Phytoremediation Potential and Nutrient Status of Barringtonia acutangula Gaerth. Tree Seedlings Grown Under Different Chromium (CrVI) Treatments

To investigate the effect of different chromium (CrVI) treatments on seedlings of semi-aquatic plant Barringtonia acutangula, hydroponic experiments were conducted. Results revealed that B. acutangula could tolerate much higher CrVI concentration accumulated about 751–2,703 mg kg^?1 dry weight in roots and 50–1,101 mg kg^?1 dry weight in shoots, respectively, under 1.0, 2.0, 3.0, 4.0, and 5.0 mM chromium treatments. CrVI exposure at 1.0–4.0 mM does not exhibit toxicity signs; however, up to 4.0 mM CrVI exposure causes significant decline in growth parameters. Content of macronutrients such as Ca and K decreased under different Cr treatments in roots and shoots, while Mg content of roots and shoots did not influence at the range of 1.0–4.0 mM Cr; however, significant decrease at 5.0 mM Cr, besides P content, significantly shows increasing trends, respectively. Interestingly, sulfur content of roots and shoots show increasing trends at 1.0–2.0 mM Cr; however, severe decrease of up to 3.0–5.0 mM is shown in CrVI treatments. Furthermore, micronutrients content were enhanced under CrVI treatments excluding Cu and Fe since they show significant reduction in shoots as well as in roots. Bioaccumulation factor were also calculated on the basis of results obtained which shows the value of >1 without viewing chromium toxicity symptoms. This study demonstrated that B. acutangula could tolerate CrVI concentrations up to 1.0–4.0 mM Cr which may be useful in chromium phytoremediation programs.     

Physiological and anatomical response of foliar silicon application to <Emphasis Type="Italic">Dendrocalamus brandisii</Emphasis> plantlet leaves under chilling

The physiological and anatomical responses of different concentrations (0.0, 0.5, 1.0, 2.0 and 4.0 mM sodium silicate) of Si foliar-application in improving the chilling tolerance of Dendrocalamus brandisii plantlets were investigated. The Si-supplemented D. brandisii plantlets exhibited better chilling tolerance, associated with the enhancement of photosynthetic pigment and soluble sugar and starch content, increasing CAT and SOD activities and decreasing MDA and H₂O₂ level, as well as thicker leaf blades and mesophyll tissues. Furthermore, distinct changes in phytolith morphology were observed, including formation of a new phytolith morphotype (dumb-bell with nodular shark), significantly higher frequency of elongated phytoliths, and the increased length of elongated and elliptical phytoliths. Results indicated the physiological and anatomical response showed weak positive linkage with increasing amount of silicon applied, and the 1.0 mM sodium silicate on D. brandisii plantlet leaves was the most effective treatment in enhancing chilling tolerance.     

Silicon Application to Rice Root Zone Influenced the Phytohormonal and Antioxidant Responses Under Salinity Stress

Silicon (Si) application shows beneficial effects on plant growth; however, its effects on the phytohormone and enzymatic antioxidant regulation have not been fully understood. We studied the effects of short-term (6, 12, and 24 h) silicon (0.5, 1.0, and 2.0 mM) application on salinity (NaCl)-induced phytohormonal [abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA)] and antioxidant regulation in Oryza sativa. The results showed that Si treatments significantly increased rice plant growth compared to controls under salinity stress. Si treatments reduced the sodium accumulation resulting in low electrolytic leakage and lipid peroxidation compared to control plants under salinity stress. Enzymatic antioxidant (catalase, peroxidase and polyphenol oxidase) responses were more pronounced in control plants than in Si-treated plants under salinity stress. Stress- and defense-related phytohormones like JA were significantly downregulated and SA was irregular after short-term Si applications under salinity stress compared to control. Conversely, ABA was significantly higher after 6 and 12 h but insignificant after 24 h in Si-treated plants under salinity stress. After 6 and 12 h, Si and salinity stress resulted in upregulation of zeaxanthin epoxidase and 9-cis-epoxycarotenoid dioxygenase 1 and 4 (NCED1 and 4), whereas 24-h treatments significantly downregulated the expressions of these genes compared to those in the control. NCED3 expression increased after 6 and 24 h but it was insignificant after 12 h of Si application compared to control. The current findings indicate that increasing the Si concentrations for longer periods of time can regulate the salinity-induced stress by modulating phytohormonal and enzymatic antioxidants’ responses.     

Physiological and biochemical mechanisms of silicon-induced copper stress tolerance in cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.)

Accumulation of excess copper (Cu) in agricultural soils can decrease growth and quality of crops grown on these soils and a little information is available on the role of silicon (Si) in reducing Cu toxicity in plants. A hydroponic study was conducted to investigate the effects of Si (1.0 mM) on growth and physiology of cotton seedlings grown on different Cu (0, 25, and 50 µM) concentrations. Elevated levels of Cu decreased growth, biomass, photosynthetic pigments, and gas exchange characteristics, and increased the electrolyte leakage (EL), hydrogen peroxide (H₂O₂), and thiobarbituric acid reactive substances (TBARS) contents in leaf, stem, and roots of cotton seedlings. Cu stress alone decreased the activities of key antioxidant enzymes in cotton seedlings. Exogenous application of Si alleviated the toxic effects of Cu on cotton seedlings by improving growth, photosynthetic pigments, and gas exchange characteristics under Cu stress. The Si application decreased Cu concentrations in leaves, stem, and roots as compared with the control plants. Furthermore, Si decreased oxidative stress as evidenced by decreased EL, H₂O₂, and TBARS contents, and increased the antioxidant enzyme activities in cotton seedlings. This study provides evidences of Si-mediated reduction of Cu toxicity in cotton seedlings at physiological and biochemical levels.     

Influence of Short-Term Silicon Application on Endogenous Physiohormonal Levels of Oryza sativa L. Under Wounding Stress

The current study was conducted in order to investigate the short-term effects (6, 12, and 24?h) of silicon (Si) on the endogenous hormonal composition of rice (Oryza sativa L. cv. Dongjin-beyo), with and without wounding stress. Si applied in different concentrations (0.5, 1.0, and 2.0?mM) significantly promoted shoot length, plant biomass, and chlorophyll content of rice plants. Plants treated with different concentrations of sole Si for 6, 12, and 24?h had higher endogenous jasmonic acid contents than control. However, a combined application of wounding stress and Si induced a significantly small quantity of endogenous jasmonic acid as compared with control. On the contrary, endogenous salicylic acid level was significantly higher in sole Si-treated plants, while after wounding stress, a similar trend was observed yet again. After 6, 12, and 24?h of Si applications, with and without wounding stress, ethylene levels were significantly lower in comparison to their respective controls. The findings of the present study perpetrate the beneficial role of Si on the growth and development of rice plant by relieving physical injury and stress. Si also affects endogenous jasmonic acid and ethylene levels, while an inverse correlation exists between jasmonic acid and salicylic acid under wounding stress conditions.     

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.     

Accumulation of gamma-aminobutyric acid in the halotolerant cyanobacterium <Emphasis Type="Italic">Aphanothece halophytica</Emphasis> under salt and acid stress

γ-Aminobutyric acid (GABA) is known as an inhibitory neurotransmitter in human, while in plants, GABA is an intermediate for amino acid metabolism and also is accumulated in response to a wide range of environmental stress. In the present study, GABA accumulation in Aphanothece halophytica was increased 2-fold in mid-log phase cells grown under salt stress (2.0 M NaCl). When mid-log phase cells were subjected to changes in NaCl concentrations and pH for 4 h, the highest GABA accumulation was observed in cells adapted in medium that contained 2.0 M NaCl and that was adjusted to pH 4.0, respectively. The increase of GABA accumulation was accompanied by an increased glutamate decarboxylase activity. Addition of glutamate to growth medium stimulated GABA accumulation under acid stress but had no effect under salt stress. However, the highest GABA accumulation was detected in cells exposed to both high salt and acid stresses combined with the 5 mM glutamate supplementation with an approximately 3-fold increase as compared to the control. The unicellular A. halophytica showed a similarly high content of GABA to that of a filamentous Arthrospira platensis suggesting the possibility of genetic manipulation of the genes of A. halophytica involved in GABA synthesis to increase GABA yield.     

Effects of exogenous nitric oxide on the photosynthetic characteristics of bamboo (<Emphasis Type="Italic">Indocalamus barbatus</Emphasis> McClure) seedlings under acid rain stress

The effects of the exogenous application of nitric oxide (NO, in the form of sodium nitroprusside, SNP) on the diurnal variation in photosynthesis, chlorophyll content, chlorophyll fluorescence, light response curve and the net assimilation of CO₂ against intercellular CO₂ concentration (A-Ci) curve parameters were investigated in the leaves of bamboo (Indocalamus barbatus McClure) exposed to simulated acid rain (SAR, pH 3.0) stress. According to the results of the diurnal variation in photosynthesis, foliar applications of 100–400 mg/L SNP effectively inhibited the decrease in net photosynthetic rate (Pn) as a result of non-stomatal factors, and mitigated midday depression under acid rain stress. The mitigating effect was most pronounced at 400 mg/L SNP. However, at higher concentrations of SNP (700 and 1000 mg/L), the mitigating effect became weak and even counterproductive. The results of the chlorophyll content, light response and A-Ci curve parameters suggested that the regulating role of NO against acid rain in the photosynthetic processes occurs through improving not only the efficiency of the light-harvesting and the activity of photosynthetic apparatus, but also the absorption of CO₂ and the availability of CO₂ for photosynthesis. The results of the chlorophyll fluorescence investigation further indicated that NO protected PSII activity from the damage of acid rain toxicity by enhancing the electron transport activity and photochemical efficiency, especially concerning the increase in the proportion of PSII open reaction centers. Furthermore, NO induced an increase in photorespiration (Rp), rather than an increase in non-photochemical quenching (NPQ), to dissipate the excessive excitation energy, which provided some protection to the photosynthetic apparatus under acid rain stress.     

Alleviation of NaCl toxicity in the cyanobacterium <Emphasis Type="Italic">Synechococcus</Emphasis> sp. PCC 7942 by exogenous calcium supplementation

Salinity (NaCl) is one of the major problems associated with irrigated agricultural lands, especially rice fields. Being the common inhabitants of rice fields, cyanobacteria frequently experience high concentration of NaCl which in turn causes cellular damage. Therefore, mitigation of NaCl stress in cyanobacteria, plant growth-promoting microorganisms, is of utmost importance. The present study was designed to investigate the role of calcium in the alleviation of NaCl stress-induced cellular in Synechococcus sp. PCC 7942. The cyanobacterium was subjected to sub-lethal concentration of NaCl (800 mM) with and without the supplementation of calcium (1 mM CaCl₂) for 8 days. The results showed a drastic reduction in growth due to excess NaCl, but supplementation of CaCl₂ reduced the salt stress damage and partially restored growth. Application of calcium increased pigment contents, photosynthetic efficiency, antioxidative enzyme activity, osmolyte contents and reduced the intracellular sodium ion concentration, MDA content, electrolyte leakage and free oxygen radical generation. Furthermore, proteins involved in photosynthesis, respiration, ATP synthesis and protein synthesis along with two hypothetical proteins were also observed to be upregulated in the cyanobacterium in presence of calcium. Furthermore, proteins related to oxidative stress defence, nitrogen metabolism, carbohydrate metabolism, fatty acid metabolism and secondary metabolism were found to be upregulated by several fold. Therefore, our study suggests that calcium suppresses salt toxicity in Synechococcus sp. PCC 7942 by restricting the entry of Na⁺ into the cell, increasing osmolyte production and upregulating defence-related proteins.     

The alleviation of zinc toxicity by silicon is related to zinc transport and antioxidative reactions in rice

The objective of this study is to elucidate the roles of silicon (Si) in enhancing tolerance to excess zinc (Zn) in two contrasting rice (Oryza sativa L.) cultivars: i.e. cv. TY-167 (Zn-resistant) and cv. FYY-326 (Zn-sensitive). Root morphology, antioxidant defense reactions and lipid peroxidation, and histochemical staining were examined in rice plants grown in the nutrient solutions with normal (0.15 μM) and high (2 mM) Zn supply, without or with 1.5 mM Si. Significant inhibitory effects of high Zn treatment on plant growth were observed. Total root length (TRL), total root surface area (TRSA) and total root tip amount (TRTA) of both cultivars were decreased significantly in plants treated with high Zn, whereas these root parameters were significantly increased when Zn-stressed plants were supplied with 1.5 mM Si. Supply of Si also significantly decreased Zn concentration in shoots of both cultivars, indicating lower root-to-shoot translocation of Zn. Moreover, superoxide dismutase (SOD), catalase (CAT), and asorbate peroxidase (APX) activities were increased, whereas malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) concentrations were decreased in Si-supplied plants of both Zn-sensitive and Zn-resistant rice cultivars exposed to Zn stress. These alleviative effects of Si, further confirmed by the histochemical staining methods, were more prominent in the Zn-resistant cultivar than in the Zn-sensitive one. Taken together, all these results suggest that Si-mediated alleviation of Zn toxicity is mainly attributed to Si-mediated antioxidant defense capacity and membrane integrity. The possible role of Si in reduction of root-to-shoot translocation of Zn can also be considered.     

Morpho-physiological and antioxidant response to NaCl-induced stress in in vitro shoots of pomegranate (<Emphasis Type="Italic">Punica granatum</Emphasis> L.)

The physiological and antioxidant response to salinity was studied in pomegranate (Punica granatum L.) by exposing in vitro growing shoots of the Italian variety Profeta Partanna to 125 or 250 mM NaCl for 10 and 20 days. 250 mM NaCl significantly reduced shoot length, leaf area and water content of the shoots, regardless the length of the salt treatment,with respect to the control and to the 125 mM NaCl treatment. After 20 days the shoots treated with 250 mM NaCl also showed a significant reduction in relative growth rate (RGR) together with marked necroses and abscission of the oldest leaves. Salt treatments significantly decreased the contents of chlorophylls and carotenoids in both exposure times, depending on NaCl concentration. Proline, total phenolic compounds and ellagic acid did not increase or even decrease with the salt treatments. The levels of lipid peroxidation decreased, ascorbate peroxidase (APX) activity significantly increased in both treatment times and concentrations, while guaiacol peroxidase (G-POD) activity significantly increased in shoots treated with 250 mM NaCl for 20 days suggesting the rapid involvement of APX in controlling the oxidative stress in this species, even at low salt concentrations, and a delayed complementary role of G-POD.     

Production of potential anti-inflammatory compounds in cell suspension cultures of <Emphasis Type="Italic">Sphaeralcea angustifolia</Emphasis> (Cav.) G. Don

Sphaeralcea angustifolia is used in Mexican traditional medicine to treat inflammatory processes. SCopoletin (SC), TOmentin (TO), and sphaeralcic acid (SA) were reported as the main anti-inflammatory compounds in this species. The aim of this study was to establish in vitro conditions for the development of calli and cell suspension cultures that are the producers of these active compounds. Callus cultures of plant leaf explants were set up using different auxin levels of α-naphthalene acetic acid (NAA) in combination with a constant concentration (0.1 mg L^?1) of Kinetin (Kn) in Murashige and Skoog (MS) medium. Optimal combinations for callus induction were 1.0 and 2.0 mg L^?1 of NAA. SC, TO, and SA were not detected in callus tissues. Employing a 4 % inoculum in fresh biomass, cell suspension was established from friable callus with 1.0 mg L^?1 of NAA in combination with 0.1 mg L^?1 of Kn in MS liquid medium (27.4 mM nitrate). The cellular suspension synthesized SC and SA, SC was excreted into the culture medium, while SA was excreted into the culture medium and accumulated in biomass. To improve SC and SA production, total nitrate content was reduced in MS medium. On diminishing nitrate content to 2.74 mM, cellular suspension growth was not modified. SC concentration (0.04 %) was 60-fold higher than that detected in the wild plant (0.00067 %), TO was produced (0.096 %), and SA content (0.0036 %) was not improved. SA production in MS medium with 0.274 mM nitrate (0.004 %) was enriched 12-fold (0.0003 %) in relation to that of the wild plant. The anti-inflammatory effects at 5 h of intraperitoneal (i.p.) administration (100 mg per kg BW) of dichloromethane extracts from the medium (42 ± 3 %) and biomass (39 ± 9.3 %) of S. angustifolia cell suspensions cultivated in MS with 2.74 mM nitrate were similar. The effect of the biomass dichloromethane extract was dose dependent with a median Effective Dose (ED₅₀) of 137.63 mg per kg BW.     

Silicon reduces aluminum accumulation and mitigates toxic effects in cowpea plants

Aluminum (Al) is the third most abundant metal in the Earth’s surface, and Al toxicity promotes several negative effects in plant metabolism. Silicon (Si) is the second most common mineral in soil and is considered a beneficial element for plants, improving their tolerance to biotic and abiotic stresses. The aim of this study is to determine whether Si can reduce the accumulation of Al, explain the possible contribution of Si in mitigating Al toxicity, and indicate the better Si dose–response for cowpea plants. The experiment had a factorial design with two levels of aluminum (0 and 10 mM Al) and three levels of silicon (0, 1.25 and 2.50 mM Si). The utilization of Si in plants exposed to Al toxicity contributed to significant reductions in the Al contents of all tissues, corresponding to reductions of 51, 29 and 41% in roots, stems and leaves, respectively, upon treatment with 2.50 mM Si + 10 mM Al compared to the control treatment (0 mM Si + 10 mM Al). Al toxicity promoted decreases in Φ_PSII, q_P and ETR, whereas 2.50 mM Si induced increases of 54, 185 and 29%, respectively. Plants exposed to Al had lower values of P _N, WUE and P _N/C _i, whereas Si application at a concentration of 2.50 mM yielded improvements of 53, 32 and 67%, respectively. Al exposure increased SOD, CAT, APX and POX activities, whereas treatment with 2.50 mM Si + 10 mM Al produced significant variations of 72, 97, 48 and 32%, respectively, compared to 0 mM Si + 10 mM Al. Our results proved that Si reduced the Al contents in all tissues. Si also improved the photochemical efficiency of PSII, gas exchange, pigments and antioxidant enzymes, contributing to a reduction in the accumulation of oxidative compounds. These benefits corroborate the multiple roles exercised by Si in metabolism and reveal that Si immobilizes the Al in roots and reduce the accumulation of this metal in other organs, mitigating the damage caused by Al in cowpea plants. In relation to dose–response, plants exposed to 1.25 mM Si without Al presented better results in terms of growth, whereas the toxic effects of plants exposed to Al were mitigated with 2.50 mM Si.     

Silicon nutrition alleviates the lipid peroxidation and ion imbalance of <Emphasis Type="Italic">Glycyrrhiza uralensis</Emphasis> seedlings under salt stress

Soil salinity reduces growth of Glycyrrhiza uralensis in arid and semi-arid areas of north-west in China. Silicon (Si) nutrition may alleviate salt stress in many crops including grain crop, fruit crop, and vegetable crop. In this study, the alleviating effects of Si on growth characteristics, antioxidant enzyme activity (SOD and POD) and MDA concentration, and K⁺ and Na⁺ concentrations in G. uralensis seedlings subjected to 50 mM NaCl stress were investigated. The results showed that NaCl stress imposed significant reduction in root length, secondary root number, leaf number, and stem and total dry weight of G. uralensis. NaCl stress also significantly reduced the activities of SOD and POD, and ration of K⁺/Na⁺, but significantly increased MDA concentration in leaves of G. uralensis seedling. The addition of Si increased SOD and POD activities, and reduced MDA concentration, which resulting in greater reactive oxygen species detoxification and lower lipid peroxidation. Si also significantly increased the ratio of K⁺/Na⁺ in stem and leaves of G. uralensis. In conclusion, Si could alleviate adverse effects of salt stress probably by decreasing Na⁺ concentration and improving antioxidant enzyme activity of G. uralensis, and these alleviating effects were dependent on Si concentration and on Si processing time.     

Silicon increases salt tolerance by influencing the two-phase growth response to salinity in wheat (Triticum aestivum L.)

Salt usually stresses plants in two ways, osmotic stress and ion toxicity. Plant responds to salinity in two distinct phases through time. It is known that silicon (Si) could alleviate salt stress by decreasing the Na⁺ accumulated in the leaf. In order to determine the function of Si in the two-phase growth response (osmotic and ion toxicity) to salinity, we selected the wheat cultivar “Changwu 134” out of 10 wheat cultivars, and confirmed that it responds to salinity in two distinct phases through time. The fresh weight, leaf area, and leaf Na⁺ concentration were measured during 31 days of 120 mM NaCl supplemented with 1 mM Si treatment. The results revealed that the growth of plants under salinity conditions both with and without Si application were in accordance with the two-phase growth model. Si alleviated the salt stress in the both two-phase growth, but the alleviative effects were more pronounced in the osmotic stress phase than ion toxicity phase. These results clearly showed that Si can enhance plant salt tolerance by alleviating the salt-induced osmotic stress.     

Growth and Fatty Acid Composition of Borage (Borago officinalis L.) Leaves and Seeds Cultivated in Saline Medium

The effects of salinity on growth and fatty acid composition of borage (Borago officinalis L.) leaves and seeds grown in hydroponic medium were investigated. Three different levels of NaCl (25, 50, and 75 mM) were applied. The first results showed that salinity significantly reduced plant growth by 56.5 % at 75 mM compared with the control, suppressed seed yield at 50 and 75 mM, and increased lipid peroxidation. Raising NaCl concentrations led to an important decrease in total fatty acid (TFA) content by 77 % at 75 mM NaCl. Moreover, the polyunsaturated fatty acid (PUFA) content decreased, whereas the saturated fatty acids increased with respect to increasing salinity. The 25 mM NaCl level did not modify the fatty acid composition of seeds and their contents.     

<Emphasis Type="Italic">In vitro</Emphasis> regeneration of <Emphasis Type="Italic">Melothria maderaspatana</Emphasis> via indirect organogenesis

An effective protocol was developed for in vitro regeneration of the Melothria maderaspatana via indirect organogenesis in liquid and solid culture systems. Organogenesis was achieved from liquid culture calluses derived from leaf and petiole explants of mature plants. Organogenic calluses (98.2?±?0.36 and 94.8?±?0.71%) were induced from both leaf and petiole explants on Murashige and Skoog (MS) liquid medium containing 6.0 µM 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.5 µM thidiazuron (TDZ); and 6.0 µM 2,4-D and 1.0 µM benzyladenine (BA) combinations, respectively. Adventitious shoot regeneration (68.2?±?0.06 shoots per explant) was achieved on MS medium supplemented with 2.0 µM BA, 4.0 µM TDZ, 10% v/v coconut water and 0.06 mM glutamine from leaf-derived calluses. Petiole-derived calluses produced adventitious shoots (45.4?±?0.09 shoots per explant) on MS medium fortified with 2.0 µM BA, 4.0 µM TDZ, 10% v/v coconut water, and 0.08 mM glutamine. Elongation of shoots occurred in MS medium with 2.0 µM gibberellic acid (GA₃). Regenerated shoots (2–3 cm in length) rooted (74.2?±?0.38%) and hardened (85?±?1.24%) when they were transferred to 1/2-MS medium supplemented with 3.0 µM indole-3-butyric acid (IBA) followed by garden soil, vermiculate, and sand (2:1:1 ratio) mixture. The elongated shoots (4–5 cm in length) were exposed simultaneously for rooting as well as hardening (100%) in moistened [(1/8-MS basal salt solution with 5 µM IBA and 100 mg l^?1 Bavistin® (BVN)] garden soil, vermiculate, and sand (2:1:1 ratio) mixture. Subsequently, the plants were successfully established in the field. The survival percentage differed with seasonal variations.     

Methyl jasmonate regulated diploid and tetraploid black locust (<Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> L.) tolerance to salt stress

Methyl jasmonate (MeJA) is an essential and promising plant growth regulation factor that can improve plant development and growth. Here, we explored the mechanism by which MeJA regulates the tolerance of black locust (Robinia pseudoacacia L.) to salt stress. In this study, diploid and tetraploid R. pseudoacacia were subjected to three treatments: 500 mM NaCl; 100 μM MeJA; and 500 mM NaCl and 100 μM MeJA, and the changes in plant growth, endogenous MeJA levels and the anti-oxidative metabolism of leaves were investigated. The results showed that salt stress significantly inhibited plant growth and induced the accumulation of Na⁺ and Cl^? ions, malondialdehyde (MDA) content and reactive oxygen species. However, these adverse effects could be alleviated by applying MeJA, which was followed by a marked increase in the activities of antioxidant enzymes. In addition, some genes encoding several antioxidant enzymes were also up-regulated. Simultaneously, the endogenous MeJA content in MeJA-treated plants was lower than in salt-treated plants. It is noteworthy that tetraploids always possessed higher salt tolerance and obtained greater positive effects from MeJA than diploids. These results suggested that MeJA might play a protective role in defense responses, enabling diploid and tetraploid black locust, especially tetraploid, to better tolerate the adverse effects of salt stress.     

模拟酸雨对毛竹叶片抗氧化酶活性及释放绿叶挥发物的影响

为了探讨酸雨胁迫与毛竹(Phyllostachys pubescens)绿叶挥发物(green leaf volatiles, GLVs)释放规律以及抗氧化酶活性的关系, 通过盆栽试验, 采用不同pH值(5.6、4.0、2.5)的模拟酸雨对毛竹三年生实生苗进行处理, 研究酸雨对毛竹叶片可溶性蛋白质含量、丙二醛(MDA)含量和抗氧化酶活性的影响, 并采用热脱附/气相色谱/质谱联用技术对毛竹释放的GLVs成分和含量进行分析。结果表明: 酸雨胁迫下毛竹叶片MDA含量明显增加, pH 2.5模拟酸雨胁迫处理45天毛竹叶片MDA含量与对照相比增加了43.0% (p < 0.01); pH 4.0处理MDA含量增加缓慢, 处理75天时MDA含量比对照增加了0.36倍(p < 0.01)。pH 4.0和pH 2.5模拟酸雨胁迫处理45天时, 毛竹叶片可溶性蛋白质含量极显著增加, 与对照相比分别增加了32.0%和65.0% (p < 0.01)。在酸雨胁迫下, 毛竹叶片超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)的响应时间存在一定差异, 表现为互相协调, pH 2.5模拟酸雨胁迫处理SOD活性和POD活性分别在45天和60天时达到最大值, 分别为对照的1.67倍和1.31倍(p < 0.01), 随后降低。pH 4.0和pH 2.5模拟酸雨胁迫处理, 毛竹叶片GLVs含量比对照分别增加26.4%和132.9% (p < 0.01), 新增GLVs为 (E)-2-辛烯醛、2-乙基己醛、(E)-2-己烯醛和(E)-2-壬烯醛。研究表明: 酸雨胁迫条件下, 毛竹可以通过调节保护酶活性、可溶性蛋白质含量和释放GLVs来提高适应环境的能力。     

Silicon does not always mitigate zinc toxicity in maize

We have investigated the influence of silicon on higher zinc concentration reducing the growth of aboveground parts by ca 50 % in young maize plants (hybrid Novania) grown in hydroponics. Eight different treatments were used: control, Zn (800 μM ZnSO₄·7H₂O), Si1/Si2.5/Si5 (1/2.5/5 mM Na₂SiO₇) and Zn+Si (combination of zinc and all silicon concentrations). The concentration of Zn and Si and their distribution in plants was determined. The growth parameters (length of primary seminal root, leaf area of first and second leaves, fresh and dry weight of below- and above-ground plant parts) of plants grown in various Zn+Si treatments were significantly decreased in comparison to all other treatments. Increasing concentration of Si in combination with Zn treatment and selected hybrid (Novania) resulted in increased physiological stress in comparison to Zn treatment. However, roots and shoots of all Zn+Si treated plants contained significantly lower amount of Zn than Zn treatment. The Si concentration in roots was the same in Si and Zn+Si plants. In general, higher amount of Si was observed in shoots than in roots of Si1- and Si2.5-treated plants and opposite was observed in Si5-treated plants. In spite of significantly decreased root and shoot accumulation of Zn in the presence of Si, no positive effect of Si on Zn toxicity in young maize plants under experimental conditions used in this work and used maize hybrid was observed.