RESPONSE OF MAIZE TO FIELD DROUGHT STRESS: OXIDATIVE DEFENSE SYSTEM, OSMOLYTES ACCUMULATION AND PHOTOSYNTHETIC PIGMENTS

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1 Pk. J. Bot., 51(3): , 219. DOI: /PJB219-3(1) RESPONSE OF MAIZE TO FIELD DROUGHT STRESS: OXIDATIVE DEFENSE SYSTEM, OSMOLYTES ACCUMULATION AND PHOTOSYNTHETIC PIGMENTS SAJJAD MOHARRAMNEJAD 1, OMID SOFALIAN 1*, MOSTAFA VALIZADEH 2, ALI ASGHARI 1, MOHAMMAD REZA SHIRI 3 AND MUHAMMAD ASHRAF 4 1 Deprtment of Agronomy n Plnt Breeing, Fulty of Agriulture n Nturl Resoures, University of Mohghegh Arili, Aril, Irn 2 Deprtment of Plnt Breeing n Biotehnology, Fulty of Agriulture Sienes, University of Triz, Triz, Irn 3 See n Plnt Improvement Institute, Agriulturl Reserh Eution n Extension Orgniztion (AREEO), Krj, Irn 4 Institute of Moleulr Biology n Biotehnology, The University of Lhore, Lhore, Pkistn *Corresponing uthor s emil: soflin@gmil.om Astrt The stuy ws performe to etermine s to whether ntioxint potentil (enzymti n non-enzymti ntioxints) s well s some other ttriutes oul e use s potentil rought resistne mrkers in two mize lines (B 73 n MO 17 ). Uner wter efiit onitions, growth trits, reltive wter ontent (RWC), hlorophyll, totl hlorophyll n rotenois s well s grin yiel erese signifintly in oth lines ompre to those uner ontrol onitions. In ontrst, wter efiit use signifint inrese in the tivities of superoxie ismutse (SOD) n tlse (CAT) isozymes s well s levels of glyine etine (GB), proline n mlonilehye (MDA), wheres totl phenolis, totl solule protein, H 2 O 2, hlorophyll, hlorophyll / rtio, nthoynin n peroxise (POX) isozyme tivity remine unffete in oth mize lines. Although wter efiit stress inue oxitive stress in oth mize lines, the enzymti n non-enzymti ntioxints n key orgni osmolytes inrese signifintly in oth mize lines. For exmple, SOD isozyme tivities, n GB n proline ontents were onsierly greter in reltively rought resistnt MO 17 thn those in reltively rought sensitive B 73. However, in ontrst, CAT tivity ws higher in B 73. Overll, SOD isozyme tivities, n GB n proline ontents were foun to e potentil iohemil initors of rought resistne in the two mize lines use in the present stuy. Key wors: Antioxint, Chlorophyll, Glyine etine,, Proline, Wter efiit. Introution Drought stress n pose verse effets on growth, evelopment n yiel output of severl rops, n it is known to e the most mging to rops ompre to other ioti stresses (Ashrf, 21; Ho et l., 211). However, plnts employ myri of strtegies thrive uner wter efiit onitions. For exmple, uner rought stress, most plnts respon y synthesizing/ umulting vriety of orgni osmolytes. Of vrious orgni osmolytes, proline n GB ommonly umulte in plnts sujete to rought stress s well s other stresses. However, their efinite roles in plnt stress resistne remin etle, ut oth hve een onsiere enefiil for mintining the stility of enzymes n memrnes uner stress onitions (Ashrf & Fool, 27). However, mny reports hve shown onsierle intertion etween GB n proline umultion n rop stress resistne (Suro et l., 21; Hsu et l., 23). Wter efiit stress lso poses onsierle verse effet on plnt photosynthesis euse in most plnts the ontents of key photosyntheti pigments