African Journal of Biotechnology Vol. 9(41), pp. 6937-6942, 11 October, 2010 Available online at http://www.academicjournals.org/AJB DOI: 10.5897/AJB10.780 ISSN 1684–5315 © 2010 Academic Journals Full Length Research Paper The effects of salt stress on the growth, biochemical parameter and mineral element content of some maize (Zea mays L.) cultivars Emine Budakli Carpici*, Necmettin Celik and Gamze Bayram Department of Field Crops, Faculty of Agriculture, Gorukle Campus, Uludag University, 16059 Bursa, Turkey. Accepted 26 August, 2010 Six cultivars of maize (Zea mays L.) (Ada-523, Bora, C-955, PR 3394, Progen-1550 and Trebbia) were subjected to 0 and 100 mM NaCl and their response to salt stress were determined by growths related to relative shoot growth weight (RSGR), shoot and root dry weight and stress tolerance index by biochemical parameters associated with total chlorophyll and proline contents and by mineral element + + + + contents such as Na and K contents and K \Na ratio. Cultivars were grown in greenhouse in perlit supplied with a complete nutrient solution and salt treatment started 14 days after planting. The results indicate that salinity decreased RSGR, shoot and dry weight, stress tolerance index, total chlorophyll + + + + and K contents and K \Na ratio, but increased proline and Na accumulations. Especially, proline accumulation appears to react to salt stress damage rather than a plant response associated with salt + tolerance. Another striking point is that the rates of increase in Na content were higher in shoots than + + in roots. According to the results, salt tolerance index, Na and K contents are reliable criteria for preliminary selection in early growth stage of maize. + Key words: Maize, salt stress, relative shoot growth rate, total chlorophyll, proline, Na . INTRODUCTION Salinity is one of the most important problems in irrigated reasons are important and have part in reduction of plant soils of the arid and semi-arid areas in the world. growth under salt stress. The first one is lowering of Currently, there is about 275 million hectars of irrigated external water potential due to salt present outside the land of which about 20% is salt affected (Ghassemi et al., root. The second is the senescence of leaves due to the 1995). On the other hand, the ever growing world popu- accumilation of ion in the older leaves; there is a true lation causes great pressure on marginal lands to be difference in salt tolerance appearance (Akram et al., brought into cultivation in the developing and under 2007). Sensitive cultivars accumulate ions more quickly developing countries, which were previously not cropped than tolerant cultivars and this ion accumulation leads to due to their high degree of natural salinity (Flowers and leaf death and progressive death of plant (Munns, 2002). Yeo, 1995). In Turkey, there are approximately 2 - 2.5 Ion inbalances due to ion accumilation caused by salt million hectars of arable land suffering from salinity stress show their negative effects by reducing shoot and problems (Kaya et al., 2003). root growths and increasing some amino acids including Salinity has three potential effects on plants: Lowering proline. Proline is a very important indicator because it is of water potential, specific ion toxicity (sodium and chloride) osmotically very active and regulates the accumulation of and interference with the uptake of essential nutrients. useable nitrogen (N), contributes to membrane salinity The latter may not be considered because it has no and mitigates the effect of NaCl on cell membrane dis- immediate effect due to mobile reserve nutrients present truption (Ashraf et al., 2004). However, its role in salt in plants (Flowers and Flowers, 2005). Two of the above tolerance of plants is not so clear. Some findings indicate that there is no healing effect of proline on salt stress (Lacerda et al., 2003) but others indicate clearly that proline enhances