Hindwi Pulishing Corportion The Sientifi World Journl Volume 213, Artile ID 649326, 1 pges http://dx.doi.org/1.1155/213/649326 Reserh Artile Response of Rie Nitrogen Physiology to High Nighttime Temperture during Vegettive Stge Song Chen, Xioguo Zhng, Xi Zho, Dnying Wng, Chunmei Xu, Chenglin Ji, nd Xiufu Zhng Chin Ntionl Rie Reserh Institute, Chinese Ademy of Agriulturl Sienes, Hngzhou, Zhejing 316, Chin Correspondene should e ddressed to Xiufu Zhng; xzhng169@sohu.om Reeived 24 June 213; Aepted 13 July 213 Ademi Editors: R. Inoue nd V. Shlyonsky Copyright 213 Song Chen et l. This is n open ess rtile distriuted under the Cretive Commons Attriution Liense, whih permits unrestrited use, distriution, nd reprodution in ny medium, provided the originl work is properly ited. The effets of night temperture on plnt morphology nd nitrogen umultion were exmined in rie (Oryz stiv L.) during vegettive growth. The results showed tht the shoot iomss of the plnts ws greter t 27 C (high nighttime temperture, HNT) thn t 22 C (CK). However, the inrese in oth shoot nd root iomsses ws not signifint under 1 mg N/L. The shoot nitrogen onentrtions were 16.1% nd 16.7% higher in HNT thn in CK under 16 nd 4 mg N/L. These results suggest tht plnt N uptke ws enhned under HNT; however, the positive effet might e limited y the N sttus of the plnts. In ddition, lef re, plnt height, root mximum length, root nd shoot nitrogen onentrtions, solule lef protein ontent, nd solule lef rohydrte ontent were greter in HNT thn in CK under 4 nd 16 mg N/L, while fresh root volume, root numer, nd the ontent of free mino id in lef were not signifintly different etween HNT nd CK regrdless of nitrogen levels. Moreover, lef GS tivity under HNT ws inresed t 16 mg N/L ompred with tht under CK, whih might prtly explin the positive effet of HNT on solule protein nd rohydrte ontent. 1. Introdution High temperture stress is n importnt yield limiting ftor in rie (Oryz stiv L.). The glol verge temperture hs een inresing over the pst 1 yers nd is projeted to inrese in the rnge of 1.4 to 5.8 C y the end of the twenty-first entury t the present rtes of greenhouse gs emissions nd popultion growth [1]. In ddition, limte models foresee tht reltively greter inrese in nighttime tempertures thn dytime tempertures will our euse of less rdint het loss due to inresed loudiness [2]. Over the pst entury the inreses in glol dily minimum tempertures were more those twie tht of dily mximum tempertures [3]. Evidene of historil yields of rie [4] nd whet [5] shows tht erel yield ws strongly orrelted with minimum nighttime tempertures rther thn dytime mximum tempertures. For exmple, deresing rie yields in the Philippines [4] nd inresing whet yields in Mexio [5] were relted to inresing nighttime tempertures. The influene of high tempertures on ron nd nitrogenmetolisminriendotherropsiswelldoumented. High tempertures dmge photosyntheti memrnes nd use hlorophyll loss [6], derese lef photosyntheti rte, inrese emryo ortion [7], lower grin numer, nd derese grin filling durtion nd rtes [8 11], resulting in lower grin yield [1, 12 15]. On the other hnd, photosyntheti pity is losely ssoited with lef nitrogen [16, 17]. High N level enhnes photosynthesis nd delys senesene [18]. The two key enzymes involved in ssimilting intrellulr mmonium into orgni ompounds re glutmte dehydrogense (GDH) nd glutmine synthetse (GS), whih lso prtiipte in photosynthesis nd rohydrte metolism [19, 2]. Het stress will result in derese in lef N ontent [18, 21] swellsgdhndgstivities[2, 22] euse GDH nd GS re ssoited with mino id onversion [19] nd mino id omposition might e ltered due to het stress, whih ould promote stress resistne [23]. However, most studies on the effets of high tempertures on rop plnts hve not differentited etween dy- nd nighttime temperture regimes. Generlly, rop development nd growth rtes nd durtion of ritil phses n e differently sensitive to minimum
