Growth, gas exchange and ion content in Olea europaea plants during salinity stress and subsequent relief

Olive ( Olea europaea L. cv. Frantoio) plants grown hydroponically in a glasshouse were supplied with half-strength Hoagland solutions containing 0, 50, 100, and 200 m M NaCl for 4 weeks and subsequently supplied with the standard solution without NaCl to relieve salinity stress. Two complete stress-relief cycles were repeated on the same plant material during one growing season. Growth was inhibited at all salt levels, but most growth parameters of plants treated with 50 or 100 m M NaCl returned to control levels after 4 weeks of relief. More severely stressed plants (200 m M NaCl) recovered to only 60% of the growth of the controls after 4 weeks. During relief, plants treated with 50 and 100 m M NaCl had net photosynthetic rates and stomatal conductances higher than the controls. Increasing the NaCl concentration of the external solution from 0 to 200 m M decreased both leaf pre-dawn water potential (from -0.3 to -1.0 MPa) and osmotic potential (from -2.1 to -2.7 MPa). The sodium concentration in the leaves of plants treated with 200 m M NaCl reached maximum levels of 211 and 388 m M (expressed on a tissue water basis) at the end of the first salinity and relief periods, respectively. Leaf chloride concentrations were 359 and 223 m M at the same sampling dates. These data indicate that the inhibitory effects of salinization on growth and gas exchange of the salt-tolerant olive cv. Frantoio can be readily reversed when salinity is relieved, despite the marked accumulation of potentially toxic ions (Na⁺. Cl) in the leaf.     

Salinity-induced changes in essential oil,pigments and salts accumulation in sweet basil (Ocimum basilicum) in relation to alterations of morphological development

The objective of the project was to study salinity-induced effects on essential oil, pigments and salts accumulation in sweet basil (Ocimum basilicum, the cultivar Perrie) in relation to the alteration of plant morphological development and yield production. Hydroponically grown plants were exposed to one of six NaCl concentrations (1, 25, 50, 75, 100 and 130 mM NaCl). Inhibitory effects of salinity on biomass production of the shoot and the root, and area of individual leaves were apparent already under cultivation with 25 mM NaCl. Elevation of salinity from 1 to 100 mM NaCl induced 63% and 61% reductions in fresh and dry herb biomass production, respectively. The stress-induced reduction of foliage biomass sourced mainly from inhibition of leaf area development rather than reduction of internode and leaf number. Cl and Na concentrations in the leaves, stems and roots increased with elevation of NaCl concentration in the cultivation solution. While the extent of Cl accumulation was leaves>stems>roots, Na was largely excluded from the leaves and was preferentially accumulated in roots and the stems, potentially accounting for the moderate sensitivity of the leaf tissue to salinity. Salt stress increased the contents of essential oil and carotenoids in the leaves that may further account for the moderate sensitivity of sweet basil to salinity and suggest a potential for agro-industrial production. A twofold increase in both carotenoid concentration and the percent of essential oil in the fresh tissue was observed by elevation of the salinity from 1 to 130 mM NaCl. Overall, the stress induced increase of the percent of essential oil in the tissue in the salinity range 1–75 mM NaCl was about 50%, and thereby compensated for the similar reduction of biomass production in this salinity range, so that oil production on per plant basis was not reduced by salinity.     

Interaction effects of root-zone salinity and solar irradiance on the physiology and biochemistry of Olea europaea

