Salt-induced regulation of photosynthetic capacity and ion accumulation in some genetically diverse cultivars of radish (Raphanus sativus L.

Transcription

1 Joural of Applied Botay ad Food Quality 8, (1) 1 Departmet of Botay, Uiversity of Agriculture, Faisalabad, Pakista Departmet of Botay ad Microbiology, Kig Saud Uiversity, Riyadh, Saudi Arabia 3 Departmet of Botay, GC Uiversity, Faisalabad, Pakista Salt-iduced regulatio of photosythetic capacity ad io accumulatio i some geetically diverse cultivars of radish (Raphaus sativus L.) 1 Zahra Noree, 1, Muhammad Ashraf, * 3 Nudrat Aisha Akram (Received April 8, 11) * Correspodig author Summary Salt-iduced chages i growth, various gas exchage characteristics, ad io accumulatio were examied durig a greehouse experimet o six radish (Raphaus sativus L.) cultivars i.e., Radish Red Neck, Radish Lal Pari, Radish Mio Japai, Radish 4 Days, Mau Early ad. Varyig levels of salt (, 8, ad 16 mm NaCl) of the growth medium markedly decreased the shoot ad root dry weights, relative water cotets, osmotic potetial, photosythetic ad traspiratio rates, stomatal coductace, substomatal CO cocetratio, C i /C a ratio, water use efficiecy, leaf ad root K + ad Ca +, while icreasig the leaf ad root Na + ad Cl - of all six radish cultivars. Of all cultivars, Mau Early ad were higher i shoot ad root dry weights tha the other cultivars, ad thus, they were raked as relatively salt tolerat. However, oe of the earlier metioed physiological attributes was foud to be a effective criterio i discrimiatig the six radish cultivars. Overall, the respose of each cultivar to salt stress appraised usig various physiological attributes was specific. Itroductio It is ow well established that high salt cocetratios i water or soil adversely affect various biochemical ad physiological processes leadig to poor plat vigor ad yield i most plat species (ASHRAF, 4; MUNNS ad TESTER, 8). Salt-iduced osmotic stress ad io toxicity are the major causes of plat growth reductio (ZHU, 1; SAIRAM ad TYAGI, 4). A umber of mechaisms ivolved i plat salt tolerace, io homeostasis, ad differetial regulatio of biochemical ad physiological processes have gaied a sigificat importace (ASHRAF, 4; MUNNS, ; GENC et al., 7). Previously, it was foud that growth suppressio may be a ospecific effect of salts, depedig more o the total cocetratio of soluble salts tha o specific ios (MAAS ad NIEMAN, 1978). It is well documeted that the accumulatio of Na + ad CI - ios i the leaves is the most importat factor which causes cosiderable ijury to ultra-structure of differet orgaelles of plats subjected to salt stress (MARTINEZ-BARROSO ad ALVAREZ, 1997). It is suggested that geerally crop cultivars which show more tolerace to salt stress, accumulate CI - i their roots ad as a whole prevet the egative effects of salt o plat growth (SAIED et al., 3). Cellular K + /Na + ad Ca + /Na + ratios also ca affect salt tolerace of plats to a varyig extet (YASAR, 7; YILDIZ et al., 8). Salt stress also adversely affects plat photosythesis (DUBEY, ; ARFAN et al., 7; NOREEN ad ASHRAF, 8). However, it is difficult to assess whether a reduced rate of photosythesis is the cause of growth reductio, or merely the cosequece of growth reductio (MUNNS ad TESTER, 8). For istace, salt-iduced reductio i growth of barley (FRICKE et al., 4) ad maize (CRAMER ad BOWMAN, 1991) has bee due to rapid chage i leaf expasio rate resultig ito a buildup of uused photosythates i growig tissues (MUNNS, 1993; MUNNS et al., ). I view of PAUL ad FOYER (1) accumulatio of uused photosythates uder salie coditios may geerate feedback sigals to dow-regulate photosythesis to compesate the reduced demad arisig from growth ihibitio. However, at high salt stress, excessive accumulatio of salts i the cytoplasm or chloroplast of mesophyll cells ihibits photosythetic ezymes thereby reducig the photosythetic rate (MUNNS, 1993; DUBEY, ). The reductio i