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Tomato (Solanum lycopersicon) is a widely produced and consumed fruit vegetable worldwide. Silicon (Si) and selenium (Se) can promote crop growth and development. However, the effects of these elements on tomato fruit quality have not been investigated comprehensively, nor are their combined effects on yield and quality clear. The aim of this study was to investigate the effects of foliar application of Si and Se on tomato growth, yield and fruit quality. The tomato plants were foliarly applied with 1 mM Si and 25 μM Se individually or in combination, and the experiment was carried out in a plastic arch shed at Yangling in spring. Our results demonstrated improved plant growth by application of Si and Se, with the effect of combined treatment being more obvious. Application of Si individually or in combination with Se increased the yield. Se addition increased the concentrations of soluble sugars, vitamin C, phenols, anthocyanin, lycopene, carotenoids, Se and protein, and decreased the nitrate level, but did not affect the concentration of total organic acids in the fruit. Si application induced similar changes to Se addition in the levels of sucrose and protein in the fruit, but had no effect on other quality traits. The combined Si and Se treatment did not show significant superior effects on the fruit quality over their individual applications. Our results suggest that Si and Se application improved the tomato plant growth. Si and Se application, respectively, had obvious effects in the yield increase and quality improvement, and the combined treatment had positive effects on both aspects. The study may provide a theoretical base for the application of Se and Si fertilizers in tomato production. [ABSTRACT FROM AUTHOR]

Background and Aims Silicon has been proven to exert beneficial effects on plant growth and stress tolerance, and silicon accumulation varies among different plant species. Cucumber (Cucumis sativus) is a widely used dicot model for silicon accumulation, but little is known about the molecular mechanism of its silicon uptake. Previously, we isolated and characterized CsLsi1, a silicon influx transporter gene from cucumber. In this study, we cloned a putative silicon efflux transporter gene, CsLsi2, from cucumber and investigated its role in silicon uptake. Methods The expression pattern, transport activity, and subcellular and cellular localizations of CsLsi2 were investigated. The transport activity of CsLsi2 was determined in Xenopus laevis oocytes. The subcelluar and cellular localizations were conducted by transient expression of fused 35S:: CsLsi2 - eGFP in onion epidermal cells and expression of ProCsLsi2:: CsLsi2 - mGFP in cucumber, respectively. Key Results CsLsi2 was mainly expressed in the roots. Expression of CsLsi2 - eGFP fusion sequence in onion epidermis cells showed that CsLsi2 was localized at the plasma membrane. Transient expression in Xenopus laevis oocytes showed that CsLsi2 demonstrated efflux but no influx transport activity for silicon, and the transport was energy-dependent. Expression of CsLsi2-mGFP under its own promoter revealed that CsLsi2 was mainly expressed on endodermal cells, showing no polar distribution. In combination with our previous work on CsLsi1, a model for silicon uptake in cucumber roots is proposed. Conclusion The results suggest that CsLsi2 is a silicon efflux transporter gene in cucumber. The coordination of CsLsi1 and CsLsi2 mediates silicon uptake in cucumber roots. This study may help us understand the molecular mechanism for silicon uptake in cucumber, one of the few dicots with a relatively high capacity for silicon accumulation. [ABSTRACT FROM AUTHOR]

Background and aims: The mechanism for silicon-mediated salt tolerance is still not very clear. The aim of this study was to investigate the possible role of silicon in regulating carbohydrate metabolism in cucumber ( Cucumis sativus L.). Methods: Two cucumber cultivars ('JinYou 1' and 'JinChun 5') grown hydroponically were subjected to 75 mM NaCl stress in the absence or presence of added silicon (0.3 mM). Plant growth, oxidative damage, chlorophyll fluorescence and carbohydrate metabolism were investigated. Results: Added silicon improved plant growth and photosynthetic performance, while alleviated oxidative damage of cucumber under salt stress. Salt stress increased the soluble sugar levels in both leaves and roots. Starch was accumulated in the leaves but decreased in the roots under salt stress. Added silicon decreased the soluble sugar levels in leaves through regulating the activities of carbohydrate metabolism enzymes. The starch content was decreased in leaves but increased in roots by added silicon under stress. Silicon addition increased the root sucrose content in 'JinYou 1' but decreased it in 'JinChun 5' under salt stress. Conclusions: Silicon-mediated decrease of assimilate accumulation in leaves may alleviate photosynthetic feedback repression, while silicon-enhanced assimilate transport provides more energy storage in the roots, which is beneficial for salt stress tolerance. [ABSTRACT FROM AUTHOR]

