Changes Related to Salt Tolerance in Thylakoid Membranes of Photoautotrophically Cultured Green Tobacco Cells

A line of cultured tobacco cells (Nicotiana tabacum cv. SamsunNN) was established that was able to grow photoautotrophicallyin a medium that contained 0.2 M NaCl or in a medium withoutNaCl. Thylakoid membranes of the NaCl-adapted cells had higheroxygen-evolving activities, on the basis of chlorophyll, thanthose of unadapted cells. Furthermore, the oxygen-evolving activitiesof thylakoid membranes from NaCl-adapted cells were more tolerantto high concentrations of NaCl than those from unadapted cells. Glycinebetaine at 1 M protected the oxygen-evolving activityof thylakoid membranes from unadapted cells but not that fromadapted cells. Examination of the dissociation of 23-kDa and33-kDa polypeptides from the water-splitting complex of photosystemII at high concentrations of NaCl indicated that the affinitywith which the 23-kDa polypeptide was bound to thylakoid membranesof salt-adapted cells had been altered. (Received March 22, 1993; Accepted November 15, 1993)     

Calcium Stimulates the Adaptation of Cultured Liquorice Cells to PEG-Induced Water Stress

Calcium may be involved in plant tolerance to water deficit by regulating antioxidant metabolism or/and water relations. This study was designed to examine whether external Ca²⁺ would stimulate drought tolerance in cultured liquorice cells. Water stress induced by 15% PEG significantly reduced fresh weight and relative water content in liquorice cells, but external Ca²⁺ markedly increased them after stress for 7 days. The activities of catalase (CAT), superoxide dismutase (SOD) declined and activity of peroxidase (POD) slowly increased during water stress imposition. External calcium significantly enhanced SOD and CAT activities, but the effect on POD activity was weak. The effect of external Ca²⁺ on water deficit tolerance in liquorice cells was not due to the osmotic adjustment in culture medium. Under nonstress conditions, external calcium slightly increased the activities of SOD, CAT, and POD. Ca²⁺ signal in liquorice cells may be different under stress and nonstress conditions. Under water stress, Ca²⁺ signal involves in reactive oxygen species transduction pathway and affects the processes participating in regulation of antioxidative enzymes; under nonstress conditions, Ca²⁺ signal coming from external calcium might not participate in ROS signal transduction pathway resulting in antioxidative defense response in liquorice cells. Less malondialdehyde was accumulated after water stress for 7 days in Ca²⁺-treated cells than in untreated cells. It was proposed that external calcium could reduce the damage of water deficit and stimulate tolerance to it in liquorice cells by mitigating oxidative stress.     

Relationship between Sodium Influx and Salt Tolerance of Nitrogen-Fixing Cyanobacteria

The relationship between sodium uptake and cyanobacterial salt (NaCl) tolerance has been examined in two filamentous, heterocystous, nitrogen-fixing species of Anabaena. During diazotrophic growth at neutral pH of the growth medium, Anabaena sp. strain L-31, a freshwater strain, showed threefold higher uptake of Na⁺ than Anabaena torulosa, a brackish-water strain, and was considerably less salt tolerant (50% lethal dose of NaCl, 55 mM) than the latter (50% lethal dose of NaCl, 170 mM). Alkaline pH or excess K⁺ (>25 mM) in the medium causes membrane depolarization and inhibits Na⁺ influx in both cyanobacteria (S. K. Apte and J. Thomas, Eur. J. Biochem. 154:395-401, 1986). The presence of nitrate or ammonium in the medium caused inhibition of Na⁺ influx accompanied by membrane depolarization. These experimental manipulations affecting Na⁺ uptake demonstrated a good negative correlation between Na⁺ influx and salt tolerance. All treatments which inhibited Na⁺ influx (such as alkaline pH, K⁺ above 25 mM, NO₃⁻, and NH₄⁺), enhanced salt tolerance of not only the brackish-water but also the freshwater cyanobacterium. The results indicate that curtailment of Na⁺ influx, whether inherent or effected by certain environmental factors (e.g., combined nitrogen, alkaline pH), is a major mechanism of salt tolerance in cyanobacteria.     