Root-zone salinity stress and high solar irradiance concomitantly occurs in the Mediterranean basin, where Olea europaea is the dominating fruit-tree crop-species. Although the effect of each individual stressor on plant performance has been widely investigated, much less is known on the interaction effects of salinity stress and solar irradiance on the physiology and biochemistry of olive plants. Here we analyzed how changes in root-zone NaCl concentration and sunlight radiation affect relevant physiological and biochemical features in olive cv. Cipressino. Two-year-old plants were supplied with 0 or 125 mM NaCl and exposed to 15% (shade) or 100% sunlight (sun) over a 5-week period, starting from July 10th, 2005. Measurements were conducted of (i) gas exchange and plant growth, (ii) the concentrations of cations and chloride, (iii) the concentrations of soluble carbohydrates, violaxanthin-cycle pigments and polyphenols, and (iv) the protein oxidation and the lipid peroxidation in the leaves. Salt-induced reductions in gas exchange performance and plant growth were greater at the sun than at the shade site, mostly due to light-induced changes in leaf water relations and vapour pressure deficit (vpd), rather than in the concentration of potentially toxic ions. Light-induced increases in leaf Na⁺ and Cl^? concentrations were countered by parallel enhancements in the concentrations of K⁺ and Ca²⁺. Sun leaves had sharply greater concentrations of mannitol and xanthophylls, irrespective of root-zone salinity. The amount of “newly assimilate carbon” allocated to polyphenols, especially to flavonoids, increased in response to salinity stress and high sunlight. Remarkably, the protein oxidation was greater in shade than in sun leaves of well-watered plants, and increased more at the shade than at the sun site because of high salinity. We suggest that heat-stress (on average maximum T exceeded 33 °C for 50% of the experimental period), which acted in concert with salinity stress and sunlight irradiance in determining plant responses in our experiment, was responsible for leaf oxidative damage in plants growing under contrasting solar radiation. Indeed, sun leaves of salt-stressed plants were equipped with an extraordinary-rich arsenal of antioxidant compounds, distributed in different cell compartments, i.e., mannitol, zeaxanthin and flavonoids, which likely countered effectively the oxidative damage driven by heat-stress, a clear example of cross-tolerance.     

Proline accumulation and glutamine synthetase activity are increased by salt-induced proteolysis in cashew leaves

In this study cashew (Anacardium occidentale) plants were exposed to a short- and long-term exposure to NaCl in order to establish the importance of the salt-induced proteolysis and the glutamine synthetase activity on the proline accumulation. The cashew leaf showed a prominent proline accumulation in response to salt stress. In contrast, the root tissue had no significant changes in proline content even after the drastic injury caused by salinity on the whole plant. The leaf proline accumulation was correlated to protease activity, accumulation of free amino acid and ammonia, and decrease of both total protein and chlorophyll contents. The leaf GS activity was increased by the salt stress whereas in the roots it was slightly lowered. Although the several amino acids in the soluble pool of leaf tissue have showed an intense increment in its concentrations in the salt-treated plants, proline was the unique to show a proportional increment from 50 to 100 mol m-3 NaCl exposure (16.37 to 34.35 mmol kg-1 DM, respectively). Although the leaf glutamate concentration increased in the leaves of the salt-stressed cashew plants, as compared to control, its relative contribution to the total amino acid decreased significantly in stressed leaves when compared to other amino acids. In addition, when the leaf discs were incubated with NaCl in the presence of exogenous precursors (Glu, Gln, Orn or Arg) involved in the proline synthesis pathways, the glutamate was unique in inducing a significant enhancement of the proline accumulation compared to those discs with precursor in the absence of NaCl. These results, together with the salt-induced increase in the GS activity, suggest an increase in the de novo synthesis of proline probably associated with the increase of the concentration of glutamate. Moreover, the prominent salt-induced proline accumulation in the leaves was associated with the higher salt-sensitivity in terms of proteolysis and salt-induced senescence as compared to the roots. In conclusion, the leaf-proline accumulation was due, at least in part, to the increase in the salt-induced proteolysis associated with the increments in the GS activity and hence the increase in the concentration of glutamate precursor in the soluble amino acid pool.     

