The effects of different timings and severity of drought stress on gas exchange parameters of mungbean

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1 DESERT DESERT Online t DESERT 3 (8) The effets of different timings nd severity of drought stress on gs exhnge prmeters of mungen A. Mordi *, A. Ahmdi, A. Hossin Zdeh Deprtment of Agronomy nd Plnt Breeding, Fulty of Agriulture, University of Tehrn, Krj, Irn Reeived Jnury 8; Reeived in revised form Mrh 8; Aepted 5 April 8 Astrt Mungen (Vign rdit (L.) Wilzek) or green grm s drylnd grin legume is exposed to vried timings nd severity of drought stress, resulting in vriility in photossimilte prodution. In order to evlute some physiologil responses in one mungen ultivr to timing nd severity of drought stress, 3-replite RCBD (rndomized omplete lok design) field experiment ws rried out during yer yer t the experimentl frm of University College of Agriulture nd Nturl Resoures, University of Tehrn. Plnts were exposed to either moderte or severe wter defiit t either vegettive (VS) or reprodutive growth stges (RS). Prmeters were reorded t the middle stges of vegettive growth. In generl, wter stress redued net photosynthesis rte (Pn), stomtl ondutne (g s ), trnspirtion rte (Tr) nd lef reltive wter ontent (RWC) while inresing lef temperture (T). The gretest effets of drought on these prmeters ourred t reprodutive stge. Photosyntheti wter use effiieny inresed nd deresed during VS nd RS respetively. The results showed lerly lose orreltion etween RWC nd g s in VS (r=.9 ** ) nd RS (r=.976 ** ) tretments. Although wter stress t vegettive growth stge signifintly deresed Pn, g s, Tr, nd RWC, these prmeters were reovered upon rewtering t reprodutive stge. It is onluded tht to mximize mungen Pn in dry zones, irrigtion should e extended ross ll growth stges, espeilly during the reprodutive stge. Keywords: Mungen; Drought stress; Net photosynthesis rte; Stomtl ondutne. Introdution Mungen (Vign rdit (L.) Wilzek), grown minly in the entrl nd southern regions of Asi, is one of the lest reserhed nd the most underexploited of the mjor grin legumes rops (De Cost et l., 999). Mungen rops re grown in the short riny seson in southern Asi (Thoms et l., 3). A ommon feture of the limte in this region is the unertinty of rinfll, therefore prole signifint soil wter defiit leding to plnt wter defiit t vrious stges of growth. Most prominnt spet of growth nd development mungen is tht the plnt is sensitive to drought stresses, s onsequene of whih Corresponding uthor. Tel.: ; fx: E-mil ddress: _mordi@yhoo.om growth nd development go signifintly elow potentil (El Hfid et l., 998). The derese in rop iomss prodution is frequently oserved in response to wter defiit. This ould either rise from derese in the extent of solr rdition interepted y the nopy or derese in the effiieny with whih the interepted rdition is used to umulte dry mtter, or omintion of oth. The loss in umultion effiieny is e ssoited with deline in photosynthesis pity (Muhow et l., 986; Lopez et l., 996 nd Siddique et l., 999). During mny yers pst, mny workers hve een interested in understnding how drought limits photosynthesis. While muh of the reported drought-indued derese in CO ssimiltion ould e ttriuted to stomtl losure, prt of it hs lso een ttriuted to diret effets of dehydrtion on iohemil retions of