Tolerance to Water Stress in Tomato Cultivars

Photosynthetica - The effects of plant water stress imposed at vegetative, flowering, and fruiting stages of four cultivars of tomato (Lycopersicon esculentum Mill.) on net photosynthetic rate (P...     

Tolerance to Water Stress in Tomato Cultivars

The effects of plant water stress imposed at vegetative, flowering, and fruiting stages of four cultivars of tomato (Lycopersicon esculentum Mill.) on net photosynthetic rate (P _N), stomatal conductance (g _s), transpiration rate (E), osmotic adjustment, and crop water stress index (CWSI) were investigated. Osmotic adjustment was the highest in cv. Arka Meghali, followed by cv. RFS-1. CWSI was lowest in cv. Arka Meghali and highest in cv. Pusa Ruby. Significant reduction in g _s, E, and P _N was observed in all the cultivars. The maximum reduction in E was observed in cv. Arka Saurabh during the fruiting stage (62.4 %) and maximum reduction in P _N at the flowering stage in Pusa Ruby (53.1 %). Maximum P _N was observed in Arka Meghali under water stress. The values of internal CO₂ concentration (C _i) did not follow the decrease in g _s which might be taken as an indication of mesophyll (non-stomatal) limitation to P _N. Magnitude of P _N decrease accompanying g _s reductions varied in the four cultivars. Arka Meghali which had highest rate of gas exchange efficiency (P _N/g _s) under water deficits can be recommended for rainfed cultivation. This revised version was published online in August 2006 with corrections to the Cover Date.     

棉花两品种耐盐性与抗氧化能力的相关性

对‘新陆早17’和‘中棉49’两个棉花（Gossypium hirsutumL.）品种在氧化剂甲基紫精（MV）和NaCl胁迫下的生理应答进行了研究,以期阐明棉花抗氧化能力与耐盐性的关系。研究结果表明,在40μmol·L-1MV胁迫3d,‘新陆早17’的丙二醛（MDA）和活性氧含量比‘中棉49’低,而抗坏血酸（AsA）、超氧化物岐化酶（SOD）、过氧化氢酶（CAT）和抗坏血酸过氧化物酶（APX）活性则高于‘中棉49’,表明‘新陆早17’抗氧化能力更强。在200mmol·L-1NaCl胁迫25d,‘新陆早17’的株高和叶绿素降低量、根部Na＋含量、相对电导率都低于‘中棉49’,说明‘新陆早17’耐盐更强。盐胁迫下‘新陆早17’的抗氧化酶活性上升而‘中棉49’却降低,表明‘新陆早17’通过上调SOD、CAT和APX活性来提高其耐盐性。结合棉花两品种的抗氧化和耐盐性差异,说明棉花抗氧化能力的高低能够影响品种的耐盐性。     

The Arabidopsis AtAAE13.1 Gene Enhances Salt Stress Tolerance in Angiosperms and Gymnosperm Plant Cells

In Vitro Cellular & Developmental Biology - Plant - The Arabidopsis malonyl-CoA synthetase gene AAE13.1 (AtAAE13.1) plays important roles in cell metabolism, plant growth and development, and...     

The Relationship between Water Binding and Desiccation Tolerance in Tissues

In an effort to define the nature of desiccation tolerance, a comparison of the water sorption characteristics was made between tissues that were resistant and tissues that were sensitive to desiccation. Water sorption isotherms were constructed for germinated and ungerminated soybean axes and also for fronds of several species of Polypodium with varying tolerance to dehydration. The strength of water binding was determined by van't Hoff as well as D'Arcy/Watt analyses of the isotherms at 5, 15, and/or 25°C. Tissues which were sensitive to desiccation had a poor capacity to bind water tightly. Tightly bound water can be removed from soybean and pea seeds by equilibration at 35°C over very low relative humidities; this results in a reduction in the viability of the seed. We suggest that region 1 water (i.e. water bound with very negative enthalpy values) is an important component of desiccation tolerance.     