erese mrkely therey resulting in reue rte of CO 2 ssimiltion (Cielnik et l., 26; Cruz e Crvlho, 28; Gill & Tutej, 21; Zltev & Lion, 212; Ashrf & Hrris, 213). Furthermore, rought stress genertes high umultion of retive oxygen speies whih my mge the iologil memrnes (Ashrf, 21). For exmple, ifferent types of ellulr ROS [superoxie ril (O 2 - ), hyrogen peroxie (H 2 O 2 ), singlet oxygen ( O 2 ), n the hyroxyl ril (OH)] re frequently generte in ells uner rought stress (Ashrf, 21). All these oxints n pertur vriety of iohemil retions y isrupting numer of metolites (Mittler, 22). However, to ountert the exess proution/ umultion of ROS, most plnts hve the ility to generte ntioxints, enzymti n nonenzymti. The most promising enzymti ntioxints re peroxise (POX), superoxie ismutse (SOD), n tlse (CAT). Some of the key non-enzymti ntioxints inlue rotenois, polyphenols, glutthione, sorte, toopherols, nthoynins, et. whih n esily svenge O 2 n OH. It is elieve tht lines/ultivrs iffering in stress tolerne n synthesize/umulte the ntioxints ifferently. For exmple, Ashrf (21) reporte tht mlonilehye (MDA) n H 2 O 2 ontents were higher in the leves of sensitive genotype of mize thn those in tolernt ones uner rought stress. Mny reports inite tht rought stress inues MDA ontent in leves n roots (Cruz e Crvlho, 28). Drought stress enhne the MDA n H 2 O 2 ontents in leves of mize lines (Chugh et l., 211). An inrese in ontent of MDA uner rought stress hs een reporte in leves of thought sensitive mize line t seeling stge, wheres no hnge is oserve intolernt lines (Azooz et l., 29). In view of numer of reports ntioxint response is orrelte with tolerne of iniviul rop ultivrs to ioti stresses inluing rought stress (Athr et l., 28; Kolrovi et l., 29). For exmple, ehyrtion uring pre- n post-flowering stges of mize rop inrese the tivity of vrious ntioxint enzymes (Azooz et l., 29). In nother stuy, positive orreltion etween mize oil qulities, phenoli ontents n rotenoi levels hve een oserve uner wter efiit onitions (Ali et l., 21). The present stuy ws performe with hypothesis tht wter efiit-inue hnge in ntioxint system oul ffet yiel n

2 8 SAJJAD MOHARRAMNEJAD ET AL., growth of mize plnts grown uner rought onitions. Therefore, the present stuy ws performe to evlute the effet of wter efiit stress on plnt growth, plnt height n grin yiel of mize. In ition, it ws exmine s to whether RWC, photosyntheti pigments, GB n proline ontents, enzymti tivities (SOD, POX n CAT) n non-enzymti ntioxint ontents in two well-known lines of mize (B 73 n MO 17 ) were influene ue to rought stress n whih of them oul e use s initors of rought tolerne in mize. Mterils n Methos Plnt mterils n fiel experiments: A fiel tril ws rrie out, uring two pproprite growing sesons ( ) t the Reserh Sttion of University of Triz. The experiment ws performe in rnomize omplete lok esign with two ftors: two mize inre lines (B 73 n MO 17 ), n two wter efiit onitions (one with ommonly ville irrigtion wter referre to s ontrol n the other interrupte irrigtion uring 27 ys efore flowering). The mize sees were plnte on My 3, 214, n April 25, 215. The experimentl plots inlue two rows of 3 m long n.75 m wie. The soil t the