Physiological parameters in sugarcane cultivars submitted to water deficit

Transcription

1 21 rzilin society of plnt physiology DOI./S--- RESERH RTILE Physiologicl prmeters in sugrcne cultivrs sumitted to wter deficit José Perez d Grç 1,2, Fin precid Rodrigues 2, José Rento ouçs Fris 2, Mri ristin Neves de Oliveir 2, lr etriz Hoffmnn-mpo 2 * nd Soni Mrli Zingretti 3 1 Universidde Estdul Pulist Júlio de Mesquit Filho, Vi de cesso Prof. Pulo Donto stellne, s/n, , Joticl, SP, rsil. 2 Emrp Soj, ix Postl 231, Londrin, PR, rsil. 3 Universidde de Rieirão Preto, venid ostáile Romno, 221, , Rieirão Preto, SP, rsil. * orresponding uthor: hoffmnn@cnpso.emrp.r. Tel ; fx: Received: 21 June 21; ccepted: 29 Octoer 21 strct To investigte the processes involved in the susceptiility of sugrcne plnts to wter deficit, severl physiologicl prmeters were evluted in drought tolernt (SP nd T15) nd sensitive () cultivrs. The wter deficit ffected the photosynthetic pprtus of ll the plnts in different wys, within nd mong cultivrs. The photosynthetic rte nd stomtl conductnce decresed significntly in ll cultivrs sumitted to wter deficit. In control plnts of the tolernt cultivrs (SP nd T15) the photosynthetic rte ws higher thn in the sensitive cultivr (). ultivr T15 showed the highest reltive wter content during the dry period. The quntum efficiency photosystem II of cultivr SP ws more stle in the lst dys of the experimentl tretment, suggesting tht the decline in reltive wter content stimulted n djustment of photosynthetic cpcity to tolerte the chnges in wter vilility. s whole, the tolernt SP nd T15 cultivrs exhiited etter photosynthetic performnce thn the sensitive cultivr. The dt suggest tht these physiologicl prmeters cn e used in the evlution nd distinction of drought tolernt nd sensitive sugrcne genotypes. Key words: Photosynthetic efficiency, reltive wter content, Scchrum, wter stress, drought. Resumo Prâmetros fisiológicos de cultivres de cn-de-çúcr sumetids o déficit hídrico. Pr investigr o processo envolvido n susceptiilidde de plnts de cn-de-çúcr o déficit hídrico, diferentes prâmetros fisiológicos form vlidos em cultivres tolerntes (SP e T15) e sensível () o déficit hídrico. O déficit hídrico fetou o prto fotossintético de tods s plnts de form diferencid dentro e entre s cultivres. tx fotossintétic e condutânci estomátic diminuírm significtivmente pr tods s cultivres sumetids o déficit hídrico. Ns plnts controle ds cultivres tolerntes (SP e T15) tx fotossintétic foi mior do que cultivr sensível (). cultivr T15 presentou O teor reltivo de águ mostrou que cultivr T15 presentou o mior teor reltivo de águ durnte o período de déficit hídrico. eficiênci fotossintétic d cultivr SP foi mis estável nos últimos dis do trtmento experimentl, sugerindo que o decréscimo do teor reltivo de águ estimulou o justmento d cpcidde fotossintétic pr tolerr s mudnçs d disponiilidde hídric. De modo gerl, s cultivres tolerntes SP e T15, presentrm melhor desempenho fotossintético do que cultivr rz. J. Plnt Physiol., 22(3): , 21

2 19 J. p. grç et l. sensível. Os ddos permitem sugerir que tis prâmetros fisiológicos podem ser usdos n vlição e distinção de genótipos de cn-de-çúcr tolerntes e sensíveis o déficit hídrico. Plvrs-chve: Eficiênci fotossintétic, teor reltivo de águ, Scchrum, estresse hídrico, sec. INTRODUTION Sugrcne (Scchrum spp.) is n importnt source for the production of sucrose nd ethnol in mny tropicl regions. rzil is the mjor world producer of sugrcne, followed y Indi, hin nd Thilnd. In the 29/21 seson, rzilin enterprises processed round 612 million tons, nd the 21/211 production is estimted t 664 million tons (on, 21). It is well known tht the ctul productivity of crops in mny regions is only prtly of the genetic potentil of the plnts (Tiz nd Zeiger, 26). Wter deficit is one of the min fctors reducing production for mny crops (ry et l., 2), nd sugrcne is