Salinity effects on leaf ion composition and salt secretion rate in Avicennia germinans (L.) L.

Transcription

1 BRAZILIAN JOURNAL OF PLANT PHYSIOLOGY The offiil journl of the Brzilin Soiety of Plnt Physiology RESEARCH ARTICLE Slinity effets on lef ion omposition nd slt seretion rte in Avienni germinns (L.) L. Nthlie Suárez 1,2 * nd Ernesto Medin 1 1 Lortorio de Eofisiologí Vegetl, Instituto Venezolno de Investigiones Científis, Crs 12-A, Aprtdo , Venezuel. 2 Present Address: Deprtmento de Biologí de Orgnismos, Universidd Simón Bolívr, Aprtdo 89., Crs 18-A, Venezuel. * Corresponding uthor: ntsure@us.ve. Fx: Reeived: 13 My 28; Returned for revision: 19 June 28; Aepted: 25 June 28 The effet of slinity on lef wter reltions, nd rte nd ioni omposition of lef seretion ws investigted in plnts of Avienni germinns growing under ontrolled slinity onditions. Inreses in slinity from to 94 mol NCl m redued the predwn wter potentil from -.56 to MP nd the solute potentil from to MP, wheres the pressure potentil remined positive in ll tretments. Compred to the ontrol, t 94 mol NCl m N + nd Cl onentrtions of lef sp inresed 19 nd 7 times, respetively. With the ddition of slt the min ions umulted in leves were N + nd Cl wheres plnts grown without slt umulted K + in leves t levels similr to those of N + with slt tretments. Seretion rtes of N + nd Cl ions inresed up to the highest slinity tretment, mounting to 59 nd 46 times respetively, ompred to ontrol plnts. The inrese in seretion rte ontriuted to ountert the inrese of slt onentrtion in the lef. In the tretments reeiving slts, the N + /K + rtio of lef sp rnged from 4 to 1, wheres tht of the seretion rnged from 24 to 56. The rtio of Cl vs the rest of nions remined round 3 in the lef sp of slt-treted plnts wheres it vried etween 96 nd 243 in the seretion. With inresing slinity higher seretion rtes mintined the internl ion lef onentrtion reltively low. The seletive hrter of the seretion ontriutes to mintin fvourle N + /K + nd Cl /nion rtios in the lef ells. Key words: ion onentrtion, mngroves, N + /K + rtio, slt stress, wter reltions Efeitos d slinidde sore omposição iôni folir e tx de sereção de sis em Avienni germinns (L.) L.: Investigrm-se os efeitos d slinidde sore s relções hídris folires e sore tx e omposição iôni d sereção folir em plnts de Avienni germinns ultivds so ondições ontrolds de slinidde. Inrementos de slinidde, de 94 mol NCl m, rretrm reduções do potenil hídrio de ntemnhã, de -,56-4,16 MP, e do potenil osmótio, de -2,27-4,48 MP, enqunto o potenil de pressão permneeu positivo ns plnts de todos os trtmentos. Em relção às plnts-ontrole, so 94 mol NCl m, s onentrções de N + e Cl d seiv folir umentrm 19 e 7 vezes, respetivmente. Com dição de sis, os prinipis íons umuldos ns folhs form N + e Cl, enqunto ns plnts ultivds sem sl íons K + umulrm-se ns folhs em extensão similr à dos íons N + so dição de sl. As txs de sereção de N + e Cl umentrm om o umento d onentrção extern de sl, sendo, so 94 mol NCl m, respetivmente 59 e 46 vezes miores em relção às ds plnts-ontrole. O umento d tx de sereção ontriuiu pr ontrlnçr o inremento d onentrção de sis ns folhs. Ns plnts de todos os trtmentos que reeerm sl, rzão N + /K + d seiv folir vriou de 4 1, e de 24 56, n sereção. A rzão Cl / demis ânions permneeu em torno de 3 n seiv folir ds plnts trtds om sl, enqunto n sereção ess rzão vriou de Com o umento d slinidde, miores txs de sereção permitirm mnutenção de onentrções iônis reltivmente ixs ns folhs. O ráter seletivo d sereção ontriuiu pr mnter rzões N + /K + e Cl / ânions fvoráveis ns éluls folires. Plvrs-hve: onentrção de íons, estresse slino, mngue, rzão N + /K +, relções hídris Brz. J. Plnt Physiol., 2(2):131-14, 28