experimentl site ws sny-lom (sn 49.8%, ly 18.5%). The soil properties were etermine efore plnting following Crter & Gregorih (28) n presente in Tle 1. The fertiliztion ws one 25 ys fter plnting y ing 6 kg h -1 ure. The grin yiel per plnt, plnt height, plnt ry weight, numer of leves n stem imeter were evlute. Physiologil trits: The lef wter ontent (RWC) ws estimte following the grvimetri metho s esrie y Chen et l., (212). The pigments suh s nthoynins, hlorophyll, n rotenois were nlyze using 2 mg of fresh lef smple in pestle n mortr ontining liqui N, n t the power stge, preoole extrtion solvent [2. ml etone (85%) n Tris stok uffer (15%), ph 8.] were e. The mixture ws entrifuge t 12, g for 3 min n the optil ensity of the superntnts ws mesure t 537, 663, 647 n 47 nm using spetrophotometer (Yryur et l., 29). Biohemil trits: Glyine etine ws etermine using the protool esrie y Grieve & Grttn (1983). To smple of 5 mg fresh leves, 5 ml otoluene (.5%) were e. All tues ontining the lef smples were shken on n eletril shker t 25 C for one y. Then n liquot (1 ml) fter filtrtion ws mixe with 1 ml of 2 N HCl, therefter.1 ml of KI 3 solution ws e n vortexe in n ie ol wter th for one hour. An ie-oole wter (2 ml) n 1 ml of hille 1, 2 ihloroethne were e to eh tue. Two lyers of the mixture ppere when n ir strem ws psse for 1-2 min. The OD of the lower lyer (orgni) ws reore t 365 nm. Proline ontent of fresh leves ws mesure using the proeure esrie y Btes et l., (1973). Smples of the lef (eh 5 mg) were groun in 3% (w/v) sulfosliyli i, n entrifuge (4 g) for 1 min t 4 C. The superntnt so resulte ws trete with glil eti i n i ninhyrin. By treting the mixture with toluene the ODs of ll smples were reore t 52 nm. The levels of hyrogen peroxie (H 2 O 2 ) were reore following the proeure reporte y Velikov et l., (2) using.1% (w/v) TCA, 1 mm potssium phosphte (ph 7.) uffer n 1 ml (1 M) KI. The optil ensity of the superntnt ws note t 39 nm. The level of lef lipi peroxition ws mesure following Ckmk & Horst (1991). For etermining totl phenolis, lef tissue (.5 g) ws groun well in 8% etone n sujete to entrifugtion t 1, g for 1 min. To n liquot of 1 µl of the superntnt, 2 ml of wter n 1 ml of Folin Ciolteu s phenol regent were e n shken vigorously. Therefter, 5 ml of 2% soium ronte solution were e n the volume ws rise to 1 ml y ing istille wter. The sorne of ll trete smples ws re t 75 nm (Noreen & Ashrf, 29). Antioxint enzymes n eletrophoresis: The rue extrts of fresh leves were prepre in tris-hcl extrtion uffer (Tris 5 mm, ph 7.5, sori i (5 mm), surose 5%, soium metisulfite (2 mm), PEG (2%) n 2- merptoethnol (.1%) efore use (Vlizeh et l., 213), with rtio of.5 mg μl -1 (1W: 2V) n entrifuge t 4 C n 1, g for 1 min using smll Eppenorf tues. The enzyme extrts were immeitely sore on filter pper n loe onto 7.5% horizontl sl polyrylmie gels ( m) using the TBE (Tris-Borte-EDTA) eletroe uffer (ph = 8.8). Eletrophoresis ws rrie out t 4 C for 3 h. Three enzymti systems were nlyze in this stuy. Two slies prepre from the sl gels were stine fter eletrophoresis for enzyme tivities. The stining protool for superoxie ismutse (SOD) ws performe oring to Soltis & Soltis (199), peroxise (POX) n tlse (CAT) oring to Olson & Vrner (1993). The stine gels were fixe n snne t suitle stte. The protein ontent of the enzyme extrts ws etermine following Brfor (1976). An imge nlysis MCID softwre ws use to mesure optil ensity re for eh isozyme tivity. Sttistil nlysis The tril ws onute in rnomize omplete lok esign with two ftor ftoril rrngement n three replites. Anlysis of vrine n signifint ifferenes mong the tretment mens were lulte y the lest-signifint-ifferene (LSD) test t p<.5 level. ph CCE (%) OM (%) N Tle 1. Chemil properties of the soil use. K P Fe Mn Cu Zn CCE: Clium ronte equivlent, OM: Orgni mtter

3 Dry weight (g) Lef numer/plnt Stem imeter (mm) Grin yiel (g) Plnt height (m) RESPONSE OF MAIZE TO DROUGHT STRESS Fig. 1. Effets of wter efiit on the grin yiel per plnt of mize lines. The t re the verges of vlues oserve uring the two fiel experiments in 214 n 215. Mens with the sme letter re not signifintly ifferent y the lest signifint ifferene (LSD) t p<.5. Results Wter efiit Wter efiit impose in this stuy le to hnges in grin yiel n growth trits in the two mize lines (Figs. 1 n 2, n Tle 2). The verge grin yiels over the two yers were 35.4 n 62.9 g plnt -1 for B 73 n MO 17, respetively, uner ontrol irrigtion. Wter efiit stress use signifint erese in grin yiel in oth lines. This erese ws 67% n 47% for B 73 n MO 17, respetively. Thus, MO 17 oul e onsiere s rought resistnt n B 73 s rought sensitive to wter efiit (Fig. 1). Plnt height ws lso reue mrkely in oth mize lines uner wter efiit onitions (Fig. 2). This erese ws 46% for B 73 n 4% for MO 17. Plnt ry weight ws lso mrkely erese in oth mize lines uner wter efiit onitions (Fig. 2). This erese ws 25% for B 73 n 33% for MO 17. Wter efiit stress reue RWC in oth inre lines when ompre with the ontrol onitions (Fig. 3). The reution in lef RWC ws higher in B 73 (27%) thn tht in MO 17 (14.5%). Lef pigment ontents from oth ontrol n stress onitions of the two mize lines re presente in Tle 3. The B 73 n MO 17 lines i not show signifint ifferenes in pigment ontent uner ontrol onitions exept for rotenoi ontent. Wter efiit stress use mrke reution in hlorophyll, totl hlorophyll n rotenois in oth mize lines, ut this erese ws signifintly higher in MO 17 thn tht in B 73. These reutions were pproximtely 4, 22 n 23 perent for rotenois, totl hlorophyll n hlorophyll, respetively. The lef hlorophyll, hlorophyll / rtio n nthoynins in oth mize lines were not signifintly hnge uner wter efiit stress ompre to those ontrol onitions. Glyine etine (GB) n proline onentrtions in the two mize lines were inrese uring wter efiit (Tle 4). The onentrtions of GB n proline were signifintly higher in line MO 17 thn those in B 73. Totl solule protein ontent ws not signifintly hnge in oth lines uner wter stress (Tle 4). Drought stress h n opposite effet on totl phenolis in oth mize lines. The totl phenoli ontent ws inrese in B 73 (3.6%), wheres it ws erese in MO 17 (6%). H 2 O 2 ontent in oth mize lines ws not signifintly hnge uner wter efiit stress ompre to tht uner ontrol onitions (Tle 4). MDA ontent ws inrese in oth mize lines uner rought stress, ut it ws muh higher in B 73 thn tht in the other line (Tle 4) Wter efiit Fig. 2. Effets of wter efiit on the plnt height, stem imeter, lef numer n ry weight of two mize lines (B 73 n MO 17 ). The t re the verges of vlues oserve uring the two fiel experiments in 214 n 215. Mens with the sme letters re not signifintly ifferent y the lest signifint ifferene (LSD) t p<.5. Wter efiit Wter efiit Wter efiit