plants aganist salt stress (Ahmad et al., *Corresponding author. E-mail: ebudakli@uludag.edu.tr. 1981; Chowdhury et al., 1993; Petrusa and Winicov, 1997; 6938 Afr. J. Biotechnol. Taban et al., 1999). Beside these, there are findings indi- nutrient solution. The nurtient solution was prepared according to cating negative relation between proline and salt tolerant Maas et al. (1986) and contained 2.5 mM Ca(NO3)2, 3.0 mM KH2PO4, 1.5 mM MgSO4, 0.1 mM KNO3, 0.1 mM Fe-EDTA, 0.023 characters of plants (Lutts et al., 1996; Aziz et al., 1998; mM H3BO3, 0.005 mM CuSO4 and 0.01 mM H24Mo7N6O24.4H2O. Lutts et al., 1999). Salt treatment was started 14 days after planting. Sodium chloride The mechanism of plant adaptation required to survive of 100 mM was added to the nutrient solution, and after salt in saline conditions is the same in all the plants. How- -1addition, its electrical conductivity was 12.58 dS m . The control ever, adaptations are at their extreme in halophytes, but pots were treated with NaCl-free nutrient solution, with an electrical -1 can be found at different degress in glycophytes (Flowers conductivity of 1.37 dS m . To avoid osmotic shock, saline treatment was imposed incrementally, increasing the concentration by 50 mM and Flowers, 2005). Variation in salt tolerance of every 12 h until the final concentration of 100 mM was reached. glycophytes occurs between and within species and has Day and night temperatures were 35.8 and 19.7°C, respectively in been quantified for many crops (Mass and Hoffman, the greenhouse. 1976; Francois and Mass, 1994; Flowers and Yeo, 1981). Quick screening procedure has been adopted by many researchers for different crops in their early growth phase RSGR and dry weights of shoot and root (Ashraf et al., 2002; Eker et al., 2006; Khan et al., 2006). To determine the dry weight of shoots and roots, plants were After wheat and rice, maize (Zea mays L.) is the third harvested at 1, 9, 17 and 25 days after salt application. Thus, most important cereal crop grown all over the world in a obtained samples were dried at 78°C for 48 h and then weighed. wide range of climatic condition. Maize, being highly Hereafter, the shoot samples obtained at 1, 9, 17 and 25 days after cross pollinated, has become highly polymorphic through salt application were used for calculation of RSGR values. A formula for this calculation was used which was developed by the course of natural and domesticated evolution and Kingsbury et al. (1984). Samples obtained only 25 days after salt thus contains enormous variability (Paternian, 1990) in application were used to calculate the shoot and root dry weights. which salinity tolerance may exist. Maize is considered as moderately salt sensitive (Mass + + and Hofffman, 1977; Katerji et al., 1994; Ouda et al., Measurement of total chlorophyll, proline, Na and K 2008; Carpici et al., 2009). Despite its high place among Fully expanded leaves were sampled at 25 days after salt cereals, few findings have been obtained to improve salt application for total chlorophyll and proline analyses. Fresh samples tolerance in this crop. Improvement for salt tolerance were used for these analyses. For total chlorophyll content analysis, would be of considerable value for this moderately sensitive each sample of 0.1 g was extracted with 10 ml of 80% (v/v) acetone crop when it is grown on irrigated areas with salt problems. and filtered. Then, absorbancies were determined with a spectro- -1 Thus, the effective and accelarated improvement of salt photometer at 645 and 663 nm. Total chlorophyll content (mg g tolerance cultivars through screening is urgently needed. FW) was estimated by the equations of Arnon (1949). -1 Extraction and determination of proline (μmol g FW) was With this urgency in mind, the present research was determined spectrophotometrically by an acid ninhydrin procedure conducted to assess the extent of variability in salt (Bates et al., 1973). Leaf samples