photosythesis uder salt stress ca also be attributed to a decrease i stomatal closure because higher stomatal coductace is kow to icrease CO diffusio ito leaves thereby favorig higher photosythetic efficiecy (DOWNTON, 1977; SEEMANN ad CRITCHLEY, 198). Durig a greehouse experimet o radish plats, salt stress (9 ad 4 mm NaCl) cosiderably decreased the photosythetic activity resultig i reduced plat growth, leaf area, chlorophyll cotets ad chlorophyll fluorescece (JAMIL et al., 7). Radish (Raphaus sativus L.), beig a potetial vegetable, is utilized i a variety of ways, e.g., fresh, pickled, dried, cooked as well as a fodder. It is a importat source of medicial foods ad oe of the most recalcitrat crop plats i ature (CURTIS, 3). Geerally, radish is categorized as moderately sesitive to saliity (MAAS ad HOFFMAN, 1977), while SONNEVELD (1988) reported a low sesitivity of radish to salt stress. Despite of beig a potetial vegetable crop world-over, little is kow about its mechaism of salt tolerace. Thus, the premier objectives of this study were to observe the effect of varyig levels of salt o some key physiological processes such as photosythetic capacity ad mieral utriet accumulatio i six geetically diverse radish cultivars. It was also examied whether photosythetic capacity ad patter of accumulatio of utriets could be used as effective selectio criteria for salt tolerace i radish. Materials ad methods To examie chages i growth, gas exchage characteristics, some water relatio attributes ad utriet accumulatio i six cultivars/ lies of radish (Raphaus sativus L.) i.e., Radish Red Neck, Radish Lal Pari, Radish Mio Japai, Radish 4 Days, Mau Early ad, a greehouse experimet was coducted at the Botaical Garde, Uiversity of Agriculture, Faisalabad. The seeds of all cultivars were obtaied from the Ayub Agricultural Research Istitute, Faisalabad, Pakista. Five seeds of each cultivar were sow per plastic pot (3. cm diameter ad 9 cm deep) filled with 1 kg dry river sad. The plats were thied to two plats per pot after 14 d of growth. Three NaCl treatmets (, 8, ad 16 mm) i Hoaglad s utriet solutio were applied to three week-old plats. The NaCl cocetratio was icreased step-wise i aliquots of 4 mm every day util the appropriate cocetratio attaied. After days of salt treatmet, two plats from each pot were uprooted carefully ad separated ito shoots ad roots. The plat samples were ove dried at 6 C ad dry weights recorded. Before harvestig the plats, the data for the followig parameters were recorded:

2 9 Z. Noree, M. Ashraf, N.A. Akram Leaf osmotic potetial Oe fully expaded yougest leaf from each plat was excised ad froze i a freezer below - o C for more tha seve days after which time the froze leaf material was thawed ad the sap extracted by pressig the material with a glass rod. The sap was used directly for the determiatio of osmotic potetial i a vapor pressure osmometer (Vapro, ). Relative water cotet (RWC) Relative water cotet was determied followig JONES ad TURNER (1978) by usig a leaf of uiform size from each replicate. Gas exchage characteristics To measure differet gas exchage parameters such as et CO assimilatio rate (A), traspiratio (E), stomatal coductace (g s ) ad sub-stomatal CO cocetratio (C i ), a ifra-red gas aalyzer (Aalytical Developmet Compay, Hoddesdo, Eglad) was used. All measuremets were made o a fully expaded yougest leaf of each plat from 1. to 1. h with the followig specificatios/ adjustmets of the leaf chamber: atmospheric pressure 99.9 kpa, water vapor pressure ito the chamber raged from 6. to 8.9 mbar, temperature of leaf raged from 8.4 to 3.4 o C, ambiet temperature raged from.4 to 7.9 o C, molar flow of air per uit leaf area 43.3 mmol m - s -1, PAR at leaf surface was maximum up to 918 µmol m - s -1, ad ambiet CO cocetratio was 3 ppm. Determiatio of mieral elemets i plat tissues The dried groud plat leaf or root material (.1 g) was take i a digestio flask ad to