Effects of exogenous nitric oxide on cadmium toxicity, element contents and antioxidative system in perennial ryegrass

The effects of sodium nitroprusside (SNP, a donor of NO) on cadmium (Cd) toxicity in ryegrass seedlings (Lolium perenne L.) were studied by investigating the symptoms, plant growth, chlorophyll content, lipid peroxidation, H⁺-ATPase enzyme and antioxidative enzymes. Addition of 100???M CdCl₂ caused serious chlorosis and inhibited the growth of ryegrass seedlings, and dramatically increased accumulation of Cd in both shoots and roots, furthermore, the absorption of macro and micronutrients were inhibited. Addition of 50, 100, 200???M SNP significantly decreased the transport of Cd from roots to shoots, alleviated the inhibition of K, Ca, Mg and Fe, Cu, Zn absorption induced by Cd, reduced the toxicity symptoms and promoted the plant growth. The accumulation of reactive oxygen species (ROS) significantly increased in ryegrass seedlings exposed to Cd, and resulted in the lipid peroxidation, which was indicated by accumulated concentration of thiobarbituric acid-reactive substances. Addition of 50, 100, 200???M SNP significantly decreased the level of ROS and lipid peroxidation. Activities of antioxidant enzymes also showed the same changes. Addition of 50, 100, 200???M SNP increased activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase in ryegrass seedlings exposed to Cd. Addition of 100???M SNP had the most significant alleviating effect against Cd toxicity while the addition of 400???M SNP had no significant effect with Cd treatment.     

Effects of root and foliar applications of exogenous NO on alleviating cadmium toxicity in lettuce seedlings

The effects of sodium nitroprusside (SNP, a donor of NO) on cadmium (Cd) toxicity in lettuce seedlings were studied. SNP was added into hydroponic systems or sprayed directly on the leaves of plants grown with and without Cd. Excess supply of Cd (100 μM) caused growth inhibition, dramatically increased Cd accumulation in both leaves and roots, and inhibited the absorption of Ca, Mg, Fe and Cu. Excess Cd also decreased activities of superoxide dismutase peroxidase and catalase in leaves and roots, and increased the accumulation of superoxide anion (O ₂ ^·? ), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA). Root or foliar applications of exogenous NO alleviated Cd-induced growth suppression, especially root application of 250 μM SNP and foliar addition of 500 μM SNP. Addition of SNP promoted the chlorophyll synthesis suggesting that the photosynthesis was up-regulated. Exogenous NO increased Cd-decreased activities of antioxidant enzymes and markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation. Moreover, the absorption of Ca, Mg, Fe and Cu was increased, indicating that exogenous NO stimulated H⁺-ATPase activity to promote sequestration or uptake of ions. In addition, exogenous NO also inhibited Cd transfer from roots to shoots, which may indicate that Cd retention in roots induced by NO plays a significant role in Cd tolerance in lettuce seedlings. These data suggest that under Cd stress, exogenous NO improves photosynthesis by increasing chlorophyll synthesis, protects lettuce seedlings against oxidative damage by scavenging ROS, helps to maintain the uptake of nutrient elements, and inhibits Cd transferred to shoots effectively.     

Role of Exogenous Nitric Oxide in Alleviating Iron Deficiency Stress of Peanut Seedlings (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

A greenhouse hydroponic experiment was performed to evaluate how peanut seedlings (Arachis hypogaea L.) responded to iron (Fe) deficiency stress in the presence of sodium nitroprusside (SNP), a nitric oxide (NO) donor. The results showed that Fe deficiency inhibited peanut plant growth, decreased chlorophyll and active Fe concentrations, and dramatically disturbed ion balance. The addition of 50, 100, 250, and 500 µM SNP, significantly promoted the absorption of Fe in the cell wall, cell organelles, and soluble fractions, increased the concentrations of active Fe and chlorophyll in peanut plants, and alleviated the excess absorption of manganese (Mn) and copper (Cu) induced by Fe deficiency. In addition, SNP also significantly increased the activities of superoxide dismutase, peroxidase, and catalase, which is beneficial to inhibit the accumulation of malondialdehyde and reactive oxygen species. Addition of 250 µM SNP had the most significant alleviating effect against Fe-deficiency stress, and after 15 days of treatment, the plants with the 250 µM SNP treatment achieved comparable NO levels with those grown under optimal nutrition conditions. However, the effects of SNP were reversed by addition of hemoglobin (Hb, a NO scavenger). These results suggest that NO released from SNP decomposition was responsible for the effect of SNP-induced alleviation on Fe deficiency.     