2 The Sientifi World Journl nd mximum tempertures [24]. High nighttime tempertures (HNT) re onsidered to e disdvntgeous euse they n stimulte respirtion, therey ffeting yield [25]. HNT lso ffets the lef photosyntheti rte [26 28], whih is ttriuted to its indiret effets on lef hlorophyll ontent [29], lef re [3], lef nitrogen onentrtion (LNC), nd vrious enzymes involved in photosynthesis. Therey, the effet of HNT on plnt growth seems to e losely relted with the hnges of the oupled plnt metolisms, ron nd nitrogen ssimiltion. It hs een suggested tht etter understnding of plnt responses to HNT is needed to etter quntify nd redue unertinties in limte hnge impt ssessments [24]. However, there hs een very little study of the influene of HNT (t onstnt dytime temperture) on nitrogen nd ron metolism of rie plnts. The ojetive of this study ws to investigte the omined effets of different nighttime tempertures (22 nd 27 C) nd different nitrogen levels in hydroponi solution (1, 4, nd 16 mg N/L) imposed during the vegettive phse (trnsplnting to pnile initil stge) on dry mtter prodution, plnt nitrogen umultion, nd plnt morphologil trits under hydroponi solutions. We lso investigted the effets of HNT on the ontent of solule rohydrte, solule strh, solule protein nd free mino id (FAA) onentrtion, nd the tivities of GS, GDH, GPT, nd GOT in lef. The min purpose of this study ws to test whether the negtive effet of inresed nighttime temperture on plnt growth ould e llevited y the nitrogen supply in the vegettive stge. 2. Mterils nd Methods 2.1. Plnt Mteril, Growth, nd Tretments. Rie (Oryz stiv L. v. N2Y-6) plnts were grown hydroponilly for 54 dys fter germintion. Seeds were soked in tp wter for 1dyndthengermintedt32 Cfor2dys.Thegerminted seeds were rodsted on the soil pot nd grown in greenhouse, with 12 h photoperiod of 1 15 μmol qunt m 2 s 1 of photosyntheti photon flux density (PPFD), 56 85% reltive humidity, nd n verge dy/night temperture regime of 33/23 C for 21 dys. Seedlings with four leves were trnsplnted to si nutrient hydroponis solution ontining 2.9 mm NH 4 NO 3,.32mMNH 2 PO 4, 1. mm K 2 SO 4,1.mMCCl 2, 1.7 mm MgSO 4 7H 2 O, 9.1 μm MnCl 2 4H 2 O,.52 μm(nh 4 ) 6 Mo 7 O 24 4H 2 O, 18 μmh 3 BO 3,.15 μm ZnSO 4 7H 2 O,.16 μm CuSO 4 5H 2 O, nd 36 μm FeCl 3 6H 2 O. The ph vlue of the solution ws djusted to 5.5 using 1 M HCl or NOH solution s required [31]. Hlf onentrtion of the nutrient solution ws pplied for the first 3 dys s pretretment nd then hnged to the set nutrient solution. Nutrient solutions were renewed every four dys. A plsti pot (length width height: 4 3 3 m) ws used, with seedlings plnted on the fom nd fixed y sponge. The plnting sping ws 1 1 m with two seedlings per hill. Three pots with 36 hills were set s one replition. Four environmentlly ontrolled growth hmers (PGB-4; Lifu, Chin) were used for one rie Air temperture ( C) 35 3 25 2 15 1 5 1 3 5 7 9 11 13 15 17 19 21 23 HNT-T CK-T Hour of dy 1 95 9 85 8 75 7 65 6 55 5 Figure 1: Chnges in the ir temperture