this digestio flask, 1 ml of digestio mixture (.4 g of Se ad 14 g of LiSO 4. H O to 3 ml of H O, mixed well ad 4 ml of coc. H SO 4 were added slowly to it keepig it i a ice bath) was added ad placed the flask o a hot plate. The temperature was icreased gradually from C to C. Whe the mixture tured black,. ml of HClO 4 was added to the sample, ad heated agai util the material became colorless (ALLEN et al., 1986). The flasks were removed from the hot plate ad cooled dow. The solutio was diluted up to ml i a volumetric flask ad filtered. The filtrate was used for the determiatio of K +, Ca + ad Na +. Statistical aalysis Aalysis of variace of all parameters was computed usig the MSTAT computer package (Mstat Developmet Team, 1989). Stadard errors of meas were also calculated to observe itra-mea variatio. Results Salt stress markedly suppressed the shoot ad root dry weights of all radish cultivars, though radish cultivars differed sigificatly i respose to varyig NaCl cocetratios of the growth medium (Fig. 1). From the mea data, it is apparet that lies Mau Early ad had greater shoot ad root dry biomass tha the other cultivars at all salt regimes. Leaf osmotic potetial i all radish cultivars sigificatly decreased (P.1) with icrease i NaCl cocetratio i the growth medium. Cultivar followed by Radish Red Neck was the lowest i leaf osmotic potetial of all radish cultivars at the highest salt regime, whereas followed by Radish Mio Japai was lower tha the other cultivars at 8 mm NaCl. Salt stress mm Salt stress 8 mm Salt stress 16 mm Salt stress mm Salt stress 8 mm Salt stress 16 mm Shoot dry wt (g/plat) S,.6***; Cvs,.7***; S x Cvs,.6s Root dry wt (g/plat) S,.86***; Cvs,.1**; S x Cvs,.6s Leaf osmotic potetial (-MPa) S,.8***; Cvs,.17***; S x Cvs,.8* RWC (%) S, 8.4***; Cvs, 137.7***; S x Cvs, 11.74s Leaf Na + (mg g -1 d.wt) 1 7 S, ***; Cvs, 1.8s; S x Cvs, 18.8s Radish 4 days Fig. 1 Shoot ad root dry weights, lea osmotic potetial, relative water cotets ad shoot ad root Na cocetratio of six radish Fig. 1: Shoot ad root dry weigh hts, leaf osmotic potetial, relative water cotets ad shoot ad root Na + cocetratio ce of six radish (Raphaus sativus L.) cultivars subjected to differet cocetratios of NaCl (Meas ±S.E; = 4). Values showig mea squares from aalysis of variace of data for each variable. *, ** ad *** sigificat at.,.1 ad.1, 1, respectively; s = o-sigificat; S = Salt stress; Cvs = cultivars. Root Na + (mg g -1 d.wt) S, 71.34***; Cvs,.7***; S x Cvs, 1.8* Radish 4 days

3 Photosythetic capacity ad io accumulatio i radish 93 Leaf relative water cotet (RWC) of all radish cultivars sigificatly decreased with icrease i NaCl of the growth medium (Fig. 1). The cultivars also differed sigificatly i this water relatio attribute. Leaf RWC was foud to be highest i Radish Red Neck followed by Radish Lal Pari at the highest (16 mm) NaCl level (Fig. 1). Additio of salt to the rootig medium caused a sigificat reductio i all gas exchage attributes (et CO assimilatio rate, traspiratio rate, stomatal coductace, sub-stomatal CO, C i /C a ratio, water use efficiecy) (Fig. ) ad the cultivars did ot differ sigificatly i all these gas exchage attributes except i traspiratio rate. However, Radish Lal Pari followed by Radish Red Neck ad Radish Mio Japai had greater traspiratio rate tha the other cultivars at the highest salt regime. Na + cocetratios i the leaves ad roots of the six radish cultivars icreased sigificatly with icrease i salt level of the rootig medium (Fig. 1). Cultivar Radish 4 Days had cosiderably higher leaf Na + cocetratio tha the other cultivars at the highest salt cocetratio. I cotrast, root Na + cocetratio was the highest i cv. of all cultivars at the highest salt stress. While, at 1 mm NaCl, cvs. ad Mau Early were higher i root Na + as compared with the other cultivars. Leaf ad root Cl - cocetratios icreased sigificatly i the six radish cultivars with the additio of NaCl to the