László Erdei

The Effects of Cadmium on the Fluidity and H+-ATPase Activity of Plasma Membrane from Sunflower and Wheat Roots

Summary The effects of cadmium on the H + -ATPase activity and on the membrane fluidity were studied in plasma membrane prepared from roots of sunflower and wheat. Plasma membrane purified from the microsomal fraction by phase partitioning showed a decreased ATPase activity by in vivo Cd 2+ treatment (30 % and 90 % decrease in wheat and sunflower, respectively) and the in vitro application caused an inhibition, as well. The ordering state of the membrane at the C-5 and C-16 levels of the fatty acid chains and at the membrane surface was determined by electron spin resonance (ESR) and by fluorescence spectroscopy, respectively. The presence of Cd 2+ increased the ordering of the plasma membrane in both in vivo treatments and in vitro experiments. Under Cd 2+ treatment, a more rigid structure of the PM was found at different depths in the membrane; changes were larger in sunflower than in wheat. The alterations can be the results of direct effects on the membrane constituents (proteins, lipids) or of the modification in lipid composition. Preliminary studies suggest that there are changes caused by Cd 2+ in the fatty acid composition of the phospholipid fraction in PM, which were different in the case of wheat and sunflower.

Effects of NaCl Salinity on Growth, Cation Accumulation, Chloroplast Structure and Function in Wheat Cultivars Differing in Salt Tolerance

Summary The effects of salinity on four cultivars of wheat differing in salt tolerance were investigated with respect to growth, accumulation of K + and Na + in the roots and the shoots, and Mg 2+ and chlorophyll concentrations in the leaves. Growth and K + accumulation were stimulated by intermediate salinity in the known salt tolerant cultivars, Kharchia and Sakha-8, whereas these responses were less in the intermediate and sensitive cultivars, Sakha-69 and T-79. At high salinity, the degradation of chlorophyll was somewhat lower in the salt tolerant than in the sensitive cultivars and it coincided with a higher capability of the maintenance of intracellular Mg 2+ concentrations. Electron microscopic studies revealed that NaCl at 200 mM caused swelling of membranes in chloroplasts of the sensitive cultivars while it had little effect in the tolerant ones. Chlorophyll fluorescence measured in intact leaves showed that at 150–200 mM NaCl, the non-photochemical quenching decreased considerably in the sensitive T-79 but not in the tolerant Kharchia. The relaxation patterns of the non-photochemical quenching have also shown differences between the tolerant and sensitive cultivars. The Chl a /Chl b ratio increased considerably more in the sensitive cultivars than in the tolerant ones. These results suggest that the chloroplasts under saline conditions in the leaves of salt tolerant wheat cultivars, are not exposed to excess Na + , in contrast to those in the sensitive ones.

Effects of osmotic and salt stresses on the accumulation of polyamines in leaf segments from wheat varieties differing in salt and drought tolerance

Summary Polyamine accumulation under short-term non-ionic osmotic and salt stress was compared in leaf segments of 8 wheat varieties differing in drought and salt tolerance in order to test whether various stress conditions impair different steps of polyamine biosynthesis. The highest putrescine accumulation occurred in the known salt and drought tolerant varieties under non-ionic osmotic stress (400 mOSm L -1 sorbitol for 10 h), while in the presence of NaCI of the same osmolarity, only the known salt tolerant variety responded with increased putrescine level. Spermidine titer was slightly influenced by both stress conditions and spermine content increased only under salinity. The putrescine precursor agmatine accumulated under osmotic stress, while the end product 1,3-diaminopropane appeared only under salt stress. These results suggest that with respect to the onset of polyamine biosynthetic and degradative processes, osmotic and salt stresses are two distinct conditions.

Responses in polyamine titer under osmotic and salt stress in Sorghum and maize seedlings