Grafting of watermelon (Citrullus lanatus cv. Mahbubi) onto different squash rootstocks as a means to minimize cadmium toxicity

To test the possibility that using appropriate rootstocks could improve the tolerance of watermelon to cadmium (Cd) toxicity, a greenhouse experiment was conducted to determine growth and antioxidant activities of watermelons, either nongrafted or grafted onto summer squash and winter squash. We provided nutrient solutions having four levels (0, 50, 100, and 200 μM) of cadmium to treat the plants. Shoot and root biomass reduction were significantly lower in summer squash rootstock-grafted watermelon than winter squash rootstock-grafted and nongrafted watermelons. Cadmium induced a smaller decrease in leaf area index in grafted watermelons compared with nongrafted plants. The Cd- related reductions in chlorophyll content and efficiency of photosynthesis were more severe in nongrafted watermelons compared with dose grafted onto summer squash. Cd accumulation in shoot at the highest dose (200 µM) of CdCl₂ was significantly lower (19.76 mg/kg) in summer squash rootstock-grafted watermelon compared with winter squash rootstock-grafted (37.58 mg/kg) and nongrafted watermelon (72.12 mg/kg). H₂O₂, MDA production and electrolyte leakage of summer squash rootstock-grafted watermelon showed less increase, which was associated with a significant increase in the activities of antioxidant. The improved crop performance of grafted watermelons was attributed to their strong capacity to inhibit Cd accumulation in the aerial parts.     

In vitro biochemical evaluation of cadmium tolerance mechanism in callus and seedlings of Brassica juncea

In vitro grown callus and seedlings of Brassica juncea were treated with equimolar concentrations of cadmium and compared for their respective tolerance to cadmium. Calli cultures were grown on Murashige and Skoog medium supplemented with α 6-benzyl aminopurine (200 µg L^?1, naphthalene acetic acid 200 µg L^?1) and 2,4-dichloro-phenoxy acetic acid (65 µg L^?1) while the seedlings grown on Hoagland's nutrient solution have been carried out. Cellular homeostasis and detoxification to cadmium in B. juncea were studied by analyzing the growth in terms of fresh weight and dry weight, lipid peroxidation, proline accumulation, and antioxidative enzymes (superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT)). At 200 µM cadmium, callus and seedlings showed 73.61% and 74.76% reduction in tolerance, respectively. A significant increase in malondialdehyde (MDA) content was found in both calli and seedlings; however, the amount of MDA content was more in seedlings. Proline content increased on lower concentration of cadmium (up to 50 µM), and it further decreased (up to 200 µM). But the accumulation of proline was higher in callus cultures. The overall activity of antioxidative enzymes (SOD, CAT, and APX) was found to be higher in callus in comparison to seedlings of B. juncea. Callus and seedlings showed a significant (P?≤?0.5) increase in SOD activity in a concentration-dependent manner up to 50 µM cadmium concentration but decreased further. APX activity increased significantly at low cadmium levels but CAT activity decreased significantly throughout on increasing cadmium concentrations from 5 to 200 µM, respectively. Hence, it was observed that callus of B. juncea was more tolerant in comparison to seedlings exposed to equimolar concentrations of cadmium. Thus, from the present studies, it is concluded that calli were more tolerant toward cadmium-induced oxidative stress. Hence, it is suitable material for the study of cadmium tolerance mechanisms and for the manipulations within them for better understanding of cadmium detoxification strategies in B. juncea.     