nd reltive humidity over dy. Plnts were grown under two different night tempertures (22 nd 27 C) nd the sme dy temperture (3 C). vriety, with two temperture tretments, three nitrogen tretments, nd three replitions. After the pretretment, the seedlings were trnsferred into solutions with different nitrogen onentrtions: low (LN, 1 mg N/L), moderte (MN, 4 mmg N/LL), nd high (HN, 16 mg N/mL). A totl of 18 plots with different nitrogen levels were plnted. Two temperture tretments (dy/night) were set s HNT (3 C/27 C) nd CK (3 C/22 C). Dytime ws from 5: to 18: with PPFD of 12 μmol qunt m 2 s 1 nd reltive humidity of 75% throughout the whole dy. The detils of ir/wter temperture nd reltive humidity over dy n e found in Figure 1. 2.2. Determintion of Plnt Biomss, Lef Are, nd Morphologil Trits. Twelve plnts from eh replition were smpled t 54 dys fter germintion. The plnts were divided into shoot nd root nd oven-dried seprtely t 8 Cuntil the dry weight ws onsistent. The plnt height, mximum root length, nd root numer were mesured mnully. Root volume ws equl to the volume inrese of wter in grduted ylinder when the fresh root ws sumerged. Lef re ws mesured using Lior31C (LICOR, USA). Then, the dry weight ws mesured nd plnt tissues were ground into powder for further nlysis. Additionl 12 plnts were smpled for hemil nlysis. Fresh lef nd root were seprted immeditely nd stored t 2 Cforfurtheruse. 2.3. Nitrogen Conentrtion, Solule Protein, Solule Free Amino Aid, nd Solule Crohydrte nd Strh. Totl nitrogen onentrtion ws determined with n utonlyzer (Foss 21, FOSS Kjelte, USA) using the Kjeldhl method following vitriol digestion. Solule protein ontent ws determinedytheprotein-dyeindingmethodintroduedy Brford [32] using ovine serum lumin s the stndrd. Amino id onentrtion in the lef ws determined y the Ninhydrin method [33] using L-leuine s the stndrd. Reltive humidity (%)
The Sientifi World Journl 3 Tle 1: Night temperture effet on the plnt height, mximum root length, root volume, root numer, lef re, nd shoot nd root dry weights of rie seedlings. Nitrogen level (N) 16 4 1 ANOVA Temp. (T) Plnt height (m) Mximum root length (m) Root volume (m 3 plnt 1 ) Root numer (plnt 1 ) Lef re (m 2 plnt 1 ) Shoot dry weight (g/1 plnts) Root dry weight (g/1 plnts) 22 C 42.87± 1.49 15.58 ± 3.1.92 ±.8 92 ± 16 49.3 ± 8.3 5.82 ±.2 2.41 ±.21 27 C 45.53± 1.6 17.38 ± 3.75 1.1 ±.11 83 ± 14 55.9 ± 6.8 6.4 ±.28 2.2 ±.19 22 C 39.88 ± 2.43 17.46 ± 2.61.82 ±.14 72 ± 2 42.8 ± 3.6 5.51 ±.1 2.23 ±.15 27 C 44.33 ± 1.82 2.58 ± 2.56.8 ±.9 85 ± 18 48.7 ± 9.1 6.1 ±.19 2.5 ±.3 22 C 4.71 ± 1.65 18.63 ± 2.1.75 ±.13 66 ± 16 35.3 ± 3.6d 5.2 ±.26d 1.97 ±.11 27 C 4.17 ± 1.77 23.99 ± 2.46.72 ±.14 56 ± 12 39.6 ± 6.8 5.27 ±.1d 1.68 ±.1 N ns ns N T ns ns ns ns ns ns ns Rie seedlings were grown under two different night tempertures of 22 Cnd27 C with three nitrogen levels of 1 mg N/L, 4 mg N/L, nd 16 mg N/L. Vlues were expressed s mens ± stndrd error (n =3), nd the sme smll letter in the sme olumn mens tht the vlues re not signifintly different t P <.5 y Tukey s HSD. Solule rohydrtes nd strh were determined following the method of Zhu et l. [34] using surose s the stndrd. 2.4. GOT, GPT, GS, nd GDH Ativities. Glutmi-oxloeti trnsminse (GOT) nd glutmi-pyruvi trnsminse (GPT) tivity were ssyed y the method of Wu et l. [35]; one unit (U) of tivities ws defined s the inrese in pyruvi id ontent per g protein per hour. Glutmine synthetse (GS) tivity ws ssyed y the method of Sprio nd Stdtmn [36]; one unit (U) of tivity ws defined s the inrese in glutmylhydroxmte per g protein per hour. Glutmte dehydrogense (GDH) tivity ws determined following the method of Zhng et l. [37]; one unit (U) of tivity ws defined s the inrese in NADH per g protein per minute. 