Polyamines are phytohormones that regulate plant growth and development as well as the response to environmental stresses. To evaluate their functions in high-temperature stress responses, the effects of exogenous spermidine (Spd) were determined in tomato leaves using two-dimensional electrophoresis and MALDI-TOF/TOF MS. A total of 67 differentially expressed proteins were identified in response to high-temperature stress and/or exogenous Spd, which were grouped into different categories according to biological processes. The four largest categories included proteins involved in photosynthesis (27 %), cell rescue and defense (24 %), protein synthesis, folding and degradation (22 %), and energy and metabolism (13%). Exogenous Spd up-regulated most identified proteins involved in photosynthesis, implying an enhancement in photosynthetic capacity. Meanwhile, physiological analysis showed that Spd could improve net photosynthetic rate and the biomass accumulation. Moreover, an increased high-temperature stress tolerance by exogenous Spd would contribute to the higher expressions of proteins involved in cell rescue and defense, and Spd regulated the antioxidant enzymes activities and related genes expression in tomato seedlings exposed to high temperature. Taken together, these findings provide a better understanding of the Spd-induced high-temperature resistance by proteomic approaches, providing valuable insight into improving the high-temperature stress tolerance in the global warming epoch.

We investigated the effects of exogenous spermidine (Spd) on the carbohydrate, nitrogen (N), and endogenous polyamine status of tomato ( Solanum lycopersicum ) seedlings exposed to high-temperature stress [38/28 °C (day/night)]. High-temperature stress reduced the contents of pyruvate and succinate and inhibited plant growth. The application of exogenous Spd alleviated the inhibition of plant growth induced by high temperature, and also led to an increase in pyruvate, citrate, and succinate levels. High temperature markedly increased the NH 4 + -N content and reduced the activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate dehydrogenase (GDH). Spd significantly alleviated the negative effects on NH 4 + -N assimilation induced by high-temperature stress. Moreover, Spd significantly increased the activities of NR and GDH in the high-temperature-stressed tomato leaves. In contrast, Spd application to high-temperature-stressed plant leaves counteracted high-temperature-induced mRNA expression changes in N metabolism. Spd significantly upregulated the transcriptional levels of NR, nitrite reductase, GS, GDH, and glutamate synthase (GOGAT). In addition, exogenous Spd significantly increased endogenous polyamines. These results suggest that Spd could improve carbohydrate and N status through regulating the gene expression and activity of key enzymes for N metabolism, thus confers the tolerance to high temperature on tomato seedlings.

This study evaluated the effects of exogenous spermidine (Spd) on chlorophyll (Chl) biosynthesis and catabolism in the leaves of cucumber (Cucumis sativus L.) seedlings under high temperature stress. Substrate culture experiments were performed using the high temperature-sensitive variety ‘Jinchun No. 2’ in an artificial climate chamber at 42/32 °C with foliar applications of 1.0 mmol L−1 Spd. The results suggested that high temperature stress markedly reduced the leaf Chl concentrations and inhibited plant growth; the harmful effect of high temperature on the cucumber seedlings was mitigated by exogenous Spd, which increased the leaf Chl concentration and promoted plant growth. Under high temperature stress, the conversion of porphobilinogen (PBG) into uroporphyrinogen III (UroIII) in the Chl biosynthetic pathway and the catabolic process of Chl were accelerated. Following the application of exogenous Spd, the conversion of PBG into UroIII was suppressed, and the accumulation of certain intermediates, e.g., protoporphyrin IX (ProtoIX) and Mg-protoporphyrin IX (Mg-ProtoIX), was decreased in the Chl biosynthetic pathway. Additionally, exogenous Spd reduced chlorophyllase (Chlase) and Mg-dechelatase (MDCase) activity and transcript levels and markedly downregulated pheophorbide A oxygenase (PaO), red Chl catabolite reductase (RCCR), Chl b reductase 1 (CBR1) and stay-green reductase 1 (SGR1) transcript levels. These results indicate that although high temperature stress accelerated Chl biosynthesis, it concurrently facilitated Chl catabolism in cucumber leaves. Exogenous Spd delayed the conversion of PBG into UroIII in the Chl biosynthetic pathway, effectively preventing oxidative bleaching of Chl in cucumber leaves. Meanwhile, Spd clearly decreased PaO pathway-related enzyme activity and transcript levels, thereby slowing Chl catabolism and increasing Chl concentrations.

The effects of foliar spraying with spermidine (Spd) on antioxidant system in tomato (Lycopersicon esculentum Mill.) seedlings were investigated under high temperature stress. The high temperature stress significantly inhibited plant growth and reduced chlorophyll (Chl) content. Application of exogenous 1 mM Spd alleviated the inhibition of growth induced by the high temperature stress. Malondialdehyde (MDA), hydrogen peroxide (H2O2) content and superoxide anion (O2) generation rate were significantly increased by the high temperature stress, but Spd significantly reduced the accumulation of reactive oxygen species (ROS) and MDA content under the stress. The high temperature stress significantly decreased glutathione (GSH) content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), but increased contents of dehydroascorbic acid (DHA), ascorbic acid (AsA), and oxidized glutathione (GSSG) in tomato leaves. However, Spd significantly increased the activities of antioxidant enzymes, levels of antioxidants and endogenous polyamines in tomato leaves under the high temperature stress. In addition, to varying degrees, Spd regulated expression of MnSOD, POD, APX2, APX6, GR, MDHAR, DHAR1, and DHAR2 genes in tomato leaves exposed to the high temperature stress. These results suggest that Spd could change endogenous polyamine levels and alleviate the damage by oxidative stress enhancing the non-enzymatic and enzymatic antioxidant system and the related gene expression.

Our results based on proteomics data and physiological alterations proposed the putative mechanism of exogenous Spd enhanced salinity tolerance in cucumber seedlings.

[目的]本文的目的是研究外源24-表油菜素内酯(EBR)对低氧胁迫植株氮代谢的影响.[方法]以低氧耐性较弱的‘中农6号’黄瓜品种为材料,采用营养液通N2形成低氧逆境的方法,深入探讨了EBR对低氧胁迫下植株叶片和根系中与氮代谢相关的酶活性的影响.[结果]低氧处理显著降低了植株叶片的总氮含量,EBR使胁迫植株叶片总氮积累恢复至对照水平.低氧处理后,硝态氮含量在叶片中增加而在根系中降低,铵态氮的变化趋势与硝态氮相反,而EBR显著促进了胁迫植株根系的铵态氮积累.低氧胁迫下,植株根系硝酸还原酶(NR)和谷氨酰胺合成酶(GS)活性升高,随后恢复至对照水平,而谷氨酸合成酶(GOGAT)活性显著低于对照.叶片NR活性受到低氧抑制,亚硝酸还原酶(NiR)、GOGAT、氧化型谷氨酸脱氢酶(NAD+-GDH)活性则先升高,随后降低;叶片还原型谷氨酸脱氢酶(NADH-GDH)活性也受到低氧促进,至处理末期时显著高于对照植株.EBR显著提高了胁迫植株根系的NR活性及叶片的NiR、NAD+-GDH活性.[结论]黄瓜植株通过增强硝酸还原,加强氮代谢缓解低氧胁迫伤害;EBR通过增强根系NR活性及叶片NAD+-GDH活性,提高了植株的低氧耐性.