Effect of exogenous nitric oxide on sulfur and nitrate assimilation pathway enzymes in maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) under drought stress

The present study aimed at investigating the effects of foliar applied nitric oxide (as SNP [sodium nitroprusside]) on sulfur (glutathione reductase, guaiacol peroxidase, and glutathione S-transferase) and nitrate assimilation (nitrite and nitrate reductase) pathway enzymes in maize (Zea mays L.) exposed to water deficit conditions. The seedlings of a drought tolerant (NK8711) and sensitive (P1574) maize hybrid were applied with various SNP doses (0, 50, 100, 150, and 200 µM) under normal and drought stress conditions. Foliar spray of 100 µM markedly improved water status and chlorophyll contents and alleviated drought-induced oxidative damages through increased antioxidant (catalase, ascorbate peroxidase, and superoxide dismutase) activities in both maize hybrids. Moreover, exogenous SNP supply increased nitrite and nitrate reductase activities and upregulated glutathione reductase, glutathione S-transferase, and guaiacol peroxidase compared to no SNP supply. Interestingly, the negative effects of excess NO generation at high SNP doses (150, 200 µM) were more pronounced in P1574 than NK8711 leading to lower biomass accumulation in drought-sensitive hybrid.     

Selenium mitigates cadmium-induced oxidative stress in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> L.) plants by modulating chlorophyll fluorescence,osmolyte accumulation,and antioxidant system

Pot experiments were conducted to investigate the role of selenium in alleviating cadmium stress in Solanum lycopersicum seedlings. Cadmium (150 mg L^?1) treatment caused a significant reduction in growth in terms of height and biomass accumulation and affected chlorophyll pigments, gas exchange parameters, and chlorophyll fluorescence. Selenium (10 μM) application mitigated the adverse effects of cadmium on growth, chlorophyll and carotenoid contents, leaf relative water content, and other physiological attributes. Lipid peroxidation and electrolyte leakage increased because of cadmium treatment and selenium-treated plants exhibited considerable reduction because of the decreased production of hydrogen peroxide in them. Cadmium-treated plants exhibited enhanced activity of antioxidant enzymes that protected cellular structures by neutralizing reactive free radicals. Supplementation of selenium to cadmium-treated plants (Cd + Se) further enhanced the activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) by 19.69, 31.68, 33.14, and 54.47%, respectively. Osmolytes, including proline and glycine betaine, increased with selenium application, illustrating their role in improving the osmotic stability of S. lycopersicum under cadmium stress. More importantly, selenium application significantly reduced cadmium uptake. From these results, it is clear that application of selenium alleviates the negative effects of cadmium stress in S. lycopersicum through the modifications of osmolytes and antioxidant enzymes.     

Effects of Nitrate and L-Arginine on Content of Nitric Oxide and Activities of Antioxidant Enzymes in Roots of Wheat Seedlings and Their Heat Resistance

Separate and combined effects of nitrate (NaNO₃) and L-arginine as potential sources of nitric oxide (NO) on the content of endogenous NO in roots of wheat (Triticum aestivum L.) seedlings and on their heat resistance were studied. Both agents increased the seedling resistance to the damaging heating; the effect was maximal at 20 mM NaNO₃ or 5 mM L-arginine. The treatment with L-arginine elevated the NO content in the roots within the first 2 h of the treatment. Nitrate caused a stronger and longer rise in nitric oxide. Activity of nitrate reductase considerably (2–3 times) increased in the roots exposed to nitrate. The augmentation in the nitric oxide level caused by nitrate or L-arginine was prevented by the root pretreatment with an inhibitor of nitrate reductase (sodium tungstate) or an inhibitor of animal NO-synthase—N^G-nitro-L-arginine methyl ester (L-NAME). Upon the combined treatment with NaNO₃ and L-arginine, the nitrateinduced stimulation of the nitrate reductase activity, NO level in the roots, and seedling heat resistance were less pronounced than after separate application. In the presence of L-NAME, the negative influence of L-arginine on nitrate effects was markedly attenuated. The plant exposure to nitrate or L-arginine increased the activities of antioxidant enzymes (superoxide dismutase, catalase, and guaiacol peroxidase). A mixture of NaNO₃, and L-arginine caused weaker effects. It was suggested that nitrate-dependent and arginine-dependent pathways of NO formation are antagonistic to each other in wheat roots.     

