The influence of arbuscular mycorrhizal colonisation on key growth parameters and fruit yield of pepper plants grown at high salinity

This study investigated the effects of arbuscular mycorrhizal (AM) colonisation by Glomus clarum on growth and fruit yield of pepper (Capsicum annum cv. 11B 14) grown at high salinity. The experiment was conducted in pots containing a mixture of perlite and sand (1:1, v/v) under glasshouse conditions. Treatments were: (1) no added NaCl without arbuscular mycorrhizae (NS-AM), (2) no added NaCl with arbuscular mycorrhizae (NS + AM), (3) added 50 mM NaCl without arbuscular mycorrhizae (S1-AM) and (4) added 100 mM NaCl without arbuscular mycorrhizae (S2-AM), (5) added 50 mM NaCl with arbuscular mycorrhizae (S1 + AM) and (4) added 100 mM NaCl with arbuscular mycorrhizae (S2 + AM). The NaCl treatments reduced pepper shoot and root dry matter, and fruit yield compared with the non-saline treatments. The concentrations of N, P and K, in the leaves were significantly reduced by salinity stress, however, mycorrhizal colonisation of the salt-stressed plants restored leaf nutrient concentrations to the levels in non-stressed plants in most cases. AM inoculation improved pepper growth under salt or saltless conditions and reduced cell membrane leakage.     

Stock-Scion Incompatibility in Citrus and its Cause

Summary

The effects of 75 mM and 150 mM NaCl (EC 8.50 and 15.35 dS m^–1) were studied on a salt-tolerant and a salt-sensitive pepper (Capsicum annuum L.) genotype. The salt-tolerant genotype showed lower declines in relative water content (RWC), no change in chlorophyll (Chl) content, lower increases in lipid peroxidation, and greater increases in superoxide dismutase (SOD) activity, total protein content, and glutathione content. The salt-sensitive genotype showed greater decreases in RWC, Chl content, SOD activity, and in guaiacol peroxidase (GPOX) activity, and higher increases in lipid perxidation and the amount of proline, with a negligible increase in glutathione content.These results revealed that increases occurred in some anti-oxidative stress enzymes in the salt-tolerant pepper genotype, as well as increases in glutathione content under salinity stress. These may provide better protection against reactive oxygen species (ROS).     

Physiological response of the medicinal plant artichoke (Cynara scolymus L.) to exogenous salicylic acid under field saline conditions

Alleviating salinity stress by modifying the physiology of the medicinal plant globe artichoke (Cynara scolymus L.) was investigated in a field experiment using salicylic acid (SA). The objectives were to determine: (1) the physiological response of artichoke under salinity stress, and (2) whether SA can alleviate the adverse effects of salinity by affecting artichoke physiology. The factorial combination of salty water (control, 8 dS/m, and 14 dS/m) and foliar application of SA (control, 0.1, 1 mM) was tested. A 1500-L tank was used in the field to establish the favorable salinity levels. Salinity increased chlorophyll a and total chlorophyll; however, at the medium level of SA, chlorophyll a decreased. Increasing salinity and SA decreased total phenolic contents. Increased salinity increased plant proline and ionic leakage. Interestingly, SA significantly decreased ionic leakage, compared with the control. SA increased proline production at different levels of salinity. SA at 0.1 mM was the most suitable and effective treatment under salinity stress. It is possible to alleviate the stress of salinity on artichoke growth by modifying plant physiology using the appropriate concentration of SA.     

Microtuberization of Andean potato species (Solanum spp.) as affected by salinity

The effects of NaCl stress on in vitro tuberization of potato species were studied. Three species of potato (Solanum tuberosum L., S. curtilobum Juz. and Bukasov, and S. juzepczuckii Bukasov) differing in frost resistance were subjected to 0, 25, 50, 75, and 100 mmol l⁻¹ NaCl. Stolon growth and microtuberization were evaluated. The in vitro induced microtubers were characterized with respect to their carbohydrate composition by measuring reducing, non-reducing, total soluble sugars and starch contents. Tuberization and stolon growth, expressed by stolon height or fresh mass, were significantly affected by salinity. The highest saline level (100 mmol l⁻¹ NaCl) completely inhibited tuber development in all species, but not stolon growth. Stolon growth for sensitive species (S. tuberosum) had a significant decrease, whereas both frost tolerant species (S. juzepczuckii and S. curtilobum) tended to increase stolon length with increasing saline levels. Salinity differentially influenced sugar accumulation among potato genotypes. The starch levels in both, S. curtilobum and S. juzepczuckii, remained constant under all salt levels, whereas starch increased in S. tuberosum microtubers.     

