters. The insensitive allele of the Ppd-D1 gene shortened the time required for first node appearance and heading both in autumn and spring sowing.

Changes in the photosynthetic efficiency of winter wheat in response to abiotic stress

The assessment of heat and drought tolerance is of primary importance in breeding programmes designed to improve heat and drought tolerance in cereals. Three winter wheat varieties grown in controlled growth chambers were exposed to heat (H) and drought (D) stress singly and in combination (H+D). The combined effects of H and D stress were much more severe than those of individual treatments for both physiological and yield parameters during grain filling. The chlorophyll content, effective quantum yield of PSII, net assimilation rate, transpiration, stomatal conductance and intercellular CO2 concentration were greatly reduced by H, D and their interaction. Grain yield decreased to a greater extent (48.3%) in Plainsman V, averaged over the stress treatments, than in Mv Magma (67.8%) and Fatima 2 (53.7%). The least decline was found in grain number, except in Plainsman V. Mv Magma tolerated heat stress better than Fatima 2. In terms of photosynthetic activity, Plainsman V showed better drought tolerance than Mv Magma. The results showed that changes in physiological properties during stress treatment are not always associated with changes in yield parameters, so a combination of methods may be needed to give a more precise picture of the stress tolerance of wheat varieties.

Study of physiological and agronomic traits in winter wheat under low water supplies

Oil rape is a valuable fodder because in early spring and late autumn it produces green forage used for the nutrition of domestic animals. It has been replacing sunflower and soy in colder and wetter regions. It is additionally advantageous because it leaves behind more nitrogen in soil, which is beneficial to other plants in plant rotation. There are some possible ways for the fixation of nitrogen in soil and they are as follows: by the means of oil rape straw ; by relatively long roots ; by the action of nitrogen bacteria, which perform the nitrogen synthesis within their root system, which is the case in some leguminous plants. Oil seed rape is expected to be wider used in crop rotation of West and Middle Europe, Croatia included. Due to this various sorts have been introduced and potential positive impacts have been studied in order to boost the process. This paper presents information on barley and wheat yield in case when they were sown after oil seed rape and corn. The aim of the research is to determine the presence of positive impacts upon the soil with special attention paid to a potential increase of nitrogen content after oil seed rape was grown. The preceding crops had statistically significant effect. Rape yield was significantly higher compared to the one with corn as preceding crops. Very similar results were obtained in 2007.The maize hybrids seed from three different FAO groups (FAO 400, FAO 500 and FAO 600) in four fractions (KO, KP, SO and SP) produced in two climatically different years (extremely dry 2000 and extremely wet 2001) had been different in quality and chemical composition. The effects of year, genetic specifity and seed fraction at the kernel mass, chemical composition (starch, proteins, cellulose, oil and moisture content) and seed vigour have been evaluated. The influence of agroecological conditions during two production years have been exposed at seed chemical composition and vigour indicators (cold test – CT and bulk seed electrical conductivity - EC). The genetic specificity and seed fraction had significant influence at all tested indices, with the exception of the influence of the fraction at the starch content