Search

Freeze‐drying (FD) is a useful technique for removing water from biological tissues, such as food samples. Cellular components freeze at once, and the ice sublimates under conditions of high vacuum and low temperatures. Because biological activity is restricted during FD, the degradation of cellular metabolites is often believed to be limited. However, the cellular structure is damaged by several factors, such as the increase in cell volume during freezing, and this has serious effects on the levels of some cellular metabolites. We studied these effects of FD on metabolite levels when using it as a sample preparation step in metabolome analysis. We observed significant decreases in the levels of some metabolites, such as succinate and choline, in Arabidopsisand pear, respectively. We also found that the effects of FD on certain metabolite levels differed between Arabidopsisplants and pear fruits. These results suggest that it is necessary to confirm the metabolite recovery in each sample species when FD is used for sample preparation.

The mode of action of a potent elicitor, N-acetylchitooligosaccharide, in rice plants was examined. In intact seedlings, no significant uptake of the elicitor viathe roots was observed within 3 h, whereas rapid uptake was observed in excised leaves. Rapid and transient expression of an elicitor-responsive gene, EL2, was induced in the leaves of intact seedlings sprayed with the elicitor or in the roots and leaves of intact seedlings by immersing roots in the elicitor solution. Histochemical analysis indicated that EL2was expressed in cells exposed to the elicitor of root and leaves. In seedlings treated with the elicitor for 1 d or longer, hyphal growth of rice blast fungus was significantly delayed, and an accumulation of auto-fluorescence around the infection site was observed. Two defense-related genes, PR-1and PR-10(PBZ1), were induced in a systemic and local manner by elicitor treatment, in correlation with the induction of resistance against rice blast fungus. N-Acetylchitoheptaose did not inhibit the hyphal growth of the fungi. These results indicate the occurrence of systemic signal transmission from N-acetylchitooligosaccharide in rice plants.

Several types of jasomonic acid (JA) derivatives, including JA–amino acid conjugates, a JA–biotin conjugate, a JA–dexamethasone heterodimer, and a JA–fluoresceine conjugate, were prepared as candidates for molecular probes to identify JA-binding proteins. These JA derivatives, excepting the JA–fluoresceine conjugate, exhibited significant biological activities in a rice seedling assay, a rice phytoalexin-inducing assay, and/or a soybean phenylalanine ammonia-lyase-inducing assay. These JA derivatives could therefore be useful probes for identifying JA-binding proteins. The activity spectra of the prepared compounds were different from each other, suggesting that different types of JA receptors were involved in the perception of JA derivatives in the respective bioassays.

Light is critical for supplying carbon for use in the energetically expensive process of nitrogen-fixing symbiosis between legumes and rhizobia. We recently showed that root nodule formation in phyBmutants [which have a constitutive shade avoidance syndrome (SAS) phenotype] was suppressed in white light, and that nodulation in wild-type is controlled by sensing the R/FR ratio through jasmonic acid (JA) signaling. We concluded that the cause of reduced root nodule formation in phyBmutants was the inhibition of JA-Ile production in root. Here we show that the shoot JA-Ile level of phyBmutants is higher than that of the wild-type strain MG20, suggesting that translocation of JA-Ile from shoot to root is impeded in the mutant. These results indicate that root nodule formation in phyBmutants is suppressed both by decreased JA-Ile production, caused by reduced JAR1 activity in root, and by reduced JA-Ile translocation from shoot to root.

The jasmonic acid (JA)-responsive gene RERJ1isolated from suspension-cultured rice cells encodes a transcription factor with a basic helix-loop-helix motif. In this study, we found that RERJ1is also expressed in rice plants in response to JA, and that its expression in rice leaves is up-regulated by exposure to wounding and drought stress. It is also suggested that JA but not abscisic acid is involved in the up-regulation of RERJ1expression caused by wounding and drought stress.