Matricaria chamomilla is not a hyperaccumulator, but tolerant to cadmium stress

The influence of low (3 μM) and high (60 and 120 μM) cadmium (Cd) concentrations were studied on selected aspects of metabolism in 4-week-old chamomile (Matricaria chamomilla L.) plants. After 10 days’ exposure, dry mass accumulation and nitrogen content were not significantly altered under any of the levels of Cd. However, there was a significant decline in chlorophyll and water content in the leaves. Among coumarin-related compounds, herniarin was not affected by Cd, while its precursors (Z)- and (E)-2-β-d-glucopyranosyloxy-4-methoxycinnamic acids (GMCAs) increased significantly at all the levels of Cd tested. Cd did not have any effect on umbelliferone, a stress metabolite of chamomile. Lipid peroxidation was also not affected by even 120 μM Cd. Cd accumulation was approximately seven- (60 μM Cd treatment) to eleven- (120 μM Cd treatment) fold higher in the roots than that in the leaves. At high concentrations, it stimulated potassium leakage from the roots, while at the lowest concentration it could stimulate potassium uptake. The results supported the hypothesis that metabolism was altered only slightly under high Cd stress, indicating that chamomile is tolerant to this metal. Preferential Cd accumulation in the roots indicated that chamomile could not be classified as a hyperaccumulator and, therefore, it is unsuitable for phytoremediation.     

Enhanced Phytoextraction by As Hyperaccumulator Isatis cappadocica Spiked with Sodium Nitroprusside

The present study investigates the possible role of exogenous nitric oxide (NO) supplementation as sodium nitroprusside (SNP), on increasing phytoextraction and phytoremediation ability of arsenic hyperaccumulator, Isatis cappadocica. Arsenate (500, 1000 and 1500 µM) alone or in combination with 200 µM SNP was given to hydroponically grown plants for 14 days. The highest level of arsenate (1500 µM) reduced the plant growth and chlorophyll content, while SNP alleviated these inhibitory effects. The application of SNP significantly increased the As concentration in the root (from 1004 to 1943 mg/kg) and shoots (from 1304 to 1859 mg/kg) compared with As-stressed plants. However, SNP treatment did not affect translocation factor value significantly in the As-stressed plants which shows enhancement of both As uptake and translocation under SNP application. This is the first study demonstrating the favorable effects of SNP on As tolerance, uptake, and accumulation of highly valuable As hyperaccumulator, I. cappadocica.     

Physiological responses and antioxidant enzyme changes in <Emphasis Type="Italic">Sulla coronaria</Emphasis> inoculated by cadmium resistant bacteria

Plant growth promoting bacteria (PGPB) may help to reduce the toxicity of heavy metals on plants growing in polluted soils. In this work, Sulla coronaria inoculated with four Cd resistant bacteria (two Pseudomonas spp. and two Rhizobium sullae) were cultivated in hydroponic conditions treated by Cd; long time treatment 50 µM CdCl₂ for 30 days and short time treatment; 100 µM CdCl₂ for 7 days. Results showed that inoculation with Cd resistant PGPB enhanced plant biomass, thus shoot and root dry weights of control plants were enhanced by 148 and 35% respectively after 7 days. Co-inoculation of plants treated with 50 and 100 µM Cd increased plant biomasses as compared to Cd-treated and uninoculated plants. Cadmium treatment induced lipid peroxidation in plant tissues measured through MDA content in short 7 days 100 µM treatment. Antioxidant enzyme studies showed that inoculation of control plants enhanced APX, SOD and CAT activities after 30 days in shoots and SOD, APX, SOD, GPOX in roots. Application of 50 µM CdCl₂ stimulated all enzymes in shoots and decreased SOD and CAT activities in roots. Moreover, 100 µM of CdCl₂ increased SOD, APX, CAT and GPOX activities in shoots and increased significantly CAT activity in roots. Metal accumulation depended on Cd concentration, plant organ and time of treatment. Furthermore, the inoculation enhanced Cd uptake in roots by 20% in all treatments. The cultivation of this symbiosis in Cd contaminated soil or in heavy metal hydroponically treated medium, showed that inoculation improved plant biomass and increased Cd uptake especially in roots. Therefore, the present study established that co-inoculation of S. coronaria by a specific consortium of heavy metal resistant PGPB formed a symbiotic system useful for soil phytostabilization.     

Antioxidative response of metal-accumulator and non-accumulator plants under cadmium stress

The present study aims to elucidate the role of antioxidative enzyme in the adaptive responses of metal-accumulators (Thlaspi caerulescens and Brassica juncea) and non-accumulator plant (Nicotiana tabacum) to Cadmium stress. When seedlings of plants were grown in hydroponic condition for a period of 4 days in the presence of 200 or 400 μM CdCl₂, photosynthetic rate, transpiration rate and stomatal conductance in metal-accumulators decreased more slowly than that in tobacco. MDA content and electrolyte leakage increased with elevated Cd concentration and exposure time in all plant species, while the oxidative damage in tobacco was more serious than that in metal-accumulators. The activities of SOD and CAT in metal-accumulators were significantly higher than that in tobacco under normal condition, whereas there was no significant difference in the activity of POD between Indian mustard and tobacco. The activities of antioxidative enzymes increased rapidly in metal-accumulators in response to the Cd treatments, especially SOD and CAT. In tobacco, CAT activity declined rapidly by exposure to the Cd treatment, though the activity of SOD and POD was enhanced, indicating that the antioxidative enzymes in tobacco could not fully scavenge ROS generated by Cd toxicity. These results collectively indicate that the enzymatic antioxidation capacity is one of the important mechanisms responsible for metal tolerance in metal-accumulator plant species.     