2 6 A. Mordi et l. / DESERT 3 (8) photosynthesis nmely non-stomtl ftors (Siddique et l., 999). However, the reltive mgnitude of stomtl nd non stomtl ftors limiting photosynthesis, in the drought stress ondition depends upon the degree of wter on defiit, rte, durtion of exposure nd the stge of rop growth (El Hfid et l., 998; Siddique et l., 999 nd Xue et l., ). Photosyntheti wter use effiieny (PWUE), defined s the rtio of mount of ron gin to mount of wter loss, is thought to ply n importnt role limttion, in limtion, produtivity nd the pility of survivl under drought stress (Inmn-Bmer nd Smith., 5). Plnts n hieve high PWUE through either high rte of net ron ssimiltion or low rte of trnspirtion, or oth. Typilly plnts with fvorle wter sttus hve low rtio of internl to externl CO onentrtion (C i /C ) (depleted in CO ), wheres droughted plnts hve high C i /C nd re enrihed in CO, refleting the trde etween net photosynthesis nd trnspirtion (Cusly et l., ; D Mtt et l., 3). Knowledge of wter reltion is fundmentl to improved rop mngement in rid nd semirid res. Among severl methods used to hrterize internl plnt wter sttus under drought ondition, reltive wter ontent (RWC) is n integrtive inditor, used suessfully to identify drought resistnt rops (Rosles-Sern et l., ). RWC hs een used to determine the effet of soil moisture defiit in studies on mungen (Pndey et l., 98), ommon en (Rosles-Sern et l., ), dry en (Znell et l., ), nd sugrne (Inmn-Bmer nd Smith, 5). Under nturl onditions, drought usully ours in ssoition with high temperture nd this resulting in photo-inhiition of photosynthesis system (Frenh nd Turner, 99). Pndey, et l., (98) reported tht the temperture of leves inresed s lef RWC deresed. Also, Lwn, (98), oserved tht redued wter vpor ondutne ws ompnied y higher lef temperture. Reltively little work hs een done to ompre the effets of different irrigtion regimes on gs exhnge prmeters in mungen (Lwn., 98; Pndey et l., 98 nd Uprety nd Bhti., 989). The effets of drought stress on mungen photosynthesis re not yet fully eluidted, nd less is known out these effets t the different growth stges. Therefore, fundmentl understnding of the intrinsi ftors whih ould inrese the ility of reeders to improve mungen to withstnd wter defiit is indispensle (Fver et l., 996). An identifition of these trits, relted to higher ssimiltion pity nd greter photosynthesis under prolonged wter stress, followed y n inorportion of these trits into urrent reeding progrms ould improve mungen prodution in drought prone res. The ojetive of this reserh ws to investigte, under field onditions, the effets of different wter stress regimes on the gs exhnge prmeters of n indeterminte mungen ultivr t vegettive nd reprodutive growth stges.. Mterils nd methods.. Site nd limtes Experiments were ommened on My 5 nd hrvests done on August, t the Experimentl Frm of University College Agriulture nd Nturl Resoures, University of Tehrn, Krj (35 55' N, 5 5' W nd on elevtion of 3 m ove se level), Irn. The soil t the site ws flt, deep, ly-lom with grvimetri wter ontent of % t field pity nd 8.3% t permnent wilting point. Rinfll, pn evportion (lss A), mximum nd minimum tempertures were ontinuously reorded in the meteorologil sttion next to the experimentl site. Some limti onditions from sowing to mturity were s fllows: weekly verge mximum temperture rnged from 5 to 3 C with inresed trend towrds mturity. The weekly minimum temperture ws rnged from 5.5 to C. Men dy-time evportion from vpor pn rnged from.9 to 5.3 mm. Averge rinfll from sowing to mturity ws 7.9 mm, with. mm of rin from weeks 3 to 5 nd then.8 mm from weeks 9 to. From week there ws only.7 mm of rin until mturity... Experimentl design nd rop mngement The experiment ws lid out in Rndomized Complete Blok Design (RCBD) with three replitions. Three weeks fter germintion (t the four-lef stge) plnts were exposed to the following tretments: (i) Well-wtered (ontrol), (W). (ii) Moderte stress in the vegettive stge, (W) (iii) Severe stress in the vegettive stge, (W3). (iv) Moderte stress, imposed oth t vegettive nd reprodutive stges, (W). (v) Moderte stress in the reprodutive stge, (W5).

