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Light qualities are thought to affect many plant physiological processes during growth and development. To investigate how light qualities influence tomato ( Solanum lycopersicum ) seedlings, the present study evaluated the effects of different light qualities generated by light emitting diodes (LEDs) with the same photosynthetic photon flux density (PPFD), including monochromic light red (657 nm, R), blue (457 nm, B), purple (417 nm, P) or white (W), combination of R and B lights (R:B = 1:1, 1R1B and R:B = 3:1, 3R1B) on the net photosynthetic rate (Pn), growth rate, carbohydrate content and sucrose-metabolizing enzyme activities. The results showed that relative to W, the seedling plant height and stem diameter were significantly promoted by combination of R and B lights and monochromic R light. However, the level of root growth was lower under R and P light, and the seedling growth and Pn were significantly suppressed under the latter. Additionally, R light significantly increased the contents of fructose and glucose, and combination of R and B lights significantly enhanced total carbohydrate, starch and sucrose accumulation, especially for 3R1B treatment. Activity of sucrose synthase (SS) was promoted under the different treatments and reached its highest value under 3R1B, which appeared to be a major contributor to the significantly higher content of starch under this treatment. Furthermore, R, B and P light reduced activity of sucrose phosphate synthase (SPS). Activities of acid invertase (AI) and neutral invertase (NI) were significantly increased by R light, but were markedly reduced under P. The results presented here indicated that monochromic R and combination lights 3R1B, could regulate the plant morphology and photosynthesis by the effects on the metabolism of carbohydrate into fructose, glucose, sucrose and starch, mainly through the enhanced activities of AI and NI under the former treatment, while SS and SPS in the latter treatment, respectively. They also improved the end-product output in tomato leaves, and may ultimately improve the yield and quality of tomato fruit.

Melatonin, as an indoleamine molecule, is involved in multiple physiological processes in plants. In this study, the effects of exogenous melatonin on plant growth, reactive oxygen metabolism and ion homeostasis in alkaline-treated tomato seedlings were investigated. Alkaline stress caused much lower level in maximum photochemistry efficiency of PSII (Fv/Fm), chlorophyll content, the activity of antioxidant enzymes and biomass accumulation of tomato plants, accompanied by the reactive oxygen species (ROS) burst, lipid peroxidation and membrane damage. The exogenous melatonin could increase tomato plants tolerance to sodic alkaline stress, and the effect depended on the concentration. In the experiment, treatment with 0.5 μM melatonin showed the strongest powerful effect on promoting tomato plant growth under alkaline stress and reducing oxidative stress via inducing activities of antioxidant enzymes and accumulations of ascorbic acid (AsA) and glutathione (GSH), which could be partly responsible for protecting chlorophyll from degradation and keeping higher Fv/Fm. Furthermore, we found that melatonin treatment decreased Na + content and increased K + content in tomato leaves under alkaline stress, which showed the ion homeostasis maintenance by melatonin also played important role in enhancing tomato tolerance to alkaline stress

Toxicity of garlic straw to Meloidogyne incognita under lab conditions and pots of tomato was studied. Results indicated that the immobility and mortality of M. incognita juveniles were significantly increased with increasing water extract concentrations of 1%, 2% and 4% (w/v) raw garlic straw, and hatchability was significantly inhibited by application of the extract. 2% fermenting garlic straw increased mortality of M. incognita rate from 9.8% to 36.6% when compared with 2% raw garlic straw in different treatment time. While the effect of fermented garlic straw was greatly lower in toxic activity, about 11.4–49.4% lower in mortality of M. incognita in different treatment time. Pot trials also showed that M. incognita infestation of tomato roots was dramatically reduced with increasing volume of raw garlic straw application, however, higher concentration also inhibited the tomato plant growth, this might be due to the allelopathy compounds from garlic straw. Based on the analysis of above results, 2% raw garlic straw was chosen to combine with plastic film covering and rabbit manure, and it was obtained that the combinations of 2% raw garlic straw application before planting, animal manures and plastic film covering are an effective method in both inhibiting M. incognita incidence and increasing yield of tomato, which could decrease 72.39% in galling index (GI) and increase 72.64% in tomato yield when compared with control treatment. To make clear possible mechanism of garlic straw protecting tomato from M. incognita infestation, GC–MS were used to investigate the compounds constituents, and sulfur-containing compounds mainly accounted for the constituents and they might be responsible for the inhibition of M. incognita .

