Journal of Horticultural Science ISSN: 0022-1589 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/thsb19 Effects of salinity on nitrate, total nitrogen, soluble protein and free amino add levels in tomato plants F. Perez-Alfocea, M. T. Estan, A. Santa Cruz & Maria C. Bolarin To cite this article: F. Perez-Alfocea, M. T. Estan, A. Santa Cruz & Maria C. Bolarin (1993) Effects of salinity on nitrate, total nitrogen, soluble protein and free amino add levels in tomato plants, Journal of Horticultural Science, 68:6, 1021-1027, DOI: 10.1080/00221589.1993.11516443 To link to this article: http://dx.doi.org/10.1080/00221589.1993.11516443 Published online: 27 Nov 2015. Submit your article to this journal Article views: 1 View related articles Citing articles: 13 View citing articles Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=thsb19 Download by: [UNSW Library] Date: 26 October 2017, At: 21:19 Journal of Horticultural Science (1993) 68 (6) 1021-1027 Effects of salinity on nitrate, total nitrogen, soluble protein and free amino acid levels in tomato plants By F. PEREZ-ALFOCEA, M. T. ESTAN, A. SANTA CRUZ and MARIA C. BOLARIN Centro de Edafologia y Biologia Aplicada del Segura, CSIC, Apdo. 4195, E-30080 Murcia, Spain Downloaded by [UNSW Library] at 21:19 26 October 2017 SUMMARY The effects of salinity on nitrogen compounds were studied in three tomato (L. esculentum Mill.) genotypes of different salt tolerance. The plants were grown under controlled conditions, and the salt treatments (0, 70 and 140 mM NaCI) were applied for three (Harvest 1) and ten (Harvest 2) weeks. The effects of salinity on total Nand particularly N0 3 concentrations depended partly on the NaCllevel and duration of the stress, but mainly on the different degrees of salt tolerance of the genotypes. In Harvest 1, the most tolerant genotype (GC-72) showed the highest N0 3 increase in the roots and no decreases in stem and leaf with increasing salinity; the intermediate-tolerant genotype (P-73) showed a similar response to that of GC-72 only at 70 mM NaCI. However, the most sensitive genotype (Volgogradskij) showed the greatest reductions in stem and leaf N0 3 concentrations with salinity. With longer durations of stress the different responses between the more tolerant genotypes were less evident; only Volgogradskij continued to show the highest decreases in stem and leaf N0 3 concentrations. A restriction of N0 3 transport from the root to the shoot was noted in the plants of the more tolerant genotypes treated for three weeks. This capacity for retention disappeared when the salinity induced reductions in the total N0 3 contents in the plants, as in the harvest 2. There was an inverse relation between N0 3 and Cl accumulations in shoots of all genotypes and its slope decreased with the salt sensitivity of the genotype. There was no relation between the leaf protein content and the salt tolerance of the tomato genotypes. In Harvest 1, a higher accumulation of amino acids, especially proline, was found in the leaves of the more tolerant genotypes at 140 mM NaCI. However, in Harvest 2, a similar accumulation of leaf proline was found in all genotypes, independent of their salt tolerances, and the other amino acid contents remained similar or else decreased with salinity. EXPOSURE to NaCl may affect plant growth through osmotic effects, by a specific ion effect or by inadequate uptake of an essential nutrient (Greenway and Munns, 1980). Nitrogen, a substrate required for cell growth, is severely affected under salt stress (Frota and Tucker, 1978; Luque and Bingham, 1981). Wallace and Berry (1981) suggested that wheat (Triticum aestivum, L.) yield reduction due to increased salinity might not be due entirely to Cl toxicity, but partly to induced deficiency of N0 3 caused by the high external Cl concentration. However, in other cases, leaf