Interactive effects of boron and salinity stress on the growth,membrane permeability and mineral composition of tomato and cucumber plants

A greenhouse study was conducted in order to determine interactive effects of NaCl salinity and B on the growth, sodium (Na), chloride (Cl), boron (B), potassium (K) concentrations and membrane permeability of salt resistant Tomato (Lycopersicon esculentum L. cv. Lale F₁) and salt sensitive cucumber (Cucumis sativus L. cv. Santana F₁) plants. Plants were grown in a factorial combination of NaCl (0 and 30 mM for cucumber and 0 and 40 mM for tomato) and B (0, 5, 10 and 20 mg kg^–1 soil). Boron toxicity symptoms appeared at 5 mg kg^–1 B treatments in both plants. Salinity caused an increase in leaf injury due to B toxicity, but it was more severe in cucumber. Dry weights of the plants decreased with the increasing levels of applied B in nonsaline conditions, but the decrease in dry weights due to B toxicity was more pronounced in saline conditions especially in cucumber. Salinity × B interaction on the concentration of B in both plants was found significant. However, increase in B concentrations of tomato decreased under saline conditions when compared to nonsaline conditions. Contrary to this, B concentration of cucumber increased as a result of increasing levels of applied B and salinity. Salinity increased Na and Cl concentrations of both plants.Potassium concentration of tomato was not affected by salinity and B treatments, but K concentration of cucumber was decreased by salinity. Membrane permeability of the plants was increased by salinity while toxic levels of B had no effect on membrane permeability in nonsaline conditions. Membrane permeability was significantly increased in the presence of salinity by the increasing levels of applied B.     

LIGHT,TEMPERATURE AND SALINITY EFFECTS ON GROWTH,LEAF ANATOMY AND PHOTOSYNTHESIS OF DISTICHLIS SPICATA (L.) GREENE

The effects of light, temperature, and salinity on growth, net CO₂ exchange and leaf anatomy of Distichlis spicata were investigated in controlled environment chambers. When plants were grown at low light, growth rates were significantly reduced by high substrate salinity or low temperature. However, when plants were grown at high light, growth rates were not significantly affected by temperature or salinity. The capacity for high light to overcome depressed growth at high salinity cannot be explained completely by rates of net photosynthesis, since high salinity caused decreases in net photosynthesis at all environmental conditions. This salinity-induced decrease in net photosynthesis was caused largely by stomatal closure, although plants grown at low temperature and low light showed significant increases in internal leaf resistance to CO₂ exchange. Increased salinity resulted in generally thicker leaves with lower stomatal density but no significant differences in the ratio of mesophyll cell surface area to leaf area. Salinity and light during growth did not significantly affect rates of dark respiration. The mechanisms by which Distichlis spicata tolerates salt appear to be closely coulpled to the utilization of light energy. Salt-induced leaf succulence is of questionable importance to gas exchange at high salinity in this C₄ species.     

Effects of salinity and gibberellin on water content,growth and mineral composition of cowpea,calabrese and red radish plants

Salinity had generally little influence on the water content of different parts of cowpea(Vigna sinensis L.), calabrese(Brassica oleracea L. var.botrylis) and red radish(Raphanus salivus L.) plants. Salinity showed a promotive effect on the growth of cowpea, while in calabrese the effect was either promotive or depressive depending upon the concentration of the NaCl, and in red radish plants salinity progressively suppressed growth. Total nitrogen, phosphorus, potassium and sodium contents of cowpea leaves were not affected by salinity treatments, while in calabrese and red radish leaves the contents of N, P and K were generally decreased as the salinity level increased. Gibberellin (GA₃) applied to salt-treated plants had either a stimulatory or inhibitory effect on the growth, water content and contents of N, P, K and Na in the leaves depending upon the plant type, the concentration of GA₃ and level of salinity.     

Stomatal responses to humidity of coastal and interior populations of a Californian shrub

Summary Plants of two populations of Diplacus aurantiacus, a subshrub of the Californian chaparral, were compared for their stomatal response to water vapor concentration gradients. Plants of a coastal and an interior population were compared when grown under both low and high humidities. When grown at high humidity the coastal plants exhibited higher conductances and higher transpiration/photosynthesis ratios at all leaf-to-air water vapor concentration gradients than did the interior plants. Although all of the plants examined showed a pronounced stomatal response to humidity the response did not result in the degree of regulation of water-use efficiency reported for other Californian coastal species.     