3 A. Mordi et l. / DESERT 3 (8) (vi) Severe stress in the reprodutive stge, (W6). Adequtely wtered (ontrol) plots were irrigted weekly. Moderte nd severe stressed plots were wtered when 7 nd % of soil ville wter depleted. For the vegettive growth stge, stress tretments were imposed from pperne of the fourth lef to flowering, stressed plnts eing reirrigted long with ontrol plnts until mturity. In the se of reprodutive growth stge, stress ws imposed from flowering to mturity. Plnts were deemed to hve rehed the reprodutive phse when 5% of plnts in plot hd t lest one open flower (Thoms et l., 3). To determine times of smpling s well s rewtering, soil wter ontent ws mesured using moisture meter (Delt-T devie, Cmridge, UK). The depths of mesuring wter ontent were 3 nd 5 m. The soil wter ontent in -3 m lyer ws determined y grvity meter. A m plsti ess tue of with m dimeter ws instlled in the middle of eh plot in ll the tretments t sowing. The devie hd ylindril sensor equipped with light-sensitive eyes. To determine soil wter ontent, the moisture sensor ws inserted into the ess tue, nd then soil wter ontent mesured. Using the dt of soil moisture ssessed y moisture meter nd grvimetri mesurements, the perentge of ville soil wter in the root zone ws estimted y the eqution (Mrtin et l., 99), n FCi θi D(%)= () n FCi Wp Where n is the numer of depths used in the soil moisture smpling, FCi the soil moisture t field pity for ith lyer, θi the soil moisture in ith lyer nd WP the representing soil moisture t permnent wilting point. Finlly, the perentge depletion of ville soil wter in the root zone ws lulted s: Aville soil wter depletion(%)=-d () Seeds used in this experiment were of Prtov indigenous vriety, seleted from pulse Colletion of University College of Agriulture nd Nturl Resoure, University of Tehrn. The plnting dte ws My 5,. Seeds were sown y hnd, t plnting distne of 5 m 5 m. Exess seeds were sown nd then seedlings were thinned to otin desired popultion of plnts m -. A plot onsisting of 5 rows ws.5m wide nd 5m long. 3 dys fter sowing, weeds within nd etween the plots were ontrolled oth y hnd nd y field pplition of Glyphoste heriide. Fertilizer ws pplied long rows t rtes of -- (N-P O 5 -K O) ording to Thoms et l (3). Nitrogen fertilizer ws split into two pplitions, nmely t plnting nd 3 dy fter plnting..3. Gs exhnge prmeters Gs exhnge prmeters were ssessed t midwy of either vegettive or reprodutive growth stges. Net photosynthesis rte (Pn, in µmol. m -. s - CO ), trnspirtion rte (Tr, in mmol. m -. s - H O), lef temperture (T, in C), internl CO rtio (C i, in µl l - ), nd stomtl ondutne to wter vpor (g s, in mol m - s - H O.) were reorded using n LCA- portle, open-system infrred gs nlyzer (Anlytil Development Compny, Hoddeson, UK) under nturl sturting photosyntheti photon flux (>6 µmol m - s - ). Leves were inserted into lef hmer of m ross setion. For eh seleted plnt mesurements were mde, on the xil surfe of the seond fully-expnded lef in the upper nopy, three times during the morning etween 7:3 nd :3 h, so tht eh set of reordings on eh plnt ws tken s verge vlues for gs exhnge prmeters. The Photosyntheti wter use effiieny (PWUE in µmol CO. mol - H O) ws found out s the rtio of Pn nd Tr, s desried y Mroo et l. ()... Reltive wter ontent (RWC) Three individul leves of the plnts were olleted nd immeditely weighed (fresh weight, FW). Intt leves were trnsferred to seled mer flsk, rehydrted in L of distilled wter for 5 h until fully turgid t C. They were surfe dried nd reweighed (turgid weight, TW). Lef smples were then oven dried t 7 C for 8 h nd reweighed (dry weight, DW). The RWC ws lulted y the following formul (Lzno-Ferrt nd Lovtt, 99): RWC(%)=(FW DW)/(TW DW) (3).5. Sttistil nlysis Dt normlity ws tested nd onfirmed y using Minit softwre. Sttistil nlyses were performed using Mstt nd SPSS softwres. The signifine of the differene etween the tretments ws nlyzed y mens of stndrd two-wy nlysis of vrine. Mens were ompred using Dunn test with signifine level of P.5. Correltions etween prmeters were nlyzed y stndrd methods of Person-orreltion nlysis. Grphs

