The effect of salicylic acid (SA) on Cd-induced stress was investigated in young maize (hybrid Norma) plants. When SA and Cd were applied simultaneously, the damage was less pronounced than without SA. However, SA treatment itself also caused oxidative stress and damage to the root system, and inhibited the phytochelatin synthase enzyme, so when the SA treatment was used before the Cd stress, it accelerated the damaging effect

Pál, Magda

English

Pál Magda

University of Szeged

Volume 46(3-4):119-120, 2002Acta Biologica Szegediensishttp://www.sci.u-szeged.hu/ABSAgricultural Research Institute of the Hungarian Academy of Sciences, Martonvásár, HungaryMagda Pál*, Gabriella Szalai, Eszter Horváth, Tibor Janda, Emil PáldiABSTRACT                            The effect of salicylic acid (SA) on Cd-induced stress was investigated in youngmaize (hybrid Norma) plants. When SA and Cd were applied simultaneously, the damage wasless pronounced than without SA. However, SA treatment itself also caused oxidative stressand damage to the root system, and inhibited the phytochelatin synthase enzyme, so whenthe SA treatment was used before the Cd stress, it accelerated the damaging effect.Acta Biol Szeged 46(3-4):119-120 (2002)KEY WORDScadmiumphytochelatinsalicylic acidZea mays*Corresponding author. E-mail: palmagda@mail.mgki.hu119Effect of salicylic acid during heavy metal stressProceedings of the 7th Hungarian Congress on Plant Physiology, 2002S2-P21Salicylic acid, which may act as a component of the signaltransduction system important in defence mechanismsagainst pathogen attack (Raskin 1992), may also provideprotection against certain abiotic stresses, as was shown forexample in the case of heat stress in mustard seedlings (Datet al. 1998) or chilling damage in maize (Janda et al. 1999).Cadmium is one of the most aggressive heavy metals andmay induce oxidative stress in plants (Hegedûs et al. 2001).The aim of the present study was to investigate the effect ofsalicylic acid treatment on cadmium stress, under the sameconditions where it was able to protect the plants againstchilling injury.Materials and MethodsSterilized seeds of maize (Zea mays L., hybrid Norma) wereallowed to germinate for 4 days at 26°C, and were thengrown for 10 days in Hoagland solution at 22/20°C with a16/8-h light/dark periodicity in a Conviron PGV-36 plantgrowth chamber with a relative humidity of 75 %. Thephotosynthetic photon flux density (PPFD) at leaf level was200 µmol m-2 s-1, provided by metal halide lamps. Some ofthe plants were treated with 0.5 mM Cd(NO3)2 for 1 day.Salicylic acid (0.5 mM) was added either 1d before ortogether with the Cd.The chlorophyll fluorescence from the youngest fullyexpanded leaves was determined under growth conditionsusing a pulse amplitude modulated fluorometer (PAM-2000,Walz, Effeltrich, Germany).The enzyme activities were measured as described byJanda et al. (2000).Measurement of root viability: 0.1 g root was incubatedin 1.5 ml 50 mM phosphate buffer pH 7.5 containing 0.8%triphenyltetrazolium chloride for 24 h. The roots were thentransferred into 3 ml ethanol and kept at 60°C for 30 min. Theabsorption of ethanol was then measured at 485 nm.The Cd content was measured according to Hegedûs etal. (2001).The phytochelatin synthase activity was measuredaccording to Chen et al. (1997).Results and DiscussionChl-a fluorescence inductionThe DF/Fm’ chlorophyll-a fluorescence induction parameter,which indicates the quantum efficiency of photosystem 2 (PS2) (Genty et al. 1989), was measured to detect the damagingeffect of the 0.5 mM Cd treatment (Fig. 1). After 1 d thisparameter decreased from 0.7 to 0.5 in Cd-treated plants.Treatment with 0.5 mM salicylic acid alone for 1d did notcause any significant change in DF/Fm’; however, after asecond day this too decreased the quantum efficiency of PS2. The most dramatic changes occurred when 1 d SA pre-treatment was followed by Cd treatment. When Cd and SAwere applied simultaneously, they had hardly any effect onthe DF/Fm’ parameter.Root viabilityRoot viability decreased drastically after 1 d of SA or Cdtreatment. However, when both SA and Cd were applied(either together, or consecutively), the decrease in rootviability was even more pronounced (data not shown).Cd contentAs expected, Cd accumulated mainly in the root. The Cdcontent was significantly lower in plants which were pre-treated with SA for 1 day before the Cd treatment or whenSA and Cd were applied together (data not shown).Antioxidant enzyme activitiesThe antioxidant enzyme activities in the root were hardlyaffected by 1 d of Cd treatment; only the decrease in guaiacolperoxidase (POD) activity was significant. Contrary to Cd,SA caused an increase in the POD activity of the roots.However, when Cd was added simultaneously with SA, itprevented any significant increase in POD activity. On theother hand, after pre-treatment with SA, the existing increasein POD activity was not affected by Cd. Ascorbate perox-idase (APX) activity was increased about two-fold by SA andthis increase did not change when SA pretreatment