growth medium, ad the cultivars also differed sigificatly i these physiological attributes. Cultivars Radish Red Neck, Radish Mio Japai ad had greater leaf Cl - tha the other cultivars at the highest salt regime, while root Cl - was higher i Radish Red Neck ad Radish 4 Days compared with the other cultivars at 1 mm NaCl (Fig. 3). A marked reductio i K + accumulatio i the leaves ad roots of the six radish cultivars was observed due to impositio of salt stress to the growth medium, particularly at the highest salt regime (Fig. 3). A maximum leaf K + was observed i Radish Lal Pari followed by Radish Mio Japai ad at the highest saliity level, whereas the same was true for root K + i Mau Early ad (Fig. 3). Leaf ad root Ca + of the six radish cultivars decreased sigificatly with icrease i salt level of the rootig medium (Fig. 3). The cultivars also differed sigificatly i accumulatio of Ca + i the leaves or roots. Leaf Ca + was higher i Radish Red Neck ad Radish Lal Pari compared with the other cultivars at 1 mm NaCl. However, cultivar Radish Red Neck followed by Radish Mio Japai had greater accumulatio of Ca + i the roots at the highest salt regime. Discussio I the preset study, varyig levels of salt caused a marked reductio i the shoot ad root dry weights i the six radish cultivars. Salt-iduced reductio i the radish cultivars is aalogous to what has earlier bee observed i a umber of plat species icludig rice (ALAM et al., 4), wheat (ARFAN et al., 7; SHAHBAZ et al., 8), spiach, cucumber ad pepper (KAYA et al., 1), suflower (AKRAM et al., 9; NOREEN et al., 9), tomato (SATTI ad AL-YAHYAI, 199), cotto (LEIDI ad SAIZ, 1997) etc. The preset study also revealed cosiderable iter-cultivar variatio i salt tolerace i the set of six geetically diverse cultivars of radish. Earlier, a great magitude of iter-cultivar (itra-specific) variatio has bee observed i may crop plats, e.g., barley ad wheat Salt stress mm Salt stress 8 mm Salt stress 16 mm Salt stress mm Salt stress 8 mm Salt stress 16 mm A (µmol CO m - s -1 ) 1 1 S, 49.***; Cvs,.89s; S x Cvs, 3.31s E (mmol H O m - s -1 ) S, 7.7***; Cvs,.49*; S x Cvs,.3*** S, ***; Cvs, 97.3s; S x Cvs, 136.s S, ***; Cvs, 39.3s; S x Cvs, 38.9s g s (mmol m - s -1 ) C i (µmol mol -1 ) C i /C a ratio S,.36***; Cvs,.3s; S x Cvs,.4s a o ay Radish 4 days WUE (µmol CO /mmol H O) S, 1.18***; Cvs,.78s; S x Cvs,.847s Radish 4 days Fig. Differet gas exchage characteristics of six radish (Raphaus sativus L.) cultivars subjected to differet cocetratios of NaCl Fig. : Differet gas exchage characteris stics of six radish (Raphaus sativus L.) cultivars subjected to differet fer cocetratio s of NaCl (Mea ±S.E; = 4). Values showig mea squares from aalysis of variace of data for each variable. * ad *** sigificat at. ad.1, respectively; s = o-sigificat; S = Salt stress; Cvs = cultivars.

4 94 Z. Noree, M. Ashraf, N.A. Akram Leaf K + (mg g -1 d.wt) 1 1 Salt stress mm Salt stress 8 mm Salt stress 16 mm S, 73.7***; Cvs, 13.87**; S x Cvs, 3.64s Root K + (mg g -1 d.wt) 1 1 Salt stress mm Salt stress 8 mm Salt stress 16 mm S, 3.9***; Cvs, 17.74***; S x Cvs,.76*** Leaf Cl - (mg g -1 d.wt) S, 7.***; Cvs, 179.***; S x Cvs, 7.9s Root Cl - (mg g -1 d.wt) S, 876.6***; Cvs,.31**; S x Cvs, 1.9s Leaf Ca + (mg g -1 d.wt) S, 8.4***; Cvs,.663*; S x Cvs,.34s p d Fig. Fig. 3: 3 Shoot ad adroot root K +, K Cl, - ad Cl - ad Ca + cocetratios Ca cocetratios ofsix radish of (Raphaus six radish sativus (Raphaus L.) cultivars sativus subjected L.) cultivars to differet subjected cocetratios to differet of NaCl (Mea±S.E; cocetratios = 4). Values showig mea squares from aalysis of variace of data for each variable. *, ** ad *** sigificat at.,.1 ad.1, respectively; s = o-sigificat; S = Salt stress; Cvs = cultiva ars. t K Radish 4 days Root Ca + (mg g -1 d.wt) S, 16.3***; Cvs,.13s; S x Cvs,.684* ec Radish 4 days (RICHARDS et al., 1987), rice (AKBAR ad YABUNO, 1974), caola (ULFAT et al., 