4 82 SAJJAD MOHARRAMNEJAD ET AL., Tle 2. P-vlues of ANOVA nlysis of gronomil, physiologil n iohemil trits of mize inre lines uner fiel onition over two yers. Trit Min-ftor effets Intertion effets M W M W Grin yiel <.1 <.1 <.1 Plnt height <.45 <.1 <.1 Stem imeter <.825 <.72 <.842 Leves numer <.315 <.2 <.565 Dry weight <.1 <.1 <.1 RWC <.425 <.32 <.21 Chlorophyll <.42 <.19 <.1 Chlorophyll <.521 <.19 <.215 Totl hlorophyll <.1 <.32 <.222 Chlorophyll / rtio <.521 <.28 <.325 Anthoynin <.61 <.52 <.347 Crotenoi <.1 <.1 <.1 Totl phenolis <.72 <.32 <.692 Totl solule protein <.752 <.285 <.514 Glyine etine <.1 <.1 <.1 Proline <.1 <.1 <.1 MDA <.1 <.1 <.1 H 2 O 2 <.525 <.5 <.625 SOD 1 <.1 <.1 <.1 SOD 2 <.1 <.1 <.1 SOD 3 <.1 <.1 <.1 POX 1 <.1 <.52 <.1 POX 2 <.41 <.219 <.321 POX 3 <.35 <.56 <.12 CAT <.1 <.1 <.1 M : Effet of mize inre lines; W : Effet of wter efiit onitions; M W: Intertion effets Tle 3. Effets of wter efiit stress on pigment ontents (±S.E; n=6) in B 73 n MO 17 lines uner fiel onition over two yers. line B 73 MO 17 Wter efiit Wter efiit Pigment ontents (μmol/g fresh weight) Chlorophyll.19 ±.1.15 ±.1.18 ±.2.1 ±.3 Chlorophyll.5 ±.1.5 ±.2.5 ±.1.4 ±.1 Totl hlorophyll.24 ±.1.2 ±.2.23 ±.1.14 ±.2 Chlorophyll / rtio 3.8 ± ± ± ± 1.25 Anthoynin.64 ± ±.2.66 ± ±.22 Crotenoi.11 ±.1.9 ±.1.9 ±.1.7 ±.1 Mens with the sme smll letters were not signifintly ifferent from the lest signifint ifferene (LSD) t p<.5. Tle 4. Antioxints n other iohemil stress mrkers (±S.E; n=6) in two mize lines (B 73 n MO 17 ) uner fiel in ontrol n wter efiit onitions. line Trit B 73 MO 17 Wter efiit Wter efiit Totl phenolis (mg/g fresh weight) 2.327± ± ± ±.322 Totl solule protein (mg/g fresh weight).938± ± ±.47.87±.1 Glyine etine (μmol/g ry weight).666±.1.761±.16.7± ±.23 Proline (μmol/g fresh weight) 3.8± ± ± ±.4 MDA (nmol/g fresh weight) 2.19± ± ± ±.13 H 2 O 2 (μmol/g fresh weight) 1.949±.2.955± ± ±.7 Mlonilehye (MDA); Hyrogen peroxie (H 2 O 2 ). Mens with the sme smll letters were not signifintly ifferent from the lest signifint ifferene (LSD) t p<.5

5 Reltive wter ontent (%) RESPONSE OF MAIZE TO DROUGHT STRESS Fig. 3. Lef reltive wter ontent (RWC) in oth mize lines uner ontrol n wter efiit onitions. The t re the verges of vlues uring the two fiel experiments in 214 n 215. Mens with the sme letter re not signifintly ifferent y the lest signifint ifferene (LSD) t p<.5. Apprisl of ntioxint enzyme tivities in the leves of two mize lines uner ontrol n wter efiit onitions ws se on stining onto the sme gels, whih showe signifint inrese in SOD n CAT ntioxint isoforms in wter efiit onition ompre to those uner ontrol. But this ws not true for the POX isozymes (Figs. 4 n 5). For SOD, POX n CAT, three, two n one isoforms were oserve, respetively (Fig. 4 A, B n C). The ntioxint tivity of the three SOD isozymes ws exhiite minly y SOD 2 in MO 17 mize