Intra- and inter-cultivar impacts of salinity stress on leaf photosynthetic performance,carbohydrates and nutrient content of nine indigenous Greek olive cultivars

Nine indigenous Greek olive cultivars (‘Aetonicholia Kynourias’, ‘Arvanitolia Serron’, ‘Ntopia Atsicholou’, ‘Koroneiki’, ‘Lefkolia Serron’, ‘Ntopia Pierias’, ‘Petrolia Serron’, ‘Smertolia’ and ‘Chryssophylli’) were evaluated for their tolerance to salinity stress (four levels of sodium chloride salt, i.e., 0, 50, 100 and 200 mM) under hydroponic conditions. Their photosynthetic performance, leaf carbohydrates (mannitol, glucose, fructose and sucrose) and nutrients (nitrogen, potassium, calcium, sodium and chloride) were assessed. Photosynthetic performance was reduced under salt stress and this was mostly evident in ‘Koroneiki’ and ‘Ntopia Atsicholou’ (approximately 20% of the corresponding controls), while ‘Ntopia Pierias’, ‘Smertolia’ and ‘Petrolia Serron’ did not exhibit significant changes with salinity level. Photosynthesis (A) was reduced mainly due to severe stomatal limitations. A weak correlation was detected between A and intercellular CO₂ (Ci) indicating a minor role of non-stomatal limitations. Carbohydrates in the leaves did not seem to undergo significant changes. Mannitol accumulated in ‘Chryssophylli’ leaves and glucose in ‘Arvanitolia Serron’ leaves under the highest salinity level. Potassium concentration per leaf water volume was significantly reduced (especially under the highest salinity level ?45 to 60% of control). Calcium was not significantly affected although Ca/Na ratio was reduced, due to the great increase of sodium concentration. ‘Lefkolia Serron’ and ‘Arvanitolia Serron’ accumulated the least sodium in their leaves, exhibiting high K/Na ratio under the highest salinity level, indicating a better regulation of potassium influx under high sodium concentration. Based on the present data and on previous research ‘Lefkolia Serron’ and ‘Arvanitolia Serron’ are the two cultivars with the highest tolerance against salinity stress.     

The effect of NaCl stress and relief on gas exchange properties of two olive cultivars differing in tolerance to salinity

Young olive plants (Olea europaea L.) were grown either in hydroponic or soil culture in a glasshouse over two growing seasons. Plants were exposed to NaCl concentrations between 0 and 200 mM for 34–35 days followed by 30–34 days of relief from stress to determine the effect of salinity on gas exchange of two cultivars ('Frantoio' and 'Leccino') differing in salt-exclusion capacity. Salinity stress brought about a reduction in net CO₂ assimilation and stomatal conductance in both cultivars, but the effect was more pronounced in the salt tolerant 'Frantoio' than in the salt-sensitive 'Leccino' cultivar. Therefore, gas exchange parameters may be misleading if used to evaluate the salt tolerance of olive genotypes. Recovery in gas exchange parameters during relief from stress was slower in the salt sensitive cultivar. In general, the decline in assimilation reflected the salt-induced reduction in stomatal conductance, but a marked effect on carboxylation efficiency and CO₂ compensation point was measured in plants treated with 200 mM NaCl for four weeks. The cultivar 'Frantoio' showed a 50% reduction in assimilation and stomatal conductance at 146 and 78 mM leaf Na+ concentration (tissue water molar basis) respectively, whereas the corresponding 50% thresholds for the cultivar 'Leccino' were at 275 and 264 mM, respectively.     

Gas Exchange and Carbon Partitioning in the Leaves of Celery (Apium graveolens L.) at Various Levels of Root Zone Salinity