Antioxidant system and photosynthetic characteristics responses to short-term PEG-induced drought stress in cucumber seedling leaves

The effect of short-term drought stress on the water content, antioxidant system and photosynthetic characteristics was investigated using cucumber (Cucumis sativus L.) seedlings. The results indicated that polyethylene glycol induced water stress reduced water content in shoots of cucumber seedling after treatment of 36 hours, and caused obvious reductions in net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration and transpiration of leaves. In addition, water stress significantly reduced the photosynthetic pigment content and inhibited photochemical activity, including actual photochemical efficiency, maximal quantum yield of photosystem II photochemistry and coefficient for photochemical quenching. Meanwhile non-photochemical quenching increased. As responses to drought stress, significant increases in electrolyte leakage, malondialdehyde, superoxide anion and hydrogen peroxide levels were detected in leaves. The superoxide dismutases, catalase, glutathione reductase and dehydroascorbate reductase activities, protein, ascorbate and glutathione content, all decreased and peroxidases activity increased, while ascorbate peroxidase and monodehydroascorbate reductase activities exhibited different trend under different degree of water stress. Therefore, it can be concluded that water stress strongly disrupted the normal metabolism of leaves and restrained water absorption.     

Effect of 24-Epibrassinolide on Antioxidative Defence System Against Lead-Induced Oxidative Stress in The Roots of <Emphasis Type="Italic">Brassica juncea</Emphasis> L. Seedlings

Lead (Pb) toxicity causes oxidative stress by increasing the production of reactive oxygen species. The aim of the present study was to investigate the role of 24-epibrassinolide (24-EBL) on the antioxidant defence system as a response to Pb stress in Brassica juncea L. Surface-sterilized seeds were exposed to Pb ion (0 and 2 mM) toxicity in Petri dishes and subsequently, the seeds were sprayed with either (i) deionized water or (ii) different concentrations (10^–12, 10^–10, and 10^–8 M) of 24-EBL on alternate days. After nine days, the roots of the B. juncea seedlings were harvested to analyze the heavy metal content, root length, hydrogen peroxide level, lipid peroxidation, total protein content and activities of the antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, glutathione reductase and glutathione-S-transferase). According to our results, the Pb ions accumulated by the B. juncea roots led to oxidative stress by increasing the level of H₂O₂ and malondialdehyde, and thus, increased the activity of the antioxidative enzymes (except for catalase) and the growth and total protein content decreased. Whereas, the 24-EBL treatment to the roots of Pb stressed seedlings was able to alleviate the Pb-induced oxidative stress. Upon the application of 24-EBL, a reduction in Pb accumulation, H₂O₂ and malondialdehyde levels as well as an increased total protein content and activity of antioxidative enzymes detoxifying hydrogen peroxide (catalase, ascorbate peroxidase and peroxidase) were observed. As a result, the stress protective properties of 24-EBL depending on concentration in B. juncea roots were revealed in this study.     

Wild relatives of wheat: <Emphasis Type="Italic">Aegilops</Emphasis>–<Emphasis Type="Italic">Triticum</Emphasis> accessions disclose differential antioxidative and physiological responses to water stress

Wild relatives of wheat are an outstanding source of resistance to both abiotic and biotic stresses. In the present study, we evaluated the activity of four antioxidant enzymes—superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX)—along with photosynthetic pigments and shoot biomass in 12 Aegilops–Triticum accessions with different genomic constitutions and two tolerant and sensitive control varieties under well-watered (WW; 90% FC), moderate (MS; 50% FC) and severe (SS; 25% FC) water stress treatments. The analysis of variance for measured traits indicated highly significant effects of the water stress treatments, accessions, and their interactions. The 12 domesticated and wild relatives of wheat exhibited more variability and greater activity in the expression of antioxidative enzymes than cultivated wheats. While domesticated forms of wheat, T. aestivum (AABBDD) and T. durum (AABB) seem to have a functionally active antioxidant mechanism, other accessions with alien genomes—Ae. umbellulata (UU), Ae. crassa (MMDD), Ae. caudata (CC), Ae. cylindrica (DDCC) and T. boeoticum (A^bA^b)—respond to water stress by increasing enzymatic antioxidants as the dominant mechanism that contributes to the retention of oxidative balance in the cell. Furthermore, abovementioned accessions with alien genomes had higher photosynthetic pigment contents (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid) under water stress than well-watered conditions. Hence, these accessions could be used in future breeding programs to combine beneficial stress-adaptive characters of alien genomes into synthetic hexaploid wheat varieties in the field, even at limited water supply.     