Resistance to Water Uptake in a Mature Citrus Tree

Resistance to water uptake in an irrigated and a water-stressed22-year-old citrus tree was examined during 7 weeks. Frequentirrigation maintained the soil water potential of one citrustree between 0.0 and –0.016 MPa in the upper 0.6 m, whilethe other tree received no water for 44 d. Sap flow in the trunkswas measured once a week from dawn to dusk at hourly intervalswith a calibrated heat pulse technique. At the same time leafwater potential was measured on sunlit and shaded leaves. Sap flow in the stressed tree decreased with time at a higherrate than the water potential difference between soil and leaf,which implies an increase in the resistance of the transportsystem. Diurnal sap flow and diurnal leaf water potential ofthe irrigated and stressed trees were linearly related throughoutthe experimental period. The slope of the linear relationshipbetween flow and potential for both trees remained nearly constant,indicating that the resistance within the tree remained constant.The effect of drying appeared to be a progressive decline ofthe leaf water potential at zero flow (computed by linear regression).This was ascribed to a reduction of the transport of water inthe soil toward the roots. Key words: Transpiration, Leaf water potential, Plant water relations, Soil water stress     

Abscisic Acid Reduces Leaf Abscission and Increases Salt Tolerance in Citrus Plants

This paper describes the physiological effects of abscisic acid (ABA) and 100 mM NaCl on citrus plants. Water potential, leaf abscission, ethylene production, photosynthetic rate, stomatal conductance, and chloride accumulation in roots and leaves were measured in plants of Salustiana scion [Citrus sinensis (L) Osbeck] grafted onto Carrizo citrange (Citrus sinensis [L.] Osbeck × Poncirus trifoliata [L.] Raf) rootstock. Plants under salt stress accumulated high amounts of chloride, increased ethylene production, and induced leaf abscission. Stomatal conductance and photosynthetic rates rapidly dropped after salinization. The addition of 10 mM ABA to the nutrient solution 10 days before the exposure to salt stress reduced ethylene release and leaf abscission. These effects were probably due to a decrease in the accumulation of toxic Cl- ions in leaves. In non-salinized plants, ABA reduced stomatal conductance and CO2 assimilation, whereas in salinized plants the treatment slightly increased these two parameters. The results suggest a protective role for ABA in citrus under salinity.     

Relationship between the Accumulation of Putrescine and the Tolerance to Oxygen-Deficit Stress in Gramineae Seedlings

The accumulation of putrescine under anoxia was studied in seedlingsof 6 Gramineae species showing tolerance to the stress in thefollowing order: rice, barnyard grass>maize>rye, barleyand wheat. The accumulation of putrescine in shoots and rootsduring 6 h of oxygen deprivation was different among the speciesand correlated with their tolerance to anaerobic conditions.In both tissues, rice and barnyard grass accumulated more than0.6 µmol/g fresh weight. The lower increase in the putrescinetiter was observed in wheat tissues with less than 0.1 µmol/gfresh weight. Feeding experiments with [^l4C]arginine showedthat rice tissues have a greater capacity than wheat tissuesto synthesize putrescine under anoxia. The better tolerant speciesto anaerobic conditions showed high arginine decarboxylase activityin shoots and roots than the sensitive species. The presenceof exogenous Put partially increased the survival of wheat rootsafter 7.5 h of oxygen-deficit stress. The role of putrescinein determining differences in the tolerance to anoxia in Gramineaeseedlings is discussed. (Received December 20, 1989; Accepted March 12, 1990)     

Exogenous Nitric Oxide (as Sodium Nitroprusside) Ameliorates Polyethylene Glycol-Induced Osmotic Stress in Hydroponically Grown Maize Roots