2.5. SOD, POD, CAT, nd MDA. The tivity of superoxide dismutse (SOD) ws determined ording to the method of Dhinds et l. [38]. One unit of enzyme tivity ws tken s the tivity to use 5% inhiition. The nitrolue tetrzolium redution rte ws mesured y monitoring the sorne t 56 nm. The tivity of peroxidse (POD) ws determined in retion solution omposed of 5 mm PBS (ph 7.), 2 mm H 2 O 2, 2.7 mm guiol, nd.5 ml enzyme extrt y monitoring the inrese in sorne t 47 nm due to guiol oxidtion [39]. The tivity of tlse (CAT) ws ssyed in ordne with the method of Jing nd Hung [4]. The mlondildehyde (MDA) ontent ws determined y the method of Heth nd Pker [41]. 2.6. Dt Anlysis. The experiments were lid out in omplete rndomized design nd were repeted totl of three times. To test the signifine of nighttime tempertures effet on growth development nd physiology prmeters, the dt were sttistilly nlyzed using two-wy nlysis of vrine (ANOVA; SAS sttistil nlysis pkge version 9., SAS Institute, Cry, NC, USA). The mens were seprted using Tukey s HSD t P <.5. Thestndrderrorsofthe men were lso lulted nd presented in the grphs s error rs. 3. Results 3.1. Morphologil Chrteristis. Four-lef ge seedlings were trnsplnted nd exposed to HNT (27 C) t three nitrogen levels for out 33 dys. Ovious symptoms of the nitrogen levels in rie seedling were oserved. For exmple, there ws differene in plnt height, nd the leves turned yellow in the low nitrogen level ondition. To illustrte the effet of HNT on the morphologil hrteristis of rie seedlings, we determined the plnt height, mximum root length, totl numer of roots, root volume, lef re, nd shoot nd root dry weights (Tle 1). Generlly speking, ll the morphologil hrteristis improved long with the nitrogen inrese exept for the mximum root length. The effet of HNT on morphologil trits vried within nitrogen levels. Plnt height, lef re, nd shoot dry weight were greter in HNT (27 C) thn in CK (22 C) under the nitrogen level sof 16 nd 4 mg N/L, ut little differene ws found with nitrogen of 1 mg N/L. The mximum root length in HNT ws inresed ompred with tht in CK in the low nitrogen level ondition (1 mg N/L), ut little differene ws found in plnts under 4 nd 16 mg N/L. In omprison with 22 C, plnt height in 27 C ws 11.1% nd 6.2% higher under 4 nd 16 mg N/L, respetively. The root length ws 28.7% greter in 22 Cthnin 27 C t 1 mg N/L. There ws little differene in root volume, root numer, nd root dry weight etween HNT nd CK. 3.2. Nitrogen Conentrtion nd Aumultion in Shoot nd Root. The HNT effet on nitrogen onentrtion nd umultion in shoot nd root is shown in Figure 2. Root nitrogen onentrtions were 7.72%, 23.5%, nd 1.2%greterinHNTthninCKt16,4,nd1mgN/L, respetively. Shoot nitrogen onentrtions were 16.1% nd