Summary Changes in leaf water potential, K + /Na + ratio and in polyamine titers in maize ( Zea mays L. cv. Pioneer 3950) and sorghum ( Sorghum bicolor (L.) Moench cv. ICSV 112) were investigated as the function of increasing equi-osmotic concentrations of NaCl or polyethylene glycol 6000 applied for 3 days in the nutrient solution. For both treatments, sorghum responded with a more intensive decrease in leaf water potential compared with maize. Plant analysis showed that under salinity, a higher level of Na + was accumulated in the roots of maize than in those of sorghum while shoot Na + concentrations were nearly the same. Internal K + concentration was always higher in sorghum, leading to a K + /Na + ratio 2 to 4-fold higher in the roots of sorghum compared with that in maize. In maize, NaCl and osmotic stresses evoked similar rates of polyamine accumulation, while in sorghum, osmotic stress was more effective in comparison to salt treatment. In maize, spermidine was apparently absent, indicating its fast turnover. In sorghum, the accumulation of di- and polyamines was proportional to the strength of the osmotic stress and the impairment of polyamine synthesis was also observed at high degrees of stress. The present data support the idea that the initiation of polyamine accumulation needs an osmotic signal; however, when a permeable ion is present, salt accumulation can contribute to the osmotic adjustment and thus the onset of polyamine biosynthesis is delayed or does not take place. Some enzymes in the polyamine biosynthetic pathway may be sensitive for high salinity and the biosynthetic processes shift towards oxidative degradation.

Responses to osmotic and NaCl stress of wheat varieties differing in drought and salt tolerance in callus cultures

Abstract Callus cultures of four varieties of wheat ( Triticum aestivum L.) were maintained on media containing 0, 0.5 and 0.7 M mannitol as osmotic condition, and six varieties were grown on media containing 0, 0.1, 0.2 and 0.34 M NaCl as saline condition. To reveal genotype-dependent adaptive responses, growth, total N, total P, and changes in the internal Na + and K + concentrations were determined. Under osmotic stress, the calli derived from the drought tolerant varieties, Plainsman and Saberbeg showed less reduced growth as compared to the sensitive varieties, Cappelle Desprez and Chinese Spring. Furthermore, low levels of total N and P, and high initial intracellular K + concentration were recorded in the calli of the resistant varieties. In contrast, the sensitive varieties elicited increased N and P levels, as well as low initial intracellular K + concentrations. Under salinity at 0.1 M NaCl, Plainsman, Caribo and the salt tolerant Sakha-8 maintained their growth rate, while an inhibition was observed in Cappelle Desprez, Chinese Spring and Regina. Total N and P levels were similar to that under osmotic stress. Plainsman maintained low and constant levels, while a slight increase was recorded in the drought and the salt sensitive Regina. Cappelle Desprez and Regina excluded Na + , whereas the rest of the varieties accumulated it. Only Sakha-8 and Caribo elicited enhanced intracellular K + concentration with increasing salinity, while in the other varieties it remained unchanged or decreased. Patterns of changes in water status, as shown by the fresh weight to dry weight ratio, were also characteristic for the genotypes. It is concluded that the growth parameters, total N, P, and changes in Na + and K + concentrations can be considered as factors of adaptive value under osmotic and/or salt stress conditions. Results suggest that callus cultures may give genotype dependent responses under osmotic and salt stress conditions.

Dependence of wheat callus growth, differentiation and mineral content on carbohydrate supply

Abstract The effects of different carbon sources on the growth, differentiation and mineral content of wheat callus were investigated. Callus originating from immature embryos showed optimal growth produced the highest ratio of shoots when it was cultured on the medium containing 0.058 M sucrose. Higher carbohydrate concentrations reduced both shoot formation and growth. On the other hand, when sucrose concentration was less than 0.029 M neither differentiation nor greening was observed. Mannitol had a stimulating effect on shoot formation when the medium containing 0.029 M sucrose was supplemented by mannitol to get the final concentration of 0.058 M. The respiration rate increased along with increasing concentration of sucrose and glucose, and reached a maximum in the case of sucrose at the concentration of 0.263 M. On the addition of different concentrations of mannitol to a 0.058 M sucrose medium the respiration remained essentially unchanged. The mineral content of the tissue cultures also depended on the carbohydrate concentration. The water content decreased with increasing carbohydrate concentrations and among carbohydrates examined, sucrose was the most effective. The nitrogen and potassium contents of the calli reached their maximum values at 0.117 M–0.175 M carbohydrate content. The highest phosphorus contents were detected at 0.350 M–0.468 M carbohydrates. Phosphorus proved to be the most sensitive to osmotic changes.

Benzylaminopurine-induced coupling between calmodulin and Ca-ATPase in wheat root microsomal membranes

The properties of the Ca‐ATPase prepared from roots of wheat seedlings treated with benzylaminopurine were studied. The affinity of the ATPase towards Ca2+, plant or erythrocyte calmodulin increased after the hormonal treatment. It seems that in the membrane calmodulin‐bonding sites were induced by benzylaminopurine, contributing to an increased affinity of the ATPase. The lower Ca‐content of the hormone‐treated plants suggests that in vivo the Ca‐ATPase is involved in a Ca‐extrusion process.