The present study was designed to examine whether exogenous sodium nitroprusside (SNP) supplementation has any ameliorating action against PEG-induced osmotic stress in Zea mays cv. FRB-73 roots. Twenty percent or 40 % polyethylene glycol (PEG6000; ?0.5 MPa and ?1.76 MPa, respectively) treatment alone or in combination with 150 and 300 μM SNP was applied to hydroponically grown maize roots for 72 h. Although only catalase (CAT) activity increased when maize roots were exposed to PEG-induced osmotic stress, induction of this antioxidant enzyme was inadequate to detoxify the extreme levels of reactive oxygen species, as evidenced by growth, water content, superoxide anion radical (O ₂ ^?? ), hydroxyl radical (OH^?) scavenging activity, and TBARS content. However, supplementation of PEG-exposed specimens with SNP significantly alleviated stress-induced damage through effective water management and enhancement of antioxidant defense markers including the enzymatic/non-enzymatic systems. Exogenously applied SNP under stress resulted in the up-regulation of glutathione peroxidase (GPX), glutathione S-transferase (GST), ascorbate peroxidase (APX), glutathione reductase (GR), total ascorbate, and glutathione contents involved in ascorbate–glutathione cycle. On the other hand, growth rate, osmotic potential, CAT, APX, GR, and GPX increased in maize roots exposed to both concentrations of SNP alone, but activities of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase decreased. Based on the above results, an exogenous supply of both 150 and 300 μM SNP to maize roots was protective for PEG-induced toxicity. The present study provides new insights into the mechanisms of SNP (NO donor) amelioration of PEG-induced osmotic stress damages in hydroponically grown maize roots.     

Stomatal Response of Citrus jambhiri to Water Stress and Humidity

Seven-month-old rough lemon (Citrus jambhiri Lush.) seedlings were subjected to high- and low-humidity treatments (vapor pressure deficits of 8.0 and 19.6 mbar) for 3 weeks. Half of each group was well supplied with water and half was subjected to a series of three drying cycles in which xylem pressure potential fell to below ?25 bar. The relationship between leaf conductance and xylem pressure potential was similar during each drying phase and was unaffected by atmospheric humidity. Several days elapsed after rewatering before normal stomatal opening occurred. When all the plants were subsequently kept well watered, leaf conductances decreased as the leaf-to-air vapor pressure difference was increased. However, the conductances of previously stressed plants were lower than those of unstressed plants, and consequently previously stressed plants had lower transpiration rates.     

Expression of Genes for Photosynthesis and the Relationship to Salt Tolerance of Alfalfa (Medicago sativa) Cells

The basis for the salt tolerant phenotype of a line of Medicagosativa (alfalfa) cells (HG2-N1) derived by selection from asalt sensitive line (HG2) was studied. The salt tolerant HG2-N1cell line shows eleven fold elevated chlorophyll content overthat of the parent salt sensitive HG2 cell line, with an additionaltwo fold increase in chlorophyll levels when the cells are grownin 1% NaCl. In this study, we demonstrate that the chlorophyllaccumulation and response to salt was associated with largeincreases in the two photosynthesis related mRNAs, rbcL (ribulose-l,5-bis-phosphatecarboxylase [Rubisco] large subunit) and rbcS (Rubisco smallsubunit) and a substantial increase in the activity of the holoenzyme.The salinity-induced increase in catalytically competent Rubiscoprotein in the salt tolerant cell line was highly responsiveto light and correlated with the salt tolerant phenotype. Inaddition, NaCl stimulated rbcL and rbcS mRNA and Rubisco accumulationin dark grown salt tolerant cells, indicating that salt couldsubstitute to some degree for light in stimulating increasesin specific mRNA and protein concentrations. Increased photosyntheticcompetence associated with these increased protein levels wasapparently important in contributing to the salt tolerant phenotypeof HG2-N1, since PS II electron transport inhibitors (DCMU,cyanazine) were found to significantly reduce the growth ofthis cell line in the presence of salt, but not in the absenceof salt. These results suggest that the salt-induced increasein mRNA and protein accumulation involved in photosynthesismay play a significant role in the salt tolerant capabilityof HG2-N1 alfalfa cells. (Received April 2, 1990; Accepted September 10, 1990)     