line uner wter stress (Fig. 5). Wter efiit stress inue hnges in POX 1 n POX 3 were non-signifint, ut POX 2 inrese to slight extent in MO 17, ut no suh signifint hnge ws oserve in B 73 line ompre with tht uner ontrol onitions (Fig. 5). Wter efiit stress signifintly inrese the CAT tivity in oth mize lines. The CAT tivity ws higher in B 73 thn tht in line MO 17 uner wter efiit stress (Fig. 5). The pplie wter efiit stress enhne SOD n CAT tivities out 32 n 76 perent, respetively. Wter efiit A multiple regression nlysis on grin yiel of mize lines ws employe uner wter stress onitions. This nlysis showe tht grin yiel reution in ifferent mize inre lines ws interrelte with SOD isozyme tivities, n GB n proline ontents (Tle 5). Tle 5. Multiple regression nlysis showing the epenene of grin yiel in per plnt on plnt growth, reltive wter ontent (RWC), pigment ontents n iohemil ttriutes of oth mize inre lines uner wter efiit in fiel onitions (R 2 =.89). Vrile Coeffiient Interept -.2 ns Plnt height.5 ns Stem imeter.112 ns Leves numer.82 ns Dry weight.211 ns RWC -.46 ns Chlorophyll -.9 ns Chlorophyll -.5 ns Totl hlorophyll -.11 ns Chlorophyll / rtio.15 ns Anthoynin -.5 ns Crotenoi -.6 ns Totl phenolis.12 ns Totl solule protein -.18 ns Glyine etine.445 * Proline.69 * MDA.5 ns H 2 O 2.3 ns SOD * SOD * SOD ** POX ns POX ns POX ns CAT -.8 ns Reltive wter ontent (RWC); Mlonilehye (MDA); Hyrogen peroxie (H 2 O 2 ); Isoforms of superoxie ismutse (SODs); Isoforms of peroxise (POXs); Ctlse (CAT) ns, *, **: non-signifint n signifint ifferenes t 5 n 1% proility, respetively Fig. 4. (A) Bning pttern of superoxie ismutse (SOD), (B) peroxise (POX), n (C) tlse (CAT) in ontrol n wter efiit stress uner fiel onitions in B 73 n MO 17 lines.

6 CAT (Dnsitometri tivity) SOD3 (Dnsitometri tivity) POX3 (Dnsitometri tivity) SOD2 (Dnsitometri tivity) POX2 (Dnsitometri tivity) SOD1 (Dnsitometri tivity) POX1 (Dnsitometri tivity) 84 SAJJAD MOHARRAMNEJAD ET AL., Wter efiit Wter efiit Wter efiit Wter efiit Wter efiit Wter efiit Fig. 5. Men tivities of superoxie ismutse (SODs), peroxise (POXs), n tlse (CAT) isoforms of B 73 n MO 17 lines uner file ontrol n wter efiit onitions. Mens with the sme letter re not signifintly ifferent from the lest signifint ifferene (LSD) t p<.5. Wter efiit

7 RESPONSE OF MAIZE TO DROUGHT STRESS 85 Disussion Perent inhiition in grin yiel uner wter stress inite tht line MO 17 ws reltively rnke s rought resistnt n B 73 s rought sensitive to wter efiit (Fig. 1A). Reution in grin yiel n plnt growth in the two mize liens use y wter stress oul e ttriute to some key physio-iohemil proesses regulting plnt growth (Chugh et l., 211), e.g., hnge in photosynthesis, nutrient uptke/umultion, osmolyte umultion, enzyme tivities, et. Chnges in ll these proesses re elieve to ffet rop growth (Anjum et l., 211; Mohrrmnej et l., 215). In some other stuies with mize, rought stress hs een foun to e etrimentl for rop growth n yiel. For exmple, Cmpos et l., (26) foun 45-6% yiel reution in mize when rought ws impose t the silk emergene stge. In similr stuy, Ckir (24) reporte mrke erese in grin yiel n plnt height in mize when it ws sujete to short-term rought. In nother stuy