especilly ffected y drought (Venktrmn et l., 1986). One lterntive to mitigte wter deficit in sugrcne is irrigtion (Inmn- mer, 24); however, wter is limited in some regions, nd equipment costs mke this strtegy expensive (oyer, 1996; Silv et l., 27). The selection of genotypes tht re tolernt to wter deficits nd their introduction in genetics reeding progrms is one mens of reducing these costs (Silv et l., 27). The stress cused y wter deficit ffects the entire plnt, from root hirs to stomt. Morphologicl ltertions including reductions in lef re nd root growth nd stomtl closure when the plnt is cclimting to drought re the min symptoms of wter deficit (Dvies et l., 22; Gomez-Del- mpo et l., 22; Tiz nd Zeiger, 26; Lopez et l., 28). Physiologicl responses cn vry ccording to plnt genotype, ut in generl, modifictions relted to wter deficit include lower wter potentil in the soil nd in the leves (Steudle, 2; Lierto et l., 26), increses in osmoprotectors such s proline nd sugrs (Molinri et l., 27; Mcormick et l.; 28), reduction in photosynthetic efficiency photosystem II (ngelopoulos et l., 1996; Silv et l., 27), reduction in the reltive wter content in leves (Silv et l., 27; Whid nd lose, 27; Loto et l., 28), nd decrese in stomt conductnce nd the photosynthetic rte (restic et l., 1995; Du et l., 1996; Dvies et l., 22; zevedo Neto et l., 24; Smit nd Singels, 26). In plnts, the hydric lnce is controlled y folir trnspirtion nd wter cpittion from the soil, which in dverse conditions such s wter deficit, reduces the reltive wter content nd photosynthetic ctivity (Lwlor nd ornic, 22; zevedo Neto et l., 24; Smit nd Singels, 26). Quntum efficiency photosystem II nd stomtl conductnce re lso rpidly reduced during wter deficit (Miyshit et l., 25). Different methods cn e used to distinguish wter deficits etween tolernt nd sensile genotypes. Our reserch group hs crried out moleculr studies to investigte gene expression in sugrcne plnts tht re tolernt or sensitive to wter deficit (Rodrigues et l., 29). Thus, the ojective of this study ws to investigte the wter deficit tolernce nd sensiility process during the vegettive stge in sugrcne cultivrs sumitted to wter deficit conditions. MTERILS ND METHODS Experiment instlltion: Sugrcne plnts were otined from the entro de Tecnologi nvieir (T) t Pircic nd the Usin Snt déli t Joticl, oth in the stte of São Pulo. The evlutions were performed on the wter deficit tolernt SP nd T15 cultivrs nd the wter deficit sensitive cultivr. These cultivrs were evluted in field experiments nd clssified ccording to their productivity during long drought periods (opersucr, 1999; T, 27). The experiment ws performed in greenhouse with temperture of 26 ± 2º nd reltive humidity of 6 %. The plnts were irrigted y utomtic sprinklers, four times dy (1h, 12h, 15h nd 17h) for ll cultivrs. Plnts were cultivted individully in 4 L pots, using oxysoil sustrte. For ech cultivr, 72 plnts were rrnged in rndomized locks in the greenhouse. The experimentl procedure consisted of 12 dt collections (under wter deficit conditions), using three replictes for control (irrigted) nd three for treted (wter deficit) plnts. The wter deficit tretment consisted of no irrigtion, nd the plnts were nlyzed on dys 1, 2, 4, 5, 7, 8, 9, 1, 11, 12, 13, nd 14 fter the eginning of rz. J. Plnt Physiol., 22(3): , 21

