The WD-repeat proteins are found in eukaryotes and play an important role in the regulation of a wide variety of cellular functions such as signal transduction, transcription, and proliferation. In this study, we have isolated a cDNA encoding a novel WD-repeat protein, PFWD, from the anthocyanin-pigmented leaves of Perilla frutescens using AN11 cDNA from Petunia hybrida as the probe. The C-terminal region of PFWD contains a WD repeat that is highly conserved in homologous proteins from a variety of organisms that do not produce anthocyanin such as yeast, nematodes and mammals. Transgenic Arabidopsis plants overexpressing PFWD exhibited phenotypic changes including enhancement of anthocyanin production and reduced viability. A study of the interaction between PFWD and anthocyanin regulatory proteins using a yeast two-hybrid system showed strong interaction between PFWD and MYC-RP, a MYC-like protein from P. frutescens. PFWD fusion proteins transiently expressed in onion epidermal cells were localized in the cytosol under both dark and light conditions. However, co-expression of PFWD and MYC-RP fusion proteins resulted in nuclear localization of PFWD. We propose a model of genetic regulation in which the PFWD protein acts in signal transduction process in a variety of pathways through protein interaction with MYC proteins.

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Regeneration efficiency was enhanced by adding auxin and cytokinin at different concentrations to the media. It was found that the two highest frequencies-90 and 85%-of callus induction occured when the buds were cultured in an MS medium supplemented with 2 mgL-1 α-naphthalene acetic acid (NAA) plus 1 mgL-1 N 6-benzylaminopurine (BAP) (CIM2) and in the same medium supplemented with 2 mgL-1 NAA plus 1 mgL-1 kinetin (CIM5), respectively. When cultured further in a plant regeneration medium supplemented with 1 mgL-1 NAA and 2 mgL-1 BAP (PRM1), these calli regenerated with high efficiencies, 80% for calli grown in CIM2 and 85% for calli grown in CIM5. The low BAP concentration in CIM1 (2 mgL-1 NAA and 0.5 mgL-1 BAP) resulted in a low regeneration efficiency and fewer shoots per callus even though the PRM3 regeneration medium had a high concentration of cytokinins (2 mgL-1 BAP and 2 mgL-1 kinetin). However, the calli cultured in CIM2 without kinetin but with a suitable level of BAP still regenerated with high efficiencies in PRM2 and PRM3 that contained 1 and 2 mgL-1 kinetin, respectively. Similarly, when calli cultured in CIM5 without BAP but with kinetin were regenerated in PRM1 with BAP alone, they also regenerated with a high regeneration efficiency. These results showed that culturing a specific tissue in a medium with suitable concentrations of NAA and BAP or kinetin resulted in a large number of multiple shoots, and BAP and kinetin worked synergistically to produce a high plant regeneration efficiency.

The presence of Titanium dioxide nanoparticles (TiO2 NPs) contamination in the environment is of concern because of their oxidative effect on organisms. Transgenic tobaccos that overexpressed PAP1, a MYB75 gene, were used to investigate the response of plants to the presence of TiO2 NPs and the results were compared to those for wild type (WT) plants. The experiment was performed under tissue culture conditions with daylight fluorescence. The physiological responses of the plants under moderately low concentrations of TiO2 NPs (20–40 mg L-1) were analyzed in relation to metabolic responses and the results were compared to those of plants under zero TiO2 conditions. Under conditions of 20 mg L-1 TiO2, WT and PAP1 plants showed better physiology than plants under other conditions. These plants had higher chlorophyll and carotenoid levels, and better membrane stability than plants under non TiO2 conditions. The WT plants grown in medium at 40 mg L-1 TiO2 showed deteriorated physiology, while PAP1 plants grown under the same condition were shown various changes in physiology depending on the line. Moreover, the content of total soluble sugar (TSS) and flavonoids in the extracts of plant were increased in response to the concentrations of TiO2. However, all PAP1 transgenics had flavone and flavonol contents that were approximately 2–3 times the levels found in WT plants, while TSS and anthocyanin subgroup levels were not different among the WT and transgenic plants. Excessive nanoparticles can induce oxidative damage in cells, and it appears that PAP1 transgenics can alleviate such damage by enhancing flavonoid accumulation.

Zinc is an essential micronutrient element for plant. Nowadays, Zinc oxide nanoparticles (ZnO NPs) are widely used and have been shown adverse effects to plant physiology. The optimal concentration of ZnO NPs added in plant regeneration medium (PRM) is studied in this experiment. Six-weeks old calli induced from the aseptic axillary buds of vetiver grass were cultured in PRM with various concentrations of ZnO NPs (5, 10, 20, 40 mgL-1). PRM containing 5, 10 mgL-1 ZnO NPs showed the highest percentage of plant regeneration frequency (95%) but did not have a statistic difference with other treatments. However, the averages of shoot length regenerated under both concentrations were 1.32-1.33 cm. These averages of shoot length had statistically different from averages of shoot length of the others. Moreover, calli regenerated under PRM containing 5 mgL-1 ZnO NPs condition showed the highest average number of shoots per callus (9.75 shoots) with a statistic difference. ZnO NPs at 20-40 mgL-1 in the PRM did not enhance the percentage of plant regeneration, but retarded calli development and shoot elongation. The optimal concentration of ZnO NPs in PRM has positive effects on regeneration and development of vetiver grass under tissue culture condition.