4 The Sientifi World Journl Nitrogen onentrtion of root (%) 3.5 3 2.5 2 1.5 1.5 d N d Nitrogen umultion of root (mg/1 plnts) 8 7 6 5 4 3 2 1 N d CK HNT () () Nitrogen onentrtion of shoot (%) 4.5 4 3.5 3 2.5 2 1.5 1.5 N Nitrogen umultion of shoot (mg/1 plnts) 3 25 2 15 1 5 N d d () (d) Figure 2: Nitrogen onentrtion nd umultion in the root nd shoot of rie seedling (() (d)). Plnts were grown under two tempertures of 22 C(CK)nd27 C (HNT) with three nitrogen levels of 1 mg N/L (low nitrogen level: LN), 4 mg N/L (moderte nitrogen level: MN), nd 16 mg N/L (high nitrogen level: HN). Rnge rs indite the stndrd devition (n =3). ANOVA results re emedded in the figure: ns: not signifint; P <.1. Columns with the sme letter re not signifintly different t P <.5 y Tukey s HSD. 16.7% greter in HNT thn in CK t 16 nd 4 mg N/L, respetively, ut little differene ws found t 1 mg N/L. The effet of HNT on nitrogen umultion nd ontent ws similr in root nd shoot exept tht there ws no signifint differene in root nitrogen umultion etween HNT nd CK in the high nitrogen ondition (16 mg N/L). 3.3. Lef Solule Protein, Free Amino Aid, nd Solule Crohydrte Content. Metoli produtions of lef nitrogen nd rohydrte metolism (i.e., solule protein, free mino id, nd solule rohydrtes) were determined (Figure 3). The results showed tht there ws no signifint differene in lef solule protein ontent etween CK nd HNT t 4
The Sientifi World Journl 5 Solule protein ontent (mg g 1 FW) 25 23 21 19 17 N Free mino id ontent (mg g 1 FW).35.3.25.2.15.1 15.5 () () 2 Solule rohydrte ontent (mg g 1 FW) 18 16 14 12 1 8 N 6 () Figure 3: Lef solule proteins ontent (), solule sugr ontent (), nd free mino id ontent () of rie seedling. Plnts were grown under two tempertures of 22 C(CK)nd27 C (HNT) with three nitrogen levels of 1 mg N/L (LN), 4 mg N/L (MN), nd 16 mg N/L (HN). Rnge rs indite the stndrd devition (n =3). ANOVA results re emedded in the figure: ns: not signifint; P <.5; P <.1. Columns with the sme letter re not signifintly different t P <.5 y Tukey s HSD. nd 16 mg N/L. However, positive effet of HNT on lef solule protein ontent ws signifint t 1 mg N/L, eing 5.8% greter in HNT thn in CK. The effet of HNT on the lef free mino id nd solule rohydrte ontent vried withnlevels.thediffereneinleffreeminoidnd solule rohydrte ontent etween CK nd HNT ws not signifint t 16 mg N/L. A signifint differene in solule rohydrte ontent ws found t 4 nd 1 mg N/L, with HNT eing signifintly greter thn CK. A positive effet ofhntonfreeminoidontentwsonlyoservedt 1 mg N/L. 3.4. GOT, GPT, GS, nd GDH Ativities. Lef GOT, GPT, GS, nd GDH tivities were determined to gin etter understnding of the nitrogen ssimiltion response to HNT (Figure 4). Lef GOT tivity in HNT ws inresed in the 1 nd 16 mg N/L onditions ompred with CK, while the opposite results were found for lef GPT. HNT effets on GS nd GDH tivities were ltered y nitrogen levels. Lef GS tivity under HNT ws inresed t 16 mg N/L nd styed onsistent t 4 mg N/L, ut deresed t 1 mg N/L ompred with tht under CK. The effet of HNT on lef GDH tivity ws the opposite t 16 mg N/L ut no
6 The Sientifi World Journl GOT tivity (U mg 1 protein hr 1 ) 12 1 8 6 4 2 GPT tivity (U mg 1 protein hr 1 ) 8 7 6 5 4 3 2 1 N CK HNT () () GS tivity (U mg 1 protein hr 1 ) 12 1 8 6 4 2 GDH tivity (U mg 1 protein min 1 ) 6 5 4 3 2 1 () (d) Figure 4: GOT (), GPT (), GS (), nd GDH (d) tivities of rie seedling lef. Plnts were grown under two different tempertures of 22 C (CK) nd 27 C (HNT) nd three different nitrogen levels of 1 mg N/mL (LN), 4 mg N/mL (MN), nd 16 mg N/mL (HN). Sttistil nlysis ws rried out etween temperture tretments using n ANOVA with Tukey s HSD. Columns with the sme letter re not signifintly different (P <.5). signifint differene ws found t 4 nd 1 mg N/L etween HNT nd CK. 4. Disussion 4.1. High Nighttime Temperture Effet on Plnt Biomss, Lef, nd Root Trits. A high temperture effet on plnt iomss hs een well