Effects of exogenous NO supplied with different approaches on cadmium toxicity in lettuce seedlings

The study aimed to test the effects of sodium nitroprusside [SNP, a nitric oxide (NO) donor], supplied with different approaches on cadmium (Cd) toxicity in lettuce seedlings (Lactuca sativa) in a pot experiment. SNP (8.94 mg) was applied into Cd-contaminated soil directly or added into a capsule, a paper bag, starch-coated granules, or foliar application. Cd (50 mg kg^? 1) reduced chlorophyll content, caused oxidative stress, increased Cd accumulation in roots and leaves, and inhibited the uptake of calcium (Ca), magnesium (Mg), and iron (Fe). The addition of exogenous NO in Cd-contaminated soil increased chlorophyll content, improved antioxidant enzyme activities, promoted the uptake of Ca, Mg, and Fe, reduced Cd-induced oxidative damages, and inhibited Cd transferred from roots to shoots. Moreover, SNP supplied with different approaches had varied effects on Cd tolerance of lettuce seedlings. The alleviated effect of SNP applied into soil directly was the worst, and the three SNP slow release materials had better alleviation effects on Cd toxicity. Foliar SNP application had the best effects on increasing Cd tolerance in lettuce seedlings.     

Role of exogenous nitric oxide in alleviating iron deficiency-induced peanut chlorosis on calcareous soil

This study examined the effects of exogenous nitric oxide (NO) on physiological characteristics of peanut (Arachis hypogaea L.) growing on calcareous soil. Sodium nitroprusside (SNP), a NO donor, was root application (directly; slow-release bag; slow-release capsule; slow-release particle) and foliar application. The results showed that SNP application alleviated iron (Fe) deficiency-induced chlorosis, increased the yield of peanut and increased the Fe concentration in peanut grain. SNP, especially supplied by slow-release particle improved the available Fe in soil by reducing pH of soil and increasing available Fe of soil. Furthermore, SNP application significantly increased the H⁺-ATPase and Fe³⁺ reductase activities and increased the total Fe concentration in the leaves. Meanwhile, SNP application, especially foliar application enhanced the availability of Fe in the plant by significantly increasing the active Fe content and chlorophyll content in the leaves. In addition, SNP also increased the antioxidant activities, but decreased the superoxide anion (O₂^??) generation rate and malondialdehyde content, which protected peanut against the Fe deficiency-induced oxidative stress. Therefore, these results support a physiological action of SNP on the availability, uptake and transport of Fe in the plant and foliar application SNP had the best effects in leaves and SNP supplied by slow-release particle had the best effects in roots. In addition, on the whole, the effects of SNP supplied by slow-release ways were better than directly supplied into the soil.     

Effects of silicon nutrition on cadmium uptake, growth and photosynthesis of rice plants exposed to low-level cadmium

The effect of silicon (Si) nutrition on low-level cadmium (Cd) toxicity symptoms was investigated in hydroponically-grown rice seedlings (Oryza sativa L.). Silicon (0.0, 0.2, or 0.6 mM) was added when seedlings were 6 or 20 days old representing early (Si^E) or late (Si^L) Si treatment, respectively. Cadmium (0.0 or 2.5 μM) was added when seedlings were 6 days old. Measurements included generation of CO₂ and light response curves; chlorophyll fluorescence analysis; growth; and tissue-element content analysis. Our results showed that low-level Cd treatment generally inhibited growth and photosynthesis. However, the addition of 0.2 or 0.6 mM Si^E or Si^L significantly reduced root- and leaf-Cd content. Consequently, the addition of 0.6 mM Si^L significantly alleviated low-level Cd-induced inhibition of growth. Furthermore, 0.2 mM Si treatment significantly reduced g _s compared to 0.0 or 0.6 mM Si without inhibiting A, especially in +Cd plants, suggesting an increase in instantaneous water-use-efficiency (IWUE). Additionally, in +Cd plants, the addition of 0.6 mM Si^E significantly reduced F _o but increased F _v/F _m, while treatment with 0.2 mM Si^L significantly increased q_P, suggesting an increase in light-use-efficiency. We thus, propose that 0.6 mM Si^L treatment is required for the alleviation of low-level Cd-mediated growth inhibition. Furthermore, we suggest that 0.2 mM Si concentration might be close to the optimum requirement for maximum Si-induced increase in IWUE in rice plants, especially when under low-level Cd-stress. Our results also suggest that Si alleviates low-level Cd toxicity by improving light-use-efficiency.     