3 Physiologicl prmeters in sugrcne cultivrs sumitted to wter deficit 191 wter deficit. The control plnts were irrigted dily during the experiment. Physiologicl prmeters nlysis: ll nlyses were performed t the Ecophysiology Lortory t Emrp Soyen, Londrin, Prná, rzil, from Mrch through My 28. The third totlly expnded lef (Mcormick et l., 26) t ech collection dte (dys 1, 2, 4, 5, 7, 8, 9, 1, 11, 13, nd 14 of wter deficit) ws used to evluted s follows: difference etween lef temperture nd ir temperture (º), trnspirtion rte (E), photosynthetic rte () nd stomtl conductnce (g s ). ll vriles were nlyzed in the Portle Photosynthesis System (LIor, model LI-64, IRG ) with photosyntheticlly ctive rdition 1 µmol m -2 s -1. In these nlyses, ll vlues were tken considering coefficient of vrition less thn 1%. Quntum efficiency photosystem II (PSII) nd reltive wter content (RW) were determined in ll experimentl tretments. PSII ws estimted using Plnt Efficiency nlyser portle system (PE, Hnstech Instruments, Norfolk, UK). The RW ws mesured sed on Mtin et l. (1989), with some modifictions. Three lef frgments were collected from the second totlly developed lef (Mcormick et l., 26) nd immeditely plced in covered glss continer to mesure fresh smple weight. The turgid weight ws otined with rehydrted tissue y using deionized wter (Milli-Q, Millipore) for 48 h, t room temperture in the sence of light. fter rehydrtion, the turgid weight ws mesured, nd the smples were then plced in 8 º for 48 h to otin the dry weight. The RW ws clculted ccording to Mtin et l. (1989), using the formul: (fresh weight dry weight)/ (turgid weight - dry weight) *1. During the experiment, we lso evluted the cpcity of cultivrs to recover physiologicl prmeters fter eing kept under wter deficit nd rehydrted on dys 8 nd 1. Sttisticl nlyses: The experiment ws performed in rndomized lock with fctoril rrngement, with three locks, nd three replictes per tretment in ech lock, s follows: three cultivrs, two irrigtion levels (irrigted nd wter deficit), nd smpling time under wter deficit, totling 216 plnts. Stomtl conductnce dt were converted to squre root (x+1) for nlyses. fter the NOV, the mens were compred y Tukey test multiple comprison t the 5% proility level. ll nlyses were performed y mens of the SS - Sttisticl nlysis System (SS Institute, 1996) sttisticl pckge. RESULTS Reltive wter content nd folir temperture: Tles 1 nd 2 show the NOV vlues etween the different tretments, which indicted highly significnt differences. The results showed significnt difference in reltive wter content (RW) in the stressed plnts compred to the irrigted plnts (Figure 1). ccording to the Tukey test (P<.5), the RW showed significnt differences etween collecting times throughout the wter deficit experiment, especilly from dy 7 on, for ll the cultivrs. lso t dy 7, cv T15 showed reduction of 1.52% in RW in the wter deficit plnts. Reductions of 19.55% nd 23.12% were oserved in SP nd RW, respectively, in the sme dy. The tolernt nd sensitive cultivrs were rehydrted t dys 8 nd 1 during wter deficit nd t the first rehydrtion (dy 8) the plnts showed ltertions in the lef wter sttus, where cultivrs under wter deficit showed RWs similr to the control plnts. However, in the second rehydrtion period on dy 1, the responses of the plnts were not oserved. notle increse in RW ws detected in the stressed plnts tht were rehydrted on dy 8. These plnts ehved differently on dy 1, suggesting tht criticl point for the recupertion cpcity of these plnts is t mximum of pproximtely 8 dys (Figure 1). During wter deficit conditions, the RW on dy 7 in the tolernt cv T15 ws reduced to 88.29%, to 78.56% in the tolernt SP nd to 76.37% in the sensitive. ompring the RW mong the cultivrs under wter deficit (Figure 1), significnt vrition ws oserved etween the cultivrs on dys 7, 1 nd 13; cv T15 showed the highest RW in most evlutions. In the control plnts, significnt differences mong cultivrs were not oserved, nd the RW remined etween 95 nd 1 % (dt not shown). Tle 1. nlysis of vrince resume (degrees of freedom (DF) nd F vlue) for quntum efficiency photosystem II (PSII) nd reltive wter content (RW) estimted on three sugrcne cultivrs under wter deficit conditions. Vrition DF PSII F vlue RW Irrigtion level (IL) *** *** ultivr (V) ** 3.46* Dys (DS) *** 51.98*** IL V 2 4.8** 5.96** IL DS *** 61.45*** V DS *** 9.59*** IL V DS *** 9.41*** Residul *P<,1, **P<,1, ***P<,1 rz. J. Plnt Physiol., 22(3): , 21