Distribution of the Mo-enzymes aldehyde oxidase, xanthine dehydrogenase and nitrate reductase in maize (Zea mays L.) nodal roots as affected by nitrogen and salinity

The distribution of the Mo-enzymes aldehyde oxidase (AO; EC 1.2.3.1) xanthine dehydrogenase (XDH; EC 1.2.1.37) and nitrate reductase (NAD(P)H NR; EC 1.6.6.1-2) was studied along the longitudinal and transversal axes of maize (Zea mays L. cv. Jubily) nodal roots as affected by nitrogen sources and salinity. Activities of the Mo-enzymes were considerably enhanced under mild saline conditions. The activities of AO and XDH increased following addition of ammonium to the nutrient solution. Immunoblot analysis with antibodies raised against maize AO protein revealed increased levels of AO proteins in root tips of ammonium fed plants. Application of salinity to nitrate fed plants did not affect the enzyme protein level, although it enhanced the activity of the Mo-hydroxylases. The specific activities of the Mo-enzymes were the highest in root tips (0-1 cm segments) while on the transversal axis maximal activity was observed in the stele or vascular cylinder. Activity staining of AO after native PAGE of root extracts revealed four bands of AO proteins (AO1-4) capable of oxidizing a number of aliphatic and aromatic aldehydes. Increased AO activity in maize nodal roots grown with ammonium, and salinity were observed mainly at the AO3 and AO4 bands. Tips and stele contained primarily AO3 and AO4, and only traces of AO1 and AO2. SDS-PAGE of root extracts followed by Western blots revealed, besides the major 150 kD subunit of AO, two polypeptides with molecular masses of 72 and 85 kD located specifically in the cortex. Part of the polymorphism of AO in plant roots may be related to the allocation of distinct isoforms to different regions of the root, although the specific metabolic roles of the different bands have not been established.

Induction of soluble phosphatases under ionic and non-ionic osmotic stresses in wheat

Summary The effects of phosphorus deficiency, salt stress (NaCl) and non-ionic osmotic stresses (caused by mannitol or polyethylene glycol) were compared in plants and calli of wheat varieties differing in salt and drought tolerance. In calli, phosphorus deficiency induced a high increase in soluble acid phosphatase activity; under osmotic stress conditions a similar increase was found only in cells subjected to NaCl, while in cells grown in the presence of mannitol, phosphatase activity did not change. In wheat seedlings, phosphatase activity increased both in roots and shoots under phosphorus deficiency and, especially in the shoot, under salt and non-ionic osmotic stresses as well. Contrary to phosphorus deficient conditions, the induction of phosphatase activity under ionic and non-ionic osmotic stresses was not accompanied by a decrease in phosphorus content. These results suggest that the induction of acid phosphatase under osmotic and salt stresses may have a cause other than a low phosphate level. The Mg2+ activated alkaline phosphatase activity specific for the shoot decreased under all stress conditions.

Effects of excess UV-B irradiation on the antioxidant defence mechanisms in wheat (Triticum aestivum L) seedlings

Summary In the present experiments, changes in the antioxidant defence systems of wheat ( Triticum aestivum L. cv. Tiszataj) as affected by excess UV-B irradiation were investigated. Wheat seedlings were grown hydroponically in phytotrons for 11 days. In one of the phytotrons 2.5 Wm −2 excess UV-B irradiation was applied and samples were taken daily. Catalase, guaiacol peroxidase, superoxide dismutase (SOD) and glutathione reductase (GR) activities were measured and changes in the level of glutathione disulfide (GSSG) were determined by HPLC technique. It was found that catalase, guaiacol peroxidase and SOD activities decreased, while GSSG level and GR activity increased under excess UV-B irradiation. In plant responses, the alarm and adaptation phases were recognised. During the alarm reaction, inhibition of stem and leaf elongation, accumulation of flavonoid pigments, decreased antioxidant enzyme activities, increased GSSG level and triggering of GR activity were observed, while normalisation of growth, disappearance of stem pigmentation, levelling of antioxidant enzyme activities, high GR activity and decreased level of GSSG were found as parts of adaptation to UV-B irradiation. Afier 3 days of UV-B treatment, the activities of Ca 2+ -dependent protein kinases (52 and 65 kDa) increased, suggesting that they may participate in the UV-B signal transduction pathway.