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Key message: The inhibitory effect of eugenol on rice germination is mediated by a two-step modulatory process: Eugenol first regulates the antagonism of GA and ABA, followed by activation of catalase activity. The natural monoterpene eugenol has been reported to inhibit preharvest sprouting in rice. However, the inhibitory mechanism remains obscure. In this study, simultaneous monitoring of GA and ABA responses by the in vivo GA and ABA-responsive dual-luciferase reporter system showed that eugenol strongly inhibited the GA response after 6 h of imbibition, whereas eugenol significantly enhanced the ABA response after 12 h of imbibition. Gene expression analysis revealed that eugenol significantly induced the ABA biosynthetic genes OsNCED2, OsNCED3, and OsNCED5, but notably suppressed the ABA catabolic genes OsABA8ox1 and OsABA8ox2. Conversely, eugenol inhibited the GA biosynthetic genes OsGA3ox2 and OsGA20ox4 but significantly induced the GA catabolic genes OsGA2ox1 and OsGA2ox3 during imbibition. OsABI4, the key signaling regulator of ABA and GA antagonism, was notably induced before 12 h and suppressed after 24 h by eugenol. Moreover, eugenol markedly reduced the accumulation of H2O2 in seeds after 36 h of imbibition. Further analysis showed that eugenol strongly induced catalase activity, protein accumulation, and the expression of three catalase genes. Most importantly, mitigation of eugenol-inhibited seed germination was found in the catc mutant. These findings indicate that catalase associated with antagonistic changes of ABA and GA is involved in the sequential regulation of eugenol-inhibited seed germination in rice. [ABSTRACT FROM AUTHOR]

Cut flowers of the orchid Oncidium Gower Ramsey are valuable agricultural produce around the world because of their yellow color contributed by carotenoids in adaxial and abaxial epidermal layers in petals and labellum. Here, we investigated the regulation of carotenogenic genes in response to different light qualities in Oncidium flowers. Total chlorophyll content was high in young flower buds and reduced during flower development, but carotenoid content was increased during flower development. We detected 11 key carotenoid biosynthesis genes and determined their expression profiles with light treatment. Real-time PCR revealed high mRNA levels of most genes, except OncCHYB and OncSDR, in vegetative tissues; only OncLCYe showed low expression in flowers. White light upregulated OncPSY, OncLCYb, and OncNCED but downregulated OncPDS, OncZDS, OncCrtISO, OncLCYe, OncCHYB, OncZEP, OncCCD1, and OncSDR; red light upregulated OncPSY, OncLCYb, OncLCYe, and OncCCD1; and UV light upregulated OncPSY, OncPDS, OncLCYb, OncZEP, and OncNCED. We cloned the promoter region of the phytoene synthase gene and found it to have potential cis-regulatory elements, such as TATA-box and CAAT-box, in addition to multiple light-responsive elements such as G-box, I-box, GT-1 motif, GAG-motif, and H-box. Our results of light-regulated carotenogenic gene expression and promoter analysis in flowers of Oncidium Gower Ramsey suggest ways to manipulate carotenoid content for high-quality cut-flower production. [ABSTRACT FROM AUTHOR]

Background: Haworthia are desert succulents belonging to the Asphodelaceae family. Haworthia species are cultivated commercially as ornamentals and some rare species are quite valuable at retail market but growth slowly and difficult to propagation. However, an efficient micropropagation protocol was remained insufficient. Results: The organogenic cultures obtained from inflorescence explants were cultured on Murashige and Skoog (MS) medium supplemented with various combinations of 6-benzylaminopurine (BA) and α-naphthalene acetic acid (NAA) under a light intensity of 10 μmol m−2 s−1 or 45 μmol m−2 s−1. The highest callus proliferation index (93.15%) with 1.0 mg L−1 BA + 0.1 mg L−1 NAA under a light intensity of 10 μmol m−2 s−1. The best shoot proliferation rates were on media with either 1 mg L−1 BA + 0–0.4 mg L−1 NAA (65.57–81.01%) under a light intensity of 45 μmol m−2 s−1. The highest root length (15.57 mm) and the highest rooting frequency (17 roots per shoot) were obtained when adventitious shoots were inoculated on MS medium with 0.4 mg L−1 NAA + 0.4 mg L−1 IBA. The survival rate of the transplanted plantlets was about 100%. The efficient micropropagation protocol proliferated Haworthia regenerate plants from inflorescence within 11 weeks. Conclusions: The present study determined the best combination of light intensity and plant growth regulators (PGRs) for improved organogenesis of Haworthia during propagation by tissue culture. This optimized protocol showed light intensity is an important factor for efficient callus or shoot regeneration. These results indicate that it will be useful to optimize the light conditions for future commercial cultivation, germplasm conservation, genetic engineering and molecular biology research of this ornamental plant. [ABSTRACT FROM AUTHOR]