Physiological and Biochemical Responses of Lettuce to Thymol,as Allelochemical

Nowadays, allelopathic investigations have focused to identify action mechanisms of this compounds on target organisms in natural habitats. It may tend to introduce new natural herbicides and pesticides for replacing the synthetic ones. In the present study, the allelopathic effects of thymol on lettuce (Lactuca sativa L.) as a model plant were investigated in physiological and biochemical aspects. At the first stage, the effect of different concentrations of thymol on some growth parameters, including seed germination, radicle and plumule growth were evaluated to determine the optimum concentration for the continuation of our experiment. Then, the lettuce seedlings were cultured in pots containing peat and were irrigated with Hoagland nutrient solution supplemented with thymol at the concentration of 50 and 100 μg/mL. The effect of these treatments on physiological, biochemical aspects of the plant were studied following the plant growth. The results showed whereas, the shoot fresh and dry weights and photosynthetic rate in the treated group were decreased significantly compared to the control group at P ≤ 0.05, photochemical efficiency of photosystem II, total protein concentration, proline content and the activity of some antioxidant enzymes such as polyphenol oxidase, ascorbate peroxidase and catalase were increased in treated plants than control ones. However, there was no significantly change in chlorophyll content in treated group than control. It can be concluded that the thymol as an allelochemical caused some physiological and biochemical responses in the lettuce which are much similar to induced responses under abiotic stress. Indeed, it induces a kind of stress named as allelochemical stress.     

<Emphasis Type="Italic">Piriformospora indica</Emphasis> Alleviates Salinity by Boosting Redox Poise and Antioxidative Potential of Tomato

More than 20% of irrigated land has been influenced by salt stress, decreasing crop production. In this research, we investigated the effect of different levels of salinity (0, 50, 100 and 150 mM NaCl) and the efficiency of Piriformospora indica on growth, biochemical traits, antioxidative defense system in tomato (Solanum lycopersicum L.). NaCl stress reduced chlorophyll content, height and biomass of plants. Higher level of salinity (150 mM) declined the plant height by 22.65%, total dry weight by 56.44% and total chlorophyll by 44.34%, however, P. indica inoculation raised plant height by 43.47%, dry weight by 69.23% and total chlorophyll content by 48.09%. Salinity stress increased H₂O₂, malondialdehyde (MDA), superoxide anion and 1,1-diphenyl-2-picrylhydrazyl (DPPH) level in leaves and roots tomato seedlings. However, P. indica inoculation reduced H₂O₂, MDA and superoxide anion and enhanced DPPH compared to non-inoculated plants at all NaCl levels. The total phenol and flavonoids increased with NaCl treatment. On the other hand, the total phenolic and flavonoid increased more in P. indica inoculated plants compared to non-inoculated ones. Moreover, inoculation of P. indica implicated noteworthy improvement of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR) activity in tomato upon salinity. Notably, colonization with P. indica significantly improved the content of reduced ascorbic acid (AsA), glutathione (GSH) and redox ratio in the tomato plants under salinity resulting in reduced redox state. Our findings confirmed that salinity had negative effect on tomato seedling; however, P. indica inoculation increased tolerance to salinity by improving the content of phenolic compounds, non-enzymatic antioxidants, and increasing the activity of antioxidant enzymes.     

Exogenous salicylic acid improves salinity tolerance of <Emphasis Type="Italic">Nitraria tangutorum</Emphasis>

In the present study, the physiological responses of Nitraria tangutorum Bobr. seedlings to NaCl stress and the regulatory function of exogenous application of salicylic acid (SA) were investigated. NaCl in low concentration (100 mM) increased while in higher concentrations (200–400 mM) decreased the individual plant dry weights (wt) of seedlings. Decreased relative water content (RWC) and chlorophyll content were observed in the leaves of seedlings subjected to salinity stress (100–400 mM NaCl). Furthermore, NaCl stress significantly increased electrolyte leakage and malondialdehyde (MDA) content. The levels of osmotic adjustment solutes including proline, soluble sugars, and soluble protein were enhanced under NaCl treatments as compared to the control. In contrast, exogenous application of SA (0.5–1.5 mM) to the roots of seedlings showed notable amelioration effects on the inhibition of individual plant dry wt, RWC, and chlorophyll content. The increases in electrolyte leakage and MDA content in the leaves of NaCl-treated seedlings were markedly inhibited by SA application. The SA application further increased the contents of proline, soluble sugars, and soluble protein. The activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) were up-regulated by NaCl stress and the activities of SOD, POD, and CAT were further enhanced by SA treatments. Application of SA in low concentration (0.5 mM) enhanced while in higher concentrations (1.0 and 1.5 mM) inhibited APX activities in leaves of NaCl-treated seedlings. These results indicate that SA effectively alleviated the adverse effects of NaCl stress on N. tangutorum.     

