It emerged recently that there is an inter-relationship between drought and ultraviolet-B (UV-B) radiation in plant responses, in that both stresses provoke an oxidative burst. The purpose of this investigation was to compare the effects and interaction of drought and UV-B in wheat and pea. The absence of changes in relative leaf water content (RWC) after UV-B treatments indicate that changes in water content were not involved. RWC was the main factor resulting in reduced growth in response to drought. Increases in anthocyanin and phenols were detected after exposure to UV-B. The increases do not appear to be of sufficient magnitude to act as a UV-B screen. UV-B application caused greater membrane damage than drought stress, as assessed by lipid peroxidation as well as osmolyte leakage. An increase in the specific activities of antioxidant enzymes was measured after UV-B alone as well as after application to droughted plants. Proline increased primarily in drought-stressed pea or wheat. Proline may be the drought-induced factor which has a protective role in response to UV-B. The physiological and biochemical parameters measured indicate the UV-B light has stronger stress effectors than drought on the growth of seedlings of both species. The two environmental stresses acted synergistically to induce protective mechanisms in that preapplication of either stress reduced the damage caused by subsequent application of the other stress.

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Drought is a major environmental constrain with a deleterious effect on plant development leading to a considerable reduction of crop productivity worldwide. Wheat is a relatively drought tolerant crop during the vegetative stage. The herbicide Serrate® (Syngenta) is a preparation containing two active chemical substances with different modes of action, which inhibit the biosynthesis of fatty and amino acids. It is commonly used as a systemic and selective chemical agent to control annual grass and broadleaf weeds in cereal crops and particularly in wheat, which is tolerant to Serrate®. Seventeen-day-old wheat seedlings (Triticum aestivum L., cv. Sadovo-1) grown as soil culture under controlled conditions were sprayed with an aqueous solution of Serrate®. Seventy-two hours later the plantlets were subjected to drought stress for seven days to reach a severe water deficit followed by four days of recovery with a normal irrigation regime. Oxidative stress markers, non-enzymatic, and enzymatic antioxidants were analyzed in the leaves of plants from the different treatment groups (herbicide-treated, droughts-stressed, and individuals which were consecutively subjected to both treatments) at 0, 96, and 168 h of drought stress, and after 96 h of recovery. Herbicide treatment did not alter substantially the phenotype and growth parameters of the above-ground plant parts. It provoked a moderate increase in phenolics, thiol-containing compounds, catalase, superoxide dismutase, glutathione reductase, and H2O2. However, significant variations of malondialdehyde, proline, and peroxidase activity caused by the sole application of the herbicide were not detected during the experimental period. Drought and herbicide + drought treatments caused significant growth inhibition, increased oxidative stress markers, and activation of enzymatic and non-enzymatic antioxidant defense reaching the highest levels at 168 h of stress. Plant growth was restored after 96 h of recovery and the levels of the monitored biochemical parameters showed a substantial decline. The herbicide provoked an extra load of oxidative stress-related biochemical components which did not aggravate the phenotypic and growth traits of plants subjected to drought, since they exhibited a good physiological status upon recovery.

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Todorova, D., Sergiev, I., Alexieva, V., Karanov, E., Smith, A., Hall, M. (2007) Polyamine content in Arabidopsis thaliana (L.) Heynh during recovery after low and high temperature treatments. Plant Growth Regulation, 51:3, 185-191. Keywords: Arabidopsis thaliana (L.) Heynh - Ethylene insensitive mutant (eti5) - High temperature - Low temperature - Polyamines - Putrescine - Spermidine - Spermine Sponsorship: INCO-COPERNICUS Programme ERBIC15CT960914Comparative studies on the effect of temperature treatment on the endogenous polyamine content in wild type and the ethylene insensitive mutant eti5 of Arabidopsis thaliana (L.) Heynh were performed. The levels of free and conjugated putrescine, spermidine and spermine were measured in rosette leaves of 38-day-old plants subjected to low and high temperature for 24 h in darkness. Data for fractions measured in treated wild type plants during recovery suggest that alterations in polyamine levels may be a consequence of the conversion of the supernatant-bound into free form and vice versa, while in treated eti5 plants de novo synthesis of spermidine and spermine could not be excluded. It was found that high temperature provoked more significant changes in polyamine levels than low temperature. The results suggest that the eti5 mutant showed a better ability to recover after the temperature treatments than wild type partly as a consequence of changes in polyamine content.Peer reviewe

The effects of high temperature and the polyamine spermine on the physiological and biochemical status of garden pea plants were investigated. The plants were preliminary treated with 1 mM spermine and 24 h later were subjected for 48 h to conditions with daily temperature up to 38°C. High temperature stress caused more than 20% decrease of leaf pigments content and significant suppression of net photosynthesis rate. An enhanced level of lipid peroxidation was observed in leaves suggesting that oxidative stress occurred. A decrease in the content of free proline, total phenolics, and hydrogen peroxide accompanied by an increase of the activity of catalase, superoxide dismutase, and guaiacol peroxidase was established in plants subjected to high temperature. The harmful physiological effects of high temperature were alleviated by spraying the plants with spermine. The preliminary application of spermine retarded leaf pigment loss and maintained photosynthetic rate and antioxidant enzyme activities, as well as content of non-enzymatic antioxidants.

The effects of exogenously applied hydrogen peroxide on the antioxidant system of pea plants were investigated. Ten-day-old pea seedlings were sprayed with 2.5 mM H 2 O 2 and 24 h later with 0.2 mM PQ. Samples were taken 0, 2 and 5 h after the start of illumination. The protective effect of H 2 O 2 was evaluated by monitoring of parameters related to the damage caused by PQ. The treatment with PQ led to a severe leakage of electrolytes from leaf tissues. Malondialdehyde level increased in PQ treated plants, but remained unchanged in H 2 O 2 pretreated ones after 5 h of illumination. Increased catalase and glutathione-S-transferase activity was observed in pea plants treated with H 2 O 2 and PQ. Ascorbate peroxidase activity decreased significantly after paraquat application, but pre-treatment with H 2 O 2 prevented ascorbate peroxidase inhibition to some extent. Increased guaiacol peroxidase activity was detected after H 2 O 2 application. PQ application caused a drastic decline in the levels of thiol-group bearing compounds, reduced glutathione and ascorbate, while the quantity of oxidized glutathione and dehydroascorbate were increased. The results presented on changes in enzymatic and nonenzymatic antioxidants suggest that preliminary H 2 O 2 application to pea plants treated with PQ, alleviates the toxic effects of the herbicide.

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