Both mannitol and sucrose (Suc) are primary photosynthetic products in celery (Apium graveolens L.). In other biological systems mannitol has been shown to serve as a compatible solute or osmoprotectant involved in stress tolerance. Although mannitol, like Suc, is translocated and serves as a reserve carbohydrate in celery, its role in stress tolerance has yet to be resolved. Mature celery plants exposed to low (25 mM NaCl), intermediate (100 mM NaCl), and high (300 mM NaCl) salinities displayed substantial salt tolerance. Shoot fresh weight was increased at low NaCl concentrations when compared with controls, and growth continued, although at slower rates, even after prolonged exposure to high salinities. Gas-exchange analyses showed that low NaCl levels had little or no effect on photosynthetic carbon assimilation (A), but at intermediate levels decreases in stomatal conductance limited A, and at the highest NaCl levels carboxylation capacity (as measured by analyses of the CO2 assimilation response to changing internal CO2 partial pressures) and electron transport (as indicated by fluorescence measurements) were the apparent prevailing limits to A. Increasing salinities up to 300 mM, however, increased mannitol accumulation and decreased Suc and starch pools in leaf tissues, e.g. the ratio of mannitol to Suc increased almost 10-fold. These changes were due in part to shifts in photosynthetic carbon partitioning (as measured by 14C labeling) from Suc into mannitol. Salt treatments increased the activity of mannose-6-phosphate reductase (M6PR), a key enzyme in mannitol biosynthesis, 6-fold in young leaves and 2-fold in fully expanded, mature leaves, but increases in M6PR protein were not apparent in the older leaves. Mannitol biosynthetic capacity (as measured by labeling rates) was maintained despite salt treatment, and relative partitioning into mannitol consequently increased despite decreased photosynthetic capacity. The results support a suggested role for mannitol accumulation in adaptation to and tolerance of salinity stress.     

Nitrosative stress in plants

Nitrosative stress has become a usual term in the physiology of nitric oxide in mammalian systems. However, in plants there is much less information on this type of stress. Using olive leaves as experimental model, the effect of salinity on the potential induction of nitrosative stress was studied. The enzymatic l-arginine-dependent production of nitric oxide (NOS activity) was measured by ozone chemiluminiscence. The specific activity of NOS in olive leaves was 0.280nmol NOmg(-1) proteinmin(-1), and was dependent on l-arginine, NADPH and calcium. Salt stress (200mM NaCl) caused an increase of the l-arginine-dependent production of nitric oxide (NO), total S-nitrosothiols (RSNO) and number of proteins that underwent tyrosine nitration. Confocal laser scanning microscopy analysis using either specific fluorescent probes for NO and RSNO or antibodies to S-nitrosoglutathione and 3-nitrotyrosine, showed also a general increase of these reactive nitrogen species (RNS) mainly in the vascular tissue. Taken together, these findings show that in olive leaves salinity induces nitrosative stress, and vascular tissues could play an important role in the redistribution of NO-derived molecules during nitrosative stress.     

On the mechanism of salt tolerance in olive (Olea europaea L.) under low- or high-Ca2+ supply

The effect of changes in Ca²⁺/Na⁺ ratios at the root zone has been reported in Olea europaea, a species mostly cultivated in calcareous soils. Plants were exposed to low (2.0 mM, low-Ca) or high-Ca²⁺ supply (9.0 mM, high-Ca) and supplied with 0 or 200 mM NaCl. Measurements were performed on water relations, gas exchange and photosynthetic performances, ion fluxes at whole-plant and leaf level, Na⁺ allocation at organismal level, the elemental and soluble carbohydrate concentration in the leaf. Most parameters were also measured during a period of relief from salinity stress, as Olea europaea suffers from fluctuating root zone NaCl concentrations over the whole growing season. High-Ca²⁺ supply decreased stomatal conductance, especially during the first two weeks of treatment. In response to salinity stress (i) leaf turgor potential was more severely depressed in high-Ca than in low-Ca plants, whereas net CO₂ assimilation rate and relative growth rate were unaffected by root zone Ca²⁺ concentrations (ii) high-Ca plants had a markedly superior ability to both exclude Na⁺ from the shoot and to selectively transport K⁺ over Na⁺ than low-Ca plants; (iii) both CO₂ carboxylation efficiency and maximal efficiency of PSII photochemistry (F_v/F_m) were significantly smaller in low-Ca than in high-Ca plants, likely as a result of a greater accumulation of toxic ions. Consistently, when osmotic stress was relieved by supplying plants with good quality water (relief period), both photosynthetic (+44%) and growth rates (+65%) recovered to a markedly superior degree in high-Ca than in low-Ca plants which had been previously treated with 200 mM NaCl. We conclude that (1) high-Ca²⁺ supply expose olive leaves to a more severe dehydration, but allowed to restrict both the entry and the allocation of potentially toxic ions to sensitive shoot organs; (2) a transient restriction of water-mass flow to the shoot during salinization may be of relatively minor significance in Olea europaea, which is very tolerant to drought; (3) overall salt tolerance in Olea europaea, as in most evergreen sclerophylls inhabiting Mediterranean areas, tightly depends upon the ability to reduce water uptake and transpiration during the dry/warm period and to recover photosynthetic and growth rates when low-salinity flood water is available. Therefore, data from the present experiment allow conclude that an increase in root zone Ca²⁺ concentration enhances tolerance to salinity stress in olive plants.     