nitrogen concentrations were unaffected or increased by salinity (Bhivare and Nimbolkar, 1984; Seemann and Critchley, 1985). Contradictory results have also been found in tomato; total N and/or N0 3 contents have been reported to increase (Pessarakly and Tucker, 1988), to remain the same (Hernando eta/., 1967) or to decrease (Papadopoulos eta!., 1985). Thus, effects of salt stress on N and/or N0 3 contents in the plant are inconsistent and unpredictable. Salinity affects the metabolism of nitrogen containing compounds, e.g. protein synthesis and free amino acid pool composition (Poljakoff-Mayber, 1982). In general, rates of protein synthesis are lower in NaCl treated plants (Aspinall, 1986) but there is no clear evidence that this causes growth reductions; in many Downloaded by [UNSW Library] at 21:19 26 October 2017 1022 Salinity and tomato plants cases, salinity induces an increase in total amino acids and the accumulation of proline, as in tomato (Shannon et al., 1987). Different degrees of salt tolerance were found in the three tomato genotypes used in this study (Caro et al., 1991). However, the mechanisms of salt tolerance were similar, because they excluded Na and Cl from the shoots when plants were salt treated in the short-term, and they accumulated in the roots. In treatments of longer duration, the ability to Na and Cl regulate was only absent in the most salt sensitive genotype (Volgogradskij), resulting in a massive influx of both ions into the shoot system (Perez-Alfocea et at., 1993). To complete this study of the physiological responses of these tomato genotypes to salinity, the effects of NaCl-induced salinity on total N and different nitrogen compounds (N0 3, soluble proteins and free amino acids) were determined in different plant parts of these genotypes. MATERIALS AND METHODS Plant material and culture conditions Seeds of three genotypes of tomato (Lycopersicon esculentum Mill) Volgogradskij, P-73 and GC-72, were germinated and plants grown in washed silica sand under controlled conditions, as described previously (Perez-Alfocea et al., 1993). Briefly, a half-strength Hoagland's solution was applied from the apperance of the first leaf, and increased to full-strength two weeks after sowing until the end of the experiment. NaCI treatments (0, 70 and 140 roM) were applied from the appearance of sixth to seventh leaves (3 weeks). The NaCI was added to the nutrient solution in increments of around 25 mmoll- 1• Three replicate plants per treatment were harvested three and ten weeks after the salt treatment was completed. The plants were cut into roots, stems (including petioles) and leaves (lamina) only, rinsed with distilled water and then analyzed. Analyses Nitrate and total N contents of roots, stems and leaves were determined and expressed as concentrations of dry material. N0 3 content was analyzed by the method of Lambert and Dubois (1971). Total N was determined by the micro-Kjeldahl method. Analyses of soluble proteins, total free amino acids and proline were made on lyophilized leaf tissue. A 100 mg leaf sample was homogenized with 5 ml of 50 mM phosphate buffer, at pH 7.8 in the presence of 1% (w/v) PVP and 0.01% (w/v) Triton X-100, and centrifuged at 8000 g for 15 min. Aliquots of the supernatant were used to determine the soluble proteins following the method of Bradford (1976). Total free amino acids (Moore and Stein, 1948) and proline (Bates et at., 1973) were measured using ninhydrin. Analysis of variance and regression were performed according to SYSTAT standard methods (Wilkinson, 1990). RESULTS Nitrate and total nitrogen concentrations Concentrations of N0 3 were higher in stems than in roots and leaves for all treatments and all genotypes (Figure 1). In Harvest-1, N0 3 concentration increased significantly in roots of salt treated plants compared with the controls with GC-72 showing