on mize plnts, wter efiit onitions signifintly isrupte plnt height, lef numer plnt -1, totl lef re plnt -1, shoot ry weight plnt -1, root ry weight plnt -1, numer of grins plnt -1, n grin yiel plnt -1 (Tlt et l., 215). Plnts, for their survivl uner wter efiit onitions, ten to retin resonle mount of wter so s to ensure the norml funtioning of ll ellulr metoli proesses. It is generlly elieve tht RWC ereses in most plnts in response to wter efiit stress (Shw et l., 22; Bürling et l., 213). Our results lso show tht, RWC ws erese in the two mize lines in response to rought stress, lthough the erese in RWC ws muh slower in line MO 17 thn tht in B 73 (Fig. 3). These oservtions re similr to those of Yn et l., (216). Wter shortge is known to inhiit photosynthesis y mging the photosyntheti pprtus (Nyyr & Gupt 26). In this experiment, wter stress use signifint erese in hlorophyll ontent in oth mize lines. Anlogous to these finings, in n erlier stuy, reution in hlorophyll pigments ws reporte in mize plnts sujete to progressive rought stress (Anjum et l., 211). Plnt iomss proution ws ffete iretly y the hlorophyll pigments reution in stresse plnts. Drese in photosyntheti pigments my le to less utiliztion of energy n ron emn for hlorophyll synthesis (Zhng et l., 212; Zltev & Lion, 212). Some pigments n e funtion s essory pigments in photosynthesis, lthough their onentrtion oul lso e eline s prt of plnt response (Silv et l., 21; Zhng et l., 212; Mohrrmnej et l., 215). Among vrious seonry metolites, solule phenolis re elieve tht they hve n importnt role in plnts expose to ioti stresses (Ruiz & Romero, 21). For exmple, inrese synthesis/umultion of solule phenolis ws reporte to e importntly orrelte with the het n slt tolerne in sugrne (Whi & Ghznfr, 26). In ontrst to our stuy, wter efiit stress use higher erese in totl phenolis in the rought resistnt mize line MO 17 thn tht in the rought sensitive one, showing negtive reltionship etween rought resistne n umultion of totl phenolis in mize plnts. Lef phenoli ompouns on the R 5 growth of penut genotypes grown t fiel pity or terminl rought were not signifintly ifferent t ifferent stges in two yers (Aninon et l., 216). In nother stuy, rought reue polyphenols in ll otton genotypes irrespetive of their egree of rought resistne (Yiliz- Akts et l., 29; Ali et l., 21). Glyine etine (GB) n proline onentrtions in stresse plnts n resist memrne integrity, my erese lipi memrne oxition, protetion n stilize ROS svenging enzymes, n tke prt in stilizing su-ellulr strutures, svenging free rils, n uffering ellulr reox potentil (Tun et l., 27; Ashrf & Fool, 27). In the present stuy, umultion of GB n proline ourre in oth mize lines expose to wter efiit onitions. These osmolytes re elieve to ply vitl role in ellulr osmoti justment (Kvi Kishore et l., 25; Mohrrmnej et l., 215; Tlt et l., 215). In our stuy, higher levels of GB n proline in oth lines might hve een involve in osmoregultion, whih in turn my llow itionl wter to e tken up y the mize plnts from the growth meium therey ounterting the verse effets of rought stress on plnt metolism (Kumr et l., 23). Wter efiit inue, inrese in GB n proline umultions in mize plnts n