Evaluation of salinity tolerance in honeysuckle (Lonicera japonica) using growth,ion accumulation,lipid peroxidation,and non-enzymatic and enzymatic antioxidants system criteria

To evaluate their salt tolerance, two-year-old potted honeysuckle plants were exposed to 50, 100, and 150 mM NaCl, respectively. The effects of salt stress on growth parameters, ion concentration, lipid peroxidation, and the enzymatic antioxidant system in honeysuckle were studied. Salt stress reduced biomass accumulation and root activity, and also induced oxidative stress, as indicated by elevated levels of O₂^·-, malondialdehyde content, and electrolytic leakage. Increased salinity resulted in a slight decline in the K⁺ concentration in different plant tissues, but a significant boost in Na⁺ levels, which were much higher in roots than in other tissues. The concentrations of Ca²⁺ and Mg²⁺ increased significantly in leaves, but remained unchanged in shoots and decreased slightly in roots. Higher levels of soluble sugars and proline were observed in the plants after 30 days of NaCl treatment, suggesting that compatible osmolytes had been synthesised to acclimatise to the salinity. Under the treatments, major antioxidant enzymes involved in the reactive oxygen species scavenging system, including superoxide dismutase, ascorbate peroxidase, catalase and peroxidase were activated. The increased activities of the antioxidant enzymes were significant and occurred in a time-dependent manner.     

Positive effects of plant growth regulators on physiology responses of Fragaria × ananassa cv. ‘Camarosa’ under salt stress

This experiment was conducted to investigate the impact of foliar spraying salicylic acid (SA) and methyl Jasmonate (MJ) on the physiology responses of strawberry (Fragaria × ananassa cv. ‘Camarosa’) grown under salinity stress. According to results, SA and MJ significantly reduced the injuries caused by salt stress, possibly through promoting K⁺ accumulation as well as decreasing the electrolyte leakage and Na⁺ contents in the leaves. The best protective effects resulted from 0.75 mM SA and 0.25 mM MJ treatments. These results indicate that SA and MJ can effectively improve the defense system and antioxidant capacity of strawberry in the salt affected environments.     

Application of chlorophyll fluorescence for the diagnosis of salt stress in tomato “Solanum lycopersicum (variety Rio Grande)”

To study the response of tomato (Solanum lycopersicum cv. Rio Grande) to salinity, the effect on plant growth, water relations, stomatal conductance and Chlorophyll fluorescence was investigated. Tomato plants were grown in peat culture under controlled conditions and submitted during 28 days to saline stress ranging from 0 to 25, 50, 100, 150 and 200 mM of NaCl. At the end of the experiment period, plant growth was significantly decreased with increasing salinity.     

Growth,biomass allocation and leaf ion concentration of seven olive (Olea europaea L.) cultivars under increased salinity

Olive (Olea europaea L.) is the major fruit tree in the Mediterranean region, often grown in locations where plants are exposed to increased salinity. To determine the effect of NaCl on shoot and root growth, dry matter allocation, leaf Na⁺ and K⁺ concentration, electrolyte (EL) and K⁺ leakage (KL), seven olive cultivars of different origins were grown in nutrient solution containing 0, 33, 66, 100 or 166 mM NaCl for three months. The general effect of salinity was linear and quadratic decrease of observed plant growth parameters. Different responses of tested cultivars to applied levels of salinity were found for stem dry weight, shoot length and number of leaves. As salinity increased, growth of ‘Manzanillo’ declined sharply, whereas ‘Frantoio’ was the most tolerant to growth reduction in most of the observed growth parameters. Allometric analysis showed that biomass allocation under salinity stress was similar in all cultivars, but the slope between shoot weight and total plant weight decreased as salinity increased. Since the higher allocation in roots was not found, it seems that salinity only slowed the above ground plant canopy growth. Sodium concentration in leaves of all cultivars increased as salinity increased with the highest increment reached when the salinity of nutrient solution was raised from 100 to 166 mM NaCl. Significant differences among genotypes were found in leaf Na⁺ and K⁺ concentration and K⁺:Na⁺ ratio, but they were not related to the growth rate. Generally, ‘Frantoio’ and ‘Oblica’ accumulated less Na⁺ and were able to maintain higher K⁺:Na⁺ ratios as compared to other genotypes. Electrolyte leakage and KL linearly increased with increasing salinity and the magnitude of the response depended upon the olive cultivar.     