2 132 N. SUÁREZ nd E. MEDINA INTRODUCTION Mngrove speies ontinuously inorporte slts from sustrte nd trnsport them to the leves in the trnspirtion strem (Bll, 1988). Slt uptke helps to mintin positive pressure potentil through their ontriution to osmoti djustment of growing tissues (Downton, 1982; Clough, 1984; Suárez nd Sordo, 2). However, under high slinity onditions, the survivl of the plnt depends on its ility to regulte the internl slt onentrtions nd prevent ions from rehing toxi levels (Sholnder et l., 1962; Atkinson et l., 1967; Bll, 1988). It hs een shown tht during wter uptke, roots of some mngrove speies exlude 8-95% of the slt in the soil solution (Sholnder et l., 1962; Atkinson et l., 1967). In ddition, plnts my regulte shoot ion onentrtion nd redue slt onentrtion in lef tissue y other mens suh s slt seretion through lef glnds, suulene, nd relotion of slt to other orgns (Sholnder et l., 1962; Atkinson et l., 1967; Leshem nd Levinson, 1972; Sordo, 21). In vrious mngrove speies, slt is sereted y slt glnds in the leves, nd their tivity seems to e ssoited with the slinity of the nutrient solution. Thus, slt seretion ontriutes to eliminte the exess of slt rehing the leves (Lüttge, 1971; Drennn nd Pmmeter, 1982; Wisel et l., 1986; Sordo, 21). The tivity of slt glnds is highly seletive, sereting mostly NCl nd thus ontriuting to mintin fvorle K + /N + rtio in the lef ells (Wisel et l., 1986; Sordo nd Greves, 2). However, other ions suh s K +, Mg 2+, C 2+ nd SO 4 n e present in the sereted solution (Sholnder et l., 1962; Atkinson et l., 1967; Rozem et l., 1981; Boon nd Allwy, 1986; Sordo nd Greves, 2). Thus, seretion regultes internl slt onentrtions nd ontriutes to uild speifi ioni rtios fvorle for the mintenne of the metoli tivity of lef ells (Atkinson et l., 1967; Lüttge, 1971; Rozem et l., 1981; Popp et l., 1985; Wisel et l., 1986). The qulity nd quntity of the slt tken up nd sereted vries widely, depending on soil slinity nd speies (Alert nd Popp, 1977). As in other mngrove speies, in Avienni germinns, the lef seretion rte inreses with soil slinity. In this speies, the seretion solution ontins essentil mronutrients suh s K, C nd S, nd mironutrients suh s Zn (Sordo nd Greves, 2). In the numerous ppers deling with slt seretion in Avienni speies, severl spets hve reeived ontrditory reports: (i) suulene does not inrese with slinity of the nutrient solution nd hs little signifine for regultion of lef slt onentrtions (Tomlinson, 1986) or tends to inrese, ontriuting with slt regultion (Suárez nd Sordo, 2), or tends to derese under hypersline onditions (Sordo, 21); (ii) the rte of slt seretion inreses with slinity (Bll, 1988) or tends to sturte following sigmoid pttern in plnts grown under hypersline onditions (Sordo, 21); nd (iii) the rte of slt seretion ppers to e nerly onstnt (Sholnder et l., 1962; Sordo, 21) or to vry diurnlly (Drennn nd Pmmeter, 1982; Wisel et l., 1986). In the present study we, therefore, reevlute previous findings y performing full ssessment of the effet of slinity on the rte nd ioni omposition of lef seretion in plnts of mngrove speies, A. germinns growing under ontrolled slinity onditions, in ddition to ompring these prmeters with slt omposition of the sereting leves. The importne nd physiologil relevne of the seretion for the mintenne of the internl onentrtions of lef ions, s well s the role of seletive ion seretion on lef ion rtios were exmined. MATERIALS AND METHODS Plnt mterils: Avienni germinns (L.) L. propgules with fresh mss of 1.9 ±.37 g were olleted in Cumná (1º27' N, 64º1' W), Venezuel, nd plnted in 2.5 L pots filled with wshed snd. Seedlings were mintined under well-wtered onditions for 18 weeks, y pling the pots in 7 m deep trys filled with 4% Hoglnd nutrient solution. After tht, the seedlings were seprted into five groups of 2 plnts eh nd mrine slt ws dded to the nutrient solution, inresing the onentrtion t rte of 15 mol NCl m per dy until otining five slinity tretments:, 17, 43, 68, nd 94 mol NCl m, orresponding to slinities of 15, 25, 4 nd 55 s mesured with refrtometer lirted for NCl. Mrine slt ws preferred to pure NCl euse it simultes the effet of slinity under nturl onditions. Eh group of plnts, orresponding to tretment, ws onneted in series to 2 L tnk, with Hoglnd s nutrient solution t 4% strength. The Brz. J. Plnt Physiol., 2(2):131-14, 28

