In this study, we determined the effects of raising seedlings with different light spectra such as with blue, red, and blue + red light-emitting diode (LED) lights on seedling quality and yield of red leaf lettuce plants. The light treatments we used were applied for a period of 1 week and consisted of 100 μmol·m−2·s−1 of blue light, simultaneous irradiation with 50 μmol·m−2·s−1 of blue light and 50 μmol·m−2·s−1 of red light, and 100 μmol·m−2·s−1 of red light. At the end of the light treatment, that is 17 days after sowing (DAS), the leaf area and shoot fresh weight (FW) of the lettuce seedlings treated with red light increased by 33% and 25%, respectively, and the dry weight of the shoots and roots of the lettuce seedlings treated with blue-containing LED lights increased by greater than 29% and greater than 83% compared with seedlings grown under a white fluorescent lamp (FL). The shoot/root ratio and specific leaf area of plants irradiated with blue-containing LED lights decreased. At 45 DAS, higher leaf areas and FWs were obtained in lettuce plants treated with blue-containing LED lights. The total chlorophyll (Chl) contents in lettuce plants treated with blue-containing and red lights were less than that of lettuce plants treated with FL, but the Chl a/b ratio and carotenoid content increased under blue-containing LED lights. Polyphenol contents and the total antioxidant status (TAS) were greater in lettuce seedlings treated with blue-containing LED lights than in those treated with FL at 17 DAS. The higher polyphenol contents and TAS in lettuce seedlings at 17 DAS decreased in lettuce plants at 45 DAS. In conclusion, our results indicate that raising seedlings treated with blue light promoted the growth of lettuce plants after transplanting. This is likely because of high shoot and root biomasses, a high content of photosynthetic pigments, and high antioxidant activities in the lettuce seedlings before transplanting. The compact morphology of lettuce seedlings treated with blue LED light would be also useful for transplanting.

The significance of NAD biosynthesis in plant development and NADP biosynthesis in plant stress tolerance is summarized in this Briefing. Further investigation of cells expressing a set of NAD biosynthetic genes would facilitate understanding of regulatory mechanisms by which plant cells maintain NAD homeostasis.

The Antirrhinum majus transposon Tam3 undergoes low temperature-dependent transposition (LTDT). Growth at 158C permits transposition, whereas growth at 258C strongly suppresses it. The degree of Tam3 DNA methylation is altered somatically and positively correlated with growth temperature, an exceptional epigenetic system in plants. Using a Tam3-inactive line, we show that methylation change depends on Tam3 activity. Random binding site selection analysis and electrophoretic mobility shift assays revealed that the Tam3 transposase (TPase) binds to the major repeat in the subterminal regions of Tam3, the site showing the biggest temperature-dependent change in methylation state. Methylcytosines in the motif impair the binding ability of the TPase. Proteins in a nuclear extract from plants grown at 158C but not 258C bind to this motif in Tam3. The decrease in Tam3 DNA methylation at low temperature also requires cell division. Thus, TPase binding to Tam3 occurs only during growth at low temperature and immediately after DNA replication, resulting in a Tam3-specific decrease in methylation of transposon DNA. Consequently, the Tam3 methylation level in LTDT is regulated by Tam3 activity, which is dependent on the ability of its TPase to bind DNA and affected by growth temperature. Thus, the methylation/demethylation of Tam3 is the consequence, not the cause, of LTDT.

The transposition frequency of Tam3 in Antirrhinum majus, unlike that of most other cut-and-paste-type transposons, is tightly controlled by temperature: Tam3 transposes rarely at 25°C, but much more frequently at 15°C. Here, we studied the mechanism of the low-temperature-dependent transposition (LTDT) of Tam3. Our results strongly suggest that LTDT is not likely to be due to either transcriptional regulation or posttranscriptional regulation of the Tam3 TPase gene. We found that temperature shift induced a remarkable change of the methylation state unique to Tam3 sequences in the genome: Higher temperature resulted in hypermethylation, whereas lower temperature resulted in reduced methylation. The methylation state was reversible within a single generation in response to a temperature shift. Although our data demonstrate a close link between LTDT and the methylation of Tam3, they also suggest that secondary factor(s) other than DNA methylation is involved in repression of Tam3 transposition.Tam3 in Antirrhinum majus is exceptional among cut-and-paste-type transposons (TEs) in that it is the only known TE whose transpositional behavior can be strictly controlled by environmental influence. Tam3 transposition is strongly affected by temperature: It is active at low temperatures (around 15°C) and stable at high temperatures (around 25°C; Harrison and Fincham, 1964). Shifting the temperature controls the activity mitotically and probably meiotically. Based on a study of variegation spots, Carpenter et al. (1987) reported that the Tam3 excision rate was approximately 1,000-fold greater at 15°C than at 25°C. Thus, Tam3 is remarkably sensitive to the growth temperature. This trait has provided a great advantage for the isolation and analysis of a variety of genes involved in pigmentation and development in A. majus (Coen et al., 1989).Among the regulatory factors associated with TE activity, DNA methylation is widely involved in the inhibition of transpositional events in plant TEs. DNA methylation can regulate TE transposition at the levels of both transposase (TPase) gene expression and the TPase binding process (Schlappi et al., 1994;Ros and Kunze, 2001). Martin et al. (1989) suggested that Tam3 inactivation is also associated with DNA methylation. Kitamura et al. (2001) showed that at high temperatures, the repression of transposition occurs simultaneously for all Tam3 copies in the genome, whereas at low temperatures, the repression is released to various degrees depending on the location of the copies. The degree of the Tam3 transposition activity was found to be influenced by chromosomal position and related to the degree of methylation of the element ends.Here, we attempted to find differences between the active and inactive states of Tam3 in plants grown at different temperatures. We compared the amounts of the transcript of the TPase gene and compared the enzymatic activity of Tam3 TPase between plants grown at 25°C and 15°C. The results showed that neither the transcription of the TPase gene nor its enzy...

Nicotinamide nucleotides (NAD and NADP) are important cofactors in many metabolic processes in living organisms. In this study, we analyzed transgenic Arabidopsis (Arabidopsis thaliana) plants that overexpress NAD kinase2 (NADK2), an enzyme that catalyzes the synthesis of NADP from NAD in chloroplasts, to investigate the impacts of altering NADP level on plant metabolism. Metabolite profiling revealed that NADP(H) concentrations were proportional to NADK activity in NADK2 overexpressors and in the nadk2 mutant. Several metabolites associated with the Calvin cycle were also higher in the overexpressors, accompanied by an increase in overall Rubisco activity. Furthermore, enhanced NADP(H) production due to NADK2 overexpression increased nitrogen assimilation. Glutamine and glutamate concentrations, as well as some other amino acids, were higher in the overexpressors. These results indicate that overexpression of NADK2 either directly or indirectly stimulates carbon and nitrogen assimilation in Arabidopsis under restricted conditions. Importantly, since neither upregulation nor down-regulation of NADK2 activity affected the sum amount of NAD and NADP or the redox state, the absolute level of NADP and/or the NADP/NAD ratio likely plays a key role in regulating plant metabolism.