Sándor Dulai

Physiological and morphological responses to water stress in Aegilops biuncialis and Triticum aestivum genotypes with differing tolerance to drought

The physiological and morphological responses to water stress induced by polyethylene glycol (PEG) or by withholding water were investigated in Aegilops biuncialis Vis. genotypes differing in the annual rainfall of their habitat (1050, 550 and 225 mm year-1) and in Triticum aestivum L. wheat genotypes differing in drought tolerance. A decrease in the osmotic pressure of the nutrient solution from -0.027 to -1.8 MPa resulted in significant water loss, a low degree of stomatal closure and a decrease in the intercellular CO2 concentration (Ci) in Aegilops genotypes originating from dry habitats, while in wheat genotypes high osmotic stress increased stomatal closure, resulting in a low level of water loss and high Ci. Nevertheless, under saturating light at normal atmospheric CO2 levels, the rate of CO2 assimilation was higher for the Aegilops accessions, under high osmotic stress, than for the wheat genotypes. Moreover, in the wheat genotypes CO2 assimilation exhibited less or no O2 sensitivity. These physiological responses were manifested in changes in the growth rate and biomass production, since Aegilops (Ae550, Ae225) genotypes retained a higher growth rate (especially in the roots), biomass production and yield formation after drought stress than wheat. These results indicate that Aegilops genotypes, originating from a dry habitat have better drought tolerance than wheat, making them good candidates for improving the drought tolerance of wheat through intergeneric crossing.

Differences in photorespiration, glutamine synthetase and polyamines between fragmented and closed stands of Phragmites australis

Abstract Physiological processes related to C and N metabolism were investigated in closed healthy, and fragmented die-back stands of Phragmites australis (Cav.) Trin. ex Steudel along the shores of Lake Balaton, Hungary. In the leaves, similar concentrations of total N and P, K+, Na+, Ca2+ and Mg2+ were found. However, higher concentrations of soluble proteins in the fragmented stand indicated alterations in N metabolism. In both types of stands, nitrate reductase (NR) activity was detectable only in the period of vegetative growth and it was higher in the fragmented than in the closed stands. Glutamine synthetase (GS) activity showed three-fold higher activities in the leaves from the fragmented stands compared to those in closed stands, indicating high substrate (NH3/NH4+) availability. Polyamine concentrations were 4–10-fold higher in the leaves of the fragmented stands than in those of closed stands. Photosynthetic activity was nearly equal in both stands, however, photorespiration was about two-fold higher in the fragmented than in the closed stands. A linear correlation between photorespiration and GS activity indicated a causal relationship (R2=0.86). Stomatal conductance data suggest that the higher photorespiration in the fragmented stands could be the consequence of disturbed stomatal regulation. It is concluded that fragmented stands of Phragmites possess an altered C/N metabolism, due to high photorespiration and intensive N metabolism. The primary reason of the cascade of events is still not clear but apparently, these metabolic malfunctions accompany an accelerated die-back of Phragmites around Lake Balaton.

Salt stress response of wheat–barley addition lines carrying chromosomes from the winter barley “Manas”

The salt stress responses of wheat–barley addition lines (2H, 3H, 3HS, 4H, 6H, 7H and 7HL) were compared to those of the parental genotypes wheat cv. Asakaze and barley cv. Manas and two other wheat genotypes [Chinese Spring (CS) and Mv9kr1] during germination and in young plants grown in hydroponic culture with or without salt treatment. Among the wheat genotypes frequently used for interspecific hybridization, Asakaze possesses relatively high salt tolerance, as indicated by the less pronounced reduction in germination % and in root and shoot growth and the retention of high leaf water content and photosynthetic activity, as compared to CS and Mv9kr1. The barley cv. Manas showed better salt tolerance than wheat cv. Asakaze, although Manas accumulated more Na in the root, but its transport to the shoots is restricted. Among the addition lines tested, the disomic addition line 7H and ditelosomic line 7HL exhibited higher salt tolerance both during germination and in the early developmental stages than the wheat parent, which may be related to the elevated osmotic adjustment capacity of these addition lines, similar to that found for barley cv. Manas. The paper also discusses the effects of other chromosomes on the salt stress response.