Effects of exogenous spermidine on antioxidant system of tomato seedlings exposed to high temperature stress

The effects of foliar spraying with spermidine (Spd) on antioxidant system in tomato (Lycopersicon esculentum Mill.) seedlings were investigated under high temperature stress. The high temperature stress significantly inhibited plant growth and reduced chlorophyll (Chl) content. Application of exogenous 1 mM Spd alleviated the inhibition of growth induced by the high temperature stress. Malondialdehyde (MDA), hydrogen peroxide (H₂O₂) content and superoxide anion (O₂) generation rate were significantly increased by the high temperature stress, but Spd significantly reduced the accumulation of reactive oxygen species (ROS) and MDA content under the stress. The high temperature stress significantly decreased glutathione (GSH) content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), but increased contents of dehydroascorbic acid (DHA), ascorbic acid (AsA), and oxidized glutathione (GSSG) in tomato leaves. However, Spd significantly increased the activities of antioxidant enzymes, levels of antioxidants and endogenous polyamines in tomato leaves under the high temperature stress. In addition, to varying degrees, Spd regulated expression of MnSOD, POD, APX2, APX6, GR, MDHAR, DHAR1, and DHAR2 genes in tomato leaves exposed to the high temperature stress. These results suggest that Spd could change endogenous polyamine levels and alleviate the damage by oxidative stress enhancing the non-enzymatic and enzymatic antioxidant system and the related gene expression.     

多裂骆驼蓬中生物碱类物质对小麦种子萌发和幼苗生长的影响

室内培养和盆栽试验结果表明,多裂骆驼蓬生物碱提取液浸种的小麦萌发种子呼吸速率、淀粉酶和蛋白酶活性受抑,种子萌发率下降并随处理浓度提高而降低。幼苗根系活性和叶绿素含量提高,叶片硝酸还原酶（NR）、超氧化物歧化酶（SOD）和过氧化物酶（POD）活性增强,过氧化氢酶（CAT）活性下降;幼苗根体积,株高、根系和地上部干重增加。多裂骆驼蓬生物碱提取液浸种对小麦种子萌发和幼苗生长作用的大小顺序为：总生物碱〉水溶性生物碱〉脂溶性生物碱。     

<Emphasis Type="Italic">Terminalia arjuna</Emphasis> bark extract alleviates nickel toxicity by suppressing its uptake and modulating antioxidative defence in rice seedlings

Terminalia arjuna (Ta) bark contains various natural antioxidants and has been used to protect animal cells against oxidative stress. In the present study, we have examined alleviating effects of Ta bark aqueous extract against Ni toxicity in rice (Oryza sativa L.). When rice seedlings were raised for 8 days in hydroponics in Yoshida nutrient medium containing 200 μM NiSO₄, a decline in height, reduced biomass, increased Ni uptake, loss of root plasma membrane integrity, increase in the level of O₂˙^?, H₂O₂ and ˙OH, increased lipid peroxidation, decline in photosynthetic pigments, increase in the level of antioxidative enzymes superoxide dismutase, catalase and glutathione peroxidase and alterations in their isoenzyme profile patterns were observed. Transmission electron microscopy (TEM) showed damage to chloroplasts marked by disorganised enlarged starch granules and disrupted thylakoids under Ni toxicity. Exogenously adding Ta bark extract (3.2 mg ml^?1) to the growth medium considerably alleviated Ni toxicity in the seedlings by reducing Ni uptake, suppressing generation of reactive oxygen species, reducing lipid peroxidation, restoring level of photosynthesis pigments and ultrastructure of chloroplasts, and restoring levels of antioxidative enzymes. Results suggest that Ta bark extract considerably alleviates Ni toxicity in rice seedlings by preventing Ni uptake and reducing oxidative stress in the seedlings.     

