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1.
J Plant Physiol ; 231: 364-373, 2018 Dec.
Article in English | MEDLINE | ID: mdl-30388676

ABSTRACT

Strategy I plants may respond to iron (Fe) deficiency by rhizosphere acidification. Here, the role of medium pH-values in silicon (Si)-induced mitigation Fe deficiency in Strategy I plants (Cucumis sativus) was investigated, particularly the metabolites regulated by a lack of Fe, using a target metabolomics approach. Plants were grown hydroponically, either with (+Fe) or in Fe-free (-Fe) nutrient solution, with (+Si) or without (-Si) a Si supply. The nutrient solution was adjusted to pH 5.0 or 6.0 and checked daily. Leaf metabolites potentially involved in Fe transport were determined. The typical Fe responses of cucumber (e.g., decrease in leaf chlorophyll, Fe imbalance) were more pronounced when plants were grown at pH 6.0 than 5.0, during long-term Fe deficiency (15 days). Major metabolites up-regulated by Fe deficiency and found in young leaf were succinic, citric and glutamic acids, respectively; their maximal concentrations occurred in Fe-starved plants grown at pH 6.0 without Si supply. Silicon (Si)-induced effects accompanied with alleviation chlorosis symptoms, were most distinct in plants grown at pH 6.0 for an extended period without Fe. Changes in abundance of metabolites specifically up-regulated by a lack of Fe may be manifested before any Si-induced changes in plant Fe content were apparent, suggesting that metabolite responses are highly sensitive to a Fe-dependent signal altered by Si treatments under Fe deficiency. The results indicate that Si supply was more evident when plants were more stressed by an increase in nutrient solution pH under Fe-limited conditions.


Subject(s)
Cucumis sativus/drug effects , Iron Deficiencies , Silicon/pharmacology , Chlorophyll/metabolism , Citric Acid/metabolism , Cucumis sativus/metabolism , Glutamic Acid/metabolism , Hydrogen-Ion Concentration , Hydroponics , Plant Leaves/drug effects , Plant Leaves/metabolism , Succinic Acid/metabolism
2.
J Plant Physiol ; 218: 100-108, 2017 Nov.
Article in English | MEDLINE | ID: mdl-28818756

ABSTRACT

Aluminium (Al) is one of the major stressors for plants in acidic soils, negatively affecting plant growth and nutrient balances. Significant efforts have been undertaken to understand mechanisms of Al tolerance in plants. However, little is known of the relevance of iron (Fe) and silicon (Si) nutrition under Al stress conditions. The objectives of this study were to determine whether effects induced by Fe and Si are of importance for limitation of Al moving via xylem in plants (Cucumis sativus L.). Cucumber plants (cv. Phoenix and Solovei) were grown (i) hydroponically in a complete nutrient solution at pH 4.0, either with (+Fe) or in Fe-free (-Fe) nutrient solution, without (-Si) or with (+Si) supply of Si, without (-Al) or with (+Al) exposure of Al and (ii) in soil. Xylem sap concentrations of Al, Fe and Si were measured. To characterise the pattern of xylem sap transport of Al and Fe, metabolomic changes of root tissues were investigated. Although the growth of cucumber plants was not significantly affected by Al3+ (Al-tolerant), Al exposure decreased xylem sap Fe (+Fe plants) and increased ferric chelate reductase (FC-R) activity of roots (-Fe plants). On the other hand, Fe supply greatly mitigated the Al-induced increase in xylem sap Al. The ameliorative effect of Fe depended on plant genotypes and was more pronounced in the more Fe-efficient cultivar Phoenix, which presented the highest level of xylem sap Fe. Xylem sap Fe was positively correlated with root serine, succinic and fumaric acids, suggesting that a probable underlying mechanism of Al tolerance might involve the chelation of Fe by biosynthesis of these chelating compounds. The Si-modulated root succinate increase appears to be of great importance for facilitating long-distance transport of Fe, thereby hindering Al transport from roots to shoots. The results highlight for the first time the importance of both Fe and Si supply in plant exclusion of Al under acidic conditions.


Subject(s)
Aluminum/metabolism , Cucumis sativus/physiology , Iron/metabolism , Silicon/metabolism , Soil/chemistry , Cucumis sativus/growth & development , Hydrogen-Ion Concentration , Plant Shoots/metabolism , Xylem/metabolism
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