Nitrate Protects Cucumber Plants Against Fusarium oxysporum by Regulating Citrate Exudation.

Fusarium wilt causes severe yield losses in cash crops. Nitrogen plays a critical role in the management of plant disease; however, the regulating mechanism is poorly understood. Using biochemical, physiological, bioinformatic and transcriptome approaches, we analyzed how nitrogen forms regulate the interactions between cucumber plants and Fusarium oxysporum f. sp. cucumerinum (FOC). Nitrate significantly suppressed Fusarium wilt compared with ammonium in both pot and hydroponic experiments. Fewer FOC colonized the roots and stems under nitrate compared with ammonium supply. Cucumber grown with nitrate accumulated less fusaric acid (FA) after FOC infection and exhibited increased tolerance to chemical FA by decreasing FA absorption and transportation in shoots. A lower citrate concentration was observed in nitrate-grown cucumbers, which was associated with lower MATE (multidrug and toxin compound extrusion) family gene and citrate synthase (CS) gene expression, as well as lower CS activity. Citrate enhanced FOC spore germination and infection, and increased disease incidence and the FOC population in ammonium-treated plants. Our study provides evidence that nitrate protects cucumber plants against F. oxysporum by decreasing root citrate exudation and FOC infection. Citrate exudation is essential for regulating disease development of Fusarium wilt in cucumber plants.

Wang M ，Sun Y ，Gu Z ，Wang R ，Sun G ，Zhu C ，Guo S ，Shen Q ... -  《-》

Nitrate Increased Cucumber Tolerance to Fusarium Wilt by Regulating Fungal Toxin Production and Distribution.

Zhou J ，Wang M ，Sun Y ，Gu Z ，Wang R ，Saydin A ，Shen Q ，Guo S ... -  《Toxins》

Plant Primary Metabolism Regulated by Nitrogen Contributes to Plant-Pathogen Interactions.

Nitrogen contributes to plant defense responses by the regulation of plant primary metabolism during plant-pathogen interactions. Based on biochemical, physiological, bioinformatic and transcriptome approaches, we investigated how different nitrogen forms (ammonium vs. nitrate) regulate the physiological response of cucumber (Cucumis sativus) to Fusarium oxysporum f. sp. cucumerinum (FOC) infection. The metabolic profile revealed that nitrate-grown plants accumulated more organic acids, while ammonium-grown plants accumulated more amino acids; FOC infection significantly increased levels of both amino acids and organic acids in the roots of ammonium-grown plants. Transcriptome analysis showed that genes related to carbon metabolism were mostly up-regulated in plants grown with nitrate, whereas in ammonium-grown plants the up-regulated genes were mostly those that were related to primary nitrogen metabolism. Root FOC colonization and disease incidence were positively correlated with levels of root amino acids and negatively correlated with levels of root organic acids. In conclusion, organic acid metabolism and expression of related genes increased under nitrate, whereas ammonium increased the level of amino acids and expression of related genes; these altered levels of organic acids and amino acids resulted in different tolerances to FOC infection depending on the nitrogen forms supplied.

Wang M ，Gu Z ，Wang R ，Guo J ，Ling N ，Firbank LG ，Guo S ... -  《-》

Vinegar residue compost as a growth substrate enhances cucumber resistance against the Fusarium wilt pathogen Fusarium oxysporum by regulating physiological and biochemical responses.

Shi L ，Du N ，Yuan Y ，Shu S ，Sun J ，Guo S ... -  《-》

Wilted cucumber plants infected by Fusarium oxysporum f. sp. cucumerinum do not suffer from water shortage.

Fusarium wilt is primarily a soil-borne disease and results in yield loss and quality decline in cucumber (Cucumis sativus). The main symptom of fusarium wilt is the wilting of entire plant, which could be caused by a fungal toxin(s) or blockage of water transport. To investigate whether this wilt arises from water shortage, the physiological responses of hydroponically grown cucumber plants subjected to water stress using polyethylene glycol (PEG, 6000) were compared with those of plants infected with Fusarium oxysporum f. sp. cucumerinum (FOC). Parameters reflecting plant water status were measured 8d after the start of treatment. Leaf gas exchange parameters and temperature were measured with a LI-COR portable open photosynthesis system and by thermal imaging. Chlorophyll fluorescence and chloroplast structures were assessed by imaging pulse amplitude-modulated fluorometry and transmission electron microscopy, respectively. Cucumber water balance was altered after FOC infection, with decreased water absorption and hydraulic conductivity. However, the responses of cucumber leaves to FOC and PEG differed in leaf regions. Under water stress, measures of lipid peroxidation (malondialdehyde) and chlorophyll fluorescence indicated that the leaf edge was more seriously injured, with a higher leaf temperature and disrupted leaf water status compared with the centre. Here, abscisic acid (ABA) and proline were negatively correlated with water potential. In contrast, under FOC infection, membrane damage and a higher temperature were observed in the leaf centre while ABA and proline did not vary with water potential. Cytologically, FOC-infected cucumber leaves exhibited circular chloroplasts and swelled starch grains in the leaf centre, in which they again differed from PEG-stressed cucumber leaves. This study illustrates the non-causal relationship between fusarium wilt and water transport blockage. Although leaf wilt occurred in both water stress and FOC infection, the physiological responses were different, especially in leaf spatial distribution.

Sun Y ，Wang M ，Li Y ，Gu Z ，Ling N ，Shen Q ，Guo S ... -  《-》