Leaf senescence is a developmentally programmed cell death process that constitutes the final step of leaf development and involves the extensive reprogramming of gene expression. Despite the importance of senescence in plants, the underlying regulatory mechanisms are not well understood. This study reports the isolation and functional analysis of RAV1, which encodes a RAV family transcription factor. Expression of RAV1 and its homologues is closely associated with leaf maturation and senescence. RAV1 mRNA increased at a later stage of leaf maturation and reached a maximal level early in senescence, but decreased again during late senescence. This profile indicates that RAV1 could play an important regulatory role in the early events of leaf senescence. Furthermore, constitutive and inducible overexpression of RAV1 caused premature leaf senescence. These data strongly suggest that RAV1 is sufficient to cause leaf senescence and it functions as a positive regulator in this process.

Development of an in situ technique for measuring electrochemical impedance spectra in real time during an electrochemical experiment is described. The technique is based on staircase voltammetry with relatively large step heights, in which a series of increasing potential steps are applied to an electrochemical system, and the resulting currents are sampled. The first derivatives of the currents thus obtained are then converted to ac current signals in frequency domain, and impedances are computed from them. To demonstrate the technique as a tool for studying the electrode/electrolyte interface during the electrochemical reaction, we chose an electrochemical oxidation reaction of aniline, whose reaction products have been known to continuously change the electrode surface due to the polymer film growth on its surface, and report a number of observations that would not have been obtained without such in situ experiments. A suggestion is also made on the use of staircase voltammetry for mechanistic studies on complex electrochemical reactions by simply varying the sampling time.

Phytochrome A (phyA) in higher plants is known to function as a far-red/shade light-sensing photoreceptor in suppressing shade avoidance responses (SARs) to shade stress. In this paper, the Avena PHYA gene was introduced into creeping bentgrass (Agrostis stolonifera L.) and zoysiagrass (Zoysia japonica Steud.) to improve turf quality by suppressing the SARs. In addition to wild-type PHYA, a hyperactive mutant gene (S599A-PHYA), in which a phosphorylation site involved in light-signal attenuation was removed, was also transformed into the turfgrasses. Phenotypic traits of the transgenic plants were compared to assess the suppression of SARs under a simulated shade condition and outdoor field conditions after three growth seasons. Under the shade condition, the S599A-PhyA transgenic creeping bentgrass plants showed shade avoidance-suppressing phenotypes with a 45 % shorter leaf lengths, 24 % shorter internode lengths, and twofold increases in chlorophyll concentrations when compared with control plants. Transgenic zoysiagrass plants overexpressing S599A-PHYA also showed shade-tolerant phenotypes under the shade condition with reductions in leaf length (15 %), internode length (30 %), leaf length/width ratio (19 %) and leaf area (22 %), as well as increases in chlorophyll contents (19 %) and runner lengths (30 %) compared to control plants. The phenotypes of transgenic zoysiagrass were also investigated in dense field habitats, and the transgenic turfgrass exhibited shade-tolerant phenotypes similar to those observed under laboratory shade conditions. Therefore, the present study suggests that the hyperactive phyA is effective for the development of shade-tolerant plants, and that the shade tolerance nature is sustained under field conditions.

Herbicide-tolerant Zoysia grass (Zoysia japonica Steud.) has been generated previously through Agrobacterium tumefaciens-mediated transformation. The genetically modified (GM) Zoysia grass survived Basta spraying and grew to maturity normally while the wild-type (WT) grass stopped growing and died. GM Zoysia grass will permit more efficient weed control for various turf grass plantings such as home lawns, golf courses, and parks. We examined the environmental/biodiversity risks of herbicide-tolerant GM Zoysia before applying to regulatory agencies for approval for commercial release. The GM and WT Zoysia grass' substantial trait equivalence, ability to cross-pollinate, and gene flow in confined and unconfined test fields were selectively analyzed for environmental/biodiversity effects. No difference between GM and WT Zoysia grass in substantial traits was found. To assess the potential for cross-pollination and gene flow, a non-selective herbicide, Basta, was used. Results showed that unintended cross-pollination with and gene flow from GM Zoysia grass were not detected in neighboring weed species examined, but were observed in WT Zoysia grass (on average, 6% at proximity, 1.2% at a distance of 0.5 m and 0.12% at a radius of 3 m, and 0% at distances over 3 m). On the basis of these initial studies, we conclude that the GM Zoysia grass generated in our laboratory and tested in the Nam Jeju County field does not appear to pose a significant risk when cultivated outside of test fields.

Turfgrasses are environmentally and recreationally valuable plants that are constantly subjected to various forms of stress in their artificial and natural habitats. Previously, it was shown that the transformation of a hyperactive mutant (Serine 599 Alanine, S599A) of oat phytochrome A in zoysia grass (Zoysia japonica) and creeping bentgrass (Agrostis stolonifera L.) resulted in superior quality turfgrass with improved shade tolerance response. We now examined the abiotic stress response of the transgenic turfgrasses expressing the hyperactive mutant S599A-PhyA. The transgenic S599A-PhyA plants subjected to high salinity and heavy metal toxicity stress exhibited higher chlorophyll content, lower hydrogen peroxide level, and higher proline accumulation than the controls. Furthermore, the anti-oxidative activities of four reactive oxygen species scavenging enzymes and the total biomass (above and below-ground) were higher in S599A-PhyA plants than in the controls under both the stress conditions. Moreover, higher photosynthetic efficiency (F v / F m ) of S599A-PhyA plants indicated healthier growth than the controls under stress conditions. Results suggest that the hyperactive mutant of oat phytochrome A confers abiotic stress tolerance in plants, and can be used to efficiently develop abiotic stress tolerant crops in future.