Detrimental effects of NaCl and NaHCO3 stress on tomato plants were compared. With increasing stress intensity, accumulation of biomass in tomato shoots and roots significantly decreased in both NaCl and NaHCO3 treatments. Compared to NaCl stress, NaHCO3 stress showed greater reduction of tomato plant growth, which was in accordance with stronger inhibition of photosynthesis by NaHCO3 stress. Chlorophyll (Chl) contents, the ratio of the variable fluorescence to the maximum fluorescence (Fv/Fm) and the actual quantum efficiency of photosynthetic system II (ФPSII) declined with increasing concentration of NaCl and NaHCO3, and their decreasing degree was more significant in NaHCO3 treatment. On the contrary, higher non-photochemical quenching (NPQ) was observed with increasing concentration of NaCl and NaHCO3, especially in NaHCO3 treatment. Na content in tomato leaves was positively correlated with NaCl and NaHCO3 stress intensity, while contents of K, P, and N as well as nitrogen metabolism-related enzymes including nitrate reductase (NR), glutamine synthetase (GS), glutamate dehydrogenase (GDH) and glutamate synthase (GOGAT) showed significant negative correlation with stress intensity, and their changes were much higher in NaHCO3 treatment than in NaCl treatment. Both NaCl and NaHCO3 stress induced excess reactive oxygen species (ROS) accumulation and obvious lipid peroxidation in tomato leaves, though was much higher in the NaHCO3 treatment. Compared to catalase (CAT) and guaiacol peroxidase (GPX), superoxide dismutase (SOD) and the ascorbate–glutathione cycle components including ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) showed higher levels, which could play an important role in scavenging ROS in tomato leaves under salt and alkali stress.

a b s t r a c t Alkali stress is a major factor that limits crop yield, and nitric oxide (NO) is involved in the regulation of plants tolerant to abiotic stress. In the present study, sodium nitroprusside (SNP), a NO donor, reversed the chlorosis of cucumber leaves caused by alkali stress. Physiological analysis indicated that application of SNP protected mesophyll cell ultrastructure from damage by alkali stress. SNP increased nutrient element utilization, pigment content, photosynthetic capacity and accumulation of organic acids. In this study, Solexa sequencing was used to investigate the effect of SNP on expression of genes involved in cucumber response to alkali stress. About 5.9 million (M) and 5.8 M 21-nt cDNA tags were sequenced from the cDNA library of the alkali treatment and SNP treatment, respectively. When annotated, a total of 10,271 genes for the alkali stress treatment from the Solexa sequencing tags and 10,288 genes for SNP treatment were identified. We detected 901 differentially expressed genes in two samples, of which 437 and 464 of them were up- or down-regulated by SNP under alkali stress, respectively. The expression levels of 11 differentially expressed genes were confirmed by real-time RT-PCR. The trends observed agreed well with the Solexa expression profiles, although the degree of change was diverse in amplitude. Gene ontology analysis revealed that differentially expressed genes were mainly involved in response to abiotic stress, cellular metabolic process, photosynthesis, transmembrane transportation and organelle development, which were in accordance with physiological results.

Excessive accumulation of reactive oxygen species (ROS) under salt stress can cause oxidative damage, nitric oxide (NO) is considered as a functional molecule in alleviating salt stress to plants through modulating antioxidant metabolism. In the present experiment, effects of sodium nitroprusside (SNP), a NO donor, on the growth, and antioxidant capacity of cucumber hypocotyls and radicles as well as root tip ultrastructure were studied under 100 mM NaCl stress. NaCl treatment significantly induced accumulation of H 2 O 2 and thiobarbituric acid-reactive substances (TBARS) in cucumber hypocotyls and radicles, and application of 100 μM SNP stimulated ROS-scavenging enzymes and increased α,α-diphenyl-β-picryllhydrazyl (DPPH) scavenging activity, chelating activity of ferrous ions and hydroxyl radical (OH ) scavenging activity, resulting in lower lipid peroxidation induced by NaCl stress. The ultrastructure of the root tip cells was investigated, NaCl stress induced disturbance of mitochondria and the cell wall, and SNP treatment alleviated the ultrastructure disturbance induced by NaCl stress. The above effects of SNP were reversed by addition of hemoglobin (a NO scavenger), which indicated that the function of SNP alleviating lipid perioxidation in NaCl-treated cucumber hypocotyls and radicles depended on NO. Therefore, it can be concluded that the increasing antioxidant capacity by NO might be greatly responsible for its function in alleviating the inhibition of cucumber hypocotyls and radicles growth and cell ultrastructure damage by salt stress.