7; ATHAR et al., 9), ad tomato (FOOLAD, 1996; PEREZ-ALFOCEA et al., 1996). The growth reductio i the radish cultivars might have bee due to a limited supply of metabolites to youg growig tissues, ad regulatio of a umber of biochemical or physiological processes icludig photosythesis, leaf water relatios ad utriet imbalace (MAAS ad NIEMAN, 1978; MUNNS ad JAMES, 3; ASHRAF, 4; JUAN et al., ). I the preset study, photosythetic ad traspiratio rates, stomatal coductace (g s ), sub-stomatal CO (C i ), ad relative itercellular CO (C i /C a ) of all the radish cultivars were reduced liearly with icrease i salt cocetratio of the growth medium. The reductio i photosythesis uder saliity stress ca also be attributed to a decrease i stomatal closure, because higher stomatal coductace is kow to icrease CO diffusio ito leaves thereby favorig higher photosythetic activity (SEEMANN ad CRITCHLEY, 198; DUBEY, ). I the preset study, et CO assimilatio rate (A ) had a positive relatioship with all these gas exchage variables (A vs g s or C i or C i/ca or E, r =.74***;.666***;.66***;.794***; ad g s vs C i r =.681***). These results idicate that salt-iduced reductio i growth i all six radish cultivars was due to declie i photosythesis, ad declie i et photosythesis uder salt stress occurred pricipally due to stomatal closure, which is i agreemet with a umber of earlier studies (BRUGNOLI ad BJORKMAN, 199; DIONISIO-SESE ad TOBITA, 1998; RAZA et al., 6; ULFAT et al., 7). However, it was ot possible to discrimiate amog the radish cultivars o the basis of these gas exchage attributes. For istace, salt tolerat cultivars cvs. Mau Early ad were lower i g s compared to the salt sesitive cultivars (Fig. 1), but they were similar i photosythetic capacity. These results support the argumet that g s is ot always associated with A. This has earlier bee observed i differet crops such as suflower (RAWSON ad CONSTABLE, 198), ad Adropogo glomeratus (BOWMAN, 1987). These fidigs suggest that cultivar variatio for salt tolerace i radish was ot due to differeces i stomatal coductace ad thus it caot be used as a effective selectio criterio for salt tolerace i radish. I view of some earlier reports it is evidet that a positive relatioship betwee photosythetic rate ad crop growth or yield uder salie coditios exists i differet crops such as Spiacia oleracea (ROBINSON et al., 1983), Asparagus offi cialis (FAVILLE et al., 1999), six Brassica diploid ad amphiploid species (NAZIR et al., 1; ASHRAF, 1), wheat (RAZA et al., 6), ad 34 caola cultivars (ULFAT et al., 7). All these reports suggest that the rate of photosythesis ca be used as a selectio criterio for salt tolerace, particularly where a close relatioship betwee photosythesis ad growth uder salt stress is foud (QASIM et al., 3; ASHRAF, 4). If we draw relatioships betwee shoot dry biomass ad et CO assimilatio rate of six radish cultivars differig i salt tolerace, growth i terms of dry biomass of all cultivars was positively associated with et CO assimilatio rate (A vs shoot dry weight r=.91***). However, such a relatioship was ot foud whe idividual radish cultivars differig i salt tolerace were compared with respect to their rate of photosythesis. For example, salt tolerat cvs. Mau Early ad higher i growth were similar to the salt sesitive Radish Lal Pari i et CO assimilatio rate, at differet salt cocetratios of the growth medium. These results are i close coformity with some earlier fidigs i differet crops i which a o-sigificat relatioship betwee growth ad photosythetic rate was observed such as i Diplache fusca (MYERS et al., 199), Trifolium repes (ROGERS ad NOBLE, 199), ad sprig wheat