the highest increases. In stems and leaves, the highest N0 3 decreases with salinity were found in 'Volgogradskij' treated with 70 mM NaCI. In P-73, leaf N0 3 concentration decreased only at 140 mM, whereas in GC-72, there were no decreases in N0 3 concentration in stem or leaf as salinity increased. The tendency for root N0 3 concentrations to increase with salinity was lower in Harvest 2 than in Harvest 1. However, greater decreases of stem and leaf N0 3 concentrations were found in all genotypes when salt treatments were applied for ten weeks. The total N concentration was less affected by salinity than that of N0 3 (Figure 2). Thus, only 'Volgogradskij' significantly increased the root total N concentration at 140 roM NaCl in Harvest 2. Similar variations between N0 3 and total N were shown by stem tissues. In leaves, only 'Volgogradskij' and P-73 showed significantly decreases in total-N concentration in Harvest 1, whereas in Harvest 2, all genotypes had lower total-N concentrations, especially at 140 roM NaCl, similar to the variations of N0 3 with salinity, although the reductions with salinity were lower. Total nitrate contents and relationship between N01 and Cl accumulation Mean values for total amounts of N0 3 in the F. PEREZ-ALFOCEA, M. T. EsTAN, A. SANTA CRuz and MARIA C. BOLARIN Harvest-1 0.5 Harvest-2 Root genotypes (P-73 and GC-72) and decreased slightly in their shoots. In 'Volgogradskij', shoot N0 3 decreased about 80% compared with the control plants at 70 mM NaCI. In Harvest 2, Harvest-2 Harvest -1 0.4 Root I 0.3 0.2 1023 2.0 1.5 0.1 Downloaded by [UNSW Library] at 21:19 26 October 2017 1.0 'j' 0 0 E 0 Stem 0 mM ~ 70 mM !Ill 11.0 mM 2.5 2.0 0.5 "";" ~ 0 0 _; 1.5 0 c: 0 ....0 1.0 c: cu u c: 0.5 0 Stem "' E .!: E E 4.0 c: 3.0 0 mM ~ 70 mM 0] 140 mM 0 ....0 ....c: 0 L. u ... 0 2.0 cu u c: z 0 Leaf 0.7 u 1.0 z 0.6 .... 0 0 0 0.5 1- 0.4 Leaf 4. 0 0.3 3.0 0.2 0.1 2. 0 v p GC v p GC FIG. 1 The effect of sahmty on NO, concentrations m different plant parts of three tomato genotypes (V, Volgogradskij; P, P-73: GC, GC-72) grown at three NaCIIevels for three (Harvest I) and ten (Harvest 2) weeks. Vertical bars are theSE of the mean. 1.0 n v p GC v P GC FIG. 2 plants were determined from dry weight data and N0 3 concentration in roots and shoots (Figure 3). In Harvest 1, N0 3 accumulation increased only in the roots of the more tolerant The effect of salimty on total N concentrations m different plant parts of three tomato genotypes (V, Volgogradskij; P, P-73; GC. GC-72) grown at three NaCtlevels for three (Harvest I) and ten (Harvest 2) weeks. Vertical bars are theSE of the mean. 1024 Salinity and tomato plants Harvest -2 Harvest -1 Root 60 0.12 0 0 mM ~ ITJl 70 m M HO mM 45 0.08 30 0.04 , 5 0 E E c 0 0 ~ 0 Shoot Downloaded by [UNSW Library] at 21:19 26 October 2017 ~ E :> E 3.0 30 0 2.5 25 "' 2.0 20 1.5 15 1.0 10 :> u u 0 z 0.5 0 ~v 5 0 p GC l v ~ m p GC FIG. 3 The effect of salinity on total amounts of N0 3 in root and shoot of three tomato genotypes (V, Volgogradskij; P, P-73; GC. GC-72) grown at three NaCllevels for three (Harvest 1) and ten (Harvest 2) weeks. N0 3 accumulation by roots increased slightly at 70 mM NaCI and decreased at 140 mM in all genotypes except 'Volgogradskij', which had drastically reduced N0 3 for both levels, TABLE I Lmear regresswn equatwns (y =a + bx) between N0 3 and Cl accumulations in root and shoot of three tomato genotypes grown at different NaCI levels (0, 70, and 140 mM) for three (Harvest I) and ten (Harvest 2) weeks root Harvest Genotype 2 Vol go P-73 02-72 Volgo P-73 02-72 a b shoot a b n.s. 4.9 -3.77 0.93**• 0.05 0.17 0.68* 2.3 -0.38 0.72* 0.04 0.21 0.92*** 2.0 -0.18 0.71* n.s. 36.4 -2.91 0.87** n.s. 37.1 -1.46 0.84** n.s. 15.2 -0.29 0.84** n.s .. not significant; *, **,***,significant at P=O.OS, 0.01 and 0.001, respectively. although it had the highest N0 