4 6 A. Mordi et l. / DESERT 3 (8) nd tles were drwn y help of Exel softwre. 3. Results nd disussion Gs exhnge prmeters were evluted t the vegettive nd reprodutive growth stges. To preisely ssess these prmeters under drought stress s well s plnt response fter rewtering, dt were olleted nd interpreted on the sis of growth stges. 3.. Vegettive stge 3... Stomtl ondutne (g s ), trnspirtion rte (Tr) nd lef reltive wter ontent (RWC) A ommon response to wter stress is stomtl losure, whih redues oth flux of CO nd wter vpor (Ogonny et l., 998). Results showed tht, wter defiit during vegettive growth stge signifintly (α =.) ffets stomtl ondutne (g s ) s well s trnspirtion rte (Tr) (Figures A & B). During imposition of drought, g s nd Tr were redued either of the wter defiit tretments, ut the g s nd Tr vlues under moderte stress were signifintly (P.5) higher thn those under severe stress. The oserved deline in g s nd Tr indited tht drought used stomtl ondutne inhiition with negtive reflex on the photosyntheti uptke nd trnspirtion rte (Znell et l., ). Mny experiments hve shown tht stomt lose in response to hydruli signls (i.e. RWC nd lef wter potentil) when soil moisture dereses (Mroo et l., ; Ismil et l., nd Xue et l., ). A positive reltionship ws oserved etween lef wter sttus nd stomtl losure (r=.9 ** ) t vegettive growth stge. RWC vlues showed vrition ross tretments (Fig. C). Wter stress tretments were rought out with signifint redution in the reltive wter ontent of leves. However the depression of RWC ws reltively less in moderte stress (% reltive to ontrol) tretment. On the ontrry, severe stress tretment exhiited mximum redution in RWC (% reltive to ontrol) t this stge. These results re onsistent with findings of Clvel et l. (5) Net photosynthesis rte (Pn) nd photosyntheti wter use effiieny (PWUE) Both moderte nd severe drought stress signifintly deresed Pn. Moderte nd severe drought stress indued redutions in Pn were 5 nd 5%, respetively, s ompred with the ontrol tretment (Fig. D). These results re in generl greement with Liu et l, (). Under moderte drought stress ondition, the redution in Pn ws ompnied y prllel derese in stomtl ondutne. This suggests tht the stomtl losure is the first response to wter stress. It is ssumed to e the min use of impired photosynthesis due to drought, nd sine the stomtl losure limits CO vilility to the mesophyll (Siddique et l., 999; Xue et l., ). In our experiment, it ws oserved tht the redution in Pn due to severe stress tretment (5%) ws higher thn tht of stomtl ondutne (37%), nd therefore inditing the dominne of nonstomtl ftors in reduing net photosynthesis rte in this tretment. The inrese in the C i (internl CO onentrtion) rtio (dt not shown) under severe drought is onsistent with this interprettion, sine inrese in this rtio demonstrtes deresed uptke of CO due to non-stomtl inhiition of photosynthesis. Inmn-Bmer nd Smith, (5) oserved tht under moderte stress (ψ lef <-.9MP), redution in photosynthesis ws mostly due to lower stomtl ondutne nd not initited from redued enzyme tivities nd low metoli levels. Contrry to Pn, exposure of mungen plnts to wter defiit signifintly inresed the rte of photosyntheti wter use effiieny (PWUE). However, severe stress nd ontrol tretments exhiited higher nd lower PWUE, respetively (Fig. E). The high PWUE in stressed plnts ws presumly