Ion accumulation in the cell walls of rice plants growing under saline conditions: evidence for the Oertli hypothesis

Abstract. When plants of rice ( Oryza saliva L.) are subjected to mildly saline (50mol m⁻³ NaCl) conditions, the leaves show symptoms of water deficit, even though ion accumulation has been more than sufficient to adjust to the decrease in external water potential. After a few days of exposure to salt, there is a negative correlation, in a population of leaves, between the leaf water concentration (g water per g dry weight) and their sodium concentration (mmol Na per g dry weight). Ion concentrations in the cell walls and the cytoplasm of cells of plants grown in low salinity were measured by X-ray microanalysis. The NaCl concentration in solution in the apoplast was calculated to be around 600mol m⁻³ in leaves of plants whose roots were exposed to only 50 mol m⁻³ NaCl. This constitutes strong evidence that an important factor in salt damage in rice is dehydration due to the extracellular accumulation of salt as suggested in the Oertli hypothesis. The implication, that changes in tissue ion concentration and solute potentials equivalent to the external medium is not evidence of plant osmotic adjustment to salinity, is discussed.     

盐胁迫下海马齿叶片结构变化

用石蜡切片法制片、光学显微镜观察了海马齿植物营养器官--叶片的盐适应结构变化,以明确盐生植物对盐渍生境适应的叶片结构变化特征,为盐生植物的耐盐机理研究提供依据.结果表明:(1)海马齿植物叶片表现出许多适应干旱和盐渍环境的特点,其基本特征为:叶片肉质化,为典型的等面叶;栅栏组织发达,且含有大量叶绿体;叶表皮气孔微下陷,叶表皮细胞外壁的角质层较薄,表皮细胞大小不等,外切向壁外凸,参差不齐,有些表皮细胞特化为泡状细胞,其数量与盐胁迫的浓度呈正相关.(2)叶的海绵组织中含有大量的薄壁细胞,幼叶海绵组织的薄壁细胞在0.5%～2.5% NaCl胁迫下均变大,且数量也增加;而老叶海绵组织的薄壁细胞只有在低浓度(0.5% NaCl)的盐胁迫下变大,而在高浓度下其薄壁细胞反而变小或成不规则形状.(3)盐晶广泛分布在海马齿的叶肉组织细胞内,且其数量随着盐胁迫浓度增加而增加.     

Effects of iso-osmotic NaCl and mannitol on growth, proline content, and antioxidant defense in Mammillaria gracilis Pfeiff. in vitro-grown cultures