3 accumulation · in control plants. At this stage of growth, the shoots reduced their N0 3 uptake with salinity, these decreases being higher than those observed in the first harvest. In the more tolerant genotypes P-73 and GC-72, N0 3 accumulation was directly correlated with Cl accumulation in root and inversely correlated with Cl accumulation in shoot in Harvest 1 (Table I). In the most salt-sensitive genotype (Volgogradskij), a highly significant relationship between N0 3 and Cl accumulation was found only in the shoot. The slopes of the regression decreased in relation to the salt-sensitivity of the genotypes, with 'Volgogradskij' showing the lowest value. At Harvest 2, no relationship between N0 3 and Cl was found in roots, whereas in shoots the N0 3 was inversely correlated with Cl in all cultivars and the slopes also decreased according to salt-sensitivity. Leaf soluble protein, total free amino acid and proline Results of the protein and total free amino acid analyses in leaves are shown in Table II. In Harvest 1, the protein content decreased significantly with salinity in all genotypes, whereas the total amino acid contents increased significantly with salinity, mainly in 'GC-72'. In 'Volgogradskij', total free amino acid increase was due only to proline concentration; in 'P-73' and 'GC-72', in addition to the proline, the remaining total free amino acids also increased, especially in 'GC-72'. At 140 mM NaCI, proline contents increased according to the salt-tolerance of the genotypes. In Harvest 2, protein concentrations decreased significantly only in 'P-73' and remained constant in other genotypes. Total free amino acids increased with salinity in the three genotypes, but these increases were exclusively due to proline; 'in P-73' the remaining amino acids decreased with salinity. DISCUSSION Pessarakly and Tucker (1988) indicated that total N concentration in different tomato plant parts increased markedly with increasing salinity. In this study, both total Nand N0 3 concentrations increased only in roots, but generally decreased in stems and leaves. The decrease of leaf N0 3 content with salinity has been F. PEREZ-ALFOCEA, M. T. ESTAN, A. SANTA CRUZ and MARIA C. BOLARIN 1025 TABLE II Concentrations (mg gDW- 1) of soluble protems, total free amino acids and proline in leaves of three tomato genotypes grown at different NaCllevels for three (Harvest 1) and ten (Harvest2) weeks Harvest 1 Genotype NaCl mM Volgo 0 70 140 P-73 0 70 140 0 70 140 GC-72 Proteins 1 99.3b 72.7a 78.3a 121.1b 90.0a 99.9a 101.8b 72.6a 90.lab Harvest 2 Total Aas Pro Proteins Total Aas Pro 15.0a 18.8b 22.9c 10.9a 14.7b 22.9c 8.7a 16.5b 27.0c O.la 3.lb 7.8c O.la 2.0b 9.7c O.la 3.5b 11.5c 38.7a 36.6a 38.0a 73.6b 66.3ab 54.9a 33.la 34.6a 34.2a 15.0a 20.3b 31.3c 16.1a 16.2a 27.1b 15.0a 18.6b 30.4c 0.2a 4.8b 14.8c O.la 4.9b 14.0c O.la 6.6b 14.5c Downloaded by [UNSW Library] at 21:19 26 October 2017 'Mean separation by Dunnet test, for each genotype values not sharing a common letter differ sigmficantly at P=0.05. reported not only in tomato cultivars but also in wild tomato species (Rush and Epstein, 1976; Papadopoulos and Rending, 1983). Salinity effects on N0 3 and N concentrations depend on the salinity level and the duration of stress (Sinha et at., 1986; Al-Rawahy et at., 1992). In roots, N0 3 increases with salinity were higher when the salt treatments were applied for short durations (three weeks), whereas the N0 3 decreases in leaves were higher when the salt treatments were applied for longer (ten weeks). However, effects of salinity on N0 3 concentrations in different plant parts were mainly due to the different degrees of salt tolerance of the genotypes. Thus, the most tolerant genotype (GC-72) showed the highest increase in N0 3 in roots, and no significant differences in N0 3 concentrations of the stem and leaf were found