3 SALINITY EFFECTS ON ION COMPOSITION AND SALT SECRETION RATE IN Avienni germinns 133 sline solutions were onstntly reyled through the tnk y mens of pumps. This system llowed solution ertion nd effetively ounterted slight inreses in slinity of the solution t middy, when trnspirtion peked. The nutrient solution in eh tnk ws repled every three weeks nd slinity djusted. Plnts grown t mol m slinity were used s ontrols. The plnts were grown under these tretments in greenhouse for 16 months under nturl light with 12 h photoperiod. Throughout the growing period, tempertures verged 3.5 ± 3.4ºC during the dy nd 16.3 ± 2.ºC t night, nd the reltive humidity osillted etween 5 nd 78%. Mximum level of photosynthetilly tive rdition long the experiment ws 155 ± 37 µmol m -2 s -1. Lef wter reltions: Mesurements egn 11 months fter pplying the tretments, when leves hd developed under eh prtiulr slinity tretment. Predwn wter potentil (Ψ w ) ws mesured in five rndomly seleted plnts for eh tretment using pressure hmer (model 3, Soil Moisture Equipment Corp., CA, USA). Opposite leves to those seleted for Ψ w mesurement in eh plnt were dethed, rinsed with distilled wter nd dried with soft tissue pper to eliminte slt from the surfe. After eliminting the middle vein, the lde ws pled in syringe nd frozen in liquid nitrogen. The frozen smples were thwed during 3 min t room temperture efore sp extrtion to determine lef osmollity with vpor pressure osmometer (model 55, Wesor, Logn, UT, USA). The osmollity vlues were trnsformed to solute potentil (Ψ s ) t 25ºC nd used to lulte pressure potentil (Ψ p ). The solute potentil of the sline nutrient solution (Ψ sol ) ws determined simultneously nd in the sme wy s Ψ s. The sme leves used to determine lef seretion per lef re nd fresh weight unit were used to determine lef suulene in eh slinity tretment. Lef suulene (wter ontent per unit re) ws determined in ten fully expnded leves from eh of five plnts from eh tretment. Leves were dethed efore dwn; the re of eh lef ws mesured immeditely, then it ws rinsed with distilled wter to remove slt deposits nd gently dried with tissue pper. Clen leves were weighed to determine fresh mss (M f ), dried for 48 h t 7ºC nd weighed gin to determine dry mss (M d ). The lef wter ontent (W = M f - M d ) ws then lulted on lef re nd dry mss sis. Two months efore determintion of the seretion rte, the trnspirtion rte ws mesured in 15 intt nd fully expnded leves tken from seven to ten plnts per tretment, with n open system (Lior-64, Lior In., NE, USA). The hmer temperture ws kept t 27ºC nd the vpor pressure defiit vried etween 1.3 to 2.9 kp. Reltive humidity ws kept t mient level nd CO 2 onentrtion djusted to 38 µmol mol -1. Seretion rte nd onentrtion of ions in lef nd sereted solution: Twelve months fter pplying the tretments, one lef from eh of five plnts rndomly seleted within eh tretment ws used to ssess lef slt seretion, s doumented previously y Sordo (21). All leves were young, fully expnded, nd orresponded to the third pir of leves in the rnh. They were thoroughly rinsed with distilled wter to remove from the surfe ll slt previously sereted. After 12 h the leves were rinsed with 25 ml deionized/distilled wter to remove ll slt deposits just prior to the onset of the photoperiod (6 h), nd rinsed gin 12 h lter t the onlusion of the photoperiod (18 h). Therefter, lef re nd ion onentrtions in the lef wshings were determined. We mesured tions (N +, K +, C 2+ nd Mg 2+ ) y tomi sorption spetrophotometry (Vrin AA-6, Vrin Tehtron, CA, USA), nd nions (Cl, NO 3, SO 4 nd oxlte) y ion hromtogrphy (Dionex DX- 1, Dionex Corp., CA, USA). Finlly, diurnl nd noturnl seretion rtes per unit lef re were lulted. The experiment ws repeted two months lter, when 1 leves from eh of five plnts from eh tretment were smpled. The plnts used in this seond experiment were the sme used previously nd the seleted leves were similr (third pir of leves) to those used to determine seretion rtes. In this seond experiment, we mesured the seretion rte per unit lef re during 24 h in one lef from eh of five plnts from eh tretment nd then dethed the leves to mesure the internl ion onentrtion. Dt for the seretion rte over period of 24 h, from oth experiments, were pooled sine differenes etween them were not signifint. Lef Mf ws determined fter eliminting the middle veins. Afterwrds, lef smples were dried in ventilted oven (6 C, 48 h) nd weighed. Ions were extrted (wtersolule frtion) from 1 mg of ground lef mteril with Brz. J. Plnt Physiol., 2(2):131-14, 28