of 0.5 g were extracted with 3% tolerance in six maize cultivars and to determine the most sulphosalicylic acid. Extracts of 2 ml were held for 1 h in boiling tolerant cultivars. water by adding 2 ml ninhydrin and 2 ml glacial acetic acid, after For this purpose, relative shoot growth weight (RSGR), which cold toluene of 4 ml was added. Proline content was measured by a spectrophotometer at 520 nm and calculated as shoot and root dry weights, stress tolerance index, total -1 + + + + µmol g FW aganist standard proline. chlorophyll, Na and K contents, K /Na ratio and proline Shoot and root samples were wet digested by using the HNO3 + accumulation of six maize cultivars commonly grown as + +HCIO4 (4:1) mixture. Na and K were determined by the flame grain and silage were determined in plants grown under + + emission (Horneck and Hanson, 1998). Then, K /Na ratio was normal or salty conditions and these data were used in calculated. determining salt tolerance of cultivars. Experimental design and statistical analysis MATERIALS AND METHODS The experiment was conducted by a completely randomized design with three replications. Analysis of variance was performed by Minitab Plant materials and salt treatment statistical program. Means were groupped by using the least significant difference (LSD) test at 5% level. Six cultivars of maize (Zea mays L.) (Ada-523, Bora, C-955, PR3394, Progen-1550 and Trebbia) were used as plant entries in this study. Cultivars were grown in perlit-filled plastic pots of 5.5 L in the greenhouse of the Uludag University, Turkey, from May to August, RESULTS AND DISCUSSION 2006. Seeds were graded and the big and uniform shaped seeds were Effect of salinity stress on plant growth used and their surface sterilized with 2% sodium hypochlorite for 10 min. After sterilization, seeds were washed with distilled water three Variance analysis showed that RSGR values of cultivars times. Six seeds per pot were used. Open surface of pots was covered with aluminum foil to prevent growth of algae. After were affected significantly by salt treatment at every germination, aluminum foils were removed, the seedlings were week in which samples were taken (P < 0.001). thinned to three plant per pot. Pots were irrigated twice a day with Reduction in RSGR values of genotypes continiously Carpici et al. 6939 0.180 0.160 Ada-523 0.140 0.120 Bora 0.100 C-955 0.080 PR 3394 0.060 Progen-1550 0.040 Trebbia 0.020 0.000 Control Stress Control Stress Control Stress -1 -1 Figure 1. RSGR (g plant day ) of the maize cultivars grown under control and salt stress conditions. RSGR was calculated for days after salt application 1 to 9 (Week 1), 9 to 17 (Week 2) and 17 to 25 (Week 3). -1 -1 -1 Table 1. Effect of salinity on shoot dry weight (g plant ), root dry weight (g plant ), salt tolerance index, total chlorophyll (mg g FW) and -1 proline (μmolg FW) contents of different maize cultivars. Shoot dry weight Root dry weight Salt tolerance Total chlorophyll Proline -1 -1 -1 -1 Cultivar (g plant ) (g plant ) index (%) (mg g FW) (μmolg FW) 0 mM 100 mM 0 mM 100 mM 0 mM 100 mM 0 mM 100 mM 0 mM 100 mM Ada-523 14.663b 7.415d 3.941ab 2.373c 100a 53cd 1.914ab 1.681ab 1.233ab 0.079d Bora 12.636bc 7.005d 3.896ab 2.144c-e 100a 57c 2.012ab 1.551ab 0.146cd 0.757b-d C-955 10.982b-d 9.298cd 4.221a 2.139c-e 100a 76b 2.093a 1.933ab 0.423b-d 0.863a-d PR 3394 21.276a 7.500d 3.649b 1.622e 100a 38d 1.632ab 1.632ab 0.306cd 0.940a-d Progen-1550 12.900bc 7.319d 4.005ab 1.776de 100a 54c 1.996ab 1.402b 0.317cd 1.706a Trebbia 12.082bc 7.307d 3.768ab 2.227cd 100a 60c 1.535ab 1.553ab 0.202cd 1.012a-c Mean (Salt) 14.090A 7.641B 3.913A 2.047B 100A 56B 1.863A 1.625B 0.438B 0.893A Means followed by the same small letter and by the same capital letter for each components are not statistically different by LSD at 0.05 level. increased with time. For instance, while at Week 1, the 955 decreased only about 15.33%, while reduction reduction of RSGR value was 