Silicon promotes seedling growth and alters endogenous IAA,GA3 and ABA concentrations in Glycyrrhiza uralensis under 100 mM NaCl stress

A sand culture experiment was conducted to determine the effects of Si on the growth and endogenous hormone concentrations (indole-3-acetic acid [IAA], gibberellic acid [GA₃], and abscisic acid [ABA]) in Glycyrrhiza uralensis seedlings under 100 mM NaCl stress. Si time-dependently improved the growth and increased the biomass of seedlings, and the effect was greater at 20 days than that at 10 days after Si treatment. The effects of Si on the growth parameters and biomass were dependent on Si concentration, that is, these parameters increased with increasing Si concentration. Si also increased the levels of endogenous hormones in G. uralensis seedlings in a concentration-dependent manner. The effects on IAA and GA₃ increased with increasing Si concentrations, and the effect on ABA was higher at 2 mM Si than that at the other Si concentrations. Furthermore, the effects of Si on IAA and GA₃ were greater at 10 days than those at 20 days after the treatment, whereas the effect on ABA was greater at 20 days than that at 10 days after the treatment. Hence, Si can regulate the concentrations of endogenous hormones and correspondingly improve the growth of G. uralensis seedlings under salt stress condition.     

Changes in chlorophyll,ribulose bisphosphate carboxylase-oxygenase,glycine betaine content,photosynthesis and transpiration in Amaranthus tricolor leaves during salt stress

Summary

We examined changes in leaf growth and chemical composition, including chlorophyll content, ribulose bisphosphate carboxylase-oxygenase (RuBisCO), and glycine betaine (GB) in relation to photosynthesis and transpiration responses to salt stress in Amaranthus tricolor leaves. To induce salt stress, plants were transferred to a growth medium containing 300 mM NaCl for 7 d followed by 7 d of relief from salinity. A decrease in leaf enlargement began 3 d after salt stress, and leaves subsequently showed the same degree of regrowth as controls after relief in non-salt medium. Chlorophyll content expressed on a leaf-area basis increased under conditions of salinity due to a reduction in leaf tissue water content. The decrease in chlorophyll content continued throughout the 7 d of relief from salinity. The RuBisCO and soluble protein contents when expressed on a leaf dry-weight basis decreased in response to salinity, and then gradually increased during the relief period. GB content increased slightly up to 3 d of salt stress, and showed typical accumulation during salt stress. GB content decreased sharply immediately after plants were transferred to non-stress medium, but remained at a higher level throughout the relief period. A decrease in photosynthetic activity and transpiration rate preceded any changes in leaf area, RuBisCO or GB content. During relief from salinity, photosynthesis and transpiration rates gradually recovered to control levels with restoration of stomatal conductance. The above findings suggest that the increase in GB content is important in adaptation to salt stress in Amaranthus plants, although photosynthesis and transpiration responses occurred immediately after salt-stress.     

Effects of Ascorbic Acid and Reduced Glutathione on the Alleviation of Salinity Stress in Olive Plants

The aim of this study was to evaluate the effects of low molecular mass antioxidants and NaCl salinity on growth, ionic balance, proline, and water contents of ‘Zard’ olive trees under controlled greenhouse conditions. The experiment was carried out by spraying 2 mM of ascorbic acid (Asc) and 3 mM of reduced glutathione (GSH) on the plants that were treated with two salinity levels (0 and 100 mM NaCl) on their root medium. Plant growth parameters (leaf fresh weight, leaf dry weight, leaf number, total fresh weight, and total dry weight) were significantly improved by Asc compared with growth parameters in GSH and control plants. Higher concentrations of Na⁺ and Cl^– were observed in salt-stressed plants, while Na⁺ and Cl^– concentrations were decreased in the olive leaves that were sprayed with Asc. Salinity in the root zone caused a considerable decline in both K⁺ concentration and K/Na ratio. K⁺ concentration and K/Na ratio were significantly increased by application of Asc on plant leaves. Salinity caused an increase in electrolyte leakage (EL) compared with the control plants. Lowest EL and tissue water content (TWC) was obtained in Asc-sprayed plants, whereas TWC was increased in salt-stressed plants. Plants were subjected to salt stress and showed a higher relative water content (RWC) than the control plants. Salt stress induced proline accumulation in olive leaves. In conclusion, exogenous application of Asc is recommended to improve tolerance of olive plants under saline conditions.     