4 134 N. SUÁREZ nd E. MEDINA oiling distilled wter for 1 h. Wter extrts were nlyzed for tions (N +, K +, C 2+ nd Mg 2+ ) nd nions (Cl, NO 3, SO 4 nd oxlte) s desried ove. The ion onentrtion ws expressed on molr sis per mss of wter in fresh tissue. The totl inorgni ion onentrtion ws used to lulte their ontriution to lef Ψ s y using the vn t Hoff reltionship. Dt nlysis: The sttistil signifine of the differenes etween diurnl nd noturnl seretion rtes ws tested using Student s t-test. Differenes in the ion omposition of seretion nd leves etween slinity tretments were tested using one-wy ANOVA test nd n posteriori test (Lest signifint differene, LSD). In the se of heterogeneous vrines, we used Dunnet s T3 test. Differenes etween leves sereting for 12 nd 24 h were tested y pired t-test, for eh slinity level. A signifine vlue of P <.5 ws used throughout. Detils of the sttistil proedures followed Sokl nd Rohlf (1969). RESULTS AND DISCUSSION Lef wter reltions: As slinity inresed from to 94 mol NCl m, predwn wter potentil (Ψ w ) nd lef sp solute potentil (Ψ s ) deresed from -.56 to MP nd from to MP, respetively (Figure 1). These dereses with inresing slinity re within the rnge of vlues pulished for A. germinns nd other mngrove speies growing under similr slinity onditions (Sholnder et l., 1962; Rd et l., 1989; Suárez nd Sordo, 2; Sordo, 21). In ll ses, the differenes in Ψ w etween plnt nd sline nutrient solution vried etween -.6 nd -1. MP in plnts growing from to 43 mol NCl m, llowing wter uptke y the roots (Sholnder et l., 1962). However, Ψ etween plnt nd sline nutrient solution deresed drmtilly t 68 nd 94 mol NCl m, suggesting tht t these levels of slinity leves rehed their limit of ion umultion pity. As onsequene of the osmoti djustment, the pressure potentil (Ψ p ) remined positive in the morning under ll slinity tretments, lthough lose to zero in plnts ultivted t 94 mol NCl m (.4 MP; Figure 1). In the sme speies grown in slinities of -55 mol NCl m, Ψ p t predwn ws out 1. MP (Suárez nd Sordo, 2). However, t middy, when Ψ w rehed its minimum, Ψ p pprohed zero (<.15 MP; Suárez nd Sordo, 2; Sordo, 21). These results suggest tht A. germinns under high slinity my not mintin onstnt Ψ p throughout the dy due, t lest prtilly, to limittions in diurnl osmoti djustment. Lef Ψ s my derese s onsequene of either n umultion of solutes or derese in ell wter ontent. Thus, some speies my develop suulene to vrious levels in order to mintin suitle Ψ s (Wisel, 1972). In mngrove speies it hs een reported tht progressive inrese in N + nd Cl onentrtion per unit lef re is lmost quntittively ompensted y similr inrese in the lef wter ontent (W ), the ion onentrtion per unit of lef wter thus remining lmost onstnt (Jennings, 1976; Suárez nd Sordo, 2). In this study W per unit lef re inresed y 34% when slinity hnged from to 17 mol NCl m, ut further,, (Mp) W S p Slinity (mol m ) plnt-sol (Mp) Slinity (mol m ) Figure 1. Lef wter potentil (Ψ w, ), solute potentil (Ψ s, ) nd pressure potentil (Ψ p, ) in leves from Avienni germinns plnts grown t, 17, 43, 68 nd 94 mol NCl m. The inset shows the differene etween plnt nd solution wter potentil ( Ψ plnt-sol ) for eh slinity tretment. Points re verges nd rs orrespond to SE (n = 5). Different letters indite signifint differenes mong slinity onentrtions t P <.5.. d d e d Brz. J. Plnt Physiol., 2(2):131-14, 28