between the control and the high-salt treatment in Harvest 1. At this time, stem and, especially leaf N0 3 concentrations, increased at 70 mM NaCl with respect to the control. On the contrary, the most sensitive genotype (Volgogradskij) showed greatest reductions in stem and leaf N0 3 concentrations with salinity. Substrate salinity inhibits N0 3 uptake by roots (Sanchez Conde, 1976; Papadopoulos and Rending, 1983). The results of this study suggest that genotypes with higher salt-sensitivity will show a greater inhibition of N0 3 uptake by roots. Moreover, the more tolerant genotypes showed restricted transport of NaCl to the shoot in the salt-treated plants in the shortterm. The capacity to retain N0 3 in the root was lost when the salinity induced large reductions in the total N0 3 content in the plant, as occurred in Harvest 2 with the more tolerant cultivars. At this time, N0 3 absorption in the most salt-sensitive cultivar decreased with salinity both in the shoot and in the root. The reduction in N0 3 content in salt-treated plants was probably due to the inhibition of N0 3 uptake by Cl (Aslam et at., 1984; McClure et at., 1986), which might occur by the interaction between these ions at sites for ion transport (Cram, 1983). If this is the case, an inverse relationship between N0 3 and Cl accumulations might be expected, as reported by Kafkafi et at. (1982). The inverse relationship between N0 3 and Cl accumulations in shoots of all genotypes has been clearly demonstrated. In both harvests, the more sensitive the genotype, the lower the slope of the regression, which suggests that the slopes could be used as an index of salt tolerance. Moreover, a direct relationship between N0 3 and Cl concentrations was found in the roots of the more tolerant genotypes, as both ions were accumulated in roots when the plants were salt-treated for three weeks. Decreasing leaf protein concentrations, a typical response to NaCl-stress (Cusido eta/., 1987) were found in all genotypes in the Harvest 1 and in 'P-73' in Harvest 2, but no relation between protein contents and the salt tolerances of tomato genotypes was observed (Helal and Mengel, 1979). A decrease in protein concentrations might reflect a retardation of protein synthesis or an acceleration of their degradation, leading to an increase in the free amino acids and/or an inhibition of amino acid incorporation into proteins (Poljakoff-Mayber, 1982). In our experiments the increase in free amino acids was mainly due to proline. The Downloaded by [UNSW Library] at 21:19 26 October 2017 1026 Salinity and tomato plants higher proline accumulation found in the more tolerant genotypes, when the plants were grown at 140 mM NaCI for three weeks, suggests a direct relationship between proline accumulation and salt tolerance in tomato genotypes grown at high salt levels in the shortterm. Because the higher salt tolerances of these genotypes were related to their higher capacities for excluding CI and Na from the shoots (Perez-Aifocea et al., 1993), an inverse relationship between Na and proline accumulations was found, as also reported by Aspinall and Paleg (1981) in leaves of barley. Consequently, proline accumulation would help remove excess H+ before the low Na-accumuIation capacity of these genotypes (Bellinger and Larher, 1987). Although the total free amino acid contents also increased in Harvest 2, they were not related to the decreasing protein contents and were exclusively due to the increase of proline, as the remaining amino acid contents were maintained or decreased with salinity. Moreover, similar proline accumulation was found in all genotypes, irrespective of their salt tolerance. Consequently, proline accumulation in Harvest 2 seems not to be due to the same metabolic processes that occurred in Harvest 1. 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