5 Photosythetic capacity ad io accumulatio i radish 9 (HAWKINS ad LEWIS, 1993; ASHRAF ad O LEARY, 1996). Thus, these results show that photosythetic rate caot be used as a potetial selectio criterio for salt tolerace i radish. I the preset study, leaf osmotic potetial or RWC was also ot associated with the growth of six radish cultivars. These results are supported by the coclusive statemet of MUNNS (1993) i a comprehesive review that relatioship betwee leaf turgor ad salt tolerace occurs occasioally i.e. maiteace of higher plat water status is ot associated with salt tolerace. Thus, the differetial growth of radish cultivars uder salt stress may have bee due to factors other tha water relatios. The most promiet effect of saliity o plat growth is the excessive accumulatio of Na + ad Cl - i the leaves resultig i ioic imbalace, specific io effects, ad utriet-deficiecy symptoms i plats (GRATTAN ad GRIEVE, 1999; ZHANG ad BLUMWALD, 1; MUNNS, ; ASHRAF, 4). Thus, it is imperative to assess patter of io accumulatio of toxic ios i differet plat parts of a crop species to uderstad as to whether the species uses partial exclusio or iclusio mechaism for toleratig toxic ios preset i its growth medium. I the preset study, the radish cultivars differed sigificatly i accumulatio of Na + K +, Ca + ad Cl - i the leaves ad roots. For example, the relatively salt tolerat cvs. Mau Early ad accumulated relatively higher cocetratios of Na + i their roots thereby checkig the uptake of this toxic io to the shoot. Such kid of mechaism has already bee observed i differet crops such as Hordeum vulgare (CARDEN et al., 3), tomato (FOOLAD, 1996), wheat (WYN JONES et al., 1984; MUNNS ad JAMES, 3), ad Trifolium alexadrium (ASHRAF et al., 1986). Overall, the declie i the growth of all six radish cultivars examied i the preset study was due to reductio i photosythetic capacity ad io accumulatio. However, a positive correlatio was observed betwee shoot dry weight ad photosythetic rate as well as reductio i photosythesis was foud to be closely associated with decreased stomatal coductace. However, oe of the physiological attributes determied i the preset study was foud to be effective i discrimiatig the radish cultivars for salt tolerace. Ackowledgmet The work preseted i this mauscript is a part of research work coducted by Ph.D scholar Dr. Zahra Noree, (PIN No B-49) whose study was fuded by the Higher Educatio Commissio through the Idigeous Ph.D Scheme. Refereces AKBAR, M., YABUNO, T., 1974: Breedig for salie resistat varieties of rice. I-Comparative performace of some rice varieties to saliity durig early developmet stages. Japa. J. Breed. 4, AKRAM, M.S., ASHRAF, M., AKRAM, N.A., 9: Effectiveess of potassium sulfate i mitigatig salt-iduced adverse effects o differet physiobiochemical attributes i suflower (Heliathus auus L.). Flora 4, ALAM, M.Z., STUCHBURY, T., NAYLOR, R.E.L., RASHID, M.A., 4: Effect of saliity o growth of some moder rice cultivars. J. Agro. 3, 1-1. ALLEN, S.K., DOBRENZ, A.K., SCHONHORST, M.H., STONER, J.E., 1986: Heritability of NaCl tolerace i germiatig alfalfa seeds. Agro. J. 77, ARFAN, M., ATHAR, H.R., ASHRAF, M., 7: Does exogeous applicatio of salicylic acid through the rootig medium modulate growth ad photosythetic capacity i differetly adapted sprig wheat cultivars uder salt stress? J. Plat Physiol. 6, ASHRAF, M., 1: Relatioships betwee growth ad gas exchage characteristics i some salt-tolerat amphidiploid Brassica species i relatio to their diploid parets. Eviro. Exp. Bot. 4, ASHRAF, M., 4: Some importat physiological selectio criteria for salt tolerace i plats. Flora 199, ASHRAF, M., O LEARY, J.W., 1996: Resposes of some ewly developed salttolerat geotypes of sprig wheat to salt stress, II. Water relatios ad photosythetic capacity. Acta Bot. Neerl. 4, ASHRAF, M., MCNEILLY, T., BRADSHAW, A.D., 1986: Tolerace of sodium chloride ad its geetic basis i atural populatios of four grass species. New Phytol. 13, ATHAR, H.R., ASHRAF, M., WAHID, A., JAMIL, A., 9: Iducig salt tolerace i caola (Brassica apus L.) by exogeous applicatio of glyciebetaie ad prolie: respose at the iitial growth stages. Pak. J. Bot. 41, BOWMAN, W.D., 1987: Effect of saliity o leaf gas exchage i two populatios of C 4 o halophyte. Plat Physiol. 