Phospholipase D (PLD; EC3.1.4.4) is thought to have a crucial role in plant signal transduction. Here, a full-length cDNA clone encoding PLD was isolated from cucumber ( Cucumis sativus L.) by RT-PCR and RACE. The 2756-bp full-length cDNA sequence of cucumber PLD ( CsPLD ) contains an open reading frame of 2427 bp encoding 808 amino acids. The deduced amino acid sequence showed high sequence similarities with PLDs from other plant species. According to the phylogenetic analysis, CsPLD belongs to PLDα group and contains two characteristic HKD motifs, one IYIENQFF motif and one C2 domain. The tertiary structure of the CsPLD protein was also predicted and found to be composed mainly of random coils. In both the salt-tolerant ‘Xintaimici’ and salt-sensitive ‘Shennongchunwu’ cultivars, CsPLD expression differed among roots, stems, leaves, flowers and mature fruit; expression was highest in leaves and lowest in fruit. The transcript level of CsPLD in salt-tolerant cucumber was higher than that in the salt-sensitive cucumber plants after 182 mmol L −1 nitrate treatment. CsPLD expression in both Xintaimici and Shennongchunwu increased with increasing nitrate concentration, although CsPLD mRNA expression in roots of Shennongchunwu peaked at 140 mmol L −1 nitrate and then decreased. In addition, CsPLD expression was induced in leaves of both cultivars by various treatments, including abscisic acid, salicylic acid, NaCl, drought and low temperature; however, there was no significant induction in its expression following treatment for 30 min with either H 2 O 2 or high temperature. In roots, there was a significant increase in CsPLD expression following all treatments in both cultivars, except in the roots of Xintaimici in response to H 2 O 2 . These results suggest that, in cucumber, PLD functions under conditions of excess nitrate and other abiotic stresses.

Mitogen-activated protein kinase (MAPK) cascades play a key role in plant growth and development as well as biotic and abiotic stress response. To unravel the roles of MAPK in cucumber, its expression in transgenic cucumber plants was reduced by an antisense approach. For this purpose, a 1113 bp cDNA fragment of cucumber MAPK gene ( CsNMAPK ) was expressed in antisense orientation driven by the 35S promoter of cauliflower mosaic virus. The pBI-CsNMAPK plasmid DNA was introduced into cucumber embryo by the pollen-tube pathway method. All seeds were sown in the soil and screened for transformants with kanamycin, polymerase chain reaction (PCR), Northern blot and real-time quantitative reverse transcriptative PCR (RT-PCR) analysis. Two independent transgenic plants were obtained and analyzed. The results showed that the transgenic cucumber plants exhibited retarded growth. The transgenic plant height was shorter and the leaves were smaller. Transgenic cucumber plants suppression CsNMAPK were more sensitive to salt stress than the wild-type (WT) plants. The fresh weight of shoot of the transgenic plants decreased more than WT after 50 mM NaCl treatment for 7 days. The malondialdehyde (MDA) content was higher, while the superoxide dismutase (SOD) activity and proline accumulation were lower in the transgenic plants than the WT plants after NaCl stress treatment. The evidence indicated that CsNMAPK was involved in positive regulation of reactive oxygen species (ROS) scavengence and osmotic adjustment under salt stress.

The effects of silicon (Si) application on plant growth, pigments, photosynthetic parameters, chlorophyll a (Chl a) fluorescence parameters and nitrogen metabolism were studied in Cucumis sativus L. under cadmium (Cd) toxicity. Compared with the control, 100 μM CdCl2 treatment caused dramatic accumulation of Cd in cucumber leaves, greatly induced chlorosis, and the transmission electron microscope (TEM) analysis indicated that Cd treatment cucumber chloroplast showed obvious swollen, thylakoids and chloroplast membrane were seriously damaged, and could not be observed clearly. Application of Si reversed the chlorosis, protected the chloroplast from disorganization, and significantly increased the pigments contents, which might be mainly responsible for the higher photosynthetic rate and accumulation of biomass under Cd stress. Further investigation of chlorophyll a fluorescence indicated that Cd treatment decreasing photosynthesis was not due to stomatal restriction, while was closely related integrity damage or function lost of the photosynthetic machinery which can be concluded from the higher intercellular CO2 concentration (Ci) and lower Fv/Fm and ΦPSII. Application of Si alleviated the inhibited level of photosynthesis and Fv/Fm and ΦPSII by Cd, which might imply that Si plays important roles in protecting photosynthetic machinery from damaging. The Cd treatment also greatly inhibited the enzymes of nitrogen metabolism including nitrogen reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH), and Si supply decreased the inhibiting effects of Cd.

Mitogen-activated protein kinases (MAPKs) play important roles in the transduction of extracellular signals to the intracellular targets in all eukaryotes. Here, a cucumber cDNA designated CsNMAPK, encoding a mitogen-activated protein kinase was isolated using RT-PCR, 3′ and 5′ RACE. The full-length cDNA sequence contains 1636 bp and an open reading frame (ORF) of 1113 bp, which encodes 370 amino acid residues. According to the phylogenetic analysis, CsNMAPK belongs to subgroup I MAPK in plants. Northern blot analysis revealed that CsNMAPK expressed differently in response to excess NO3−. And the CsNMAPK expression kinetics between a salt-resistant cultivar (Xintaimici) and a salt-sensitive cultivar (Shennongchunwu) was slightly different under 182 mmol L−1 NO3− treatment. The mRNA levels also increased after 24 h treatments with H2O2 and salicylic acid (SA), but decreased with abscisic acid (ABA) and low-temperature. However, there was no significant induction of CsNMAPK gene after 24 h drought and high-temperature treatments. Our results suggested that a MAP kinase cascade may function in excess NO3− and other abiotic stresses in cucumber.