Effects of iso-osmotic concentrations of NaCl and mannitol were studied in Mammilaria gracilis (Cactaceae) in both calli and tumors grown in vitro. In both tissues, relative growth rates were reduced under osmotic stress, which were accompanied by a decrease in both tissue water and K⁺ content. However, growth was inhibited to a lesser extent after exposure to NaCl, when accumulation of Na⁺ ions was observed. In calli, only salinity increased proline content, whereas with tumors proline accumulated after both osmotic stresses. Osmotic stresses also induced oxidative damage in both cactus tissues, although higher oxidative injury was caused by mannitol in calli and by salt in tumors. Low iso-osmotic concentrations of NaCl (75 mM) and mannitol (150 mM) increased peroxidase, ascorbate peroxidase, and esterase activities, whereas elevated catalase activity was recorded only after mannitol treatment in both tissues. High osmotic stress generally decreased enzymatic activities. However, in calli, esterase activity increased in response to high salinity, whereas ascorbate peroxidase activity was enhanced after high mannitol stress. In conclusion, both in vitro-grown cactus tissues were found to be sensitive to osmotic stress caused by either mannitol or NaCl, but accumulation of Na⁺ ions in response to salt somewhat contributed to osmotic adjustment. However, more prominent oxidative damage induced by NaCl compared to mannitol in tumor could be related to ion toxicity. The mechanisms that mediate responses to salt- and mannitol-induced osmotic stresses differed and were dependent on tissue type.     

Effect of NaCl concentrations in irrigation water on growth and polyamine metabolism in two citrus rootstocks with different levels of salinity tolerance

Six-months-old, uniform sized seedlings of two citrus rootstocks; Cleopatra mandarin (Citrus reshni Hort. ex Tan) and Troyer citrange (Poncirus trifoliata × Citrus sinensis) were irrigated with half-strength Hoagland nutrient solution containing 0, 40 or 80 mM NaCl for 12 weeks. Shoot height, leaf number and fresh weights of the seedlings, and relative chlorophyll contents, chlorophyll fluorescence yields (Fv/Fm), net photosynthetic and respiration rates in the leaves decreased with the increase in salinity level in the irrigation water. The decrease was greater in Troyer citrange as compared to Cleopatra mandarin. The concentrations of sugars i.e. fructose, glucose and sucrose in the leaves of Cleopatra mandarin and both leaves and roots of Troyer citrange decreased with the increase in salinity level. However, the concentrations in the roots of Cleopatra mandarin increased with the increase in salinity level. Free proline content in the leaves of Troyer citrange and root tissue of Cleopatra mandarin also increased with the increased salinity level. Among the polyamines, spermine titer increased in the leaves of both rootstocks as a response to salinity treatments. Na⁺ concentrations were higher in leaf and root tissue of Cleopatra mandarin, while that of Cl⁻ were higher in Troyer citrange.     

Interaction of NaCl and Cd stress on compartmentation pattern of cations,antioxidant enzymes and proteins in leaves of two wheat genotypes differing in salt tolerance

Physiological mechanisms of salinity–Cd interactions were investigated in inter- and intracellular leaf compartments of salt-tolerant wheat × Lophopyrum elongatum (Host) A. Löve (syn. Agropyron elongatum) amphiploid and its salt-sensitive wheat parent (Triticum aestivum L. cv Chinese Spring). In comparison with the intracellular fluid, only very low Na⁺ concentrations (up to about 4 mM) were found in the intercellular leaf compartment of wheat after a 75 mM supply of NaCl. NaCl salinity led to a higher Cd concentration in leaves of the salt-sensitive genotype. Cd in the intercellular leaf compartment was not detectable. Higher K⁺ concentrations in the intercellular leaf compartment of the salt-sensitive genotype suggest a higher plasma membrane permeability caused by NaCl + Cd stress. Ascorbate peroxidase (APX) activity was increased in leaves of the salt-sensitive genotype under the combined NaCl and Cd stress. The highest non-specific peroxidase activities were detected under the combined stresses. It is suggested that NaCl and Cd stress in combination enhance the production of oxygen radicals and H₂O₂, especially in leaves of the salt-sensitive genotype. As a consequence, disturbed membrane function may cause elevated Cd concentrations in the intracellular leaf compartment under salinity. Cd did not change protein concentration and pattern in leaves. The protein content in inter-and intracellular leaf compartments of both genotypes was increased under salinity. A different protein pattern was obtained in inter- and intracellular leaf compartments. Thus, several physiological interactions between NaCl stress and Cd were found in the two wheat genotypes.     