8, BRUGNOLI, E., BJORKMAN, O., 199: Growth of cotto uder cotiuous saliity stress: ifluece o allocatio patter, stomatal ad o-stomatal compoets ad dissipatio of excess light eergy. Plata 187, CARDEN, D.E., WALKER, D.J., FLOWERS, T.J., MILLER, A.J., 3: Sigle cell measuremet of the cotributios of cytosolic Na + ad K + to salt tolerace. Plat Physiol. 131, CRAMER, G.R., BOWMAN, D.C., 1991: Kietics of maize leaf elogatio. I. Icreased yield threshold limits short-term, steady state elogatio rates after exposure to saliity. J. Exp. Bot. 4, CURTIS, I.S., 3: The oble radish: past, preset ad future. Treds Plat Sci. 8, DIONISIO-SESE, M.L., TOBITA S., 1998: Atioxidat resposes of rice seedligs to saliity stress. Plat Sci. 13, 1-9. DOWNTON, W.J.S., 1977: Photosythesis i salt-stressed grapevies. Aust. J. Plat. Physiol. 4, DUBEY, R.S., : Photosythesis i plats uder stressful coditios. I: M. Pessarakli (ed.), Hadbook photosythesis, d Ed., CRC. Press, New York, USA. FAVILLE, M.J., SILVESTER, W.B., GREEN, T.G.A., JERMYN, W.A., 1999: Photosythetic characteristics of three asparagus cultivars differig i yield. Crop Sci. 39, FOOLAD, M.R., 1996: Geetic aalysis of salt tolerace durig vegetative growth i tomato, Lycopersico esculetum Mill. Plat Breedig 116, 3-8. FRICKE, W., AKHIYAROVA, G., VESELOV, D., KUDOYAROVA, G., 4: Rapid ad tissue-specific chages i ABA ad i growth rate i respose to saliity i barley leaves. J. Exp. Bot., GENC, Y., MCDONALD, K.G., TESTER M., 7: Reassessmet of tissue Na + cocetratio as a criterio for saliity tolerace i bread wheat. Plat Cell Eviro. 3, GRATTAN, S.R., GRIEVE C.M., 1999: Saliity-mieral utriet relatios i horticultural crops. Sci. Hortic. 78, HAWKINS, H.J., LEWIS, D.O.A.M., 1993: Combiatio effect of NaCl saliity, itroge from the calcium cocetratio o the growth, io cotet ad gaseous exchage properties of Triticum aestivum L. cv. Gamtoos. New Phytol. 14, JAMIL, M., REHMAN, S., LEE, K.J., KIM, J.M., KIM, H.S., RHA, E.S., 7: Saliity reduced growth PS photochemistry ad chlorophyll cotet i radish. Sci. Agric. 64, JONES, M.M., TURNER T.C., 1978: Osmotic adjustmet i leaves of sorghum i respose to water deficits. Plat Physiol. 61, JUAN, M., RIVERO, R.M., ROMERO, L., RUIZ J.M., : Evaluatio of some utritioal ad biochemical idicators i selectig salt-resistat tomato cultivars. Eviro. Exp. Bot. 4, KAYA, C., KIRNAK, H., HIGGS, D., 1: The effects of supplemetary potassium ad phosphorus o physiological developmet ad mieral utritio of cucumber ad pepper cultivars grow at high saliity (NaCl). J. Plat Nutr. 4, -7. LEIDI, E.O., SAIZ, J.F., 1997: Is saliity tolerace related to Na + accumulatio i uplad cotto seedligs? Plat Soil 19, MAAS, E.V., HOFFMANN, G.J., 1977: Crop salt tolerace-curret assessmet.

6 96 Z. Noree, M. Ashraf, N.A. Akram J. Irrigatio Draiage Divisio, ASCE, 13, MAAS, E.V., NIEMAN, R.H., 1978: Physiology of plat tolerace. I: Jug, G.A. (ed.), Crop tolerace to sub-optimal lad coditios, Soil Sci. Soc. Am. Spec. Pub. Madiso, USA. MARTINEZ-BARROSO, C., ALVAREZ, C.E., 1997: Toxicity symptoms ad tolerace of strawberry to saliity i the irrigatio water. Sci. Hortic. 71, MSTAT Developmet Team, 1989: MSTAT user s guide: A microcomputer program for the desig maagemet ad aalysis of agroomic research experimets. Michiga State Uiv. East Lasig, USA. MUNNS, R., 1993: Physiological processes limitig plat-growth i salie soils -some dogmas ad hypotheses. Plat Cell Eviro. 16, 1-4. MUNNS, R., : Comparative physiology of salt ad water stress. Plat Cell Eviro., 39-. MUNNS, R., : Gees ad salt tolerace: brigig them together. New Phytol. 167, MUNNS, R., JAMES, R.A., 3: Screeig methods for saliity tolerace: a case study with tetraploid wheat. Plat Soil 3, MUNNS, R., PASSIOURA, J.B., GUO, J.M., CHAZEN, O., CRAMER, G.R., : Water relatios ad leaf expasio: importace of time scale. J. Exp. Bot. 1, MUNNS, R., TESTER, M., 8: Mechaisms of saliity tolerace. Au. Rev. Plat Biol. 9, MYERS, B.A., NEALES, T.R., JONES, M.B., 199: The ifluece of saliity o growth, water relatios ad photosythesis i Diplache fusca (L.) P. Beauve. Ex Roemer ad Schultes. Aust. J. Plat Physiol. 