Fruits are more sensitive to salinity than leaves and stems in pepper plants (Capsicum annuum L.)

The effects of NaCl stress on plant growth, gas-exchange, activity of superoxide dismutase (SOD), rate of lipid peroxidation, and accumulation of Na⁺ ion and sugar were investigated in leaves and fruits of pepper plants (Capsicum annuum L.). Especially, the gene expression of l-galactono-1,4-lactone dehydrogenase (GalLDH), which is the last enzyme of ascorbic acid (AsA) biosynthesis, and the relationships between AsA level and Na⁺ concentration in plant tissue were investigated with increasing salinity. Plants were treated with three treatments: the control (0 mM NaCl) and two salinity levels (50 and 100 mM NaCl) for 21 days under greenhouse conditions. Plant growth was markedly restricted due to the reduction of photosynthetic rate and the increase of Na⁺ accumulation in leaves with the increasing intensity of NaCl stress. Salinity had more effect on fruit growth comparing to leaf growth, suggesting that fruits could be more sensitive to salinity than leaves. In comparison with the control, salt stress significantly increased lipid peroxidation (as measured as malondialdehyde content) but decreased SOD activity in both fruits and leaves although the effect was larger in fruits; and the rate of the decrease in SOD activity was greater than that of the increase in lipid peroxidation. The AsA concentration transiently increased first 7 days but it slightly decreased from the initial level in the end of treatment day 21. The change in GalLDH gene expression was similar to AsA concentration. The accumulation of Na⁺, the reduction of AsA level at severe salinity stress were greater in fruits than in leaves; and AsA level had a negative relationship with Na⁺ concentration in both leaves and fruits. These results suggest that the difference in salt sensitivity between fruits and leaves in pepper plants can be related to the difference in inhibition of AsA synthesis, which in turn is probably due to the toxicity of extreme accumulation of Na⁺.     

Methylene blue increases the tolerance of tomato plants to abiotic stresses

Summary

Environmental stresses such as high temperature and high salinity are known to cause oxidative stress in plants by enhancing the generation of reactive oxygen species (ROS), which have a strong impact on plant development. Mitochondria constitute one of the major sources of ROS in roots. Recently, it has been shown in mammalian systems that methylene blue (MB) at very low concentrations can attenuate mitochondrial ageing by scavenging ROS. In the present study, we tested whether MB could be used to protect tomato (Lycopersicon esculentum L.) seedlings against the harmful effects of high salinity and high root temperature. Tomato seedlings were grown hydroponically and were subjected to two abiotic stresses: high salinity (150 mM NaCl) in the nutrient medium, or high root temperature (35ºC) for 14 d. These stress treatments were applied with or without the addition of 10^–8 M MB. The results showed that, under normal conditions, MB enhanced root and shoot growth, increased root respiration, decreased root H₂O₂ and malonyldialdehyde (MDA) concentrations, and enhanced root superoxide dismutase (SOD) activity. Both high salinity and high root temperature stress impaired root and shoot growth, and caused an enhancement of root oxidative stress. MB had a significant protective effect against both abiotic stresses and restored the levels of oxidative stress-related components (i.e., H₂O₂ and MDA) in root and leaf tissues almost to normal levels. It is hypothesised that MB could confer its protective effect not only through interactions with root mitochondria, but also via additional cellular targets in the root.     

Physiological Responses of Cherry Rootstocks to Short Term Salinity

The physiological responses of cherry rootstocks were evaluated under moderate salinity in short term. MaxMa 14, CAB-6P and Mazzard rootstocks were treated with 35?mM NaCl solution for 1 month to assess physiological responses. Under NaCl stress, rootstocks’ physiological parameters were compared with their own control, with the greatest alterations in SPAD value, leaf relative water content (LRWC), membrane permeability and stomatal conductivity. SPAD value was reduced by 9.5, 2.17 and 2.27% in saline-treated plants of MaxMa 14, CAB-6P and Mazzard, respectively. MaxMa 14 and CAB-6P exhibited a rapid decrease in stomatal conductivity by 39.90 and 47.60%, respectively compared with their control, while in Mazzard there was a reduction by 5.28% compared with its control. Moreover, LRWC of the plants decreased by 11.24 and 13.75% in salt-treated MaxMa 14 and CAB-6P, respectively. In comparison, a lower reduction of LRWC (6.11%) was observed in NACl-treated Mazzard. As seen in the result of experiment, the inhibitory effects of NaCl were less in Mazzard compared with MaxMa 14 and CAB-6P.     