Photosynthetic responses of a wheat (Asakaze)–barley (Manas) 7H addition line to salt stress

The photosynthetic responses to salt stress were examined in a wheat (Triticum aestivum L. cv. Asakaze)–barley (Hordeum vulgare L. cv. Manas) 7H addition line having elevated salt tolerance and compared to the parental wheat genotype. For this purpose, increasing NaCl concentrations up to 300 mM were applied and followed by a 7-day recovery period. Up to moderate salt stress (200 mM NaCl), forcible stomatal closure, parallel with a reduction in the net assimilation rate (PN), was only observed in wheat, but not in the 7H addition line or barley. Since the photosynthetic electron transport processes of wheat were not affected by NaCl, the impairment in PN could largely be accounted for the salt-induced decline in stomatal conductance (gs), accompanied by depressed intercellular CO2 concentration and carboxylation efficiency. Both, PN and nonstomatal limitation factors (Lns) were practically unaffected by moderate salt stress in barley and in the 7H addition line due to the sustained gs, which might be an efficient strategy to maintain the efficient photosynthetic activity and biomass production. At 300 mM NaCl, both PN and gs decreased significantly in all the genotypes, but the changes in PN and Lns in the 7H addition line were more favourable similar to those in wheat. The downregulation of photosynthetic electron transport processes around PSII, accompanied by increases in the quantum yield of regulated energy dissipation and of the donor side limitation of PSI without damage to PSII, was observed in the addition line and barley during severe stress. Incomplete recovery of PN was observed in the 7H addition line as a result of declined PSII activity probably caused by enhanced cyclic electron flow around PSI. These results suggest that the better photosynthetic tolerance to moderate salt stress of barley can be manifested in the 7H addition line which may be a suitable candidate for improving salt tolerance of wheat.

Differing metabolic responses to salt stress in wheat-barley addition lines containing different 7H chromosomal fragments

Salinity-induced osmotic, ionic and oxidative stress responses were investigated on Asakaze/Manas wheat/barley addition lines 7H, 7HL and 7HS, together with their barley (salt-tolerant) and wheat (relatively salt-sensitive) parents. Growth, photosynthetic activity, chlorophyll degradation, proline, glycine betaine accumulation, sugar metabolism, Na+ and K+ uptake and transport processes and the role of polyamines and antioxidants were studied in young plants grown in hydroponic culture with or without salt treatment. Changes in plant growth and photosynthetic activity of plants demonstrated that the salt tolerance of the addition lines 7H and 7HL was similar to that of barley parent cv. Manas, while the sensitivity of the addition line 7HS was similar to that of the wheat parent cv. Asakaze. The Na accumulation in the roots and shoots did not differ between the addition lines and wheat parent. The activation of various genes related to Na uptake and transport was not correlated with the salt tolerance of the genotypes. These results indicated that the direct regulation of Na transport processes is not the main reason for the salt tolerance of these genotypes. Salt treatment induced a complex metabolic rearrangement in both the roots and shoots of all the genotypes. Elevated proline accumulation in the roots and enhanced sugar metabolism in the shoots were found to be important for salt tolerance in the 7H and 7HL addition lines and in barley cv. Manas. In wheat cv. Asakaze and the 7HS addition line the polyamine metabolism was activated. It seems that osmotic adjustment is a more important process in the improvement of salt tolerance in 7H addition lines than the direct regulation of Na transport processes or antioxidant defence.

Wheat-Aegilops biuncialis amphiploids have efficient photosynthesis and biomass production during osmotic stress

Osmotic stress responses of water content, photosynthetic parameters and biomass production were investigated in wheat-Aegilops biuncialis amphiploids and in wheat genotypes to clarify whether they can use to improve the drought tolerance of bread wheat. A decrease in the osmotic pressure of the medium resulted in considerable water loss, stomatal closure and a decreased CO2 assimilation rate for the wheat genotypes, while the changes in these parameters were moderate for the amphiploids. Maximal assimilation rate was maintained at high level even under severe osmotic stress in the amphiploids, while it decreased substantially in the wheat genotypes. Nevertheless, the effective quantum yield of PS II was higher and the quantum yield of non-photochemical quenching of PS II and PS I was lower for the amphiploids than for the wheat cultivars. Parallel with this, higher cyclic electron flow was detected in wheat than in the amphiploids. The elevated photosynthetic activity of amphiploids under osmotic stress conditions was manifested in higher biomass production by roots and shoots as compared to wheat genotypes. These results indicate that the drought-tolerant traits of Ae. biuncialis can be manifested in the wheat genetic background and these amphiploids are suitable genetic materials for improving drought tolerance of wheat.