Soil salinity and drought are major abiotic factors that limit crop growth and productivity worldwide. Indeed, soil salinity and drought disrupt the cellular ionic and osmotic balance. Although silicon (Si) is generally considered nonessential for plant growth and developments, Si uptake by plants can alleviate both biotic and abiotic stresses. Silicon application could therefore improve crop production under adverse climate and soil conditions. Several reports have reviewed the benefits of silicon application on crop growth, but the mechanisms of silicon action have not been systematically discussed. Here, we review recent advances on silicon uptake, transport, and accumulation in plants and how silicon alleviates salinity toxicity and drought stress. The major points are the following: (1) both passive and active silicon uptake may coexist in plants; (2) although silicon transporters have been identified in some plants, more silicon transporters remain to be identified, and the process of silicon transport needs further clarification; (3) the mechanisms for silicon-mediated tolerance of salinity and drought have been extensively investigated at both physiological and biochemical levels. The physiological aspects include increasing water uptake by roots, maintaining nutrient balance, decreasing water loss from leaves, and promoting photosynthetic rate. At the biochemical level, silicon may improve antioxidant defense abilities by increasing the activities of antioxidant enzymes and the contents of non enzymatic antioxidants; silicon may also contribute to osmotic adjustment and increase photosynthetic enzymatic activities; and (4) silicon can regulate the levels of endogenous plant hormones under stress conditions, whereas silicon involvement in signaling and regulation of gene expression related to increasing stress tolerance remains to be explored. [ABSTRACT FROM AUTHOR]

Salt stress is a continuous threat to global crop production. Here, we studied the alleviation role of exogenous silicon (Si) in NaCl-stressed cucumber, with special emphasis on plant growth, proline (Pro) and hormone metabolisms. The results showed that Si supplementation ameliorated the adverse effects of NaCl on plants growth, biomass, and oxidative stress. Salt stress greatly increased the content of Pro throughout the experiment, while Si regulated Pro content in two distinct ways. Si promoted the salt-induced Pro levels after 3 and 6 days of treatment, but decreased it after 9 and 12 days of treatment. Moreover, P5CS and ProDH activities and P5CS gene play important roles in Si and salt-regulated Pro levels in different stress phase. Under stress condition, Si addition tend to revert the content of ABA, IAA, cytokinin and SA to the control levels in most cases. Further correlation analysis revealed a negative correlation between the root cytokinin and Pro content after 3 days of treatment, suggesting the interaction between cytokinin and Pro metabolism. Exogenous application of Pro and ProDH competitive inhibitor D-Lactate confirmed the possible interplay between Pro and cytokinin metabolism. Further study identified several CKX (Csa4G647490 and Csa1G589070) and IPT (Csa7G392940 and Csa3G150100) genes that may be responsible for the regulation of cytokinin accumulation by Si and/or Pro after short-term of treatment. The results suggested that Pro is a key factor in Si-induced salt tolerance, and Si-increased Pro content may participate in the regulation of cytokinin metabolism under short-term of salt stress. • Silicon regulates cucumber proline and cytokinin content through mediating related enzymes and gene expression. • Silicon tend to revert the content of plant hormone to the control levels. • Silicon-increased proline content may participate in the regulation of cytokinin metabolism. [ABSTRACT FROM AUTHOR]

Sucrose transporters (SUTs) are involved in the transmembrane transport of sucrose. The roles of SUTs in regulating stress tolerance of plants have been reported, but differential results were observed in different plants, implying the need for more studies in different plants. Moreover, the mechanism of SUTs in regulating stress tolerance is still poorly understood. Here, we investigated the role of SlSUT4 from tomato in regulating drought tolerance by using SlSUT4 -overexpressed and -RNAi plants. The results showed that SlSUT4 overexpression decreased the drought tolerance of plants, as demonstrated by reduced seed germination, decreased plant growth, photosynthesis and relative water content, and higher oxidative damage under osmotic stress or drought stress; whereas silencing of SlSUT4 increased the stress tolerance. In the control conditions, the leaf sucrose export rate was reduced in the overexpression plants, but promoted in the RNAi plants, and all transgenic lines had higher leaf sucrose concentrations than the wild type. Accumulation of soluble sugars was more obvious in SlSUT4 -overexpressed plants and the wild type than the RNAi plants under drought. Overexpressing SlSUT4 decreased the proportion of sucrose in the vacuole in the control conditions, whereas the RNAi plants showed an opposite change. These results suggest that alteration in SlSUT4 expression modulates sucrose vacuole-cytosol compartmentation, thus affecting the responses of tomato plants to drought stress. • Silencing SlSUT4 increased drought tolerance of tomato plants. • Overexpressing SlSUT4 decreased drought tolerance of tomato plants. • Silencing SUT4 increased leaf sucrose export while overexpression reduced the export. • Silencing SlSUT4 increased the sucrose proportion in the vacuole. • Overexpressing SlSUT4 increased the sucrose proportion in the cytosol. [ABSTRACT FROM AUTHOR]

The beneficial effects of silicon on plant growth and development under drought have been widely reported. However, little information is available on the effects of silicon on seed germination under drought. In this work, the effects of exogenous silicon (0.5 mM) on the seed germination and tolerance performance of tomato (Solanum lycopersicum L.) bud seedlings under water deficit stress simulated by 10% (w/v) polyethylene glycol (PEG-6000) were investigated in four cultivars (‘Jinpengchaoguan’, ‘Zhongza No.9’, ‘Houpi L402’ and ‘Oubao318’). The results showed that the seed germination percentage was notably decreased in the four cultivars under water stress, and it was significantly improved by added silicon. Compared with the non-silicon treatment, silicon addition increased the activities of superoxide dismutase (SOD) and catalase (CAT), and decreased the production of superoxide anion (O2P ) and hydrogen peroxide (H2O2) in the radicles of bud seedlings under water stress. Addition of silicon decreased the total phenol concentrations in radicles under water stress, which might contribute to the decrease of peroxidase (POD) activity, as observed in the in vivo and in vitro experiments. The decrease of POD activity might contribute to a less accumulation of hydroxyl radical (·OH) under water stress. Silicon addition also decreased the concentrations of malondialdehyde (MDA) in the radicles under stress, indicating decreased lipid peroxidation. These results suggest that exogenous silicon could improve seed germination and alleviate oxidative stress to bud seedling of tomato by enhancing antioxidant defense. The positive effects of silicon observed in a silicon-excluder also suggest the active involvement of silicon in biochemical processes in plants. [ABSTRACT FROM AUTHOR]

Abstract: Silicon can alleviate salt damage to plants, although the mechanism(s) still remains to be elucidated. In this paper, we report the effect of silicon on chloride transport in rice (Oryza sativa L.) seedlings in saline conditions. In the absence of salinity, silicon enhanced the growth of shoots, but not roots in three cultivars (cv. GR4, IR36, and CSR10). Salinity reduced the growth of both shoots and roots in all three genotypes. In saline conditions, addition of silicon to the culture solution again improved the growth of shoots, but not of roots. Under these saline conditions, the concentrations of chloride in the shoot were markedly decreased by adding silicon and the ratio of K+/Cl− was significantly increased, while the concentration of chloride in the roots was unchanged. The decrease in chloride concentration in the shoot was correlated with the decrease in transpirational bypass flow in rice, as shown by the transport of the apoplastic tracer trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS). Addition of silicon increased the net photosynthetic rate, stomata conductance, and transpiration of salt-stressed plants in cv. IR36, indicating that the reduction of chloride (and sodium) uptake by silicon was not through a reduction in transpiration rate. Silicon addition also increased the instantaneous water use efficiency of salt-stressed plants, while it did not change the relative growth rate of shoots. The results suggest that silicon addition decreased transpirational bypass flow in the roots, and therefore decreased the transport of chloride to the shoot. [Copyright &y& Elsevier]

• Silicon addition could delay salt stress-induced senescence in different plants. • Silicon addition increased the cytokinin levels in tomato leaves under salt stress. • Silicon addition increased IPT expression in tomato leaves under salt stress. • Inhibition of cytokinin synthesis abolished the effect of Si in delaying senescence. Silicon (Si) is beneficial for plant growth and development, and many studies have shown that Si can alleviate biotic and abiotic stress-induced plant damage. Although the alleviative effect of Si on plant damage induced by salt stress has been widely reported, the underlying mechanism is still not very clear. Here, the effect of Si on salt stress-induced leaf senescence and the role of cytokinin in this process were investigated. The results showed that added Si could significantly decrease chlorophyll degradation induced by salt treatment in tomato. Under salt stress, the effect of Si on the levels of indoleacetic acid and gibberellins in tomato was irregular and dependant on the Si treatment concentrations. Si addition increased the concentrations of cytokinins and abscicic acid, and the expressions of major cytokinin sysnthesis genes in leaf discs of tomato under salt stress. Cytokinin synthesis inhibitor abolished the ameliorative effect of Si on salt-induced leaf senescence of tomato. Si could alleviate salt-induced senescence in the leaves of wild type Arabidopsis thaliana but not in the ipt1,3,5,7 mutant, which has very little amount of cytokinin. These results suggest that Si can delay salt stress-induced plant senescence by increased cytokinin synthesis. This study may help us further explore the in planta mechanism for Si-mediated stress tolerance in plants. [ABSTRACT FROM AUTHOR]