4 192 J. p. grç et l. Tle 2. nlysis of vrince resume (degrees of freedom (DF) nd F vlue) for temperture ( ), trnspirtion rte (E), photosynthetic rte () nd stomtl conductnce (g s ) of three sugrcne cultivrs under wter deficit conditions. Vrition DF F vlue E g s Irrigtion levels (IL) *** *** 36.4*** 161.1*** ultivr (V) ** 29.96*** 12.63*** 22.45*** Dys (DS) *** 17.18*** 28.17*** 45.39*** IL V ** 1.77*** 9.24** 5.19** IL DS 1 8.2*** 1.11*** 12.2*** 1.22*** V DS ** 3.43*** 2.7** 2.13** IL V DS 2 3.** 4.44*** 2.96** 4.7*** Residul **P<,1, ***P<,1 The results otined on seventh dy showed significnt increse in folir temperture in the tolernt SP nd sensitive cultivrs (Figure 2). In cv T15, the increse in lef temperture occurred erlier, on dy 4. On rehydrtion, the stressed plnts on dys 8 nd 1 showed lower temperture. During the sme period, the trnspirtion rte differed sttisticlly from dy 7 for tolernt SP nd sensitive SP cultivrs nd on dy 3 for cv T15 (Figure 3). 2 1 SP RW (%) SP Wter deficit T15 Temperture (lef - ir º) T 15 Wter deficit Time (dys) Time (dys) Figure 1. Reltive wter content (RW) in sugrcne cultivrs SP , T15 nd (lower cse letters) under wter deficit. omprison RW mong cultivrs under wter deficit (cpitl letters). Mens followed y the sme letter on dy re not significntly different y the Tukey s test t 5% proility level. Figure 2. Difference etween folir nd ir temperture. Temperture vrition within sugrcne cultivrs SP , T15 nd (lower cse letters) under wter deficit. Temperture comprison etween cultivrs under control conditions (cpitl letters in control plnts r) nd under wter deficit conditions (cpitl letters in wter deficit plnts r). Positive vlues indicte folir temperture higher thn the room temperture. Mens followed y the sme letter on dy re not significntly different y Tukey s test t 5% proility level. rz. J. Plnt Physiol., 22(3): , 21

5 Physiologicl prmeters in sugrcne cultivrs sumitted to wter deficit 193 E (µmol m -2 s -1 ) 12. SP T Wter deficit periods, dys 8 nd 1, the plnts sumitted to wter deficit showed PSII vlue very close to tht of the control plnts. When the cultivrs were compred under wter deficit conditions (Figure 4), decrese in photosynthesis efficiency (PSII) ws oserved t dys 13 nd 14 for cv T15, nd t dys 12, 13 nd 14 for. ultivr SP t dy 12 showed lower efficiency. In sensitive cv, the PSII vlues decresed to pproximtely.4 t dy 12, dropping to.36 t dy 13 of wter deficit; wheres the tolernt plnts showed vlues of pproximtely.6. In generl, tolernt cultivrs SP nd T15 sumitted to wter deficit showed etter PSII thn cv (Figure 4). ompring cultivrs, the PSII of control plnts ws not different (dt not shown) Wter deficit SP Time (dys) Figure 3. Trnspirtion rte (E) within sugrcne cultivrs SP , T15 nd (lower cse letters). omprison etween cultivrs control conditions (cpitl letters in control plnts line) nd mong cultivrs under wter deficit conditions (cpitl letters in wter deficit plnts line). Mens followed y the sme letter on dy re not significntly different y Tukey s test t 5% proility level. (F v / F m ) T Time (dys) Quntum efficiency photosystem II: Tolernt cultivrs SP nd T15 showed decline in PSII from dy 7 of wter deficit, especilly in cv SP (Figure 4). With the rehydrtion of plnts on dys 8 nd 1, the PSII of the stressed plnts showed recovery, s oserved on dys 8, 9, 1, nd 11. In sensitive cv, less ccentuted decrese in PSII ws oserved on dy 12. t oth rehydrtion Figure 4. Quntum efficiency PSII (F v /F m ) within sugrcne cultivrs SP , T15 nd (lower cse letters). omprison mong cultivrs under wter deficit (cpitl letters). Mens followed y the sme letter on dy re not significntly different y Tukey s test t 5% proility level. Photosynthetic rte: The photosynthetic rte ws significntly different etween irrigted nd wter deficit plnts for cultivrs SP nd from dy 7, nd for rz. J. Plnt Physiol., 22(3): , 21