Exogenous Diethyl Aminoethyl Hexanoate,a Plant Growth Regulator,Highly Improved the Salinity Tolerance of Important Medicinal Plant <Emphasis Type="Italic">Cassia obtusifolia</Emphasis> L.

The purpose of the present study was to investigate the mechanism of DA-6 in alleviating the salinity inhibition of Cassia obtusifolia L. seeds and seedlings. NaCl (100 mM) was used to mimic salinity stress in a series of experiments. Varying combinations of DA-6 were added to seeds and seedlings under salinity stress. Seed germination indices and seedling parameters were investigated. Seed germination and seedling growth were significantly inhibited under salinity stress. NaCl-induced inhibitory effects on seed germination and seedling growth were ameliorated by DA-6 with different concentrations. Addition of DA-6 to seeds (50 µM) and seedlings (100 µM) significantly alleviated damage to the plant cells under salinity stress. DA-6 (regardless of the presence or absence of NaCl) enhanced chlorophyll concentration, total soluble sugars, free proline, and soluble protein, and improved photosystem II (PSII) photochemical efficiency levels (F _v/F _m), PSII actual photochemical efficiency (ΦPSII), and the photochemical quench coefficient. In contrast, the initial fluorescence (F _o) and the non-photochemical quenching coefficient decreased. Application of DA-6 also enhanced the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC 1.11.1.7), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), and glutathione reductase (GR; EC 1.6.4.2), thus alleviating oxidative damage, as indicated by decreases in thiobarbituric acid-reactive substances, hydrogen peroxide concentration (H₂O₂), relative conductivity, and lipoxygenase activity (LOX; EC 1.13.11.12). Based on the experimental results, we conclude that DA-6 induces advantageous effects on the attenuation of salt-stress inhibition of C. obtusifolia seeds and seedlings and alleviates oxidative damage by conferring beneficial cytoprotection and activating antioxidant enzymes. DA-6 can be used as an effective plant growth regulator to alleviate salinity stress.     

Analysis of fatty acid composition of PGPR <Emphasis Type="Italic">Klebsiella</Emphasis> sp. SBP-8 and its role in ameliorating salt stress in wheat

A halotolerant plant-growth-promoting rhizobacteria (PGPR) can ameliorate salt stress in associated plants by various mechanisms. Therefore, the present study aimed to characterize a PGPR Klebsiella sp. SBP-8 for its ability to tolerate salt stress and to study the mechanism of PGPR-mediated mitigation of salt stress in the wheat plant. The abiotic stressors result in multiple changes in the fatty acid composition of Klebsiella sp. SBP-8, helping the membrane to keep its integrity, fluidity, and function for its growth under salt (NaCl) stress conditions. The changes in fatty acid composition of test organism were analyzed by fatty acid methyl ester (FAME) analysis under varying saline conditions. The spectroscopy (GC-MS) profile of cell extract at different salt concentrations was comprised of hydrocarbons, and fatty alcohols with varying carbon chain length. Inoculation of Klebsiella sp. SBP-8 to wheat seedling showed increase in proline, total soluble sugar, and total protein content of treated plants. Bacterial inoculation also decreased the concentration of salinity-induced malondialdehyde (MDA) content. In addition, bacterial inoculation also increased the various antioxidative enzymes like superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) in treated plants. It is likely that bacterial inoculation alleviated the salt stress to wheat plant by co-ordination of antioxidative machinery, and improvement in osmolyte contents. Therefore, the present study suggests that bacterial-inoculated wheat plants were able to cope better with salt stress than uninoculated control, therefore it can serve as a promising bio-inoculant for enhancing the growth of wheat like cereal crops under saline stress.     

Allelochemical stress produced by aqueous leachate of <Emphasis Type="Italic">Nicotiana plumbaginifolia</Emphasis> Viv.

The effects of aqueous leachate of Nicotiana plumbaginifolia Viv. on germination, seedling growth, amylase activity, sugar and starch contents of germinated seeds of maize (Zea mays L. cv. Uttam) were examined. Effects of leachate on photosynthetic pigments, protein content, activities of nitrate reductase and some antioxidants were also studied. Higher concentration of aqueous leachate of N. plumbaginifolia reduced the germination rate (GR). However, final germination percentage remained almost unaffected. Lower concentration of leachate stimulated the amylase activity and resulted in higher sugar content and GR. The increasing concentrations of leachate inhibited the conversion of starch into sugars. Allelochemicals decreased the amount of chlorophyll a, chlorophyll b, carotenoids, protein and nitrate reductase activity (NRA). The leachate of lower concentrations stimulated the activity of peroxidase but slight decrease was recorded in higher concentration. Superoxide dismutase and catalase exhibited concentration dependent increase except in seedlings treated with 100% concentration of leachate. Impairment of various metabolic activities due to leachate resulted in decreased root and shoot length.     