Salinity-induced calcium deficiencies in wheat and barley

Salinity-calcium interactions, which have been shown to be important in plants grown in dryland saline soils of the Canadian prairies, were studied in two species differing in salt tolerance. In solution culture, wheat showed a greater reduction in growth and a higher incidence of foliar Ca deficiency symptoms than barley when grown under MgSO₄ or Na₂SO₄ plus MgSO₄ salt stress. Amendment of the saline solution with Ca to increase the Ca/(Na+Mg) ratio ameliorated the effects of salt, but more so in wheat than in barley. At least part of the difference in salt tolerance between the two species must therefore relate to species differences in the interaction of salinity and Ca nutrition. The greater response of wheat to Ca was not due to a lower Ca status in leaf tissue; on the contrary, although Ca amendments improved tissue Ca/(Na+Mg) ratios in both species, salinized wheat had equivalent or higher Ca content, and higher Ca/(Na+Mg) ratios than did barley. The higher Ca requirement of wheat is apparently specific to a saline situation; at low salinity, wheat growth was not reduced as extensively as that of barley as Ca/(Na+Mg) ratio was decreased. High night-time humidity dramatically improved wheat growth under saline conditions, but increasing the Ca concentration of the saline solution had no effect on growth in the high humidity treatment. Membrane leakage from leaf tissue of wheat grown under saline conditions was increased compared to tissue from non-saline plants. Plants grown in Ca-amended saline solutions showed no increase in membrane leakage. These results confirm the importance of Ca interaction with salinity stress, and indicate differences in species response.     

Effect of air humidity on the development of functional stomatal apparatus

Phaseolus vulgaris L. seedlings were grown under different air humidities simulating conditions during micropropagation (very high humidity duringin vitro cultivation and low air humidity after transferex vitro). The functional stomatal apparatus developed after a short period of growth at low air humidity at the beginning of plant ontogeny or after transfer from high to low air humidity, but not in plants grown steadily under high air humidity. The ability of stomata to regulate gas exchange was not persistent and disappeared after transfer of plants from low to high humidity. The author thanks Mrs. L. Kolčabová for her skilled assistance. The paper is a part of the project supported by the grant No. 501/95/1303 of the Grant Agency of the Czech Republic.     

Primary and Lateral Root Development of Dark- and Light-Grown Cotton Seedlings under Salinity Stress*

Primary root growth dynamics and lateral root development of dark- and light grown cotton seedlings (Gossypium hirsutum L., cv. Acala SJ-2) were studied under control and salinity stress conditions. The seedlings were grown by two methods: A) in paper-lined, vermiculite-filled beakers with the plants growing between the paper and the glass wall (Gladish and Rost, 1993), and B) in hydroponics after germination and initial growth in germination paper rolls saturated with the treatment solutions (Kent and Läuchli, 1985). After germination, daily primary root elongation rate gradually incrased to a maximum, then gradually declined to close to zero for dark-grown seedlings, or to sustained rates of about 10 mm per day for light-grown control plants. Salinity stress delayed primary root growth and reduced peak elongation rates, without changing the general primary root growth pattern. These results suggest that salinity changed the time-scale, but did not modify the normal developmental sequence. Lateral root growth was more inhibited by salinity than primary root growth. In addition, elongation of lateral roots was more inhibited by salinity than their initiation and emergence. Light exposure of the shoot favored both sustained primary root growth from 7 days after planting, and lateral root emergence and growth. Salinity effects were more severe on seedlings germinated and grown in hydroponics (method B) than on vermiculite-grown plants (method A). These results emphasize the importance of growing conditions for the NaCl-induced effects on cotton root development. In addition, the differential effects of salinity on primary and lateral roots became evident, pointing to diverse control mechanisms for the development of these root types.     