6 194 J. p. grç et l. cv T15 from dy 4 (Figure 5). fter rehydrtion t dy 8, the plnts exhiited smll increse in photosynthetic rte for cultivrs T15 nd, s oserved from the second rehydrtion, t dy 1, for ll cultivrs. In generl, ll cultivrs were ffected y the imposition of wter deficit conditions; s shown in Figure 5, cultivrs SP (1.7 µmol m -2 s -1 ) nd (2.12 µmol m -2 s -1 ) exhiited photosynthetic rte higher thn cv T15 (.38 µmol m -2 s -1 ) t dy 14. significnt difference mong cultivrs ws oserved t dys 4 nd 7 in plnts sumitted to wter deficit (Figure 5). Photosynthetic rte lso vried in the control plnts. Tolernt cultivrs SP nd T15 exhiit etter performnce compred to sensitive cultivr (Figure 5). (µmol m -2 s -1 ) SP T15 ont rol Wter deficit Time (dys ) Figure 5. Photosynthetic rte () within sugrcne cultivrs SP , T15 nd (lower cse letters). omprison mong cultivrs control conditions (cpitl letters in control plnts line) nd mong cultivrs under wter deficit (cpitl letters in wter deficit plnts line). Mens followed y the sme letter on dy re not significntly different y Tukey s test t 5% proility level. Stomtl conductnce nd trnspirtion rte: Stomtl conductnce vlues during the entire period of wter deficit tretment re presented in Figure 6. The wter deficit of cv SP plnts ws higher (1.16 mol m -2 s -1 ) t dy 5 compred to control plnts (1.11 mol m -2 s -1 ); however, on dy 7 this vlue decresed nd remined t 1.9 mol m -2 s -1 during the remining experimentl period. From dy 4, stomtl conductnce in cv T15 plnts sumitted to wter deficit differed significntly from control plnts, nd these differences continued during the entire experimentl tretment. However, cv plnts sumitted to wter deficit differed sttisticlly from control plnts t dys 9, 11, 13, nd 14. ompring the stomtl conductnce of plnts sumitted to wter deficit, the tolernt cultivrs (SP nd T15) nd the sensitive cultivr () showed significnt differences (P<.5) t dys 1, 4 nd 5 (Figure 6). In control plnts, cv SP differed from t dys 7 nd 8, nd in generl, throughout the experimentl tretment, cv SP performed est for stomtl conductnce, followed y cv T15. g s (mol m -2 s -1 ) 1.25 SP T Time (dys) Wter deficit Figure 6. Stomtl conductnce (g s ) within sugrcne cultivrs SP , T15 nd (lower cse letters). omprison mong cultivrs control conditions (cpitl letters in control plnts line) nd mong cultivrs under wter deficit (cpitl letters in wter deficit plnts line). Mens followed rz. J. Plnt Physiol., 22(3): , 21

7 Physiologicl prmeters in sugrcne cultivrs sumitted to wter deficit 195 y the sme letter on dy re not significntly different y Tukey s test t 5% proility level. DISUSSION This study demonstrted vritions in RW, temperture, PSII, trnspirtion rte, photosynthetic rte nd stomtl conductnce mong three sugrcne cultivrs sumitted to wter deficit tretment. In generl, tolernt cultivrs SP nd T15 exhiited etter performnce under wter deficit condition compred to sensitive cv, considering physiologicl prmeters such s RW nd PSII. olom nd Vzzn (23) evluted the recovery cpcity of two tolernt nd sensitive cultivrs of Ergrostis curvul sumitted to wter deficit, nd lso oserved etter RW recovery in the drought tolernt plnts. The percentges of RW reduction in sugrcne plnts sumitted to wter deficit, in the present study, were close to 6% t dy 1 for cv SP (61.4%), cv T15 (69.33%) nd lso cv (58.52%). In Ze mys plnts under wter deficit tretment, three dys were sufficient to reduce the RW to 65% (Schlemmer et l., 25). However, in other plnt fmilies, RW reduction cn occur rpidly. In Lycopersicon esculentum, 5% reduction of RW ws oserved 2 hours fter the eginning of wter deficit tretment. However, fter 4 hours the RW dropped to 4%, suggesting tht in these plnts the stress effect ws more ccentuted in the first hours of wter deficit (Hvux, 1992). Under high temperture conditions, Whid nd lose (27) oserved tht Scchrum officinrum plnts showed reduction in