might e prt of mehnism whih prevents wter loss in plnts through osmoti justment (Tlt et l., 215). In our stuy, lipi peroxition mesure s the mount of MDA in mize leves iffere etween the two lines. However, uner wter efiit stress in line MO 17, MDA ontent ws lower thn tht in B 73 (Tle 4). In nother stuy with mize, n inrese ws oserve in MDA ontent in rought sensitive genotype t the seelings stge, wheres no hnge ws oserve in tolernt genotype (Mouss & Ael-Aziz 28; Mohrrmnej et l., 215). Furthermore, MDA onentrtion ws inrese signifintly in mize plnts uner wter efiit stress, n ws well orrelte with H 2 O 2 levels (Tlt et l., 215). Inrese SOD n CAT tivities my effiiently svenge hrmful ROS tht ws lerly inite y the erese O 2, H 2 O 2, n MDA ontents in mize plnts (Anjum et l., 211; Tlt et l., 215). Plnts hve the ility to etoxify ROS y up-regulting ntioxint enzymes, like SOD, POX n CAT. Mln et l., (199) reporte higher level of SOD in rought tolernt mize inres ompre to tht in rought sensitive ones. Kolrovi et l., (29) hve reporte enhne tivity of POX in rought tolernt s well s sensitive mize seeling expose to trete osmoti stress. Numerous stuies hve reporte tht higher levels of ntioxints re ssoite with plnt rought tolerne (Ashrf, 21; Vlizeh et l., 213; Mohrrmnej et l., 216). Tken overll, SOD isozyme tivities n GB n proline ontents were foun to e potentil iohemil initors of rought resistne in two mize lines exmine in the present investigtion.

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9 RESPONSE OF MAIZE TO DROUGHT STRESS 87 Tlt, N.B., B.T. Shwky n A.S. Irhim Allevition of rought-inue oxitive stress in mize (Ze mys L.) plnts y ul pplition of 24-epirssinolie n spermine. Environ. Exp. Bot., 113: Tun, A.L, C. Ky n M. Ashrf. 27. The effets of lium sulphte on growth, memrne stility n nutrient uptke of tomto plnts grown uner slt stress. Environ. Exp. Bot., 59: Vlizeh, M., S. Mohrmnej, M. Ahmi n H. Mohmmzeh Jlly Chnges in tivity profile of some ntioxint enzymes in lflf hlf-si fmilies uner slt stress. J. Agri. Si. Teh., 15: Velikov, V., I. Yornov n A. Arev. 2. Oxitive stress n some ntioxint systems in i rin trete en plnts; protetive role of exogenous polymines. Plnt Si., 151: Whi, A. n A. Ghznfr. 26. Possile involvement of some seonry metolites in slt tolerne of sugrne. J. Plnt Physiol., 163: Yn, W., Y. Zhong n Z. Shnggun Evlution of physiologil trits of summer mize uner rought stress. At Agri. Sn. Set B Soil Plnt Si., 66: Yryur, P., G. Coron, M. Leon, N. Kerer, N. Puheu, N. Ruio, G. Gr n G. Lgorio. 29. Effet of phosphorus efiieny on refletne n hlorophyll fluoresene of otyleons of oilsee rpe (Brssi npus L.). J. Agron. Crop Si., 195: Yiliz-Akts, L., S. Dgnon, A. Gurel, E. Geshev, n A. Erev. 29. Drought tolerne in otton: involvement of non-enzymti ROS-svenging ompouns. J. Agron. Crop Si., 195: Zhng, N., B. Zho, H.J. Zhng, S. Wee, C. Yng, Z.C. Yng, S. Ren n Y. Guo Meltonin promotes wter stress tolerne, lterl root formtion, n see germintion in uumer (Cuumis stivus L.). J. Pinel Res., 54: Zltev, Z. n F.C. Lion An overview on rought inue hnges in plnt growth, wter reltions n photosynthesis. Emir. J. Foo Agri., 24: (Reeive for pulition 15 Ferury 218)