17, NAZIR, N., ASHRAF, M., EJAZ, R., 1: Geomic relatioships i oilseed Brassica with respect to salt tolerace-photosythetic capacity ad io relatios. Pak. J. Bot. 33, NOREEN, S., ASHRAF, M., HUSSAIN, M., JAMIL, A., 9: Exogeous applicatio of salicylic acid ehaces atioxidative capacity i salt stressed suflower (Heliathus auus L.) Plats. Pak. J. Bot. 41, NOREEN, Z., ASHRAF, M., 8: Iter- ad itra-specific variatio for salt tolerace i turip (Brassica rapa L.) ad radish (Raphaus sativus L.) at the iitial growth stages. Pak. J. Bot. 41, PAUL, M.J., FOYER, C.H., 1: Sik regulatio of photosythesis. J. Exp. Bot., PEREZ-ALFOCEA, F., BALIBREA, M.E., SANTA CRUZ, A., ESTAN, M.T., 1996: Agroomical ad physiological characterizatio of saliity tolerace i a commercial tomato hybrid. Plat Soil 18, 1-7. QASIM, M., ASHRAF, M., JAMIL, A., ASHRAF, M.Y., REHMAN, S., RHA, E.S., 3: Water relatios ad leaf gas exchage properties i some elite caola (Brassica apus) lies uder salt stress. A. Appl. Biol. 14, RAWSON, H.M., CONSTABLE, G.A., 198: Carbo productio of suflower cultivars i field ad cotrolled eviromets. I. Photosythesis ad traspiratio of leaves, stems ad heads. Aust. J. Plat Physiol. 7, RAZA, S.H., ATHAR, H.R., ASHRAF, M., 6: Ifluece of exogeously applied glyciebetaie o the photosythetic capacity of two differetly adapted wheat cultivars uder salt stress. Pak. J. Bot. 38, RICHARDS, R.A, DENNETT, C.W., QUALSET, C.O., EPSTEIN, E., NORLYN, J.D., WINSLOW, M.D., 1987: Variatio i yield ad biomass i wheat, barley, ad triticale i a salt-affected field. Field Crops Res. 1, ROBINSON, S.P., DOWNTON, W.J.S., MILLHOUSE, J.A., 1983: Photosythesis ad io cotet of leaves ad isolated chloroplasts of salt-stressed spiach. Plat Physiol. 73, ROGERS, M.E., NOBLE, C.L., 199: Variatio i growth ad io accumulatio betwee two selected populatios of Trifolium repes L. differig i salt tolerace. Plat Soil 146, SAIED, S., KEUTGEN, A.J., NOGA, G., 3: Effects of NaCl stress o leaf growth, photosythesis ad ioic cotets of strawberry cvs Elsata ad Koroa. Acta Hort. 69, SAIRAM, R.K., TYAGI, A., 4: Physiology ad molecular biology of saliity stress tolerace i plats. Curr. Sci. 86, SATTI, S.M.E., AL-YAHYAI, 199: Saliity tolerace i tomato: implicatios of potassium, calcium ad phosphorus. Commu. Soil Sci. Plat Aal. 6, SEEMANN, J.R., CRITCHLEY, C., 198: Effects of salt stress o the growth, io cotet, stomatal behaviour ad photosythetic capacity of a salt sesitive species. Phaseolus vulgaris L. Plat Physiol. 8, -6. SHAHBAZ, M., ASHRAF, M., ATHAR, H.R., 8: Does exogeous applicatio of 4-epibrassiolide ameliorate salt iduced growth ihibitio i wheat (Triticum aestivum L.)? Plat Growth Regul., SONNEVELD, C., 1988: The salt tolerace of greehouse crops. Neth. J. Agric. Sci. 36, ULFAT, M., ATHAR, H.R., ASHRAF, M., AKRAM, N.A., JAMIL, A., 7: Appraisal of physiological ad biochemical selectio criteria for evaluatio of salt tolerace i caola (Brassica apus L.). Pak. J. Bot. 39, WYN JONES, R.G., GORHAM, J., MCDOWELL, E., 1984: Orgaic ad iorgaic solute cotets as selectio criteria for salt tolerace i the Triticeae. I: Staples, R.C., Oisse, G.H.T. (eds.), Saliity tolerace i plats, Wiley, New York. YASAR, F., 7: Effect of salt stress o io ad lipid peroxidatio cotet i gree beas geotypes. Asia J. Chem. 19, YILDIZ, K., UZAL, Ö., YILMAZ, H., 8: Cosequeces of NaCI saliity o growth ad o accumulatio i selected strawberry cultivars. Eur. J. Hortic. Sci. 73, ZHANG, H.X., BLUMWALD, E., 1: Trasgeic salt-tolerat tomato plats accumulate salt i foliage but ot i fruit. Nat. Biotechol. 19, ZHU, J.-K., 1: Plat salt tolerace. Treds Plat Sci. 6, Address of the correspodig author: Nudrat Aisha Akram, udrataauaf@yahoo.com, Tel.: , Fax: