Exogenous nitric oxide promotes waterlogging tolerance as related to the activities of antioxidant enzymes in cucumber seedlings

We investigated the effects of exogenous sodium nitroprusside (SNP), a nitric oxide (NO) donor, on growth of cucumber (Cucumis sativus L., cv. Jinyou No.1) seedlings and antioxidant enzyme activities in cucumber leaves under waterlogging stress. The growth of cucumber seedlings was significantly inhibited when plants were exposed to waterlogging, whereas shoot spraying with SNP significantly alleviated the inhibition of growth from this type of stress: height, fresh and dry weights of the flooded plants increased obviously. Waterlogging also caused the activation of the antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX)), the reduction of the chlorophyll content, and the accumulation of MDA and protein in leaves. It was found that SNP treatment further potentiated the antioxidant enzyme activities and maintained the chlorophyll and protein content during the entire water-logging period; however, it reduced the MDA content. Thus, NO protects plants from oxidative damage and promotes growth by activation of antioxidant enzymes in leaves in an extent sufficient for the alleviation of membrane injury. However, exogenous NO had no significant effects on cucumber seedlings growth and antioxidant enzyme activities under nonstress conditions.     

Seed Film Coating with Uniconazole Improves Rape Seedling Growth in Relation to Physiological Changes Under Waterlogging Stress

Waterlogging is an important constraint of global production of rape. The effects of seed film coating with 0.0075% uniconazole on the growth and physiology was investigated using seedlings from three varieties of rape (Brassica napus L.) subjected to waterlogging. While seed coating with uniconazole had no significant effect on germination percentage during waterlogging stress, it enhanced root vigour, increased root length, root volume and root dry weight. It also significantly enhanced leaf dry weight and ratio of root to shoot, but induced a significant decrease in shoot height and stem dry weight. Seed film coating with uniconazole also significantly increased the activities of the antioxidant enzymes, POD, CAT and SOD, and soluble sugar concentration during waterlogging. Thus, it suggests that seed film coating with uniconazole at a suitable concentration can improve rape seedling growth and increase seedling establishment during waterlogging.     

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.     

Antioxidative defense system in pigeonpea roots under waterlogging stress

Pigeonpea [Cajanus cajan (L.) Millsp.] is a waterlogging-sensitive legume crop. We studied the effect of waterlogging stress on hydrogen peroxide (H₂O₂) content, lipid peroxidation and antioxidant enzyme activities in two pigeonpea genotypes viz., ICPL-84023 (waterlogging resistant) and MAL-18 (waterlogging susceptible). In a pot experiment, waterlogging stress was imposed for 6 days at early vegetative stage (20 days after sowing). Waterlogging treatment significantly increased hydrogen peroxide accumulation and lipid peroxidation, which indicated the extent of oxidative injury posed by stress conditions. Enzyme activities of peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and polyphenol oxidase (PPO) increased in pigeonpea roots as a consequence of waterlogged conditions, and all the enzyme activities were significantly higher in waterlogged ICPL-84023 than in MAL-18. POX activity was the maximum immediately after imposing stress, therefore, it was suggested to be involved in early scavenging of H₂O₂, while rest of the enzymes (CAT, APX, SOD and PPO) were more important in late responses to waterlogging. Present study revealed that H₂O₂ content is directly related to lipid peroxidation leading to oxidative damage during waterlogging in pigeonpea. Higher antioxidant potential in ICPL-84023 as evidenced by enhanced POX, CAT, APX, SOD and PPO activities increased capacity for reactive oxygen species (ROS) scavenging and indicated relationship between waterlogging resistance and antioxidant defense system in pigeonpea.     

Effects of Common Mycorrhizal Network on Plant Carbohydrates and Soil Properties in Trifoliate Orange–White Clover Association

Common mycorrhizal network (CMN) allows nutrients and signals to pass between two or more plants. In this study, trifoliate orange (Poncirus trifoliata) and white clover (Trifolium repens) were planted in a two-compartmented rootbox, separated by a 37–μm nylon mesh and then inoculated with an arbuscular mycorrhizal fungus (AMF), Diversispora spurca. Inoculation with D. spurca resulted in formation of a CMN between trifoliate orange and white clover, whilst the best AM colonization occurred in the donor trifoliate orange–receptor white clover association. In the trifoliate orange–white clover association, the mycorrhizal colonization of receptor plant by extraradical hyphae originated from the donor plant significantly increased shoot and root fresh weight and chlorophyll concentration of the receptor plant. Enzymatic activity of soil β-glucoside hydrolase, protease, acid and neutral phosphatase, water-stable aggregate percentage at 2–4 and 0.5–1 mm size, and mean weight diameter in the rhizosphere of the receptor plant also increased. The hyphae of CMN released more easily-extractable glomalin-related soil protein and total glomalin-related soil protein into the receptor rhizosphere, which represented a significantly positive correlation with aggregate stability. AMF inoculation exhibited diverse changes in leaf and root sucrose concentration in the donor plant, and AM colonization by CMN conferred a significant increase of root glucose in the receptor plant. These results suggested that CMN formed in the trifoliate orange–white clover association, and root AM colonization by CMN promoted plant growth, root glucose accumulation, and rhizospheric soil properties in the receptor plant.     

丛枝菌根真菌对西瓜嫁接苗生长和根系防御性酶活性的影响

在温室盆栽条件下,研究丛枝菌根(AM)真菌地表球囊霉(Glomus versiforme)对连作土壤中西瓜自根苗和嫁接苗生长、根系膜透性、丙二醛(MDA)含量和防御性酶活性的影响.结果表明： 接种AM真菌能显著增加西瓜自根苗和嫁接苗的生物量,提高根系活力,降低根系膜透性和MDA含量.接种AM真菌的自根苗地上部鲜质量、地上部干质量和根系活力分别增加了57.6%、60.0%和142.1%,而接种AM真菌的嫁接苗分别增加了26.7%、28.0%和11.0%;自根苗（C）、嫁接苗（G）、接种AM真菌自根苗（C+M）和接种AM真菌嫁接苗（G+M）的根系细胞膜透性为C>G>C+M>G+M,根系MDA含量为C>G>G+M>C+M.接种AM真菌能提高西瓜自根苗和嫁接苗根系的苯丙氨酸解氨酶(PAL)、过氧化氢酶(CAT)、过氧化物酶(POD)、几丁质酶和β 1,3 葡聚糖酶活性,而且接种AM真菌的西瓜自根苗和嫁接苗根系POD、PAL和β-1,3-葡聚糖酶活性的峰值比不接种的提前2周出现.接种AM真菌能激活西瓜自根苗和嫁接苗与抗逆性有关的防御性酶反应,使根系对逆境产生快速反应,从而提高其抗连作障碍的能力.     

丛枝菌根真菌对西瓜嫁接苗生长和根系防御性酶活性的影响

在温室盆栽条件下,研究丛枝菌根(AM)真菌地表球囊霉(Glomus versiforme)对连作土壤中西瓜自根苗和嫁接苗生长、根系膜透性、丙二醛(MDA)含量和防御性酶活性的影响.结果表明： 接种AM真菌能显著增加西瓜自根苗和嫁接苗的生物量,提高根系活力,降低根系膜透性和MDA含量.接种AM真菌的自根苗地上部鲜质量、地上部干质量和根系活力分别增加了57.6%、60.0%和142.1%,而接种AM真菌的嫁接苗分别增加了26.7%、28.0%和11.0%;自根苗（C）、嫁接苗（G）、接种AM真菌自根苗（C+M）和接种AM真菌嫁接苗（G+M）的根系细胞膜透性为C>G>C+M>G+M,根系MDA含量为C>G>G+M>C+M.接种AM真菌能提高西瓜自根苗和嫁接苗根系的苯丙氨酸解氨酶(PAL)、过氧化氢酶(CAT)、过氧化物酶(POD)、几丁质酶和β 1,3 葡聚糖酶活性,而且接种AM真菌的西瓜自根苗和嫁接苗根系POD、PAL和β-1,3-葡聚糖酶活性的峰值比不接种的提前2周出现.接种AM真菌能激活西瓜自根苗和嫁接苗与抗逆性有关的防御性酶反应,使根系对逆境产生快速反应,从而提高其抗连作障碍的能力.     

The Influence of Glomus mosseae on Tylenchulus semipenetrans-Infected and Uninfected Citrus limon Seedlings

Greenhouse studies have shown that when rough lemon (Citrus limon) seedlings infected with TyIenchulus semipenetrans were transplanted into soil infested with Glomus mosseae, the mycorrhizal fungus infection increased seedling growth compared to nonntycorrhizal seedlings. Tylenchulus semipenetrans significantly suppressed seedling growth below that of mycorrhizal seedlings. Histological observations of nematode-free mycorrhizal roots showed that hyphae penetrated the epidermis and invaded the cortex, giving rise to arbuscules and vesicles. Nematode infection sites in T. semipenetrans-infected roots grown in soil infested with G. mosseae did not show evidence of vesicle development in the cortex but did show arbuscule development.     

Responses of antioxidant defense system of <Emphasis Type="Italic">Helianthus annuus</Emphasis> to abscisic acid treatment under drought and waterlogging

The effect of abscisic acid (ABA) treatment on growth pigments and antioxidant defense system were investigated in seedlings of Helianthus annuus (cvs. Nantio F1 and Özdemirbey) subjected to drought and waterlogging stress. In addition, seedlings were sprayed with 10 M ABA three times every other day. Relative growth rate (RGR) was significantly reduced in both genotypes under drought stress, however, this growth inhibition was less in ABA-treated plants. Total chlorophyll content increased by drought stress in both genotypes. Ascorbate was not influenced by drought, while α-tocopherol increased in cv. Nantio F1. Ascorbate and α-tocopherol increased with drought stress in cv. Özdemirbey. ABA treatment decreased ascorbate and β-carotene contents while it increased α-tocopherol and xanthophylls contents under drought stress. The activity of superoxide dismutase (SOD) in both genotypes increased under drought stress-ABA combinations. Catalase (CAT) activity decreased under drought stress and drought-ABA combinations while it increased under waterlogging stress. Glutathione reductase (GR) activity decreased under drought stress but recovered with ABA treatment. The results suggested that ABA treatments have different effects on the components of antioxidant defense system in H. annuus genotypes and ABA may contribute drought-induced oxidative stress tolerance but not effects under waterlogging stress.     

Combined action of antioxidant defense system and osmolytes in chilling shock-induced chilling tolerance in Jatropha curcas seedlings

Low non-freezing temperature is one of the major environmental factors affecting growth, development and geographical distribution of chilling-sensitive plants, Jatropha curcas is considered as a sustainable energy plants with great potential for biodiesel production. In this study, chilling shock at 5 °C followed by recovery at 26 °C for 4 h significantly improved survival percentage of J. curcas seedlings under chilling stress at 1 °C. In addition, chilling shock could obviously enhance the activities of antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR), and the levels of antioxidants ascorbic acid (AsA) and glutathione (GSH), as well as the contents of osmolytes proline and betaine in leaves of seedlings of J. curcas compared with the control without chilling shock. During the process of recovery, GR activity, AsA, GSH, proline and betaine contents sequentially increased, whereas SOD, APX and CAT activities gradually decreased, but they markedly maintained higher activities than those of control. Under chilling stress, activities of SOD, APX, CAT, GR and GPX, and contents of AsA, GSH, proline and betaine, as well as the ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)] in the shocked and non-shock seedlings all dropped, but shocked seedlings sustained significantly higher antioxidant enzyme activity, antioxidant and osmolyte contents, as well as ratio of reduced antioxidants to total antioxidants from beginning to end compared with control. These results indicated that the chilling shock followed by recovery could improve chilling tolerance of seedlings in J. curcas, and antioxidant enzymes and osmolytes play important role in the acquisition of chilling tolerance.     

外源GSH对盐胁迫下番茄幼苗生长及抗逆生理指标的影响

采用营养液栽培法,研究外源谷胱甘肽(GSH)对NaCl胁迫下番茄幼苗生长、根系活力、电解质渗透率和丙二醛(MDA)、脯氨酸(Pro)、可溶性糖含量以及超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性的影响,为利用外源物质减轻盐胁迫伤害提供理论依据。结果显示:(1)NaCl胁迫显著抑制了番茄幼苗的生长、根系活力和SOD、POD、CAT活性,提高了电解质渗透率及MDA、Pro、可溶性糖含量;(2)外源喷施GSH能够诱导NaCl胁迫下番茄幼苗叶片抗氧化酶SOD、POD、CAT活性上调,电解质渗透率及MDA含量下降,Pro和可溶性糖含量恢复至对照水平;(3)外源喷施还原型谷胱甘肽抑制剂(BSO)使NaCl胁迫下番茄幼苗的根系活力以及抗氧化酶SOD、POD、CAT活性下降,脯氨酸含量提高;(4)喷施GSH可诱导BSO和NaCl共处理番茄植株的根系活力、SOD、POD、CAT活性提高,MDA和Pro含量降低。研究表明,外源GSH可通过提高促进盐胁迫下番茄幼苗植株渗透调节能力及清除活性氧的酶促系统的防御能力、降低细胞膜脂过氧化程度、保护膜结构的完整性,从而有效缓解NaCl胁迫对番茄幼苗生长的抑制,提高其耐盐性。     

Physiological Responses of Pinus sylvestris var. Mongolica Seedlings to the Interaction Between Suillus luteus and Trichoderma virens

The effects of the interaction between Suillus luteus (L.) Roussel and Trichoderma virens (J.H. Mill., Giddens & A.A. Foster) Arx on Pinus sylvestris var. mongolica Litv. were studied using plant physiology, mycorrhizal science, forest pathology, and biochemistry. Seedling growth and physiological parameters were determined, including the colonization rate of mycorrhizal fungi, biomass, root activity, photosynthetic pigment content, soluble protein content, antioxidant enzyme activities, rhizosphere soil enzyme activities, and protective enzyme activities. In addition, an optimal resistance system involving T. virens, mycorrhizal fungus (S. luteus), and P. sylvestris var. mongolica seedlings was constructed. Synergies between S. luteus and T. virens were observed, and most of the parameters of P. sylvestris var. mongolica seedlings inoculated with S. luteus 30 days + T. virens were higher than other treatments. After three months, when compared the control, the S. luteus 30 days + T. virens treatment gave increases in height (42.3 %); collar diameter (66.7 %); fresh weight (54 %); dry weight (50 %); soluble protein content (69.86 %); root activity (150 %); chlorophyll a (77.6 %); chlorophyll b (70.5 %); carotenoids (144 %); CAT activity (876.9 %); POD activity (268.3 %); SOD activity (66.18 %); β-1,3-glucanase activity (125.8 %); chitinase activity (40 %); rhizosphere soil catalase activity (97.8 %); and phosphatase activity (266.7 %). These results indicate that there may be a stimulating factor between S. luteus and T. virens when they are inoculated together (S. luteus 30 days + T. virens).     

盐旱交叉胁迫对灰胡杨(Populus pruinosa)幼苗生长和生理生化特性的影响

以一年生灰胡杨幼苗为试验材料,利用田间控盐控水的方法,进行干旱和盐胁迫试验,通过测定生长和生理生化指标探讨幼苗在盐旱交叉胁迫下的生长发育及适应规律,旨在阐明干旱及盐交叉胁迫下植物抗旱抗盐机理。研究结果表明:在盐、旱及交叉胁迫下,灰胡杨幼苗抗氧化酶活性、MDA和脯氨酸含量与对照存在显著差异(P0.05)。(1)在8、11 g/L和15 g/L盐处理下,灰胡杨幼苗相对高生长、相对枝长和冠幅增量均受到抑制,且差异显著(P0.05),而干旱胁迫和盐旱交互胁迫下差异不显著。(2)在盐胁迫、盐旱交叉胁迫下,随着胁迫程度的加重,抗氧化酶SOD、POD、CAT活性表现出先增加后降低的趋势,三者协调一致;仅干旱胁迫时,抗氧化酶SOD、POD、CAT活性显著增加;(3)在盐、旱及其盐旱交叉胁迫下,脯氨酸含量呈上升趋势,MDA含量则表现出先降低后升高趋势,这与抗氧化酶活性先升高后降低的趋势相对应。因此,抗氧化酶活性对缓解脂膜过氧化的伤害具有一定限度,MDA含量与抗氧化酶活性呈负相关,灰叶胡杨幼苗在盐旱交叉胁迫下表现出一定的耐性。     

Changes in morphological, physiological, and biochemical responses to different levels of drought stress in chinese cork oak (Quercus variabilis Bl.) seedlings

Changes in growth, leaf water status, pigments, osmolytes, activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX), and ascorbic acid (ASA) content were investigated in Chinese cork oak (Quercus variabilis Bl.) seedlings. Three-month-old seedlings were subjected to four drought cycles (30, 60, 90, and 120 days) and four drought intensities (80, 60, 40, and 20% field capacity (FC)). The seedlings had optimal height, basal diameter, and leaf water status at 80% FC. These parameters significantly decreased as drought intensity increased. The total root length, diameter, and surface area at 60% FC significantly increased compared with those at 80% FC. However, at 40 and 20% FC these parameters significantly decreased compared with those at 80% FC. The ratio of total root length to seedling height significantly increased with increasing drought intensity. The contents of chlorophyll a + b (Chl _{a + b} ) and carotenoids (Car) significantly decreased at 40 and 20% FC. However, no significant changes in Chl _a /Chl _b and Car/Chl _{a + b} ratios were observed among the four drought intensities. Comparatively, the seedlings accumulated more soluble sugars and proline, as well as they demonstrated the higher POD, SOD, CAT, APX activities and ASA content at >40% FC. However, prolonged drought stress at 20% FC suppressed antioxidant activities and osmolyte accumulation, leading to a rapid increase in lipid peroxidation. These results suggest that a water supply >40% FC is required to support the growth and survival of the current-year seedlings of Chinese cork oak     

Effects of Selenium on Wheat Seedlings Under Drought Stress

The paper reports the effects of selenium (Se) supply on growth and some physiological traits of wheat (Triticum aestivum L. cv Shijiazhuang NO. 8) seedlings exposed to drought stress. The growth and physiological responses of seedlings were different depending on the Se concentration. The higher (3.0 mg Se kg⁻¹) and lower amount used (0.5 mg Se kg⁻¹) did not significantly affect on biomass accumulation. Treatments with 1.0 and 2.0 mg Se kg⁻¹ promoted biomass accumulation of wheat seedlings. Treatments at 1.0, 2.0, and 3.0 mg Se kg⁻¹ significantly increased root activity, proline content, peroxidase (POD), and catalase (CAT) activities, carotenoids (Car) content, chlorophyll content, and reduced malondialdehyde (MDA) content of wheat seedlings. Lower Se treatment did not significantly effect on chlorophyll content and MDA content, although it also increased some antioxidant index (proline and Car content, POD and CAT activities) in wheat seedlings. These results suggest that optimal Se supply is favorable for growth of wheat seedlings during drought condition.     

An alginate-derived oligosaccharide enhanced wheat tolerance to cadmium stress

Hydroponic experiments were carried out to study the role of alginate-derived oligosaccharides (ADO) in enhancing wheat (Triticum aestivum L.) tolerance to cadmium stress. Data were collected on plant biomass, chlorophyll content, photosynthetic rate, antioxidant enzyme activity and malondialdehyde (MDA) content. Under 100 μM Cd stress, plant growth was significantly inhibited. Shoot length, root length, fresh and dry weight were sharply reduced by 24.21, 34.59, 22.1 and 14.7%, respectively of the control after 10 day of Cd exposure. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were increased and MDA content increased. Wheat seeds were soaked for 5 h in 1,000 mg L⁻¹ ADO solution before cadmium stress. ADO pretreatment alleviated cadmium toxicity symptoms, which were reflected by increasing root and shoot lengths, fresh and dry weight, chlorophyll content and photosynthetic rate (P _n ). Furthermore, ADO pretreatment significantly increased antioxidant enzyme (SOD, CAT and POD) activities and reduced MDA content in leaves and roots. The results indicated that ADO pretreatment partially protected the seedlings from cadmium toxicity during the following growth period.     

The Response of Citrus limon Seedlings to a Symbiont,Glomus etunicatus,and a Pathogen,Radopholus similis

The influences of a vesicular-arbuscular mycorrhiza (Glomus etunicatus) and burrowing nematode (Radophohts similis), alone and in combination, on the growth of rough lemon (Citrus limon) seedlings were studied in the greenhouse. Growth of mycorrhizal seedlings was significantly greater than that of nonmycorrhizal seedlings or seedlings inoculated with R. sindlis. Mycorrhizal stimulation of seedling growth was inhibited by nematode infection. When seedlings were inoculated with G. etunicatus arid R. similis, suppression of seedling growth by R. similis was less on VAM seedlings than on nonmycorrhizal seedlings, Nonmycorrhizal seedlings infected with R. similis were significantly smaller than nonmycorrhizal seedlings free of R. similis. Vesicle formation and mycelia growth were less in nematode-infected roots.     

Lack of K-Dependent Oxidative Stress in Cotton Roots Following Coronatine-Induced ROS Accumulation

Coronatine [COR] is a novel type of plant growth regulator with similarities in structure and property to jasmonate. The objective of this study was to examine the relationship between increased root vitality induced by 10nM COR and reactive oxygen species scavenging under potassium (K)-replete (2.5mM) and K-deficient (0.05mM) conditions in hydroponic cultured cotton seedlings. K-replete and K-deficient conditions increased root vitality by 2.7- and 3.5-fold, respectively. COR treatment significantly decreased lipid peroxidation in cotton seedlings determined by reduction in MDA levels. These results suggest that COR improves the functioning of both enzymatic and non-enzymatic antioxidant systems. Under K-replete and K-deficient conditions, COR significantly increased the activities of antioxidant enzymes SOD (only for K-repletion), CAT, GPX, and APX comparing; COR also significantly increased DPPH-radical scavenging activity. However, COR led to 1.6- and 1.7-fold increases in superoxide anion (O₂^•-) concentrations, and 5.7- and 2.1-fold increases in hydrogen peroxide (H₂O₂) levels, respectively. Additionally, COR intensified the DAB staining of H₂O₂ and the NBT staining of O₂^•-. Therefore, our results reveal that COR-induced ROS accumulation stimulates the activities of most antioxidant enzymes but does not induce oxidative stress in cotton roots.     

Protective effects of complementary Ca2+ on low-light-induced oxidative damage in tall fescue

Low-light (LL) intensity is a primary abiotic stressor that negatively influences turf grass quality. In the present experiment, we studied the effect of exogenous Ca²⁺ (0, 10, 50, 100, and 200 mM) on the antioxidant system, the accumulation of MDA and proline, the content of photosynthetic pigments in plant leaves in order to investigate whether exogenous Ca²⁺ treatment improves LL tolerance in tall fescue (Festuca arundinacea Schreb.). We have found that LL significantly reduced a number of growth parameters (plant height, leaf width, leaf fresh weight, root fresh weight, leaf dry weight, and root dry weight), chlorophyll (Chl) a and Chl b contents, and carotenoid (Car) levels, while considerably enhancing electrolyte leakage (EL), MDA accumulation, calcium (Ca²⁺) concentration, and generation of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂) and superoxide radical (O ₂ ^·? ). Moreover, LL significantly induced the activities of antioxidant enzymes, such as peroxidase (POD) and catalase (CAT), and slightly increased the activity of superoxide dismutase (SOD) in tall fescue leaves. In contrast, POD and SOD activities declined considerably while CAT activity significantly increased in plant roots under LL stress. The application of 50 mM Ca²⁺ significantly improved the aforementioned growth parameters, the content of photosynthetic pigments, and further enhanced the activities of POD, SOD, and CAT, but decreased electrolyte leakage and MDA and H₂O₂ levels in the leaves and roots of tall fescue under LL stress. These results suggest that Ca²⁺ is likely involved in a resistance to LL by regulating antioxidant enzyme action in tall fescue leaves and roots.     

Autotoxicity in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) seedlings is alleviated by silicon through an increase in the activity of antioxidant enzymes and by mitigating lipid peroxidation

Autotoxicity in plants limits their growth and that of nearby plants of the same species, which has obvious implications in crop yield and quality. Silicon (Si) has been shown to increase plant tolerance to autotoxic stress. However, the physiological mechanisms underlying the effects of Si in alleviating autotoxicity during germination in cucumber (Cucumis sativus L.) are unknown. Cinnamic acid derivatives, such as 3-phenylpropionic acid (PA), are a class of autotoxins present in cucumber root exudates. Our objective was to investigate Si-induced autotoxic stress tolerance in cucumber seedlings by focusing on the effects of Si on the induction of antioxidant defense pathways. We found that PA treatment significantly reduced seed germination, radicle length, lateral root number, fresh weight, AsA and GSH contents, and the activities of SOD, CAT, and APX in cucumber seedlings, while it increased membrane permeability and levels of MDA, proline, O₂^-, and H₂O₂. Application of Si enhanced growth of PA-treated plants and significantly increased germination rate, radicle length, lateral root number, fresh weight, AsA and GSH levels, and SOD, CAT, POD, and APX activities. These results suggest that exogenous Si alleviates autotoxicity caused by PA during seed germination by increasing antioxidant enzyme activities and mitigating lipid peroxidation.