due to dditionl CO flux into leves. Beuse of the prtil losure of stomt, the resistne to wter movement reltively inreses more thn the resistne to CO movement, nd therefore should redue Tr more thn it redues Pn (D Mtt et l., 3) Lef temperture The lef temperture mesurements, tken in stressed nd non-stressed plnts t the hlfwy of vegettive growth stge indited signifint (P.5) overll differene (Fig. F). In generl lef temperture ws higher in the stressed tretments. Moderte nd severe stressed plnts showed.3 to. C higher lef temperture thn ontrol plnts (Fig.F). Similr results hve een reported y Hshem et l., (998) who oserved lef temperture in stressed plnts of two vrieties of Brssi npus ws generlly to C higher thn tht in wtered plnts. In view of reported deline in photosynthesis, less photohemil energy would e spent on CO ssimiltion. Consequently the photohemil energy would

5 A. Mordi et l. / DESERT 3 (8) (B) (A) Tr(mmol. m -. s - H O) need to e onsumed y lterntive pthwys. One possiility is the loss of energy s het tht leds to lef temperture inrese (D Mtt et l., 3) Reprodutive stge Wter defiit tretments t reprodutive growth stge were pplied from emergene of the first flower to 95% pod mturity ording to Thoms et l. (3). Gs exhnge prmeters were ssessed t the middle wy of this stge for ll stress tretments. In this stge, stress tretments t vegettive stge were irrigted simultneously with ontrol plnts Stomtl ondutne (g s ), trnspirtion rte (Tr) nd lef reltive wter ontent (RWC) The stomtl ehvior nd trnspirtion rte under different wter stress regimes t reprodutive stge re presented in Figures, A nd B. Similr to vegettive stge, different drought stress tretments t reprodutive growth stge signifintly redued g s nd Tr vlues. Moderte nd severe stressed plnts showed 86 to 88% lower stomtl ondutne thn did ontrol plnts, respetively. Stomtl ondutne deresed with ge of plnts regrdless of stress tretments (Figures. A, A), therefore ontrol tretment t reprodutive stge showed 75% lower stomtl ondutne thn ontrol tretment t vegettive stge. These results re in generl greement with those of Uprety nd Bhti, (989) nd Siddique et l, (999) who reported tht stomtl resistne in the leves of whet (Tritium estivum L.) nd mungen inresed with ging of the plnts. g s (mol. m - s - H O) 6 6 W W W3 W W W3 RWC (%) ( C) Pn (µmol. m -. s - CO ) (D) (E) T ( C) (F) PWUE (µmol. mol - ) W W W3 St ress levels W W W3 W W W3 Fig.. Stomtl ondutne- g s (A), trnspirtion rte- Tr (B), lef reltive wter ontent- RWC (C), Net photosynthesis rte- Pn (D), photosyntheti wter use effiieny- PWUE (E), nd lef temperture - T (F) in mungen plnts under different stress levels t vegettive growth stge. Control =W: plots were irrigted weekly; moderte stress t vegettive stge = W; severe stress t vegettive stge= W3. Moderte stressed plots were wtered when 7% of soil ville wter depleted nd severe stressed plots when % of soil ville wter depleted. Different smll letters represent sttistil signifint (p.5, Dunn test). Eh r represents men of three replites Results lso showed tht RWC deresed with ge of plnts (Fig. C). In stressed plnts t W W W3 St ress levels

6 6 A. Mordi et l. / DESERT 3 (8) RWC (%) Tr (mmol. m -. s - H O) (A) (B) g s (mol. m - s - H O) 3 (C ) reprodutive stge, RWC deresed y nd 3%, reltive to ontrol, in the moderte nd severe stress tretments, respetively. RWC in stressed plnts t reprodutive stge ws positively orrelted with g s (r=.976 ** ), suggesting tht the higher redution in g s due to geing is proly relted to lower RWC in this stge thn tht in vegettive stge. Ogonny et l., (998) oserved tht stomtl ondutne ws deresed signifintly (P <.) throughout the growing seson, ompnying the generl deline in RWC. Although the g s nd Tr prmeters deresed under oth stress tretments in the vegettive stge, they were reovered fter rehydrtion t the onset of flowering. Similr results hve een otined y Znell et l., (). 