Phosphorus-31 NMR Studies of Wild-Type and NaCl-Tolerant Citrus Cultured Cells

Ben–Hayyim, G. and Navon, G. 1985. Phosphorus–31NMR studies of wild–type and NaCl–tolerant Citruscultured cells.—J. exp. Bot. 36: 1877–1888. Theinternal pH of the cytoplasm and vacuole and the relative distributionof internal P_i concentrations between those two cell compartmentshave been determined by ³¹P nuclear magnetic resonance spectroscopyin wild–type and NaCl–tolerant cell lines of Shamoutiorange (Citrus sinensis L. Osbeck). Wild–type cells accumulatehigher amounts of P_i than the NaCl–tolerant cells whenexposed to equal external P_i concentrations. This additionalP_i is located mainly in the vacuole. When both types of cellsare exposed to increasing external P_i concentrations, the internalP_i concentrations increase. The cytoplasmic P_i concentrationreaches saturation at a rather low external P_i concentrationwhile the vacuolar P_i can be increased by a large factor. Transferof cells from aerobic to anaerobic conditions causes an immediateincrease of P_i in the cytoplasm and a slow acidification. Exposureof cells to NaCl during the period of their growth results inan increase in total P_i concentration with a large increasein the ratio of vacuolar to cytoplasmic P_i levels. When thesecells are exposed to NaCl for a short time, total internal P_iconcentration docs not change significantly but its proportionschange in favour of the vacuole. pH values of the cytoplasmand the vacuole under all these conditions are rather constant,the value being 5.8–6.0 for the vacuole and 7.4–7.6for the cytoplasm. Moreover, subjecting these cells to a widerange of external pH values does not change their intracellularpH. These results indicate that a strong regulation of internalpH is operating in both types of cells. The presence of a phosphorylatedmetabolite with an unusual pH titration curve, located in thevacuole, is also reported. Key words: Citrus, callus, ³¹P-NMR, NaCI tolerance, intracellular pH     

Resistance Mechanism of Cultured Plant Cells to Tobacco Mosaic Virus

In somaclonal tissues obtained from systemically TMV-infected tobacco plants, a relation between changes of TMV amounts and the callus growth was examined. The culture medium was suitable for maintaining a constant concentration of TMV as well as active callus growth. By using the shake-culture method, somaclonal tissues were separated into two classes on the basis of callus sizes. In large callus tissues, TMV amounts were constant during subculturing but the tissues did not either grow or release the newly divided cells after the last subculture. On the other hand, smaller callus tissues grew markedly and the TMV amounts were conspicuously lowered. After shake-subculture of smaller tissues, they were successfully regenerated to plantlets. None of the plantlets expressed any mosaic symptoms, while plantlets from the original somaclones showed severe mosaic symptoms of TMV in leaflets. Thus, the present report describes the successful production of virus-free plantlets from infected somaclonal callus cultures.     

Aluminum Tolerance Acquired during Phosphate Starvation in Cultured Tobacco Cells

Al toxicity in cultured tobacco cells (Nicotiana tabacum L. cv Samsun; nonchlorophyllic cell line SL) has been investigated in nutrient medium. In this system, Al and Fe(II) (ferrous ion) in the medium synergistically result in the accumulation of both Al and Fe, the peroxidation of lipids, and eventually death in cells at the logarithmic phase of growth (+P cells). A lipophilic antioxidant, N,N[prime]-diphenyl-p-phenylenediamine, protected +P cells from the peroxidation of lipids and from cell death, suggesting that a relationship exists between the two. Compared with +P cells, cells that had been starved of Pi (-P cells) were more tolerant to Al, accumulated 30 to 40% less Al and 70 to 90% less Fe, and did not show any evidence of the peroxidation of lipids during Al treatment. These results suggest that -P cells exhibit Al tolerance because their plasma membranes are protected from the peroxidation of lipids caused by the combination of Al and Fe(II). It seems likely that the exclusion of Fe from -P cells might suppress directly Fe-mediated peroxidation of lipids. Furthermore, since -P cells accumulated [beta]-carotene, it is proposed that this carotenoid pigment might function as a radical-trapping antioxidant in the plasma membrane of cells starved of Pi.