This research is the first to demonstrate that OsSAUR45 is involved in plant growth though affecting auxin synthesis and transport by repressing OsYUCCA and OsPIN gene expression in rice.

Miscanthus has been proposed as a promising crop for phytoremediation due to its high biomass yield and remarkable adaptability to different environments. However, little is known about the resistance of Miscanthus spp. to cadmium (Cd). To determine any differences in resistance of Miscanthus to Cd, we examined plant growth, net photosynthetic rate (Pn), activities of anti-oxidant and C4 photosynthetic enzymes, concentrations of Cd in leaves and roots, and observed the chloroplast structure in three Miscanthus species treated with 0, 10, 50, 100 or 200 μM Cd in solutions. Miscanthus sinensis showed more sensitivity to Cd, including sharp decreases in growth, Pn, PEPC activity and damage to chloroplast structure, and the highest H2O2 and Cd concentrations in leaves and roots after Cd treatments. Miscanthus sacchariflorus showed higher resistance to Cd and better growth, had the highest Pn and phosphoenolpyruvate carboxylase (PEPC) activities and integrative chloroplast structure and the lowest hydrogen peroxide (H2O2) and leaf and root Cd concentrations. The results could play an important role in understanding the mechanisms of Cd tolerance in plants and in application of phytoremediation.

Auxin and cadmium (Cd) stress play critical roles during root development. There are only a few reports on the mechanisms by which Cd stress influences auxin homeostasis and affects primary root (PR) and lateral root (LR) development, and almost nothing is known about how auxin and Cd interfere with root hair (RH) development. Here, we characterize rice osaux1 mutants that have a longer PR and shorter RHs in hydroponic culture, and that are more sensitive to Cd stress compared to wild-type (Dongjin). OsAUX1 expression in root hair cells is different from that of its paralogous gene, AtAUX1, which is expressed in non-hair cells. However, OsAUX1, like AtAUX1, localizes at the plasma membrane and appears to function as an auxin tranporter. Decreased auxin distribution and contents in the osaux1 mutant result in reduction of OsCyCB1;1 expression and shortened PRs, LRs and RHs under Cd stress, but may be rescued by treatment with the membrane-permeable auxin 1-naphthalene acetic acid. Treatment with the auxin transport inhibitors 1-naphthoxyacetic acid and N-1-naphthylphthalamic acid increased the Cd sensitivity of WT rice. Cd contents in the osaux1 mutant were not altered, but reactive oxygen species-mediated damage was enhanced, further increasing the sensitivity of the osaux1 mutant to Cd stress. Taken together, our results indicate that OsAUX1 plays an important role in root development and in responses to Cd stress.

Promotion of active oxygen synthesis in plants occurs under several stress conditions and antioxidative enzymes have relationships with the resolution. We investigated the changes in activities of antioxidative enzymes (SOD, APX) through symbiosis with arbuscular mycorrhizal (AM) fungi in strawberry plants under high temperature stress. Strawberry (Fragaria x ananassa Duch., cv. Nohime) runner plants were inoculated with two species of AM fungi. Ten weeks after AMF inoculation, plants were transferred under 35 degrees C-constant temperature and raised during the following 10 days. Dry weight of shoots and roots became greater in AM plots than in the non-AM ones 10 weeks after inoculation. The level of mycorrhizal colonization differed between the fungi. Browning of leaves and roots appeared following 10 days under stress conditions, but the severity of browning was diminished in AM plots than in the non-AM ones. Before the stress conditions were imposed, SOD activities differed little among the plots except in lateral roots with colonization. In non-AM plot, SOD activities markedly decreased under stress conditions. However, AM plots showed higher SOD activities than the non-AM one especially after 10 days under stress condition; the effect differed with plant parts; little difference appeared between the fungi. On the other hand, APX in AM plots became higher in roots before stress and especially after ten days under stress condition; Glomus mosseae showed relatively higher values than Gigaspora margarita. From these findings, tolerance to high temperature stress and the increase in activities of SOD and APX occurred in mycorrhizal strawberry plants, so that the activation of antioxidative enzymes is thought to be associated with the temperature stress tolerance.