15.67%, it was 24.60 and percentages of other five genotypes were very high and 40.21% at Week 2 and 3, respectively. Interaction effect ranged from 39.52 to 64.74% (Table 1). From these of salt stress x cultivar was of significance (P < 0.05) only results, it may be expressed that the cultivar C-955 is in Week 3. The significant interaction effect determined more salt stress tolerant than the other cultivars. Similar arose mostly from the different response of C-955, Bora results obtained from researches on maize were reported and PR 3394 to salt stress. Indeed, the reduction in by other researchers (Hoffman et al., 1983; Zalba and RSGR value of PR 3394 was very great and reached as Pienemann, 1998; Cicek and Cakirlar, 2002; high as 70.80%, while RSGR values of C-955 and Bora Ashrafuzzaman et al., 2003; Neto et al., 2004). were rather small (Figure 1). These results indicate that Interaction of salt stress x cultivar was found insignificant, the negative effect of salt stress on RSGR values although the effect of salt stress on root growth was increased as plants became older and varied with found significant (Table 1). However, the roots of all the genotypes. Similar results were reported by Netondo et cultivars were less affected by salinity than their shoots. al. (2004). Most researches on this subject yielded similar results Shoot development of each genotype was prevented (Lacerda et al., 2001; Neto et al., 2004; Eker et al., 2006; by salt stress. However, prevention degree of shoot Akram et al., 2007). Under the light of these findings, it development due to salt stress changed with genotypes. may be said that the use of the data of shoots as The lost of shoot dry weight in C-955 was lower than selection criteria obtained from plant breeding studies those of other genotypes. Indeed, shoot dry weight of C- would be more realistic than the use of root data. Roots RSGR (g plant-1 day-1) 6940 Afr. J. Biotechnol. + + + + Table 2. Effect of salinity on Na (%), K (%) and K /Na ratio of shoot and root of different maize cultivars. Shoot Root + + + + + + + + Na (%) K (%) K / Na Na (%) K (%) K / Na Cultivar 100 100 100 100 100 0 mM 100 mM 0 mM 0 mM 0 mM 0 mM 0 mM mM mM mM mM mM Ada-523 0.043f 1.117a 2.707 2.517 66.37c 2.28d 0.557d 3.603b 1.220b 0.417d 2.20c 0.12e Bora 0.043f 0.530e 2.220 2.027 53.91c 3.83d 0.533d 3.257c 1.680a 0.520d 3.15a 0.16e C-955 0.033f 0.583de 2.730 2.500 85.82b 4.37d 0.507d 3.330bc 0.710c 0.367de 1.41d 0.11e PR 3394 0.040f 0.977b 2.500 2.133 64.90c 2.18d 0.517d 3.970a 1.130b 0.487d 2.19c 0.12e Progen-1550 0.020f 0.747c 2.510 2.130 125.78a 2.86d 0.477d 3.633b 1.223b 0.237e 2.59b 0.07e Trebbia 0.020f 0.660cd 2.263 1.960 113.16a 2.97d 0.493d 3.406bc 1.077b 0.523d 2.16c 0.15e Mean (Salt) 0.033B 0.769A 2.211B 2.488A 84.99A 3.08B 0.514B 3.533A 1.173A 0.425B 2.29A 0.12B Means followed by the same small letter and by the same capital letter for each components are not statistically different by LSD at 0.05 level. + - absorb ions including Na and Cl and transfer them to great differences in the increased proline contents of tops of plants with less harms in root functions. Whereas, cultivars. Great increases in proline contents were found salt causes serious demages in biochemical functions of as 418.49% in Bora, 438.17% in Progen-1550 and top of plant. 400.99% in Trebbia. Less increases recorded in C-955 and PR 3394 were 104.01 and 207.18%, respectively (Table 1). Proline accumulation in response to environ- Salt tolerance ındex mental stresses has been considered by a number of authors as an adaptive trait concerned with stress tole- The effect of salinity on salt tolerance indices of cultivars rance, and it is generally assumed that proline is acting was significant (Table 1). The ranges of the salt tolerance as a compatible solute in osmotic adjustment (Larher et indices of cultivars were very wide. Variations were al., 1993). Its accumulation is caused by both the between 38 and 76% in