5 SALINITY EFFECTS ON ION COMPOSITION AND SALT SECRETION RATE IN Avienni germinns 135 inreses in slinity did not ugment lef suulene (Figure 2). Lef W on n re sis rnged from 265 to 375 g m -2, vlues similr to those otined for the sme (Suárez nd Sordo, 2; Sordo, 21) nd other (Bll et l., 1988; Prid et l., 24) mngroves speies. However, mximum suulene hs een previously reported in plnts growing t 34 mol m (Suárez nd Sordo, 2) nd 428 mol m (Sordo, 21). Differenes in the slinity t whih mximum W hs een oserved my e result of the lef smpling methods. In this study we used whole leves, whilst Suárez nd Sordo (2) smpled disks of the lef ldes nd Sordo (21) orreted the W per unit lef re y the reltive proportion of symplsti wter. In ontrst, with the effet of slinity on W, lef ion per unit re followed deresing exponentil urve, ttining 14% from to 94 mol NCl m. As result, ion onentrtion per unit lef wter inresed stedily with slinity, in ontrst to the ehvior oserved in this speies y Sordo (21). Lef W on dry mss nd lef re sis showed similr tendeny, euse the lef dry mss/re rtio ws not ffeted y slinity nd verged t 14 ± 16 g m -2. As result of inresed ion umultion with slinity, when ion mss ws sutrted from lef dry mss, W on the sis of dry mss showed n inrese from 8 to 13% with slinity inrese from to 94 mol NCl m (Figure 2; inset). Lef ion onentrtion: In ll slt tretments, the min ions umulted were N + nd Cl, representing nd 76-84% of ll tions nd nions present in leves, respetively. In generl, lef N + nd Cl onentrtions inresed with slinity, ut N + onentrtions stilized t 68 mol m, wheres Cl remined similr t intermedite slinity nd inresed mrkedly t the highest slinity tretment (Tle 1). The plnts grown without slt dded umulted K + in leves t levels similr to those of N + in the slt tretments. This llows Tle 1. Ction nd nion onentrtion nd seretion rte in leves of A. germinns plnts growing under ontrolled slinity onditions. Slt seretion rtes were estimted for 24 h period with 12 h photoperiod. Different letters indite signifint differenes t P <.5. n = 1 ± SD. Lef onentrtion (mol m ) Slinity (mol m ) N ± ± ± ± 78.6 d ± 44.6 d K ± ± ± ± ± Mg ± ± ± ± ± 2.11 C ± ± ± ± ± 2.1 Cl ± ± ± ± ± SO ± ± ± ± ± 2.16 NO ± ± ± ± ± 3.79 PO ± ± ± ± ± 5.83 Oxlte ± ± ± ± ± 1.6 Seretion rte (mmol m -2 d -1 ) N +.55 ± ± ± ± 8.34 d ± d K +.25± ± ± ± ±.29 Mg ±.1.22 ±.9.14 ±.7.12 ±.5.19 ±.7 C ± ± ± ± ±.25 Cl 1.21 ± ± ± ± ± 21.1 d SO 4.11 ±.6.16 ±.13.9 ±.6.16 ±.8.23 ±.12 NO 3 <.3 <.3 <.2 <.5 <.8 PO 4 <.2 <.2 <.4 <.4 <.4 Oxlte <.1 <.2 <.2 <.1 <.3 Brz. J. Plnt Physiol., 2(2):131-14, 28

6 136 N. SUÁREZ nd E. MEDINA -2 W /Are (g m ) C W/M (gg) Slinity (mol m ) Figure 2. Wter ontent (W, ) nd totl ions ( ) per unit lef re in leves from Avienni germinns plnts grown t, 17, 43, 68 nd 94 mol NCl m. The inset shows the W per unit dry mss when ion mss ws inluded ( ) or eliminted ( ). Points re verges nd rs orrespond to SE (n = 1). Different letters indite signifint differenes t P <.5. us to explin the pility of these speies to grow suessfully nd to mintin positive Ψ p in low-slinity environments (Suárez nd Medin, 26). In plnts ultivted with dded slt, the N + /K + rtio rnged from 4 to 1 nd tended to inrese only slightly with inresing slinity (Figure 3A). Similr N + /K + rtios (7-25) were mesured in mture leves of mngrove speies grown under ontrolled nd nturl onditions t lower slinity levels (Atkinson et l., 1967; Clough, 1984; Bll, 1988; Pliyvuth et l., 24; Prid et l., 24). Potssiumsodium seletive rtios (S K,N ), omputed from K + / plnt N + plnt K+ wter /N+ (Pitmn, 1977), for plnts growing in wter presene of slt rnged from 4.5 to 16.5 nd were similr to the vlues reported for other mngrove speies (Dowton, 1982; Clough, 1984; Pliyvuth, 24). The pility of A. germinns to tke up K + effiiently even in high-slinity environments my e regulted y the K + trnsporter (Trk/ HKT) fmily (Gierth nd Mäser, 27). Anywy, the vlues of S K,N otined for plnts growing t mol NCl m ws onsiderly higher thn those reported previously (16.5 vs.5; Downton, 1982; Clough, 1984). Lef Mg 2+ deresed with slinity while C 2+ onentrtions were elow 8 mol m, so tht their ontriution to the inorgni ion omposition of the lef C d Slinity (mol m ) -2 Ions/Are (mmol m ) ws negligile t ll slinities. Similr results hve een otined in A. mrin (Downton, 1982) nd other hlophytes (Mrum nd Murdoh, 1992; Pliyvuth et l., 24). Nitrte, phosphte, sulfte nd oxlte remined reltively onstnt with slinity (Tle 1). Other studies indite tht these ions only hnge with lef ge (Popp et l., 1985). In ontrol plnts K + nd Mg 2+ were the min tions (74 ± 9 nd 19 ± 6%, respetively), nd Cl nd SO 4 the min nions (45 ± 5 nd 2 ± 6%, respetively) umulted in leves (Tle 1). In plnts grown with dded slt, Cl onentrtions in leves were lwys lower thn the orresponding N + onentrtion (N/Cl > 1; Figure 3C). This hs lso een reported for Rhizophor stylos (Clough, 1984) nd A. mrin (Downton, 1982). Ction/nion rtios were lwys ove 1 (Figure 3D). Similrly, Clough (1984) reported tht lef tissues of two mngrove speies grown under sline onditions umulted times more tions thn hloride. These rtios indite tht ion lne should e ttined y the ontriution of orgni nions in ddition to oxlte (Alert nd Popp, 1977; Popp et l., 1985). Lef seretion rtes: Slt seretion rtes inresed stedily with slinity (Tle 1). We did not detet signifint differenes etween dy nd night, lthough there ws tendeny towrds higher rtes during the night period (Figure 4). The sene of diurnl rhythm in seretion rtes hs een reported for the mngrove speies A. germinns, Aegiers orniultum nd A. mrin (Sholnder et l., 1962; Wisel et l., 1986; Sordo, 21). However, Drennn nd Pmmeter (1982) oserved higher noturnl rtes in A. mrin. Seretion rtes found in leves rinsed one or twie during 24 h period were not sttistilly different (Figure 4). For A. mrin (Boon nd Allwy, 1982) nd the hlophyte Glux mritim (Rozem nd Riphgen, 1977) higher rtes of seretion were otined when lulted over short periods (minutes), ut oth studies reported stedy seretion rtes from out 2 h fter wshing. The seretion rtes of N + nd Cl inresed linerly with slinity (r 2 =.98 for N + nd.91 for Cl ). As slinity went from to 94 mm NCl m the seretion rte grew 34 times, wheres ions umulted per unit lef re inresed only 1.7 times (Tle 1). In ddition, the rtes of seretion of oth N + nd Cl were relted to the onentrtion of these ions in the lef sp (r 2 =.86 for N + Brz. J. Plnt Physiol., 2(2):131-14, 28

7 SALINITY EFFECTS ON ION COMPOSITION AND SALT SECRETION RATE IN Avienni germinns A B 2. N + /K d d d d Cl /Anion (equiv /equiv ) + - N /CI C d D Ction/Anion (equiv /equiv ) Slinity (mol m ) Figure 3. (A) N + /K +, (B) Cl /(totl nion), (C) Cl /N + nd (D) tion/nion rtios in the solution ontining sereted slt ( ) nd in lef sp ( ) from Avienni germinns plnts grown t, 17, 43, 68 nd 94 mol NCl m. Ction/nion rtios were expressed s equivlents of eh ion. Slt seretion rte ws estimted for 24 h period. Different letters indite signifint differenes t P <.5. n = 1 ± SE. nd.97 for Cl ). In ll ses, Cl seretion ws greter thn N + seretion. It seems, then, tht inresed seretion rtes ounterted prtilly the umultion of slts trnsported into the leves y the trnspirtion strem. The slt seretion rtes in A. germinns found in this study re within the rnge previously reported in A. germinns (Sordo nd Greves, 2; Sordo, 21) nd other mngrove speies (3-75 mmol m -2 d -1 ; Sholnder et l., 1962; Drennn nd Pmmenter, 1982; Bll, 1988). Our results indited tht the slt seretion proess is not sturted within the rnge of slinities pplied. This result differs from those of Sordo (21) who found in the sme speies slight derese in seretion rte t slinities ove 6 mol NCl m. However, Rozem et l. (1981) found in severl hlophyti speies derese in seretion rte ove 1 mm NCl. In ny se, our results doument the high slt seretion pility of A. germinns leves tht explins its tolerne to hypersline onditions (Tomlinson, 1986). In A. germinns, greter seretion rte t higher slinity my e relted to inresed tivity of lef slt sereting glnds, euse these remined onstnt t glnds mm -2 nd glnds mm -2 in dxil nd xil surfes, respetively, in plnts ultivted in the greenhouse t different slinities (N. Suárez, unpulished results). Lef trnspirtion rte ws 5.9 ± 1.3, 4.5 ± 1.1, 2.6 ± 1.3 nd 1.3 ±.5 mmol m -2 s -1 t 17, 43, 68 nd 94 mol NCl m, respetively. Using these vlues nd ssuming tht ll slt eing trnsported in the xylem ends up in the leves nd tht in n dult lef ll of this slt is sereted (in mture leves, slt ontent is prtilly onstnt), we estimted for eh slinity tretment tht xylem Brz. J. Plnt Physiol., 2(2):131-14, 28