3 W W W3 W W5 W6 W W W3 W W5 W6 W W W3 W W5 W6 Fig.. Stomtl ondutne- g s (A) nd trnspirtion rte- Tr (B), nd lef reltive wter ontent - RWC (C) in mungen plnts under different stress levels t reprodutive growth stge. Control=W: plots were irrigted weekly; moderte stress t vegettive stge=w; severe stress t vegettive stge= W3; moderte stress t vegettive nd reprodutive growth stges=w; moderte stress t reprodutive growth stge=w5; severe stress t reprodutive growth stge=w6. Moderte stressed plots were wtered when 7% of soil ville wter depleted nd severe stressed plots wtered when % of soil ville wter depleted. On similr smll letters represent sttistil signifint (p.5, Dunn test). Eh r represents men of three replites Net photosynthesis rte (Pn) nd photosyntheti wter use effiieny (PWUE) Similr to g s, dt showed tht during exposure to wter defiit, the redution of Pn ws greter t reprodutive thn tht t the vegettive stge (Figs. 3A nd 3B). On the other hnd, photosyntheti pity deresed signifintly (P.5) throughout the growing seson, therefore severe stress t reprodutive stge indited 37% lower Pn thn severe stress tretment t vegettive stge. These results re in generl greement with those of Mroo et l. () nd Ogonny et l. (998). Enhned rtes of respirtion onomitnt with delining photosyntheti rtes hve een reported in severl speies during lef senesene (Mroo et l., ). The importne of non-stomtl limittion of photosynthesis under wter stress in the reprodutive stge is indited y some inrese in internl CO onentrtion (C i ) (dt not shown), whih is ompnied y 87% deline in Pn s ompred to ontrol in reprodutive stge nd t severe stress tretment. Mitr nd Ghldiyl (988) suggested tht due to the higher protein ontent of grin legume seeds, the nitrogen requirement of the seed during seed development ws very high nd tht ples high nitrogen trnslotion demnd on vegettive tissues. This trnslotion my result fster deline of photosynthesis rte in stressed plnts s ompred to non-stressed ones. Although the redution in g s for moderte nd severe stress were similr, Pn deline in severe stress ws signifintly more thn in moderte tretment. The dt indite tht non-stomtl ftors were lrgely responsile for the high redution in photosynthesis when plnts were severely stressed in the reprodutive growth stge (Figs. A nd 3A). Similr to g s, the lower level of Pn for plnts stressed t vegettive stge (i.e, W nd W tretments) were similr to tht of ontrol plnts fter stress elimintion t flowering (Fig. 3A). Mishit et l. () reported tht photosynthesis rte in kidney-en following drought stress ws rpidly reovered fter rewtering. It ws thought tht remrkly omplete reovery ws prole due to the restortion of photosynthesis rte y stomtl losure nd umultion of ABA, exept in lef CO whih suffered ell destrution or metoli dmge (Ismil et l., ). Even though repeted moderte stress t oth vegettive nd reprodutive stges, reltive to ontrol tretment, signifintly deresed Pn, redution ws smller thn tht in the ses of

7 A. Mordi et l. / DESERT 3 (8) Pn (µmol. m -. s - CO) (A) PWUE (µmol.mol - ) T ( C) (C) moderte nd severe stress imposed t reprodutive stge. In ontrst to vegettive stge, wter defiit during the reprodutive stge signifintly deresed (p.5) photosyntheti wter use effiieny. Control nd severe stressed plnts showed.7 nd.5 (µmol CO. mol - H O) PWUE vlues, respetively (Fig. 3B). Oserved deline in PWUE in reprodutive stge ws minly due to the higher redution in Pn nd Tr in the reprodutive growth stge. 3 (B) Fig. 3. Net photosynthesis rte-pn (A), photosyntheti wter use effiieny-pwue (B), nd