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.     

Role of 5-aminolevulinic acid on growth,photosynthetic parameters and antioxidant enzyme activity in NaCl-stressed <Emphasis Type="Italic">Isatis indigotica</Emphasis> Fort.

5-aminolevulinic acid (ALA) is a key precursor for the biosynthesis of porphyrins such as heme and chlorophyll. ALA alleviates salinity stress damage in germinating seeds and improves seedling growth. Exogenous application of ALA at low concentrations has been shown to enhance salt tolerance in a number of plants. In the present study, we studied the effect of exogenous application of ALA on enhancing salt stress tolerance in Isatis indigotica Fort. (Anhui population as S1, Shanxi population as S2). A foliar application of 0, 12.5, 16.7, 25.0, and 50.0 mg/L ALA was given to the leaves of I. indigotica plants treated with 100 mmol/L NaCl. The fresh weight of leaves and roots; chlorophyll relative content (SPAD value); photosynthetic parameters, such as net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular carbon dioxide concentration (Ci) and water use efficiency of the treated plants were determined. The third leaf of each treated plant was used to determine the activities of antioxidant enzymes. Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutamate synthase (GOGAT), nitrate reductase (NR) activities and the malondialdehyde (MDA) content increased in response to 100 mmol/L NaCl in both S1 and S2 plants. However, the fresh weight of leaf and root, chlorophyll relative content, Pn, Gs, Ci decreased in response to salt stress in both S1 and S2 plants. In all foliar application of ALA in S1 plants, the MDA content, and the activities of SOD and POD were the highest in response to 50.0 mg/L foliar application of ALA. GOGAT and NR activities were the highest in response to 16.7 mg/L foliar ALA. Chlorophyll content and Pn were the highest in S1 plants treated with by 25.0 mg/L ALA. In S2 plants, plant fresh weight, chlorophyll relative content, SOD, CAT, NR activities and Pn treated with 16.7 mg/L ALA were higher than that of the control (CK0). POD, MDA, GOGAT activities in S2 plants treated with 25.0 mg/L ALA were the highest among all treatments. Thus, our results showed that the optimal concentration of ALA (16.7 ~ 25.0 mmol/L) increases the activity of antioxidant enzymes, which in turn helps to abate the damage caused by salt stress in I. indigotica seedlings. Furthermore, ALA also results in an increase in chlorophyll content, Pn and the activities of GOGAT and NR.     

Morphological,physiological and biochemical responses to drought stress of Stone pine (<Emphasis Type="Italic">Pinus pinea</Emphasis> L.) seedlings

In this study, the effect of irrigation intervals (drought stress) on growth, predawn xylem water potential (Ψ _w), the osmotic potential at full turgor (Ψπ ₁₀₀), the osmotic potential at the turgor loss point (Ψπ _TLP), osmotic adjustment and osmotic solutes (soluble sugars and proline) of Pinus pinea L. seedlings were examined. An experiment was carried out under greenhouse conditions using four watering treatments (control, 7-, 14- and 21-day irrigation intervals) in the first growth season; from mid-July to early November. Results showed that irrigation interval had significant effect on growth characteristics, Ψ _w, water relation parameters, and osmotic solutes. The increasing irrigation interval significantly decreased the seedling height, root collar diameter, root, stem and needle dry weight, number of lateral branches, root percentage, root:shoot ratio and diameter:height ratio. Ψ _w and total soluble sugars decreased while proline content increased with the increase of drought stress. The Ψπ ₁₀₀ and Ψπ _TLP significantly decreased in drought-stressed seedlings compared to control (no stress) seedlings. The results suggest that the impact of drought stress increased with the increase of irrigation interval. Therefore, in the drought-stressed P. pinea seedlings were indicated osmotic adjustment by increasing the proline content and decreasing Ψπ ₁₀₀ and Ψπ _TLP during drought stress. Growth decreased under drought stress conditions in P. pinea seedlings.