8 138 N. SUÁREZ nd E. MEDINA -2-1 Seretion rte (mmol m d) * Slinity (mol m ) Figure 4. Noturnl (drk), diurnl (white) nd whole dy (grey) ion seretion rtes in leves from Avienni germinns plnts grown t, 17, 43, 68 nd 94 mol NCl m. Slt seretion rtes were estimted for 12 h (noturnl or diurnl) nd 24 h (whole dy) periods. Ctions (N + + K + + Mg 2+ + C 2+ ) nd nions (Cl, SO 4, NO 3, PO 4 nd oxlte). Brs re verges. An sterisk indites signifint differenes etween seretion rtes estimted for periods of 12 nd 24 h (P <.5; n = 5 ± SE). osmollity represents pproximtely 3-9% of tht in the externl solution. These vlues re similr to those reported previously y Sholnder et l., (1962) nd Bll (1988). We estimted tht the time required for lef to reh the mesured onentrtion in eh slinity tretment deresed from 72 to 29 dys s slinity inresed from to 94 mol NCl m. This time is resonle onsidering tht the hlf-life of lef in A. germinns dereses from 425 to 96 dys under the sme slinity tretments (Suárez nd Medin, 25). Therefore, trnspiring leves of A. germinns do umulte lrge mounts of ions during their expnsion nd seretion rtes re enough to mintin dequte physiologil levels of slt in the mture lef (Atkinson et l., 1967; Bll, 1988). However, fter lef mturity is rehed nd t high slinity, the rte of slt trnsport to the lef my not e ompensted y the seretion rte nd lef senesene would e elerted. Ion omposition of the seretion: The min ions sereted were N + nd Cl. Similr results were reported for A. mrin (Boon nd Allwy, 1986), A. germinns (Sordo nd Greves, 2), nd other slt sereting hlophytes (Atkinson et l., 1967; Rozem et l., 1981). Although Cl onentrtions in lef sp ws lower thn those of N +, rtes of seretion of the former were muh higher (Tle 1). Sodium seretion rte inresed with slinity, wheres tht of K + remined reltively onstnt in tretments with slt dded. Then, the N + /K + rtio of the seretion inresed signifintly with slinity, up to 6-7 times ove the rtios in the lef (Figure 3A). While the N + /K + rtio in the nutrient solution inresed from 37 to 97 etween 17 to 94 mol m, it only inresed y 4-1 in the lef nd in the seretion. Atkinson et l. (1967) reported similr results for other slt-sereting hlophytes. In ddition to N + in our ontrol plnts K +, Mg 2+ nd C 2+ were sereted in similr proportions representing 2, 19 nd 27% of totl tions, respetively. Nitrte, phosphte nd oxlte seretion ws very low or elow detetion limits, nd on verge represented less thn 1.5% of the totl nions sereted t ny slinity tretment (Tle 1). This my e due to their rpid inorportion nd utiliztion in the plnt metolism (Rmdn, 21), nd onfirms tht seretion is seletive phenomenon llowing protetion of plnt tissues ginst toxi ions, without losing essentil nutrients (Brhoumi et l., 27). Chloride/nion rtios were high in the sereted solution ompred with lef sp nd remined in oth ses reltively onstnt (Figure 3B). This shows the high seletivity of the seretion mehnism, ontriuting to mintin the ioni lne nd metoli tivity in spite of the high totl slt ontent (Wisel et l., 1986). In ontrst to lef omposition, the tion/nion rtio of the seretion ws very lose to 1 (Figure 3D). Similrly, in other hlophyti speies the hnges of the tion seretion nd the vrition of the Cl seretion re highly orrelted (Rozem et l., 1981; Sordo nd Greves, 2). CONCLUSIONS In onlusion, in A. germinns s in other slt sereting mngrove speies, lef slt glnds serete vriety of ions, ut the seretion onsists minly of NCl. The seretion of oth N + nd Cl ws not enough to ountert the inrese in the onentrtions of these ions in the lef sp, nd suulene did not operte s mehnism to dilute slt onentrtion in lef tissues. Our results ontrst with previous reports on severl ritil points: for exmple, (i) A. germinns grows well Brz. J. Plnt Physiol., 2(2):131-14, 28

