Auxin autotrophic tobacco calli with modified aldehyde oxidase isoenzyme activities show enhanced abiotic stress tolerance

The growth, abiotic stress resistance and aldehyde oxidase (AO) activities of auxin autotrophic and heterotrophic tobacco calli were compared. The auxin-independent autotrophic calli maintained their growth rate even at 35°C temperatures, showed enhanced abiotic stress resistance in the presence of 50-300 mM NaCI, 0.1-5 mM KN02 or 0.1-10 mM H202. 0.1-5 mM H202 caused a higher increase in glutathione S-transferase (GST) and glutathione peroxidase (GPÖX) activities of heterotrophic calli, however these enzymes worked in an elevated level in autotrophic lines under control circumstances and were induced differently under oxidative stress, indicating an altered signalling mechanism. AO activity could be detected by activity staining after native PAGE with indole-3-acetaldehyde (lAAld) substrate in both calli, which means that the enzyme catalyzing the last step in IAA biosynthesis is present in both tissues. Contrary to heterotrophic calli, in the auxin autotrophic cultures an isoenzyme with low mobility (AOI) was detectable. 100 mM NaCI enhanced the AOI activity and a new isoenzyme (A02) was observed. The increase of the activities of these isoenzymes were higher in the autotrophic lines suggesting that the enhanced IAA biosynthesis can play a role in the recovery of growth under stress conditions

Effect of osmotic stress on antioxidant enzyme activities in transgenic wheat calli bearing MsALR gene

The antioxidant enzyme activities were studied in transgenic wheat calli bearing alfalfa MsALR gene. The effect of 14% PEG treatment was studied measuring the activities of some hydrogen peroxide related enzymes (SOD, CAT, POD) and the glutathione related GR, GST and GS-PX enzymes. Induction of the antioxidant enzymes is usually a complex process, one enzyme alone supposedly can not ensure enough protection under stress conditions. Our results showed that the changes of antioxidant enzyme activities are characteristic for the cultures. Some calli had higher activities of antioxidant enzymes than untransformed controls even in control circumstances. There are transgenic wheat calli with elevated SOD, CAT and/or POD activities, while in some other calli the activities of the glutathione related enzymes (GR, GS-PX) were increased comparing to the control

Starch to protein ratio and α-amylase activities in grains of different wheat cultivars

Starch and total protein contents, α-amylase activity of grains as well as falling number in the flour, an internationally accepted measure of α-amylase activity in the food industry, were compared in wheat (Triticum aestivum L.) genotypes which are widely used in the agriculture and breeding in Romania and Hungary. These cultivars were originated from Romania (20 cultivars), Hungary (cv. GK Élet, GK Öthalom and Mv Emese), France (cv. Cappelle Desprez), the USA (cv. Plainsman) and China (cv. Xiang). The starch contents of the grains were high in those cultivars, where the protein contents were relatively low. The highest starch content among the investigated wheat genotypes was found in the Romanian Gruia cultivar, which could be characterized also with low starch degrading α-amylase activity in the grain and with a high falling number. This wheat genotype can be a good candidate for utilization in starch industry. Other genotypes, which had relatively high starch contents and, a low α-amylase activity (or high falling number) were the Romanian Crina and Gloria, the Hungarian GK Öthalom, GK Élet, Mv Emese and the French Cappelle Desprez cultivars

Peroxidase activities in root segments of wheat genotypes under osmotic stress

One week old Triticum aestivum lines with different drought tolerance were subjected to polyethylene glycol (PEG 6000) treatment reaching 600 mOsm osmotic stress on the 13th day. Plant growth parameters, water status, soluble and cell wall-bound peroxidase (POD) activities were measured on the 15th day. While only small differences was found in the total peroxidase activities determined by either guaiacol or syringaldazine, the activities of some POD isoenzymes detected by benzidine substrate showed significant changes. The total density of soluble POD-containing fractions was higher in the drought stress tolerant Plainsman and Kobomugi cultivars due to osmotic stress than in controls. In Öthalom and Cappelle Desprez cultivars however, most of the soluble POD isoenzymes worked at lower level and only two isoenzymes showed enhanced activities after the PEG treatment. The changes of POD activities in the soluble fractions are in good correlation with the abiotic stress tolerance of wheat genotypes. The enzyme fraction bound covalently to cell wall showed a different isoenzyme pattern

Role of glutathione transferases in the improved acclimation to salt stress in salicylic acid-hardened tomato

Three weeks old Solanum lycopersicum L. cvar. Rio Fuego plants , which grew in hydroponic culture, were pre-treated with 10-7 M or 10-4 M salicylic acid (SA) and 100 mM NaCl was added to the nutrient solution from the 6th week. The activity of glutathione transferase (GST), glutathione peroxidase (GPOX) and dehydroascorbate reductase (DHAR) were analyzed spectrophotometrically after one week salt stress. All of these activities are connected to GST enzyme family, but the changes were different at the end of the pre-treatment or after the NaCl stress. SA enhanced the GPOX activity in the highest extent by the end of the three-week-period, while in glutathione transferase function there was no significant changes. The salt treatment mostly enhanced these enzyme activities but in the SA-pre-treated plants the GST and GPOX activities were elevated in a higher extent. In contrast to the lower SA concentration, pre-treatment with 10-4 M SA maintained the DHAR activities at the control level even in roots. Our results indicate that the increased antioxidant enzyme activities may be the part of the hardening effect of SA. GSTs can participate in the maintenance of the redox state of cells and improving the salt stress tolerance of tomato plants