RW. However, 72 hours fter the eginning of wter deficit, the stressed plnts showed RW vlues similr to the control plnts, suggesting tht plnts utilize prt of their wter content to minimize dmge due to high temperture. The vlues otined in present study suggest tht cv T15 ws le to detect minimum reduction in the mount of wter ville for sorption, fvoring wter deficit tolernce, ecuse this plnt could preserve its wter content through stomtl closure (Figure 6). ecuse wter is the principl electron donor for PSII, through the oxidtion process, decrese in RW cn decrese the electrochemicl potentil of TP synthse nd photosystem I, compromising TP formtion nd NDPH respectively nd thus negtively ffecting the photosynthetic pprtus (Tiz nd Zeiger, 26; Lwlor nd ornic, 22). This informtion grees with dt otined in the present reserch, i.e., when RW decresed in plnts sumitted to wter deficit, reduction in PSII ws lso oserved. t dy 8, when the plnts were rehydrted, the elevted RW likely led to n increse in PSII. h-um nd Kirdmnee (28) oserved significnt decrese in PSII in sugrcne sumitted to drought. These uthors demonstrted reductions in PSII, trnspirtion rte, nd stomtl conductnce which re in greement with present our oservtions. wter deficit decreses folir trnspirtion due to stomtl closure, thus incresing folir temperture. Exposure of Tritium estivum to wter deficit, ssocited with het stress, lso ltered the PSII, nd lower PSII ws oserved in irrigted plnts (control) t 35, 4 nd 45 º (Lu nd Zhng 1999). ccording to uthors, n ntgonist effect occurs etween wter deficit nd high temperture stress, the former eing responsile for incresing PSII resistnce. In the present study, PSII decresed significntly during wter deficit in ll cultivrs. This suggests tht when plnts re sumitted only to wter deficit, no increse in PSII resistnce occurs. Therefore, when RW egn to decrese from dy 7, PSII lso decresed on dy 8, in plnts under wter deficit. onsequently, the oserved efficiency of PSII in sugrcne under wter deficit my e more relted to RW thn to the other prmeters evluted. ccording to Tiz nd Zeiger (26), one of the min PSII inhiitor gents seems to e the excess of photons leding to photoinhiition, which cuses increses in phototoxic products such s superoxide (O 2- ), hydrogen peroxide (H 2 O 2 ), nd the hydroxide rdicl (OH - ) which oxidtes the PSII D1 protein. The dmge cused y wter deficit to sugrcne cultivrs my hve een less hrmful to the PSII thn to other physiologicl prmeters such s the photosynthetic rte nd stomtl conductnce, considering the rpid decreses in plnts under wter deficit. In Ergrostis curvul, n fricn grss dpted to semi-rid regions, differences were oserved in PSII in sensitive (.2) nd tolernt (.5) cultivrs, fter 15 dys no irrigtion. However, when rehydrted for five dys, the stressed plnts reched similr PSII levels to those oserved in control plnts, indicting the recovery cpcity of plnt PSII (olom nd Vzzn, 23). The time intervl etween rehydrtion nd the plnt physiologicl response vries ccording to plnt species, the rz. J. Plnt Physiol., 22(3): , 21

8 196 J. p. grç et l. prmeters evluted, nd the wter deficit imposed (Lierto et l., 26; Souz et l., 24). In Ole europe, five dys of rehydrtion were sufficient to reestlish the photosynthetic rte, wter potentil of leves, nd PSII, reching levels similr to control plnts (ngelopoulos et l., 1996). In sugrcne, only RW nd PSII incresed on dy 8 due to rehydrtion. Silv et l. (27) evluted the PSII in other wter deficit tolernt nd sensitive sugrcne genotypes, nd oserved significnt decreses in the PSII mong them. These dt re in ccordnce with the oservtions in this work, where on dys 12 nd 14, tolernt cultivrs SP nd T15 differed from sensitive cv. ccording to hrtzoulkis et l. (22), rpid decrese in photosynthetic rte is relted to stomtl closure. In the present study, the photosynthetic rte declined rpidly in ll cultivrs, minly