The dehydrogenase-mediated recycling of NADPH is a key antioxidant system against salt-induced oxidative stress in olive plants

NADPH is an important molecule in the redox balance of the cell. In this paper, using olive tissue cultures as a model of the function of the NADPH-generating dehydrogenases in the mechanism of oxidative stress induced by severe salinity conditions was studied. When olive (Olea europaea) plants were grown with 200 mM NaCl, a 40% reduction in leaf fresh weight was produced. The content of non-enzymatic antioxidants such as ascorbate and glutathione was diminished between 20% to 39%, whereas the H2O2 content was increased threefold. In contrast, the analysis of the activity and protein contents of the main antioxidative enzymes showed a significant increase of catalase, superoxide dismutase and glutathione reductase. Overall, these changes strongly suggests that NaCl induces oxidative stress in olive plants. On the other hand, while the content of glucose-6-phosphate was increased almost eightfold in leaves of plants grown under salt stress, the content of NAD(P)H (reduced and oxided forms) did not show significant variations. Under salt stress conditions, the activity and protein contents of the main NADPH-recycling enzymes, glucose-6-phosphate dehydrogenase (G6PDH), isocitrate dehydrogenase (ICDH), malic enzyme (ME) and ferrodoxin-NADP reductase (FNR) showed an enhancement of 30-50%. In leaves of olive plants grown with 200 mM NaCl, analysis of G6PDH by immunocytochemistry and confocal laser scanning microscopy showed a general increase of this protein in epidermis, palisade and spongy mesophyll cells. These results indicate that in olive plants, salinity causes reactive oxygen species (ROS)-mediated oxidative stress, and plants respond to this situation by inducing different antioxidative enzymes, especially the NADPH-producing dehydrogenases in order to recycle NADPH necessary for the protection against oxidative damages. These NADP-dehydrogenases appear to be key antioxidative enzymes in olive plants under salt stress conditions.     

Effects of chloride and sodium on gas exchange parameters and water relations of Citrus plants

Gas exchange parameters, water relations and Na⁺/Cl^- content were measured on leaves of one-year-old sweet orange ( Citrus sinensis [L.] Osbeck cv. Hamlin) seedlings grown at increasing levels of salinity. Different salts (NaCl, KCl and NaNO₃) were used to separate the effects of Cl⁻ and Na⁺ on the investigated parameters. The chloride salts reduced plant dry weight and increased defoliation. Accumulation of Cl⁻ in the leaf tissue caused a sharp reduction in photosynthesis and stomatal conductance. By contrast, these parameters were not affected by leaf Na⁺ concentrations of up to 478 m M in the tissue water. Leaf water potentials reached values near −1.8 MPa at high NaCl and KCl supplies. This reduction was offset by a decrease in the osmotic potential so that turgor was maintained at or above control values. The changes in osmotic potential were closely correlated with changes in leaf proline concentrations. Addition of Ca²⁺ (as calcium acetate) increased growth and halved defoliation of salt stressed plants. Furthermore, calcium acetate decreased the concentration of Cl⁻ and Na⁺ in the leaves, and increased photosynthesis and stomatal conductance. Calcium acetate also counteracted the reductions in leaf water and osmotic potentials induced by salinity. In addition, calcium acetate inhibited the accumulation of proline in the leaves which affected the reduction in osmotic potential. These results indicate that adverse effects of salinity in Citrus leaves are caused by accumulation of chloride.     

盐胁迫下囊果碱蓬出苗状况及苗期抗盐性

研究了盐胁迫对囊果碱蓬出苗、幼苗生长、离子积累以及光合放氧速率的影响.囊果碱蓬生长的最适盐浓度在200 mmol/L NaCl左右.高浓度NaCl(400 mmol/L和600 mmol/L)没有显著降低其出苗率,200 mmol/L NaCl对出苗率具有促进作用.400 mmol/L和600 mmol/L NaCl显著降低了光合放氧速率.囊果碱蓬在高浓度NaCl处理下能够维持叶片较高的K+/Na+ 及含水量可能是其适应高盐生境的重要机制.     

Effects of Salinity on the Extensibility and Ca Availability in the Expanding Region of Growing Barley Leaves

The growth of barley (Hordeum vulgare L.) leaves is reduced by salinity. We used the Instron extensometric technique to measure the reversible and irreversible compliance of the expanding regions of growing barley leaves from plants exposed to 1, 40, 80 and 120 mM NaCl in nutrient solution. Two barley cultivars differing in salinity resistance (cv ‘Arivat’ and cv ‘Briggs’) were compared over 5d of leaf growth. During the period of most active leaf expansion, salinity reduced reversible compliance and increased compliance in the leaf segments, although responses to salinity were complex and changed over the course of leaf expansion. Salinity increased irreversible compliance more in the salt-sensitive cultivar Arivat than in the more salt-tolerant cultivar Briggs. Elemental analysis of the basal leaf segments used for extensometry revealed an accumulation of Na and a depletion of Ca in segments from salinized plants, resulting in very high Na: Ca ratios in salinized expanding tissue. The concentrations of K and Mg in basal leaf tissue were elevated by salinity. Our data do support the hypothesis that the inhibition of leaf expansion by salinity stress is mediated by a decline in irreversible extensibility. We suggest that reduced Ca availability in expanding leaf tissue may contribute to growth reduction in salt-stressed barley seedlings.     

The effect of abiotic stresses on carbohydrate status of olive shoots (Olea europaea L.) under in vitro conditions

Olive plants produce both sucrose and mannitol as major photosynthetic products. Contrary to previously studied celery [Vítová et al., Mannitol utilisation by celery (Apium graveolens) plants grown under different conditions in vitro. Plant Sci 2002; 163: 907-16], in vitro these carbohydrates were found to be able to sustain growth of olive shoots roughly to the same extent at all tested concentrations (1-9% w/v). We studied the involvement of the particular components of the endogenous carbohydrate spectrum in response to different abiotic stresses (osmotic stress, salinity, low temperature) in vitro. Salinity (100mM NaCl) caused a decrease of total soluble carbohydrates, while an increase was observed during low-temperature treatment (0 and 4 degrees C). Mannitol accumulated primarily under salinity (up to 40% of total soluble carbohydrates compared to 10-20% in controls). Only a small (two-fold) increase of proline content in salinity stressed plants indicates proline does not play a significant role in olive stress response. Low temperature led to an increase of the raffinose family oligosaccharides (RFO) proportion in total carbohydrates. We conclude that olive plants exploit the high diversity of the carbohydrate spectrum in specific response to different stresses.     

Antioxidant and anatomical responses in shoot culture of the apple rootstock MM 106 treated with NaCl, KCl, mannitol or sorbitol

To determine whether the major influence of high salinity is caused by the osmotic component or by salinity-induced specific ion toxicity, we compared the effects of mannitol, sorbitol, NaCl and KCl (all in concentratuions corresponded to osmotic potential −1.0 MPa) on the antioxidant and anatomical responses of the apple rootstock MM 106 explants grown in the Murashige and Skoog (MS) medium. All the compounds had a significant influence on explant's mineral composition and reduced the leaf water content, whereas mannitol and salts decreased chlorophyll (Chl) content and increased proline content. Superoxide dismutase (SOD), peroxidase (POD) and non-enzymatic antioxidant activities as well as H₂O₂ content were increased in the leaves and stems. In addition, in the leaves of explants exposed to NaCl an additional Mn-SOD isoform was revealed, while specific POD isoforms were detected in the leaves and stems treated with NaCl or KCl. However, catalase activity was depressed in the salt-treated leaves. The NaCl-treated leaves had the thickest lamina, due to an extensive increase of the size of epidermal and mesophyll cells. Also, an increase of the relative volume of the intercellular spaces in response to NaCl was observed. The results suggest that Na accumulation is the first candidate for the distinct antioxidant and anatomical responses between saline and osmotically generated stress in the MM 106 explants.