wasfollowed by 1 d of recovery or Cd treatment. However, whenSA and Cd were added at the same time, their effect was120synergistic, resulting in a threefold increase in activity.Glutathione reductase (GR) activity was increased to thesame extent by 1 d of SA or SA+Cd treatment, but droppedto almost the control level when SA treatment was followedby 1 d of recovery. However, when Cd was added after pre-treatment with SA, the GR activity remained at the same highlevel. The catalase activity in the root was very low and didnot exhibit a significant change upon treatment with Cd and/or SA (data not shown).The POD activity in the leaves was not affected by eitherof the treatments. In the case of catalase and APX only 1 dof SA treatment caused a significant decrease, and after 1 dof recovery the enzyme activities reached the control level.GR activity was increased by all the treatments to the sameextent, and this high activity was maintained after 1 d ofrecovery following the SA pre-treatment as well (data notshown).PhytochelatinsPhytochelatins (PCs) are enzymatically synthesized Cys-richpeptides, which are able to create chelates with heavy metalsto decrease their damaging effects (Grill et al. 1989). PCsform a family of structures with increasing repetitions of theg-Glu-Cys dipeptide followed by terminal Gly [(g-Glu-Cys)n-Gly], where n is generally in the range of 2 to 5. Thesubstrate for PC biosynthesis is GSH. The transpeptidationof the g-Glu-Cys moiety of GSH onto initially a second GSHto form PC2 is catalysed by PC synthase. The enzyme isactive only in the presence of metal ions. The activity wasdetected in the roots and stems of tomato plants (Chen et al.1997). The biosynthesis of PC is constitutive in nature (Grillet al. 1989).The phytochelatin (PC) levels increased in the roots after1 d of Cd treatment. The PC levels were hardly affected byother treatments. The PC synthase activity decreased in allcases compared to the control in the roots. Activities werelower in SA-pretreated plants than in treated ones both whenit was applied alone and when it was followed by 1 d of Cdtreatment. SA and Cd treatment together caused a greaterdecrease in the activity than the SA treatment or pre-treat-ment alone.There were no significant changes in the PC levels in theleaves during the various treatments. PC synthase activityincreased during the treatments, especially in the case of theSA+Cd treatment, compared to the control values. Thelowest activity occurred after the SA treatment.These results suggest that SA may inhibit Cd uptake, butmay also cause damage to the roots, including a decrease inthe phytochelatin synthase activity, so SA pre-treatment mayaccelerate the damaging effect of Cd.AcknowledgementsThe authors are gratefully indebted to Zsuzsa Kóti and EditKövesdi for their technical assistance. This work was sup-ported by grants from the Hungarian National ScientificResearch Foundation (OTKA T32653, T37195) and a J.Bólyai Scholarship, which are gratefully acknowledged.ReferencesChen J, Zhou J, Goldsbrough PB (1997) Characterization of phytochelatinsynthase from tomato. Physiol Plant 101:165-172.Dat JF, Lopez-Delgado H, Foyer CH, Scott IM (1998) Parallel changes inH2O2 and catalase during thermotolerance induced by salicylic acid orheat acclimation in mustard seedlings. Plant Physiol 116:1351-1357.Genty B, Briantais J-M, Baker NR (1989) The relationship between thequantum yield of photosynthetic electron transport and quenching ofchlorophyll fluorescence. Biochim Biophys Acta 990:87-92.Grill E, Loffler S, Winnacker E-L, Zenk MH (1989) Phytochelatins, theheavy-metal-binding peptides of plants, are synthesized fromglutathione by a specific g-glutamylcysteine dipeptidyl transpeptidase(phytochelatin synthase). Proc Natl Acad Sci USA 86:6838-6842.Hegedûs A, Erdei S, Horváth G (2001) Comparative studies of H2O2detoxifying enzymes in green and greening barley seedlings undercadmium stress. Plant Sci 160:1085-1093.Janda T, Szalai G. Antunovics Zs, Horváth E, Páldi E. (2000) Effect ofbenzoic acid and aspirin on chilling tolerance and photosynthesis inyoung maize plants. Maydica 45:29-33.Figure 1. Changes in the quantum yield of PS 2 after 1 day 0.5 mMCd treatment (1d Cd) or 1 day 0.5 mM salicylic acid treatment  (1dSA).Some of the plants received 1 d SA pre-treatment before the Cd(1dSA+Cd), or SA and Cd were applied simultaneously (1dSA-Cd). Inthe 1dSA+O plants the 1 d SA pre-treatment was not followed by Cdtreatment. (*** indicates a significant difference at the 0.001 levelcompared to control plants).Figure 2. Changes in the phytochelatin synthase activity in the rootof young maize plants treated with 0.5 mM salicylic acid and/or 0.5mM Cd. For an explanation of the symbols see Fig. 1. (*, **, ***indicate significant differences compared to control plants at the0.05, 0.01 and 0.001 levels, respectively.)

Effect of salicylic acid during heavy metal stress

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Effect of salicylic acid during heavy metal stress

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