Flowering and male reproductive functions of chickpea (Cicer arietinum L.) genotypes as affected by salinity

The influence of salinity, given at germination (stage I) or 75 d after sowing (stage II), on flower production and characteristic features of male reproductive structures was studied in three promising genotypes of chickpea (Cicer arietinum L. cv. ICCV 88102, H 82-2 and C-235). In ICCV 88102 and H 82-2 salinity 20 meq 1^-1 increased the number of flowers when applied at both stages whereas in C-235 only when applied at the later stage. The salinity also delayed flowering; the higher salinity the greater was delay in flowering. In H 82-2 and C-235 salinity treatment given at stage II (when few flower buds appeared) hastened the flowering. The salinity curtailed pollen production; the reduction being minimum in C-235 and maximum in H 82-2. Germination was not significantly affected in C-235 pollen collected from plants grown under salinity conditions upto 60 meq 1^-1 applied at stage I but the tube elongation was inhibited. The inhibition of tube elongation was greatest in C-235. Salinity treatment administered at stage II did not affect significantly pollen germination excepting C-235 in which a consistent decline with increasing salinity was evident. Salinity stimulated tube growth in ICCV 88102. Na₂SO₄ in the germination medium was more detrimental for both pollen germination and tube growth than NaCl.     

Growth and water use of the mangroves Rhizophora apiculata and R. stylosa in response to salinity and humidity under ambient and elevated concentrations of atmospheric CO2

Two mangrove species, Rhizophora apiculata and R. stylosa, were grown for 14 weeks in a multifactorial combination of salinity (125 and 350 mol m^?3 NaCl), humidity (43 and 86% relative humidity at 30°C) and atmospheric CO₂ concentration (340 and 700 cm³ m^?3). Under ambient [CO₂], growth responses to different combinations of salinity and humidity were consistent with interspecific differences in distribution along natural gradients of salinity and aridity in northern Australia. Elevated [CO₂] had little effect on relative growth rate when it was limited by salinity but stimulated growth when limited by humidity. Both species benefited most from elevated [CO₂] under relatively low salinity conditions in which growth was vigorous, but relative growth rate was enhanced more in the less salt-tolerant and more rapidly growing species, R. apiculata. Changes in both net assimilation rate and leaf area ratio contributed to changes in relative growth rates under elevated [CO₂], with leaf area ratio increasing with decrease in humidity. Increase in water use efficiency under elevated [CO₂] occurred with increase, decrease or no change in evaporation rates; water use characteristics which depended on both the species and the growth conditions. In summary, elevated [CO₂] is unlikely to increase salt tolerance, but could alter competitive rankings of species along salinity × aridity gradients.     

Leaf expansion in sunflower as influenced by salinity and short-term changes in carbon fixation

Abstract With a view to defining factors regulating the growth responses of sunflower to salinity, plants were grown in solution culture (0, 50 or 100 mol m⁻³ NaCl) and under natural light, and the areas of every leaf measured once or twice daily from 22 until 38 d after germination. During this period, carbon availability for growth was manipulated by changing light levels and by the use of a photosynthesis inhibitor, DCMU. Salinity reduced relative leaf expansion rates per plant (RLER) by an average of 0.04 (50 mol m⁻³) and 0.08 (100 mol m⁻³) m² m⁻² d⁻¹ compared with control plants of equivalent leaf area: the effects were found in expanding leaves regardless of age or size. Control plants expanded faster during the day than the night, but plants grown in salt had an almost constant RLER throughout the 24 h, indicating that salt influences the rate of utilization of assimilates independently of their production. DCMU reduced RLER considerably in both control and salt-treated plants and reduced the advantage of control plants during the day. Conditions of low light also reduced the differences in RLER between control and salt-treated plants. When salt was removed from the root medium of non-DCMU plants, the expansion rates equalled that of the controls within 24 h and remained at the same levels for the following 3 d measurement period: this recovery applied to leaves of all ages. Salt-grown plants with no photosynthesis (DCMU treatments) also increased their expansion rates upon removal of salt from the root medium, thus providing further evidence that growth was not limited by carbohydrate status, i.e. that salt influences growth primarily via its effects on the rate of utilization of stored assimilates.     

Flowering and Growth Response of Peanut Plants (Arachis hypogaea L. var. Starr) at Two Levels of Relative Humidity

Peanut plants (Arachis hypogaea L. var. Starr) grown under two different relative humidities were used in all experiments. All plants were germinated and grown to flowering in the greenhouse. At this time, one group was moved to a growth room under 95% relative humidity. After 50 days the humidity of the growth room was lowered to 50%. The second group was moved into a growth room at 50% relative humidity and after 50 days the humidity was raised to 95%.     