Light Dependence of Thermostability of Photosynthetic Apparatus

PS II is one of the most sensitive component of the photosyntehtic apparatus to different environmental stresses. Heat stress causes the hyperfluidization of the thilakoid membranes, the deactivation of PS II including the dissociation of LHC from the core complexes and inactivation of oxygen evolving system(1). The heat sensitivity of plants can be caracterized by the thermostability of PS II measured by temperature-dependent changes of initial fluorescence (Fo) of dark adapted leaves (2). In parallel with the heating, the initial level of fluorescence yield increases intensively above a critical temperaure (Tc). The Fo vs T curve and the critical temperaure depend on the composition and physical state of the thylakoid membranes (3). It seems that the thermostability of the photosynthetic apparatus of preilluminated plants is higher than of the untreated samples, which manifests in the upshift of Tc measured on dark adapted leaves (4).

The role of photosynthetic activity in the vulnerability of an insular biome to invasion by alien species.

Biological invasion by alien plants has been documented to have destructive effects on the native vegetation of insular biomes. This phenomenon is widespread throughout our investigation area: the islands in the Indian Ocean. The question is why the native plant communities of small islands are so vulnerable when faced with the invasion of alien, continental species. We hypothesise that these species came from a continental environment where, over a much larger area and usually during a much longer time, competition between a higher number of species with a much smaller realised niche space and a greater degree of niche overlap led to the evolution of a higher degree of competitiveness (1). On the small islands, on the other hand, the limited number of indigenous species, living in a broad niche space with little overlap, provided little selection pressure for competitive ability. How can we define and measure competitive ability? To test our hypothesis, we have compared ecophysiological parameters of indigenous, often endemic species on the island of Reunion with those of invasive species of continental origin. There are appreciable numbers of both types of species (2), and it was easy to select five typical species from each of the groups (Table 1). Any life process taken into account must be of fundamental significance, must be closely interconnected with other life processes, must reflect well the physiological state and vitality of the whole plant individual and must have an influence on the competitive ability. These requirements are well met by photosynthetic activity: it has an essential energy-transforming function, photosynthetic metabolites and chemically bound photoenergy influence other metabolic and physiological processes, and consequently the photosynthetic productivity is reflected in some form in the competitive ability. The functioning of photosystem II (PS II) is the most sensitive indicator of environmental and interspecific effects in the photosynthetic apparatus (3–5). Measurements of chlorophyll fluorescence associated with PS II activity, and of CO2 gas-exchange, provide a means of rapidly and non-destructively probing the biophysical and biochemical bases of photosynthetic characteristics in the field (6–9). These methods can also be used to estimate plant growth, dry-matter production (10–12) and hence competitive ability.

Short-Term Responses of Photosystem II to Heat Stress in Cold-Acclimated Atrazine-Resistant and Susceptible Biotypes of Erigeron canadensis (L.)

When leaves of atrazine-resistant (AR) and atrazine-sensitive (S) Erigeron canadensis (L.) plants grown at 5 °C were exposed to an elevated temperature (35 °C) for 30 min, the critical (Tc) and peak temperatures (Tp) of the F0 vs. T curves were considerably higher for the leaves of the S biotype, but not for those of the AR biotype. The temperature dependences of Fv/Fm and ΔF/Fm′ were not greatly different for the heat-treated cold-acclimated AR biotype, in contrast with the situation for the S plants. This short-term heat treatment resulted in a more significant shift in the optimal thermal interval of CO2 fixation for the S than for the AR biotypes