Stress tolerance in auxin heterotrophic and autotrophic tobacco tissue cultures

The natures of the stress tolerance of auxin autotrophic and heterotrophic tobacco calli were compared. SO mM NaCI did not inhibit the growth of auxin autotrophic calli and they exhibited a lower level of peroxidase secretion into the media than that of heterotrophic cultures. The ascorbate peroxidase and catalase activities of these lines did not decrease in the presence of stressors. In the second half of the culturing period, the auxin autotrophic tissues expressed a higher GST activity than that of the heterotrophic lines

AtGSTU19 and AtGSTU24 as Moderators of the Response of Arabidopsis thaliana to Turnip mosaic virus

Plants produce glutathione as a response to the intercellular redox state. Glutathione actively participates in the reactive oxygen species (ROS)-dependent signaling pathway, especially under biotic stress conditions. Most of the glutathione S-transferases (GSTs) are induced in cells during the defense response of plants not only through highly specific glutathione-binding abilities but also by participating in the signaling function. The tau class of GSTs has been reported to be induced as a response under stress conditions. Although several studies have focused on the role of the tau class of GSTs in plant–pathogen interactions, knowledge about their contribution to the response to virus inoculation is still inadequate. Therefore, in this study, the response of Atgstu19 and Atgstu24 knockout mutants to mechanical inoculation of Turnip mosaic virus (TuMV) was examined. The systemic infection of TuMV was more dynamically promoted in Atgstu19 mutants than in wild-type (Col-0) plants, suggesting the role of GSTU19 in TuMV resistance. However, Atgstu24 mutants displayed virus limitation and downregulation of the relative expression of TuMV capsid protein, accompanied rarely by TuMV particles only in vacuoles, and ultrastructural analyses of inoculated leaves revealed the lack of virus cytoplasmic inclusions. These findings indicated that Atgstu24 mutants displayed a resistance-like reaction to TuMV, suggesting that GSTU24 may suppress the plant resistance. In addition, these findings confirmed that GSTU1 and GSTU24 are induced and contribute to the susceptible reaction to TuMV in the Atgstu19–TuMV interaction. However, the upregulation of GSTU19 and GSTU13 highly correlated with virus limitation in the resistance-like reaction in the Atgstu24–TuMV interaction. Furthermore, the highly dynamic upregulation of GST and glutathione reductase (GR) activities resulted in significant induction (between 1 and 14 days post inoculation [dpi]) of the total glutathione pool (GSH + GSSG) in response to TuMV, which was accompanied by the distribution of active glutathione in plant cells. On the contrary, in Atgstu19, which is susceptible to TuMV interaction, upregulation of GST and GR activity only up to 7 dpi symptom development was reported, which resulted in the induction of the total glutathione pool between 1 and 3 dpi. These observations indicated that GSTU19 and GSTU24 are important factors in modulating the response to TuMV in Arabidopsis thaliana. Moreover, it was clear that glutathione is an important component of the regulatory network in resistance and susceptible response of A. thaliana to TuMV. These results help achieve a better understanding of the mechanisms regulating the Arabidopsis–TuMV pathosystem

Plant Glutathione Peroxidases: Non-Heme Peroxidases with Large Functional Flexibility as a Core Component of ROS-Processing Mechanisms and Signalling

Glutathione peroxidases (GPXs) are non-heme peroxidases catalyzing the reduction of H2O2 or organic hydroperoxides to water or corresponding alcohols using glutathione (GSH) or thioredoxin (TRX) as a reducing agent. In contrast to animal GPXs, the plant enzymes are non-seleno monomeric proteins that generally utilize TRX more effectively than GSH but can be a putative link between the two main redox systems. Because of the substantial differences compared to non-plant GPXs, use of the GPX-like (GPXL) name was suggested for Arabidopsis enzymes. GPX(L)s not only can protect cells from stress-induced oxidative damages but are crucial components of plant development and growth. Due to fine-tuning the H2O2 metabolism and redox homeostasis, they are involved in the whole life cycle even under normal growth conditions. Significantly new mechanisms were discovered related to their transcriptional, post-transcriptional and post-translational modifications by describing gene regulatory networks, interacting microRNA families, or identifying Lys decrotonylation in enzyme activation. Their involvement in epigenetic mechanisms was evidenced. Detailed genetic, evolutionary, and bio-chemical characterization, and comparison of the main functions of GPXs, demonstrated their species-specific roles. The multisided involvement of GPX(L)s in the regulation of the entire plant life ensure that their significance will be more widely recognized and applied in the future