Sodium and boron exclusion in two Brassica juncea cultivars exposed to the combined treatments of salinity and boron at moderate alkalinity

Salinity and high boron (B) concentrations are important co-limitations to crop production on naturally occurring alkaline soils in low rainfall regions of the world. Although the interactive effects of salinity and B toxicity on Brassica juncea growth have been reported in slightly acidic soils, very little is known about the interactive effects in alkaline soils. In the current study, a moderately tolerant (Vaibhav) and sensitive (Xinyou5) variety, were grown hydroponically for four weeks to assess mild salinity (50 mM NaCl) with or without high B (1 mM B) at moderate alkalinity (pH 8.5/5 mM NaHCO₃). The growth of the two varieties was more affected under the combined treatment than either salinity or high B alone. Although growth rate reduction was similar among the varieties, Vaibhav maintained a lower sodium (Na) and B and a higher potassium (K) concentration in the leaves than Xinyou5. In response to salinity, Vaibhav demonstrated essential tolerance mechanisms of partial exclusion and presumably compartmentalization of Na, leading to greater biomass than Xinyou5. Despite being able to better exclude B, Xinyou5 suffered a greater growth penalty, indicating higher B sensitivity than Vaibhav. In conclusion, screening for individual stresses is not necessarily the best strategy because plant responses to a single stress either salinity or high B may not always be the same as observed when both stresses are present together. Therefore, Brassica germplasm screening is essential for stresses in combination but not separately.     

The strategy of Na+ compartmentation and growth of Atriplex centralasiatica in adaptation to saline environments

In this study, we investigated the adaptation strategy employed by Atriplex centralasiatica Iljin in response to high salinity. When grown in high saline environments (100–200 mM NaCl), A. centralasiatica plants were larger and more succulent. This increased growth and water uptake was correlated with a large and specific cellular accumulation of sodium, demonstrating that in A. centralasiatica Na⁺ is beneficial rather than toxic. More than 95% of Na⁺ absorbed by salt-treated A. centralasiatica plants accumulated in shoots, especially in leaves; approximately 98% of Na⁺ that accumulated in leaves was localized in leaf protoplasts, a situation that was responsible for the decreased photosynthetic rate observed with increasing salt concentration. Because of the greater leaf area per plant found under saline conditions, no reduction in biomass of individual plants was observed. Measurements on isolated tonoplast-enriched membrane vesicles derived from the leaves of A. centralasiatica revealed increased V-H⁺-ATPase hydrolytic activity and V-H⁺-ATPase proton pump activity in salt-treated leaves compared with controls. These results suggest that, as an adaptation to saline environments, A. centralasiatica can efficiently sequester Na⁺ into vacuoles, thereby increasing leaf area to maintain its CO₂ assimilation capabilities.     

Relative humidity- and ABA-induced variation in carbon and oxygen isotope ratios of cotton leaves

Cotton (Gossypium hirsutum L. cv. CS50) plants were grown at two levels of relative humidity (RH) and sprayed daily with abscisic acid (ABA) at four concentrations. Plants grown at lower humidity had higher transpiration rates, lower leaf temperatures and lower stomatal conductance. Plant biomass was also reduced at low humidity. Within each humidity environment, increasing ABA concentration generally reduced stomatal conductance, evaporation rates, superficial leaf density and plant biomass, and increased leaf temperature and specific leaf area. As expected, decreased stomatal conductance resulted in decreased carbon isotope discrimination in leaf material ( Δ ¹³C_l). Plants grown at low humidity were more enriched in ¹⁸O than those grown at high RH, as theory predicts. Within each humidity environment, increasing ABA concentration increased oxygen isotope enrichment of leaf cellulose ( Δ ¹⁸O_c) and whole‐leaf tissue ( Δ ¹⁸O_l). Values of Δ ¹³C_l and Δ ¹⁸O_l predicted by theoretical models were close to those observed, accounting for 79% of the measured variation in Δ ¹³C_l and 95% of the measured variation in Δ ¹⁸O_l. Supporting theory, Δ ¹³C_l and Δ ¹⁸O_l in whole‐leaf tissue were negatively related.     