9 SALINITY EFFECTS ON ION COMPOSITION AND SALT SECRETION RATE IN Avienni germinns 139 without dded slt, proly euse it uses K + insted of N + s inorgni osmotium under this ondition, ontrrily to wht hs een reported y others inditing tht growth of speies of the sme genus is inhiited y ultivtion without slt dditions, nd (ii) seretion rtes of oth N + nd Cl inresed with slinity without showing sturtion. Additionlly, our results show tht N + /K + rtios of the seretion inresed stedily with the slt tretment, nd give quntittive estimtion of the mintenne of K + uptke pity in spite of lrge inreses in N + onentrtion in the nutrient solution. Finlly, it is shown for the first time tht under high slinity lef umultion of N + is higher thn tht of Cl, in orrespondene with higher seretion rtes of Cl ompred to N +, leding to preferentil umultion of N + over Cl in lef tissues. Aknowledgements: To CONICIT for providing NS with PhD fellowship. Finnil support for this work ws provided y the Instituto Venezolno de Investigiones Científis nd the Interntionl Institute of Tropil Forestry (USDA-Forest Servie). To MS Guillermin Aguir for ssisting with the ion nlyses. I m grteful to the editor nd nonymous referees for helpful suggestions to improve this mnusript. REFERENCES Alert R, Popp M (1977) Chemil omposition of hlophytes from the Neusiedler lke region in Austri. Oeologi 27: Atkinson MR, Findly GP, Hope AB, Pitmn MG, Sddler HDW, West KR (1967) Slt regultion in the mngrove Rhizophor muront Lm. nd Aegilitis nnult R. Br. Aust. J. Biol. Si. 2: Bll MC, Cown IR, Frquhr GD (1988) Mintenne of lef temperture nd the optimiztion of ron gin in reltion to wter loss in tropil mngrove forest. Aust. J. Plnt Physiol. 15: Bll MC (1988) Slinity tolerne in the mngroves Aegiers orniultum nd Avienni mrin. I. Wter use in reltion to growth, ron prtitioning, nd slt lne. Aust. J. Plnt Physiol. 15: Brhoumi Z, Djeli W, Smoui A, Chïi W, Adelly C (27) Contriution of NCl exretion to slt resistne of Aeluropus littorlis (Willd) Prl. J. Plnt Physiol. 164: Boon PI, Allwy WG (1982) Assessment of lef-wshing tehniques for mesuring slt seretion in Avienni mrin (Forsk.) Vierh. Aust. J. Plnt Physiol. 9: Boon PI, Allwy WG (1986) Rtes nd ioni speifiity of slt seretion from exised leves of the mngrove, Avienni mrin (Forsk.) Vierh. Aqut. Bot. 26: Clough BF (1984) Growth nd slt lne of the mngroves Avienni mrin (Forsk.) Vierh. nd Rhizophor stylos Griff. in reltion to slinity. Aust. J. Plnt Physiol. 11: Downton WJS (1982) Growth nd osmoti reltion of the mngrove Avienni mrin s influened y slinity. Aust. J. Plnt Physiol. 9: Drennn P, Pmmenter NW (1982) Physiology of slt seretion in the mngrove Avienni mrin (Forsk.) Vierh. New Phytol. 91:1-15. Dshid WJ, Pltt-loi KA, Thomson WW (1992) Epiderml peels of Avienni germinns (L.) Stern: useful system to study the funtion of slt glnds. Ann. Bot. 7: Gierth M, Mäser P (27) Potssium trnsporters in plnts Involvement in K + quisition, redistriution nd homeostsis. FEBS Lett. 581: Jennings DH (1976) The effets of sodium hloride on higher plnts. Biol. Rev. 51: Leshem Y, Levison E (1972) Regultion mehnisms in the slt mngrove Avienni mrin growing on the Sini littorl. Oeol. Plnt. 7: Lüttge U (1971) Struture nd funtion of plnt glnds. Annu. Rev. Plnt Physiol. 22: Mrum KB, Anderson SJ, Engelkr MC (1998) Slt glnd ion seretion: slinity tolerne mehnism mong five Zoysigrss speies. Crop Si. 38: Mrum KB, Murdoh CL (1992) Slt tolerne of the ostl slt mrsh grss, Sporoolus virginius (L.) Kunth. New Phytol. 12: Pliyvuth C, Clough B, Ptnponpioon P (24) Slt uptke nd shoot wter reltions in mngroves. Aqut. Bot. 78:3496. Prid AK, Ds AB, Mittr B (24) Effets of slt on growth, ion umultion, photosynthesis nd lef ntomy of the mngrove, Bruguier prviflor. Trees 18: Pitmn MG (1977) Ion trnsport into the xylem. Annu. Rev. Plnt Physiol. 28: Brz. J. Plnt Physiol., 2(2):131-14, 28

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