Salinity stress in tomatoes can be alleviated by grafting and potassium depending on the rootstock and K-concentration employed

Plant production under salinity requires increased capacity for K⁺ homeostasis. For this purpose, supplementary K₂SO₄ in the nutrient solution and grafting on a tolerant rootstock were employed in two experiments to test whether grafting, potassium and their interactions can alleviate salinity stress in tomato (Solanum lycopersicum L.). In Exp-ion, plants were cultivated for 122 days to compare different ionic compositions: EC 9 dS m⁻¹ in EC_all (by macro-nutrients) and in EC_NaCl (by 64.2 mM NaCl), EC 12 dS m⁻¹ in EC_K (EC_NaCl + 25.8 mM K⁺). Exp-K⁺ was established to compare K⁺ concentrations of 6, 16 and 36 mM at 150 mM NaCl. In both Experiments, ‘ZS-5’, selected as a salt sensitive cultivar, was either self-grafted or grafted onto the cultivar ‘Edkawi’, reported as salt tolerant. Yield and growth, minerals, gas exchange, soluble sugars, and proline were analyzed. Different ionic treatments affected almost all characteristics considered while differences between rootstocks were rarely observed. No pronounced differences were found in shoot growth, yield and gas exchange between EC_all and EC_NaCl. EC_K did not show any salinity alleviative effects but inhibited even growth compared with the other treatments. In Exp-K⁺, 16 mM K⁺ increased plant growth, leaf soluble sugars and proline concentrations. 36 mM K⁺ did not further reduce upper leaf Na⁺ although leaf K⁺ concentration increased significantly. The results indicated that the response of tomato plant to NaCl stress was principally attributed to the osmotic component in Exp-ion, excessive K⁺ showed no mitigating effect on fruit yield and shoot growth. However, 16 mM K⁺ in the root environment enhanced the salt adaptive capacity of plants stressed at 150 mM NaCl. The use of the tolerant rootstock resulted in no ameliorative effects, owing to its susceptibility to blossom-end rot, failure in enhancing photosynthesis, and ineffectiveness of restraining the long-distance transport of Na⁺.     

Effects of high salinity and the exogenous application of an osmolyte on growth,photosynthesis, and mineral composition in two ornamental shrubs

A greenhouse experiment was carried out to determine the growth, photosynthetic activity, and mineral composition in two ornamental shrubs [Viburnum lucidum L. (arrow-wood) and Callistemon citrinus (Curtis) Stapf. (red bottlebrush)] that had been treated or not treated with 2.5 mM glycine betaine (GB) or 5.0 mM proline (Pro). Plants were supplied with a non-salinised or salinised nutrient solution containing 200 mM NaCl. Salinity caused reductions in plant growth parameters, shoot biomass production, and net CO₂ assimilation in both species. Neither Pro nor GB were able to mitigate the adverse effects of salinity in bottlebrush, whereas GB reduced the deleterious effects of salt stress on arrow-wood, indicating a differential species-specific response to these osmolytes. The application of GB to salt-stressed arrow-wood increased apical and lateral shoot lengths, the number of leaves per plant, and shoot dry biomass by 222%, 113%, 238%, and 49%, respectively, compared to untreated or Pro-treated plants. The improved performance of salt-stressed arrow-wood plants whose roots were treated with 2.5 mM GB was attributed to partial suppression of Na uptake, higher chlorophyll concentrations, and the better nutritional status (higher K) of shoots.     

Sennoside content and yield attributes of Cassia angustifolia Vahl. as affected by NaCl and CaCl2

Pot culture experiments were conducted to assess the extent of growth, photosynthetic capacity, sennoside concentration and yield attributes of Senna plant under the individual as well as combined influence of NaCl and CaCl₂. Six treatments, i.e. NaCl (80 and 160 mM), CaCl₂ (5 and 10 mM) alone and a combination of NaCl + CaCl₂ (80 + 10 and 160 + 10 mM) were given to the growing Senna plants at pre-flowering (45 DAS), flowering (75 DAS) and post-flowering (90 DAS) stages. Significant reductions were observed in pod biomass, leaf area, stomatal conductance, photosynthetic rate and sennoside concentration and yield, with each NaCl treatment. On the contrary, individual CaCl₂ treatments had a favourable effect. Under the effect of combination treatments, although these parameters were reduced, the extent of reduction was much less than one caused by NaCl treatments. The combined treatments thus mitigated the adverse effects caused by NaCl.     