Effect of salinity and waterlogging on growth,anatomical and antioxidative responses in <Emphasis Type="Italic">Mentha aquatica</Emphasis> L.

Salinity and waterlogging are two stresses which in nature often occur simultaneously. In this work, effects of combined waterlogging and salinity stresses are studied on the anatomical alteration, changes of enzymatic antioxidant system and lipid peroxidation in Mentha aquatica L. plants. Seedlings were cultured in half-strength Hoagland medium 50 days after sowing, and were treated under combination of three waterlogging levels (well drained, moderately drained and waterlogging) and NaCl (0, 50, 100, 150 mM) for 30 days. Moderately drained and waterlogging conditions induced differently aerenchyma formation in roots of M. aquatica salt-treated and untreated plants. Moreover, stele diameter and endodermis layer were also affected by salt stress and waterlogging. Salt stress significantly decreased growth, relative water content (RWC), protein level, catalase (CAT) and polyphenol oxidase (PPO) activities, and increased proline content, MDA content, H₂O₂ level and activities of superoxide dismutase (SOD), peroxidase (POX), and ascorbate peroxidase (APX). Waterlogging in salt-untreated plants increased significantly growth parameters, RWC, protein content, antioxidant enzyme activity, and decreased proline content, H₂O₂ and MDA levels. In salt-treated plant, waterlogging caused strong induction of antioxidant enzymes activities especially at severe stress condition. These results suggest M. aquatica is a waterlogging tolerant plant due to significant increase of antioxidant activity, membrane stability and growth under water stress. High antioxidant capacity under waterlogging can be a protective strategy against oxidative damage, and help to salt stress alleviation.     

Yield, transpiration and growth of tomatoes under combined excess boron and salinity stress

Boron is essential to growth at low concentrations and limits growth and yield when in excess. Little is known regarding plant response to excess boron (B) and salinity occurring simultaneously. The influences of B and salinity on tomatoes (Lycopersicon esculentum Mill. Cv `5656') were investigated in lysimeters. Salinity levels were 1, 3, 6 and 9 dSm^–1 and B levels were 0.028, 0.185, 0.37, 0.74, 1.11, 1.48 mol m^–3. Excess boron was found to decrease yield and transpiration of tomatoes. This effect was inhibited when plants were exposed to simultaneous B and salinity stresses. Both irrigation water salinity and boron concentration influenced water use of the plants in the same manner as they influenced yield. While yield was found to decrease with increased boron concentration in leaf tissue, increased salinity led to decreased boron accumulation. Yield response was found to correlate better to B concentration in irrigation water and soil solution than to plant tissue B content. A dominant-stress-factor model was assumed and validated. The model applies the principle that when a plant is submitted to conditions of stress caused by B in conjunction with salinity, the more severe stress determines yield. The results of this study have significance in modeling and management of high salinity high boron conditions. Under saline conditions, differences in crop yield and in water use may not be experienced over a significant range of boron concentrations.     

Salinity and Nitrogen Effects on Photosynthesis, Ribulose-1,5-Bisphosphate Carboxylase and Metabolite Pool Sizes in Phaseolus vulgaris L

Salinity (100 millimolar NaCl) was found to reduce photosynthetic capacity independent of stomatal closure in Phaseolus vulgaris. This reduction was shown to be a consequence of a reduction in the efficiency of ribulose-1,5-bisphosphate (RuBP) carboxylase (RuBPCase) rather than a reduction in the leaf content of photosynthetic machinery. In control plants, photosynthesis became RuBP-limited at approximately 1.75 moles RuBP per mole 2-carboxyarabinitol bisphosphate binding sites. Salinization caused the RuBP pool size to reach this limiting value for CO₂ fixation at much lower values of intercellular CO₂. Plants grown at low nitrogen and ± NaCl became RuBP limited at similar RuBP pool sizes as the high nitrogen-grown plants. At limiting RuBP pool sizes and equal values of intercellular CO₂ photosynthetic capacity of salt-stressed plants was less than control plants. This effect of salinity on RuBPCase activity could not be explained by deactivation of the enzyme or inhibitor synthesis. Thus, salinity reduced photosynthetic capacity by reducing both the RuBP pool size by an effect on RuBP regeneration capacity and RuBPCase activity by an unknown mechanism when RuBP was limiting.     