doumented. Morit et l. [42] found tht high temperture elertes the growth development, leding to deresed umultion of photosynthtes in the sheth, nd promotes lef re, therey ffeting the ultimte grin yield [42]. However, the effet of elevted nighttime temperture on plnt iomss ws just the opposite. Tnk et l. [43] oserved tht iomss prodution inresed with high nighttime wter tempertures nd tht the lef stge ws lso promoted. Hussey [44] found tht elevted night tempertures in the rnge of 15 3 Contriutetoninrese in the iomss prodution of tomto plnts. Similr effets of night temperture were lso found for Gleg offiinlis nd Medigo stiv in the rnge of 4 25 C, regrdless of the dytime temperture [45]. In the urrent study, inresed iomss under HNT ws oserved in the shoots of plnt exposed to nitrogen supply of 4 nd 16 mg N/L, whih ws onsistent with the previous reports. However, little
The Sientifi World Journl 7 SOD tivity (U mg 1 protein) 44 42 4 38 36 T ns POD tivity (U mg 1 protein) 16 14 12 1 8 6 4 T ns 34 2 32 CK HNT CAT tivity (U mg 1 protein) 3 25 2 15 1 () MDA ontent (mg g 1 FW) 3 25 2 15 1 () 5 5 CK HNT () (d) Figure 5: SOD, POD, nd CAT tivities nd MDA (() (d)) ontent of rie seedling lef. Plnts were grown under two different tempertures of 22 C(CK)nd27 C (HNT) nd three different nitrogen levels of 1 mg N/mL (LN), 4 mg N/mL (MN), nd 16 mg N/mL (HN). Sttistil nlysis ws rried out etween temperture tretments using n ANOVA with Tukey s test. Columns with the sme letter re not signifintly different (P <.5). differene etween HNT nd CK ws found in root iomss (Tle 1). Furthermore, lef re ws lso promoted under HNT from 22 to 27 C. The inrese in iomss prodution ws ttriuted to n inrese in lef development. High night tempertures pper to stimulte ell division in the meristems of the lef nd might enlrge thinner leves t the level of the single lef [46]. On the other hnd, Osone et l. [47] pointed out the importne of lef-root intertions ndfoundthtthensorptionrteoftherootwswell orrelted with lef development. In this study, the inrese in root iomss ws not signifint t 1 mg N/L, suggesting tht Nuptkeisrequiredtomintingoodorreltionetween lef development nd RGR under HNT. High night temperture my lso ffet lef or root trits during the vegettive stge nd thus indiretly ffet the grin
8 The Sientifi World Journl yield [42]. Cutler et l. [48] stted tht elevted night ir temperture elertes the lef elongtion of rie. Knno et l. [49] found greter SLA in HNT plnts, nd Tsunod [5] demonstrted tht the lef emergene rte inresed when nighttime wter tempertures inresed. However, root trits were seldom reported. In the urrent reserh, we found tht root iomss ws not signifintly different etween 22 nd 27 C, nd similr results were found in fresh root volume nd root numer, regrdless of the nitrogen level. We lso found inresed plnt height, mximum root length, nd lef re in HNT (27 C) ompred with CK (22 C) for plnts exposed to nitrogen levels of 16 nd 4 mg N/L. The mximum root length in HNT ws lso inresed ompred with tht in CK in the low nitrogen level ondition (1 mg N/L), ut little differene ws found in plnts under 4 nd 16 mg N/L. TheseresultssuggestthttheHNTeffetonshootndroot development ws not onsistent during the vegettive stge. 4.2. High Nighttime Temperture on Rie N Metolism. The effet of HNT on photosynthesis ws ttriuted to its indiret effets on lef hlorophyll ontent [29], lef re [3], lef nitrogen ontent (LNC), vrious enzymes involved in photosynthesis, or