鈴木 伸洋

Although positive effects of microwave irradiation on plants have been reported, their underlying mechanisms remain unknown. In this study, we investigated the effects of low microwave irradiation on Arabidopsis thaliana. Interestingly, we found low output (23 W) with oscillating condition (not continuous irradiation) promoted plant growth. The microwave irradiation neither raised the plants' temperature nor induced heat responsive gene expression. Furthermore, overall transcriptome profile in microwave irradiation treated plants were significantly different from heat treated plants, suggesting that growth promotion might be attributed to non-thermal effects of microwave. Transcriptome and metabolome analysis indicated that microwave irradiation altered circadian clock as well as hormonal response especially in auxin and gibberellin, which promoted plant growth by inducing amino acid biosynthesis and stress tolerance, and reducing cell wall thickness. This finding potentially contributes to develop new approach to increase food production through accelerating crop yield in environmentally friendly way.

Abstract Salt stress and waterlogging are two of the most common abiotic stresses in nature, often occurring concurrently. However, our understanding of the mechanisms underlying responses of plants to a combination of these stresses remains limited. In this study, we investigated growth, physiological and biochemical responses of Solanum lycopersicum cv. Micro‐Tom to salt stress, waterlogging and the combination of both. Under waterlogging individually, plants showed increased plant height and longer root length. However, they exhibited a significantly smaller leaf area, fewer leaves, reduced fresh and dry weights, and lower relative water content compared to plants grown under controlled conditions. These effects were more severe than those caused by salt stress alone. Interestingly, the growth inhibition from waterlogging was alleviated under combined salt and waterlogging stress. This attenuation may be associated with decreased accumulation of H₂O₂ and oxidized lipids, along with increased proline and photosynthetic pigment contents compared with waterlogging individually applied. However, ROS accumulations and contents of photosynthetic pigments were not straightforwardly linked to the activity of photosynthesis. In addition, activities of various antioxidant enzymes such as CAT, GPX and GST as well as those involved in the AsA‐GSH cycle were differently altered by salt stress and waterlogging, individually and in combination. Taken together, these results suggest that the response of tomato plants to salt stress and waterlogging, individually and in combination, can be differently modulated via fine‐tuning of acclimation mechanisms to oxidative stress.

Flooding causes severe yield losses worldwide, making it urgent to enhance crop tolerance to this stress. Since natural flooding often involves physical flow, we hypothesized that the effects of submergence on plants could change when combined with physical flow. In this study, we analyzed the growth and transcriptome of Arabidopsis thaliana exposed to submergence or flooding with physical flow. Plants exposed to flooding with physical flow had smaller rosette diameters, especially at faster flow rates. Transcriptome analysis revealed that “defense response” transcripts were highly up-regulated in response to flooding with physical flow. In addition, up-regulation of transcripts encoding ROS-producing enzymes, SA synthesis, JA synthesis, and ethylene signaling was more pronounced under flooding with physical flow when compared to submergence. Although H2O2 accumulation changed in response to submergence or flooding with physical flow, it did not lead to lipid peroxidation, suggesting a role for ROS as signaling molecules under these conditions. Multiple regression analysis indicated possible links between rosette diameter under flooding with physical flow and the expression of Rbohs and SA synthesis transcripts. These findings suggest that pathogen defense responses, regulated by SA and ROS signaling, play crucial roles in plant responses to flooding with physical flow.

Lipocalins constitute a conserved protein family that binds to and transports a variety of lipids while fatty acid desaturases (FADs) are required for maintaining the cell membrane fluidity under cold stress. Nevertheless, it remains unclear whether plant lipocalins promote FADs for the cell membrane integrity under cold stress. Here, we identified the role of OsTIL1 lipocalin in FADs-mediated glycerolipid remodeling under cold stress. Overexpression and CRISPR/Cas9 mediated gene edition experiments demonstrated that OsTIL1 positively regulated cold stress tolerance by protecting the cell membrane integrity from reactive oxygen species damage and enhancing the activities of peroxidase and ascorbate peroxidase, which was confirmed by combined cold stress with a membrane rigidifier dimethyl sulfoxide or a H2 O2 scavenger dimethyl thiourea. OsTIL1 overexpression induced higher 18:3 content, and higher 18:3/18:2 and (18:2 + 18:3)/18:1 ratios than the wild type under cold stress whereas the gene edition mutant showed the opposite. Furthermore, the lipidomic analysis showed that OsTIL1 overexpression led to higher contents of 18:3-mediated glycerolipids, including galactolipids (monoglactosyldiacylglycerol and digalactosyldiacylglycerol) and phospholipids (phosphatidyl glycerol, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine and phosphatidyl inositol) under cold stress. RNA-seq and enzyme linked immunosorbent assay analyses indicated that OsTIL1 overexpression enhanced the transcription and enzyme abundance of four ω-3 FADs (OsFAD3-1/3-2, 7, and 8) under cold stress. These results reveal an important role of OsTIL1 in maintaining the cell membrane integrity from oxidative damage under cold stress, providing a good candidate gene for improving cold tolerance in rice.

Due to recent global warming, heat stress can simultaneously occur with cadmium (Cd) stress in regions suffering from metal pollution. In this study, we investigated the effects of heat, Cd and their combination on the growth and physiological characteristics of Arabidopsis thaliana. Arabidopsis plants were more susceptible to a combination of heat and Cd stress than to each stress applied individually, although the accumulation of Cd in shoots was comparable between plants subjected to Cd stress and the combined stress. Plants subjected to this stress combination showed a dramatic reduction in the accumulation of the photosynthetic reaction center proteins in photosystem II as well as a tendency toward enhanced lipid peroxidation, suggesting that the negative effects of a combination of heat and Cd stresses might be caused by oxidative damage accompanied by damage to the photosynthetic apparatus. Interestingly, aos and lox3 mutants deficient in jasmonic acid (JA) synthesis showed attenuation of the negative effects caused by a combination of heat and Cd stresses on the growth and maximum quantum efficiency of photosystem II. The roles of JA might be altered when heat stress is combined with Cd stress, despite its significance in the tolerance of plants to Cd stress when individually applied, which has been shown in previous studies.