Overexpression of DnaK from a halotolerant cyanobacterium Aphanothece halophytica enhances growth rate as well as abiotic stress tolerance of poplar plants

The DnaK/Hsp70 family is a molecular chaperone that binds non-native states of other proteins, and concerns to various physiological processes in the bacterial, plant and animal cells. Previously, we showed that overexpression of DnaK from a halotolerant cyanobacterium Aphanothece halophytica (ApDnaK) enhances tolerance to abiotic stresses such as high salinity and high temperature in tobacco plants. Here, we tested the transformation of poplar (Populus alba) with ApDnaK for enhancing the growth of transformed poplar plants. Under control growth conditions, transgenic poplar plants exhibited similar growth rates with the wild-type plants during young seedlings under low light intensity, whereas they showed faster growth, larger plant size, and higher cellulose contents when poplar plants were grown under high light intensity. Transgenic young poplar plants exhibited more rapid recovery from the stresses of high salinity, drought, and low temperature compared with those of the wild type plants when poplar plants were grown under low light intensity. These results suggest that ApDnaK could be useful to enhance the growth rate as well as to increase the stress tolerance.     

Interaction between elevated atmospheric concentration of CO2 and humidity on plant growth: comparison between cotton and radish

Cotton plants (Gossypium hirsutum L. var Deltapine 90) and radish plants (Raphanus sativus L var Round Red) were grown under full sunlight using a factorial combination of atmospheric CO₂ concentrations (350 µmol mol^-1 and 700 µmol mol^-1) and humidities (35% and 90% RH at 32 °C during the day). Cotton plants showed large responses to increased humidity and to doubled CO₂. In cotton plants, the enhanced dry matter yield due to doubled CO₂ concentration was 1.6-fold greater at low humidity than at high humidity. Apart from the direct effect of elevated CO₂ level on photosynthesis, the greater effect of doubled CO₂ concentration on dry matter yield at low humidity was probably due to: (1) increased leaf water potential caused by reduction of transpiration resulting from the negative CO₂ response of stomata to increased CO₂ concentration the consequence being greater leaf area expansion; (2) reduction of CO₂ assimilation rate at low humidity and normal CO₂ concentration as a result of humidity response of stomata causing reduction of intercellular CO₂ concentration. In contrast, apart from the very early stage of development, radish plants do not respond to increased humidity but had a relatively large response to doubled CO₂ concentration. Furthermore, due to the determinate growth pattern as well as having a prominent storage root, the extra photoassimilate derived at doubled CO₂ level is allocated to the storage root.Abbreviatios DAE day after emergence - LAD leaf areal density (leaf dry weight/leaf area) - LAR leaf area ratio (leaf area/plant dry weight) - NAR net assimilation rate - c_i internal CO₂ concentration - PPFD photosynthetic photon flux density - RGR relative growth rate - RLAGR relative leaf area growth rate - VPD vapour pressure deficit     

The role of cotyledon metabolism in the establishment of quinoa (Chenopodium quinoa) seedlings growing under salinity

A growth chamber experiment was conducted to assess the effect of salinity on emergence, growth, water status, photosynthetic pigments, osmolyte accumulation, and ionic content of quinoa seedlings (Chenopodium quinoa). The aim was to test the hypothesis that quinoa seedlings are well adapted to grow under salinity due to their ability to adjust the metabolic functionality of their cotyledons. Seedlings were grown for 21 days at 250 mM NaCl from the start of the germination. Germination percentage and cotyledon area were not affected by salt whereas seedling height decreased 15%. FW increased in both control and salt-treated cotyledons, but the increase was higher under salinity. DW only increased in salt-treated cotyledons. The DW/FW ratio did not show significant differences between treatments. Relative water content, chlorophyll, carotenoids, lipids, and proteins were significantly lower under salinity. Total soluble sugars, sucrose and glucose concentrations were higher in salt-treated than in control cotyledons. Ion concentration showed a different distribution pattern. Na⁺ and Cl^? concentrations were higher under salinity, while an inverse result was observed for K⁺ concentration. Proline and glycinebetaine concentrations increased under salinity, but the increase was higher in the former than the latter. The osmoprotective role of proline, glycinebetaine, and soluble sugars is discussed.