lef temperture-t (C) in mungen plnts under different stress levels t reprodutive growth stge. For more detils refer to Fig Lef temperture W W W3 W W5 W6 W W W3 W W5 W6 W W W3 W W5 W6 Contrry to g s nd Pn, plnt lef temperture inresed with ge of plnt (Fig. 3C). Similr results were otined with plnts under stress. Similrly, Pndey et l., (98) oserved tht lef temperture ws low in vegettive stge while high in reprodutive stge. Similr to vegettive stge, s stress level inresed, lef temperture rse. Lef temperture of moderte nd severely stressed plnts, s ompred with ontrol, signifintly inresed (y.5 nd C), respetively. d Lef temperture reltionships re employed to estimte wter stress in plnts, euse lef temperture is funtion of trnspirtion rtes (Lwn, 98). Therefore, n inverse reltionship might e expeted etween hnges in lef temperture, nd those of lef ondutne, given the ooling due to evportion ssoited with wter loss in trnspirtion. A omprison of mens (Figures. F, A, 3C) suggested tht this ws the se, t lest for stressed plnts. Lef temperture ws the highest for the leves with the lowest stomtl ondutne (i.e, in the stressed tretments). Conversely, in the irrigted plots, lef tempertures were the lowest, while ondutne the highest. The stressed plnts, therefore, egn to fe het stress, nd tht is why reeders rrely ttempt to seprte het from drought tolerne. Het ompnied y drought uses relese of mmoni from deomposition of protein from injured plnt tissues (Ogonny et l., 998).. Conlusion It is onluded tht drought tretments in vegettive nd reprodutive growth stges negtively ffet photosynthesis s well s ll gs exhnge prmeters. This experiment demonstrted tht oth stomtl nd nonstomtl ftors limit lef gs exhnge nd ssimiltion pity in mungen. Stomtl ftors were responsile for delines in ssimiltion pity when plnts experiened mild wter defiit (i.e, depletion of 7% soil ville wter). Under severe stress (i.e, depletion of % soil ville wter), nonstomtl ftors plyed the dominnt roles in limiting lef gs exhnge nd ssimiltion pity. On the other hnd, the inhiitory effet of drought stress t vegettive stge on lef photosynthesis ould e mostly ttriuted to stomtl limittion, while drought stress t reprodutive stge minly deresed photosynthesis y mens of non-stomtl ftors. This ultivr exhiited, to some degree, voidne of dehydrtion y reduing plnt wter loss through ontrolling stomtl wter loss in response to delining RWC. Redued wter vpor ondutne ws ompnied y higher lef temperture nd lower Pn. This work enled us to further understnd the physiologil response to wter stress in this legume nd to demonstrte tht gs exhnge prmeters, mesured during nd fter wter stress tretments seem relile physiologil prmeters to evlute drought tolernt mungen ultivrs.

8 66 A. Mordi et l. / DESERT 3 (8) Aknowledgment The reserh ws finnilly supported y University of Tehrn. This nd the onstrutive ritiism of nonymous referees of the mnusript re highly ppreited. Referene Cusly, G.S., Ito, O. nd Alejr.A.A.,. Physiologil evlution of responses of rie (Oryz stiv L.) to wter defiit. Plnt Si. 63: Clvel, D., Drme, N.K., Roy-Muley, H., Bronnier, S. nd Lffry, D.. 5. Anlysis of erly responses to drought ssoited with field drought dpttion in four Shelin groundnut (Arhis hypoge L.) ultivrs. Environ. Exp. Bot. 5, 9 3. D Mtt, F.M., Chves, A.R.M., Pinheir, H.A., Dutti, C. nd lureiro, M.E., 3. Drought tolerne of two field grown lones of Coffe onephor. Plnt Si. 6, -7. De Cost, W. A. T. M., Shnmugthsn, K. N. nd Joseph, K. D. S. M., 999. Physiology of yield determintion of mungen (Vign rodit (L.) Wilzek) under vrious irrigtion regimes in the dry nd intermedite Zones of Sri lnk. Field Crops Res. 6: -. El Hfid, K., Smith, D., Krrou, M. nd Smir, K., 998. Physiologil response of spring durum whet ultivrs to erly seson drought stress in Mediterrnen environment. Ann. Bot. 8: Fver, K. L., Gerik, T. J., Thxton, P. M. nd EL-Zik, K. M., 996. Lte Seson wter stress in otton: II. Lef gs exhnge nd ssimiltion pity. Crop Si. 36: Frenh, R. J. nd Turner, N.C., 99. Wter defiit hnge dry mtter Prtitioning nd seed yield in Nrrow-Lefed Lupines (Lupinus ngustifolius L.). Aust. J. A. Res. : 7-8. Hshem, A., Amin Mujdr, M.N., Hmid, A. nd Hossin, M.M., 998. Drought stress effets on seed yield, yield ttriutes, growth, ell memrne stility of synthesized Brssi npus L. J. Agro. Crop Si. 8, Inmn-Bmer, N.G. nd Smith, D.M., 5. Wter reltions in sugrne nd response to wter defiits. Field Crops Res. 9: 85. Ismil, I.M.R., Dvies, W.J. nd Awd, M.H.,. Lef growth nd stomtl sensitivity to ABA in droughted pepper plnts. Sienti Hort. 96: Lwn, R. J., 98. Response of four legumes to wter stress in south estern Queenslnd.I. Physiologil response mehnisms. Aust. J. Agri. Res. 33: Lzno-Ferrt, J. nd Lovtt, C. L., 99. Reltionship etween reltive wter ontent, Nitrogen Pools, nd growth of Phselous vulgris nd Phselous utifolius A. gry during wter defiit. Crop Si. 39: Liu, F., Jenson, C.R. nd Anderson, M.N.,. Drought stress effet on rohydrte onentrtion in soyen leves nd pods during erly reprodutive development: its implition in ltering pod set. Field Crops Res. 86: -3. Lopez, F.B., Johnson, C. nd Chhun, Y.S., 996. Effets of timing of drought stress on phonology, yield nd yield omponents of Short durtion Pigeon Pe. J. Agro. Crop Si. 77: 3-3. Mroo, J. P., Pereir, J.S. nd Chves, M.M.,. Growth, photosynthesis nd wter use effiieny of two C shelin grsses sujeted to wter defiits. J. Arid Environ. 5: Mrtin, D.L., E.C. Stegmn nd Freres, E., 99. Irrigtion sheduling prinipls. In: Hoffmn, G.L., Howell, T.A. Solomon, K.H. (Eds.), Mngement of Frm Irrigtion Systems. ASAE Monogrph. pp Mishit, K., Tnkmur, S., Mitni, T. nd Kimur, K.,. Reovery response of photosynthesis, trnspirtion nd stomtl ondutne in kidney en following drought stress. Environ. Exp. Bot. 65: Mitr, S. nd Ghldiyl, M.C., 988. Photosynthesis nd ssimilte Prtitioning in mungen in response to Soure sink ltertion. J. Agro. Crop Si. 6: Muhow, R.C., Sinlir, T. R., Bennett, J. M. nd Hnmmond, L.C., 986. Response of lef growth, lef nitrogen, nd stomtl ondutne to wter defiits during vegettive growth of field grown soyen. Crop Si. : 5-3. Ogonny, C.I., Nwlozie, M.C., Roy-Muley, H. nd Annerose, D.J.M., 998. Growth nd wter reltions of Kenf (Hiisus nninus L.) under wter defiit on sndy soil. Ind. Crops Prodution. 8: Pndey, R.K., Herrer, W.A.T. nd Pendelton, J.A., 98. Drought response of grin legumes under irrigtion grdient. III. Agron. J. 76: Rosles-Sern, R., Kohshi-Shit, J., Aost-Gllegos, J.A., Trejo-Lopez, C., Ortiz-Cereeres, J. nd Kelly J.D.,. Biomss distriution, mturity elertion nd yield in drought-stressed ommon en ultivrs. Field Crops Res. 85: 3. Siddique, M.R.B., Hmi, A. nd Islm, M. S., 999. Drought stress effets on photosyntheti rte nd lef o exhnge of whet. Bot. Bull. Ad. Sin. : - 5. Thoms. Roertson, M. J., Fuki, S. nd Peoples, M. B., 3. The effet of timing nd severity of wter defiit on growth development, yield umultion nd nitrogen fixtion of mungen. Field rops Res. 8: 3-. Uprety, D.C. nd Bhti, A., 989. Effet of wter stress on photosynthesis, produtivity nd wter sttus of mungen (Vign rdit L. (wilzek)). J. Agron. Crop Si. 63: 5-3. Xue, Q., Weiss, A., Arkeuer, T. J. nd Benziger, P.S.,. Influene of soil wter sttus nd tmospheri vpor pressure defiit on lef gs exhnge in field grown winter whet. Environ. Exp. Bot. 5: Znell, F., Wtne, T.M., Lim, A. L. D. S. nd Shivinto, M.A.,. Phosynthetis performne in Jk en (Cnvli ensiformis L.). Aust. J. A. Res. : 7-8.