omintion of these ftors. In this study, root nd shoot nitrogen onentrtion nd umultion were nlyzed. The root nitrogen onentrtions were 7.72%, 23.5%, nd 1.2% greter in HNT thn in CK t 16, 4, nd 1 mg N/L, respetively, while shoot nitrogen onentrtions were 16.1% nd 16.7% greter in HNT thn in CK t 16 nd 4 mg N/L, respetively. Similr results were found for nitrogen umultion (Figure 2). These results indite tht plnt N uptke ws enhned under elevted nighttime temperture, similr to findings for spring whet [51]. Lef nitrogen plys key role in rohydrte ssimiltion nd protein synthesis [52]. In the present study, high nighttime temperture inresed lef solule rohydrte ontent t 1 nd 4 mg N/L nd solule protein ontent nd free mino id t 1 mg N/L (Figure 3). However, differenes in lef solule protein ontent, freeminoidontent,ndsolulerohydrteontent etween HNT nd CK were not signifint t 16 mg N/L. It my e tht inresed umultion of nitrogen under HNT onditions is relted to the N supply level. Inreses in the level of proteins or free mino ids were the result of the overll tivities of protein synthesis whih, in turn, my hve n impt on plnt nitrogen response or physiologil tolerne to high tempertures [53]. The key enzymes involved in ssimilting intrellulr mmonium into orgni ompounds re glutmine synthetse (GS) nd glutmte dehydrogense (GDH). GS plys n essentil role in the metolism of nitrogen y tlyzing the ondenstion of glutmte nd mmoni to form glutmine [54], while GDH onverts glutmte to αketoglutrte. Both enzymes prtiipte in photosynthesis nd rohydrte metolism [19, 2]. Although high N level enhnes photosynthesis nd delys senesene [18], high temperture results in derese in lef N ontent [18, 21] nd GS nd GDH tivities [2, 22].Thisisimportnt euse GDH nd GS n e ssoited with mino id onversion [19], nd mino id omposition might e ltered due to het, whih ould promote stress resistne [23]. In the present reserh, the HNT effet on GS nd GDH tivities ws ltered y nitrogen levels. Lef GS tivity under HNT inresed t 16 mg N/L nd remined onsistent t 4 mg N/L ut deresed t 1 mg N/L ompred with thtunderck.theeffetofhntonlefgdhtivity ws opposite t 16 mg N/L, nd no signifint differene ws found t 4 nd 1 mg N/L etween HNT nd CK. Further studies re needed to investigte the mehnism or mehnisms of the tion of GS nd GDH nd its possile reltion to HNT. As n environmentl stress, HNT might enhne lef senesene, involving protein degrdtion, suh s Ruiso [55]. Retive oxygen speies (ROS) prodution (i.e., superoxide dismutse (SOD), tlse (CAT), peroxide dismutse (POD), nd mlondildehyde (MDA)) hs the strongest orreltion with resistne to oxidtive stress. In the present study, no signifint differene ws found in SOD nd POD etweenckndhntregrdlessofnitrogenlevels.however, plnts exposed to HNT were signifintly greter in MDA nd CAT thn in CK t 4 nd 1 mg N/L (Figure 5). These results indite tht HNT stress on plnts ws slight, espeilly when the N supply ws suffiient. However, the rie seedlings defense mehnisms ould e stimulted when the N supply is limited, whih will, in turn, ffet the nitrogen umultion. Aknowledgments This reserh ws prtly supported y grnts from the Zhejing Provine Nturl Siene Foundtion of Chin (LQ12C131), MOA Speil Fund for Agro-Sientifi Reserh in the Puli Interest of Chin (212396), nd the ermrked fund from the Chin Agriulture Reserh System (CARS-1-27). Referenes [1] IPCC, Intergovernmentl Pnel on Climte Chnge, 27. 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