relation with salt stress. The salt activation of its biosynthesis and inactivation of its degra- tolerance index of C-955 was the highest and that of PR dation. It is believed that the accumulation of proline, a 3394 was the lowest. These striking results indicate that compatible solute, may help to maintain the relatively the salt tolerance index is a reliable criteria for preliminary high water content necessary for growth and cellular selection in early growth stage of maize. Similar findings function. Further more, it was shown that the capability of were reported by Bagci et al. (2003). a number of crop plants to accumulate proline in response to salt or other stresses was highly variable between or within species (Ashraf et al., 2004; Naqvi et al., 1994; Salt stress-total chlorophyll relationship Lutts et al., 1996; Aziz et al., 1998; Lutts et al., 1999). Salinity caused decreases in total chlorophyll of all cultivars + + + + except PR 3394 and Trebbia (Table 1). The decrease is Na and K concentration and K /Na ratio more appearent in sensitive genotypes than in tolerant ones. The reduction in total chlorophyll content is to be The earlier mentioned values were affected by salinity + expected under stress conditions. Its stability depends on and genotypes. While Na content increased, the content + + + membrane stability, which under saline condition seldom of K and K /Na ratio decreased by salinity (Table 2). remain intact (Khan et al., 2009). Similar results were The same studies were conducted and similar results also reported by Iqbal et al. (2006), Ashraf et al. (2005), were found by some other authors (Hu and Schmidhalter, Khan et al. (2009), Oncel and Keles (2002), Lacerda et 1997; Sagi et al., 1997; Bagcı et al., 2003; Beck et al., al. (2003) and Almodares et al. (2008). Total chlorophyll 2004; Netondo et al., 2004; Akram et al., 2007). Another + of plants may be considered as an indicator in improwing striking point is that the rates of increase in Na content new genotypes for salt stress depending on the present were higher in shoots than in roots. However, in contrast + + or other findings. to Na , K content had a different response to salinity in shoot and root. On the other hand, there were no + + differences in K /Na values of shoots and roots under Salt stress-proline content relation salt stress. The response of cultivars to salinity were different in respect to shoot and root growth. In saline + Salt stress in this study, increased proline content in all conditions, the increase of Na uptake in shoots of Bora cultivars except that of Ada-523. However, there were and C-955 were lower than in shoots of the other Carpici et al. 6941 + cultivars. The lowest decreases of K content in shoots of Cicek N, Cakirlar H (2002). The Effect of Salinity on Some Physiological + Ada-523, Bora and C-955 were recorded. Na contents of Parameters in Two Maize Cultivars. Bulg. J. Plant Physiol. 28(1-2). 66-74. roots in Bora, Ada-523 and C-955 indicated less in- Eker S, Comertpay G, Konuşkan O, Ulger AC, Ozturk L, Cakmak I + creases than the other cultivars. C-955 lost less K under (2006). Effect of Salinity Stress on Dry Matter Production and Ion salt stress than the other cultivars (Table 2). According to Accumulation in Hybrid Maize Varieties. Turk. J. Agric. For. 30: 1-9. + + + + the results, the value of K , Na and K /Na ratio may be Flowers TJ, Flowers SAM (2005). Why Does Salinity Pose Such a Difficult Problem for Plant Breeders? Agric. Water Manage. 78: 15- more reliable as a selection criteria when they are 24. determined in shoots than in roots. Flowers TJ, Yeo AR (1981). Variability in the Resistance of Sodium In conclusion, cultivars with lower reductions in RSGR, Chloride Salinity within Rice (Oryza sativa L.) Varieties. New Phytol. + + + total chlorophyll, K content and K /Na ratio are resistant 81: 363-373. Flowers TJ, Yeo AR (1995). 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