Darkó, Éva

English

Darkó Éva

University of Szeged

Volume 46(3-4):87-88, 2002Acta Biologica Szegediensishttp://www.sci.u-szeged.hu/ABS1Department of Cell Biology and Plant Physiology, Agricultural Research Institute of the Hungarian Academy of Sciences,Martonvásár, Hungary, 2Department of Plant Physiology, Eszterházy College, Eger, HungaryÉva Darkó1*, Ferenc Bakos1, Éva Szakács1, Sándor Dulai2, Beáta Barnabás1*Corresponding author. E-mail: edarko@mail.mgki.hu87Long-term phytotoxic effects of aluminium on Al susceptible andAl-tolerant genotypes of wheat selected from microsporesProceedings of the 7th Hungarian Congress on Plant Physiology, 2002S2-P06Aluminium toxicity is considered to be the most importantfactor limiting plant growth and production in acid soils.Thus, the selection of Al-resistant crops via plant breedingor biotechnology is of agronomic importance (Kochian1995). Since Al tolerance is expressed in both the vegetativeand generative life cycle of plants (Seary and Mulcachy1990), unicellular microspores in anther culture are suitablefor the selection of Al-resistant wheat genotypes, as reportedby Kovacs et al. (1993). The spontaneous and induceddiploidisation of uninucleate microspores may enhance thepossibility of selecting aluminium-tolerant genotypes inhomozygotic form. The present work compares the physio-logical responses of DH2 lines of Al-sensitive and Al-tolerantwheat genotypes selected from microspores.Materials and MethodsThe experiments were performed on DH2 (second generationof fertile dihaploid) plants of Al-resistant and sensitivegenotypes of cv. Mv 16 wheat. The plants were grown inHoagland solution containing 300 µM AlCl3 at pH 4.0, withcontrol experiments at pH 5.2 and at pH 4.0 without Al. Ten-day old plants were used for the investigations. Hematoxylinstaining was carried out as decribed by Cancado et al. (1999).Morin staining was used for the detection of Al in plant tissueas described by Tice et al. (1992). Quenching analysis andCO2 fixation measurements were performed as described bySchoefs et al. (2001) and Darkó et al. (1996), respectively.Results and DiscussionThe first symptom of Al toxicity is reduced root growth(Kochian 1995). This reduction was evident in the sensitiveline but was limited in resistant genotypes of microspore-selected wheat (Table 1). This result was supported by theroot regrowth after hematoxylin staining (Table 1) Alumini-um accumulates especially in the apex region of root, asdetected by morin staining (Fig. 1D). The presence of Al wassignificantly reduced in the elongation zone of the root andcould not be observed in leaves (Fig. 1B,C). As presented inFigure 1D,E,F. Aluminium accumulation was significantlyhigher in Al-sensitive lines than in Al-resistant genotypes,suggesting an Al-exclusion mechanism operating in theresistant lines.The phytotoxic effects of Al treatment were reduced inthe shoot as indicated by the slight shoot growth inhibitionin sensitive line and by the lack of inhibition in resistantgenotypes.Table 1. Root length of 10-day-old Al-sensitive (S) and Al-tolerant (R1, R2) genotypes of wheat grown in Hoaglandsolution at pH 5.2 and at pH 4.0 with or without 300 µM AlCl3.Root regrowth after hematoxylin staining.S R1 R2Root length (cm) pH 5.2 9.2±1.1 9.6±1.4 10.2±1.2pH 4.0 8.4±1 9.4±1.1 10.5±1.4pH 4.0 Al 6.8±1 8.9±1.2 9.2±1.2Hem.test (mm/day) 4.12 ±0.4 7.55±0.5 8.5±0.6Table 2. Shoot growth of 10-day- old Al-sensitive (S) and Al-tolerant (R1, R2) genotypes of wheat grown in Hoagland solution atpH 5.2 and at pH 4.0 with or without 300 µM AlCl3. NPQ is the non-photochemical quenching parameter measured on leaves byquenching analysis at 600 mmol photon m-2s-1 light intensity. Amax is the maximal CO2 assimilation rate measured at saturated lightintensity. A (in dark) and O2 uptake reflects the CO2 evolution and O2 consumption in the dark.    S    R1    R2pH 5.2 pH 4.0 pH 4.0 Al pH 5.2 pH 4.0 pH 4.0 Al pH 5.2 pH 4.0 pH 4.0 AlShoot length 18.7 19.7 17.2 19.4 20.5 20.2 19.1 20.6 19.8(cm) ±1.2 ±1.4 ±1.1 ±1.3 ±1.4 ±1.5 ±1.2 ±1.3 ±1.2NPQ 0.662 0.840 1.45 0.0624 0.887 1.11 0.0615 0.820 1.05±0.06 ±0.07 ±0.10 ±0.06 ±0.08 ±0.09 ±0.06 ±0.075 ±0.09A max 7.8 5.9 3.2 7.2 5.9 5.4 8.8 8.2 7.3(µmol CO2/m2s) ±0.5 ±0.4 ±0.3 ±0.4 ±0.4 ±0.3 ±0.6 ±0.4 ±0.4A in dark -0.430 -0.489 -1.429 -0.245 -0.325 -1.09 -0.41 -0.468 -0.794(µmol CO2/m2s) ±0.05 ±0.05 ±0.07 ±0.03 ±0.035 ±0.075 ±0.04 ±0.05 ±0.4O2 uptake 1.12 1.42 1.84 1.18 1.22 1.15 1.04 1.11 0.98µmolO2/gr FW mn ±0.2 ±0.15 ±0.26 ±0.21 ±0.26 ±0.16 ±0.1 ±0.2 .±0.288Investigations were also made on the photosyntheticprocesses, which have a fundamental role in biomass produc-tion and thus in productivity, which is well-known to belimited under aluminium stress. No significant differenceswere found in the chlorophyll content of the leaves, in the PSII activity detected by the Fv/Fm, qP and DF/Fm’ parametersof the fluorescence quenching analysis, either between thegenotypes or between the different treatments (data notshown). These results suggest, that the photochemicalprocesses of PS II are not limited by aluminium stress.However, the non-photochemical processes, reflecting thedissipation mechanism of the excitation energy, were slightlyactivated when the plants are grown at low pH and stronglyactivated in the presence of Al (Table 2.). When comparingthe genotypes, this activation was found to be limited in theresistant lines. The photosynthetic capacity, measured as CO2fixation was also altered under stress conditions (at low pHwith and without Al). Besides a reduction in the maximalCO2 fixation rate measured at saturated light intensity (appr.1400 mmol m-2 s-1), increased CO2 evolution and O2 uptakeduring dark respiration were also observed (Table 2). Theseresults suggest an alteration in the ATP and NADPH/NADHmetabolisms under Al stress. Since Al accumulation in theleaves was not detectable, these effects must be indirect (Fig.1F).Figure 1. Determination of Al content by morin staining.The autofluorescence of morin without Al is low (A). A low amount of Al can be detected in the elongation and absorption zones of rootsbut Al was not detectable in leaves by morin (C). Al accumulates in root apex (approx. 3-4 mm zone of the root tip), especially in the Al-sensitive genotype (D). Lower accumulation can be detected in AL-resistant lines (E,F).AcknowledgmentsThis work was supported by OMFB Grant No. 00669/98 andby OTKA Grant No. M36361.ReferencesCancado GMA, Loguercio LL, Martins PR, Parentoni SN, Paiva E, BorémA, Lopes MA (1999) Hematoxylin staining as a phenotypic index foraluminium tolerance selection in tropical maize. TAG. 99:747-754.Darkó E, Váradi Gy, Dulai S, Lehoczki E (1996) Atrazine-resistant biotypesof Conyza canadensis have altered fluorescence quenching andxanthophyll cycle pattern. Plant Physiol Biochem 34:843-852.Kochian LV (1995) Cellular mechanisms of aluminium toxicity andresistance in plants. Annu Rev Plant Physiol Mol Biol 46:237-260.Kovács G, Karsai I, Bedô Z, Barnabas B (1993) effect of aluminium andlow pH on the callus induction and green plant regeneration in wheatanther culture. Növénytermelés. 42:399-408.Schoefs B, Darko E, Rodelmer S (2001) Photosynthetic pigments,photosynthesis and plastid ultrastructure in RbcS antisence DNAmutants of Tobacco. Z Naturforch. 26c:1067-1074.Seary KB, Mulcachy DL (1990) Comparison of the response to aluminiumtoxicity in gametophyte and sporophyte of four tomato varieties. TAG.80:289-295.Tice-KR, Parker-DR, DeMason-DA (1992) Operationally definedapoplastic and symplastic aluminum fractions in root tips of aluminum-intoxicated wheat. Plant-Physiol 100:309-318.FR +A1+A1SD+A1RE+A1+A1-A1A B CLeafElongation zone1 2

Long-term phytotoxic effects of aluminium on Al susceptible and Al-tolerant genotypes of wheat selected from microspores

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Long-term phytotoxic effects of aluminium on Al susceptible and Al-tolerant genotypes of wheat selected from microspores

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