Effects of exogenous nitric oxide on photosynthesis,antioxidative ability,and mineral element contents of perennial ryegrass under copper stress

A hydroponics experiment was conducted to test the effects of sodium nitroprusside (SNP, a donor of NO) supplied with different concentrations on copper (Cu) toxicity in ryegrass seedlings (Lolium perenne L.). Excess Cu (200 µM) reduced chlorophyll content, resulting a decrease in photosynthesis. Cu stress induced the production of hydrogen peroxide (H₂O₂) and superoxide anion (O₂^{? ?}), leading to malondialdehyde (MDA) accumulation. Furthermore, activities of antioxidant enzymes in Cu-treated seedlings such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were decreased. In addition, Cu stress inhibited the uptake of K, Mg, Fe, and Zn and increased Ca content in roots. Moreover, in leaves of Cu-stressed seedlings, K, Fe, and Zn contents were decreased and the contents of Ca and Mg were not affected significantly. In Cu-treated seedlings, Cu concentration in roots was higher than in leaves. Addition of 50, 100, 200 µM SNP in Cu-mediated solutions increased chlorophyll content and photosynthesis, improved antioxidant enzyme activities, reduced Cu-induced oxidative damages, kept intracellular ion equilibrium under Cu stress, increased Cu concentration in roots and inhibited Cu accumulation in leaves. In particular, addition of 100 µM SNP had the best effect on promoting growth of ryegrass seedlings under Cu stress. However, the application of 400 µM SNP had no obvious alleviating effect on Cu toxicity in ryegrass seedlings.     

Cadmium tolerance in <Emphasis Type="Italic">Schinus molle</Emphasis> trees is modulated by enhanced leaf anatomy and photosynthesis

Key message

Low concentrations of cadmium cause anatomical responses in leaf chlorenchyma enhancing Schinus molle photosynthesis and tolerance.

Abstract

This work is aimed to evaluate the effects of cadmium (Cd) on leaf anatomy and photosynthesis in Schinus molle, a species that can cope with harsh environments. Seven-month-old S. molle plants were exposed over 90 days to varying Cd concentrations (0, 10, 20, 50, 125 or 250 µM using Cd(NO₃)₂ as the Cd source). The plants were placed in vases containing washed sand and vermiculite as the substrate and nutrient solution. Throughout the experiment, the substrate was maintained at field capacity, and the nutrient solution was replaced at 15-day intervals. After 90 days, leaves were collected and processed for anatomical analysis using typical plant microtechniques. In addition, plant growth, photosynthesis, chlorophyll content and A/Ci curve were evaluated using an infrared gas analyzer. S. molle growth was not affected by Cd. Lower Cd concentrations (10 and 20 µM) resulted in greater net photosynthesis, stomatal conductance and density, Vcmax, Jmax and mesophyll thickness. However, Cd concentrations of 50 µM or greater resulted in a reduction of most of the evaluated characteristics to levels close to control. All of the tested Cd concentrations resulted in reduced chlorophyll content and stomatal size. Therefore, the effect of Cd in a tolerant species such as S. molle is concentration dependent, and at low Cd concentrations, these plants can cope with the toxicity by adjusting leaf structure and function.

     

Accumulation of low-molecular-weight organic acids in roots and leaf segments of Zea mays plants treated with cadmium and copper

Maize seedlings grown in a nutrient solution were treated with Cd (50, 100 µM) or Cu (50, 100 µM). Roots and separated leaf sections (from the youngest––basal, through the middle––mature, to the oldest––apical) were analysed. Shoot and root fresh weight, and root net growth rates were reduced significantly after Cu application in comparison to Cd. Copper (50, 100 µM) and cadmium (100 µM) decreased the sum of chlorophyll and total carotenoid pools mostly in mature and old leaf sections. The concentration of Cu and Cd increased in the old and mature leaf sections. Analysis of organic acids showed that both metals differently influenced the low-molecular-weight organic acids (LMWOAs) content in maize leaf sections. In mature sections, the excess Cu increased the succinate and tartrate contents, whereas in the young ones mainly the tartrate level was elevated. Cadmium elevated citrate accumulation in mature and old sections, compared to the control plants. Malate, the main LMWOA in maize leaves, increased only after addition of 100 µM of Cd (mature and old sections) or 50 µM of Cu (old sections). Analysis of LMWOAs in roots showed that the excess of Cd or Cu induced higher accumulation of tartrate and malate and, additionally, copper increased the citrate content.     

Exogenous nitric oxide enhances cadmium tolerance of rice by increasing pectin and hemicellulose contents in root cell wall

To study the mechanisms of exogenous NO contribution to alleviate the cadmium (Cd) toxicity in rice (Oryza sativa), rice plantlets subjected to 0.2-mM CdCl₂ exposure were treated with different concentrations of sodium nitroprusside (SNP, a NO donor), and Cd toxicity was evaluated by the decreases in plant length, biomass production and chlorophyll content. The results indicated that 0.1 mM SNP alleviated Cd toxicity most obviously. Atomic absorption spectrometry and fluorescence localization showed that treatment with 0.1 mM SNP decreased Cd accumulation in both cell walls and soluble fraction of leaves, although treatment with 0.1 mM SNP increased Cd accumulation in the cell wall of rice roots obviously. Treatment with 0.1 mM SNP in nutrient solution had little effect on the transpiration rate of rice leaves, but this treatment increased pectin and hemicellulose content and decreased cellulose content significantly in the cell walls of rice roots. Based on these results, we conclude that decreased distribution of Cd in the soluble fraction of leaves and roots and increased distribution of Cd in the cell walls of roots are responsible for the NO-induced increase of Cd tolerance in rice. It seems that exogenous NO enhances Cd tolerance of rice by increasing pectin and hemicellulose content in the cell wall of roots, increasing Cd accumulation in root cell wall and decreasing Cd accumulation in soluble fraction of leaves.     

The response of maize seedlings to cadmium stress under hydroponic conditions

The effects of cadmium (Cd) supply level in nutrient solution (0, 12.5, 25, 50, 100, 200, 400, and 800 μM) on growth, Cd accumulation ability, and the related physiological indices of maize (Zea mays L.) seedlings were studied under hydroponic conditions. The results showed that the increments in the shoot height and biomass were stimulated at relatively low external Cd supply levels (<100 μM), while they were inhibited at Cd supply levels over 200 μM. Cd accumulation ability of the maize seedlings also showed the similar stimulation/inhibition pattern as shoot growth, and the Cd contents in the shoots and roots reached the peaks (389.5 and 505.5 mg/kg dry wt, respectively) at 50 μM Cd. The contents of chlorophyll a, chlorophyll b, and carotenoids in the maize leaf blades decreased with increasing external Cd supply level. At the highest Cd supply level (800 μM), the contents of chlorophyll a, chlorophyll b, and carotenoids in the leaf blade were only 38.9, 46.0, and 29.7% of the control plants, respectively. Moreover, chlorophyll b was more sensitive to the Cd stress than chlorophyll a. The increased proline content in the leaf blade of maize seedlings resulted from external Cd stress indicates that maize can adapt to the adversity menace via changing the content of proline.     

Nitric oxide (NO) counteracts cadmium induced cytotoxic processes mediated by reactive oxygen species (ROS) in Brassica juncea: cross-talk between ROS, NO and antioxidant responses

Research on NO in plants has achieved huge attention in recent years mainly due to its function in plant growth and development under biotic and abiotic stresses. In the present study, we investigated Cd induced NO generation and its relationship to ROS and antioxidant regulation in Brassica juncea. Cd accumulated rapidly in roots and caused oxidative stress as indicated by increased level of lipid peroxidation and H₂O₂ thus, inhibiting the overall plant growth. It significantly decreased the root length, leaf water content and photosynthetic pigments. A rapid induction in intracellular NO was observed at initial exposures and low concentrations of Cd. A 2.74-fold increase in intracellular NO was recorded in roots treated with 25 μM Cd than control. NO effects on Malondialdehyde (MDA) content and on antioxidant system was investigated by using sodium nitroprusside (SNP), a NO donor and a scavenger, [2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethylinidazoline-1-oxyl-3-oxide] (cPTIO). Roots pretreated with 5 mM SNP for 6 h when exposed to 25 μM Cd for 24 h reduced the level of proline, non-protein thiols, SOD, APX and CAT in comparison to only Cd treatments. However, this effect was almost blocked by 100 μM cPTIO pretreatment to roots for 1 h. This ameliorating effect of NO was specific because cPTIO completely reversed the effect in the presence of Cd. Thus, the present study report that NO strongly counteracts Cd induced ROS mediated cytotoxicity in B. juncea by controlling antioxidant metabolism as the related studies are not well reported in this species.     

Responses of in vitro-cultured <Emphasis Type="Italic">Allium hirtifolium</Emphasis> to exogenous sodium nitroprusside under PEG-imposed drought stress

Drought stress is a major threat to plant production in semi-arid and arid areas of the world. This research was laid out to asses the effects of sodium nitroprusside (SNP) as a nitric oxide donor on growth, physiological and biochemical changes of in vitro-cultured Allium hirtifolium under polyethylene glycol (PEG) induced drought stress. Basal plate explants of A. hirtifolium were cultured on MS medium containing different levels of PEG (0, 2, 4, 8 and 16 mM) and SNP (0, 10, 40 and 70 µM). After prolonged drought, growth responses, oxidative stress indicators, and phytochemical variations of regenerated plantlets with or without PEG and/or SNP treatments were recorded. Water limitation reduced regeneration potential of explants and consequently number of shoots per explant. Relative water content, total chlorophyll and carotenoid contents of regenerated A. hirtifolium plantlets decreased, but accumulation of malondialdehyde, H₂O₂ and proline and the activities of superoxide dismutase, ascorbate peroxidase, catalase and peroxidase enzymes increased with decreasing water availability. Total phenol and allicin contents were also increased in response to drought stress. Exogenous SNP in 10 and particularly in 40 µM was effective in enhancing regeneration rate and relative water content as well as protecting photosynthetic pigments under different levels of water availability. SNP also inhibited the hydrogen peroxide (H₂O₂) accumulation and lipid peroxidation in cell membranes via increasing the activities of superoxide dismutase and ascorbate peroxidase enzymes and accumulating proline and allicin. In general, these results suggest that exogenous SNP at 40 µM not only could somewhat protect A. hirtifolium from drought stress, but also can help to improve the propagation and allicin production of that plant under in vitro condition.     

Responses of nitric oxide and hydrogen sulfide in regulating oxidative defence system in wheat plants grown under cadmium stress

We conducted a study to evaluate the interactive effect of NO and H₂S on the cadmium (Cd) tolerance of wheat. Cadmium stress considerably reduced total dry weight, chlorophyll a and b content and ratio of Fv/Fm by 36.7, 48.6, 26.7 and 19.5%, respectively, but significantly enhanced the levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), endogenous H₂S and NO, and the activities of antioxidant enzymes. Exogenously applied sodium nitroprusside (SNP) and sodium hydrosulfide (NaHS), donors of NO and H₂S, respectively, enhanced total plant dry matter by 47.8 and 39.1%, chlorophyll a by 92.3 and 61.5%, chlorophyll b content by 29.1 and 27.2%, Fv/Fm ratio by 19.7 and 15.2%, respectively, and the activities of antioxidant enzymes, but lowered oxidative stress and proline content in Cd-stressed wheat plants. NaHS and SNP also considerably limited both the uptake and translocation of Cd, thereby improving the levels of some key mineral nutrients in the plants. Enhanced levels of NO and H₂S induced by NaHS were reversed by hypotuarine application, but they were substantially reduced almost to 50% by cPTIO (a NO scavenger) application. Hypotuarine was not effective, but cPTIO was highly effective in reducing the levels of NO and H₂S produced by SNP in the roots of Cd-stressed plants. The results showed that interactive effect of NO and H₂S can considerably improve plant resistance against Cd toxicity by reducing oxidative stress and uptake of Cd in plants as well as by enhancing antioxidative defence system and uptake of some essential mineral nutrients.