in cv T 15, fter 4 dys under wter deficit. In contrst, in Oryz stiv, photosynthetic efficiency decresed grdully (Yng et l., 22). The photosynthetic rte of Ole europe reched zero under wter deficit (ngelopoulos et l., 1996); however, when rehydrted for five dys, the plnts recovered their former photosynthetic rte. In sugrcne cv T 15 (9.39 µmol m -2 s -1 ) nd cv (1.47 µmol m -2 s -1 ) plnts, the photosynthetic rte recovered t dys 8 nd 1 fter wter stress, respectively. Similr results were reported for Minqurti guinensis, which lso did not lose photosynthesis nd PSII recovery cpcity fter 35 dys under wter stress conditions (Lierto et l., 26). Stomtl conductnce seems to e directly relted to reduction in RW in plnts under wter deficit, s folir trnspirtion is controlled y stomtl opening nd closure (Tiz nd Zeiger 26). In this study, when RW declined etween 1% nd 2%, ll the sugrcne cultivrs showed reduction in stomtl conductnce. The decrese of stomtl conductnce in plnts under wter deficit is similr to the ehvior of sline stressed plnts, ecuse oth conditions compromise wter sorption (López-liment et l., 28). Decreses in the photosynthetic rte nd stomtl conductnce, in generl, re relted. onsidering tht O 2 flux control in leves is medited y stomtl opening, photosynthesis is lso medited y regulr wter vilility (Tiz nd Zeiger, 26). This explins the significnt decrese in trnspirtion rte tht we oserved in ll the cultivrs during the entire wter deficit experimentl period, together with the increse in folir temperture in plnts under stress, likely due to low stomtl conductnce. In Phseolus vulgris, stomtl conductnce nd photosynthetic rte lso declined rpidly fter two dys without irrigtion (Miyshit et l., 25). The decline in stomtl conductnce seems to e common process in mny plnt species during wter deficit, nd its effects re oserved in the lower trnspirtion rte s well s n increse in folir temperture (Lierto et l., 26; zevedo Neto et l., 24). ccording to the physiologicl prmeters RW nd PSII, tolernt cultivrs SP nd T15 performed etter under wter deficit conditions compred to the sensitive cv. ultivrs SP nd T15, irrigted dily, showed higher photosynthetic rte, stomtl conductnce, nd trnspirtion rte. ontrrily, sensitive plnts did not show efficient physiologicl performnce, even under continuous irrigtion. fter the rehydrtion period, some physiologicl prmeters such s photosynthetic rte nd stomtl conductnce did not recover in ny of the tolernt or sensitive plnts. dditionl studies re needed to ssocite the dt on plnt physiologicl ehvior otined here with gene expression, or to the ction of sugr nd osmoprotectors on the plnt defense metolism, relting these to the pthwys involved in the response of sugrcne to drought. cknowledgments: The first uthor thnk to PES for the scholrship concession. REFERENES ngelopoulos K, Dichio, Xiloynnis Inhiition of photosynthesis in olive trees (Ole europe L.) during wter stress nd rewtering. J. Exp. ot. 47: zevedo-neto D, Prisco JT, Enés-Filho J, Lcerd F, Silv JV, ost PH, Gomes-Filho E. 24. Effects of slt stress on plnt growth, stomtl response nd solute ccumultion of different mize genotypes. rz. J. Plnt Physiol. 16: restic M, ornic G, Fryer MJ, ker NR Does photorespirtion protect the photosynthetic pprtus in French en leves from photoinhiition during drought stress? Plnt 196: hrtzoulkis K, Ptks, Kofidis G, oslidis, Nstou. 22. Wter stress ffects lef ntomy, gs exchnge, wter reltions nd growth of two vocdo cultivrs. Sci. Hortic. 95:39-5 h-um S, Kirdmnee. 28. Effect of osmotic stress on proline ccumultion, photosynthetic ilities nd growth of sugrcne plntlets (Scchrum officinrum L.). Pk. J. ot. 4: olom MR, Vzzn. 23. Photosynthesis nd PSII functionlity of drought-resistnt nd droght-sensitive weeping lovegrss plnts. Environ. Exp. ot. 49: rz. J. Plnt Physiol., 22(3): , 21

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