Improving the fruit yield and quality of cucumber by grafting onto the salt tolerant rootstock under NaCl stress

To investigate the feasibility of using salt tolerant rootstock to increase fruit yield and quality of cucumber under NaCl stress, a greenhouse experiment was carried out to determine fruit yield, leaf relative water content, fruit quality, and mineral composition of cucumber plants (Cucumis sativus L. cv. Jinchun No. 2), either self-grafted or grafted onto the commercial salt tolerant rootstock Figleaf Gourd (Cucurbita ficifolia Bouche) and Chaofeng Kangshengwang (Lagenaria siceraria Standl). Plants were grown in a substrate culture (peat:vermiculite:perlite = 1:1:1, v/v) and irrigated with half-strength Hoagland solutions containing 0, 30, or 60 mM NaCl. The results showed that salinity significantly reduced fruit yield of cucumber owing to a decrease both in mean fruit weight and fruit number. Rootstock had no significant effect on leaf relative water content. Plants grafted onto Figleaf Gourd and Chaofeng Kangshengwang had higher fruit number, marketable and total fruit yield than those of self-grafted plants under 0, 30, and 60 mM NaCl, which could be attributed to, at least in part, the higher K⁺ but lower Na⁺ and/or Cl⁻ contents in the leaves. Salinity improved fruit quality by increasing fruit dry matter, soluble sugar, and titratable acidity contents of all the plants, but had no significant effect on vitamin C content. In comparison to the self-grafted plants, plants grafted onto Figleaf Gourd and Chaofeng Kangshengwang had an overall improved fruit quality under NaCl stress owing to an increase in contents of soluble sugar, titratable acidity, and vitamin C, and a decrease in the percentage of non-marketable fruit and Na⁺ and/or Cl⁻ contents of fruits in comparison to the self-grafted plants, mainly under 60 mM NaCl. Overall, it is suggested that the use of salt tolerant rootstock could provide a useful tool to improve fruit yield and quality of cucumber under NaCl stress.     

Impact of exogenous salicylic acid on the growth,antioxidant activity and physiology of carrot plants subjected to combined salinity and boron toxicity

Previous studies have shown that salicylic acid (SA) plays a role in the response of plants to salt and osmotic stresses. Therefore, an experiment was conducted to investigate the impact of exogenous salicylic acid on the growth, physiology and antioxidant activity of carrot (Daucus carota L. cv. Nantes) grown under combined stress of salinity and boron toxicity. The treatments consisted of salt (control, NaCl, and Na₂SO₄), boron (−B: 0 and +B: 25 mg B kg⁻¹) and salicylic acid (−SA: 0 and +SA: 0.5 mmol SA kg⁻¹). The diameter of the storage root was increased by NaCl salinity in the absence of B toxicity, however, it was increased by Na₂SO₄ salinity under B toxicity. For the storage root yield, NaCl salinity was more toxic than Na₂SO₄ salinity. With its role in plant growth regulation, SA application positively affected the storage root dry weight, S concentration, carotenoids and anthocyanin content and increased the total antioxidant activity (AA) of the shoot and storage root. SA application regulated proline and toxic ion (B, Cl) accumulation in the storage root and shoot. This study reports the long term effects of SA under stress conditions and reveals that SA was not as effective as in alleviating abiotic stress as reported in the literature conducted with short-term studies. That means long-term effects of SA would be significantly different from its short-term effects.     

Effect of NaCl on growth,ion composition and ascorbic acid concentrations of capsicum fruit

Potted plants of Capsicum annuum, cultivar ‘Long Sweet Yellow’, were restricted to two fruits each and supplied with 0, 10, 25 and 50 mM NaCl. Chloride concentrations exceeded sodium concentrations in ripe fruit from all salt-treatments. The difference was 2.5-fold in ripe fruit from plants treated with 50 mM NaCl. Fruits from the 50 mM treatment were markedly lower in fresh weight and were of a more intense colour than control fruit. Fruit ripening was accelerated by all salt-treatments, but the fresh weight to dry weight ratio of ripe fruit was reduced; the reduction was in proportion to the stress applied.A significant correlation was found between fruit ascorbic acid and Ca^{2 +} concentrations. Fruit Ca^{2 +} was reduced by salinity, but the reduction was not in proportion to sodium chloride concentration. Additional calcium nitrate in the nutrient solution increased the Ca^{2 +} content and ascorbic acid concentration in fruit on control plants but not in fruit from plants treated with 50 mM NaCl. Instead, these fruit showed a marked increase in Na⁺.