Thiol-based redox regulation is central to adjusting chloroplast functions under varying light conditions. A redox cascade via the ferredoxin-thioredoxin reductase (FTR)/thioredoxin (Trx) pathway has been well recognized to mediate the light-responsive reductive control of target proteins; however, the molecular basis for reoxidizing its targets in the dark remains unidentified. Here, we report a mechanism of oxidative thiol modulation in chloroplasts. We biochemically characterized a chloroplast stroma-localized atypical Trx from , designated as Trx-like2 (TrxL2). TrxL2 had redox-active properties with an unusually less negative redox potential. By an affinity chromatography-based method, TrxL2 was shown to interact with a range of chloroplast redox-regulated proteins. The direct discrimination of thiol status indicated that TrxL2 can efficiently oxidize, but not reduce, these proteins. A notable exception was found in 2-Cys peroxiredoxin (2CP); TrxL2 was able to reduce 2CP with high efficiency. We achieved a complete in vitro reconstitution of the TrxL2/2CP redox cascade for oxidizing redox-regulated proteins and draining reducing power to hydrogen peroxide (HO). We further addressed the physiological relevance of this system by analyzing protein-oxidation dynamics. In plants, a decreased level of 2CP led to the impairment of the reoxidation of redox-regulated proteins during light-dark transitions. A delayed response of protein reoxidation was concomitant with the prolonged accumulation of reducing power in TrxL2. These results suggest an in vivo function of the TrxL2/2CP redox cascade for driving oxidative thiol modulation in chloroplasts.

We carried out a C18O (J = 1−0) survey for dense molecular cores in the Chamaeleon (Cha) I, II, and III dark clouds with the NANTEN millimeter-wave telescope. The present survey covered ∼ 93% of the area where the molecular column density is greater than ∼ 4 × 1021 cm-2, estimated from preceding 13CO(J = 1−0) observations. We identified 23 C18O cores, whose typical mass, radius, peak column density, line width are 22 M⊙ , 0.22 pc, 9.7 × 1021 cm-2, and 0.82 km s-1, respectively. The surface density of classical T Tauri stars abruptly increases for the area whose column density is greater than 1022 cm-2, suggesting that this value gives a certain threshold value for star formation. The star-formation efficiency varies over a wide range among the three clouds: 13%, 1%, and 0% in Cha I, II, and III, respectively. The C18O cores in Cha I are characterized by (1) a high column density, (2) being almost in virial equilibrium, and (3) a high Mcore/Mcloud ratio. The cores in Cha III show the opposite trend, and those in Cha II are in between. Such trends suggest that Cha I is a well-evolved or well gravitationally relaxed cloud-core system, which is probably related to the very high star-formation activity in the cloud.

We have made an extensive study of dense cloud cores and star formation in the Lupus dark-cloud complex. Millimeter-wave observations in the C18O (J = 1−0) emission at 2.6 mm wavelength were made with the “NANTEN,” a 4-m mm-wave telescope of Nagoya University at Las Campanas Observatory. Thirty-six dense cores were identified and mapped in the C18O emission at 2′ grid spacing with a 2′.7 beam. The typical mass, radius, H2 column density, and line width of the C18O cores are 9.7 M⊙ , 0.17 pc, 4.1 × 1021 cm-2, 0.90 km s-1, respectively. The mass spectrum of the C18O cores was fitted by a single power-law index of γ = −1.7± 0.6 for Mcore ≥ 3 M⊙ . The physical parameters of the dense C18O cores were derived and compared with those in Taurus, Ophiuchus North, and L 1333. The average characteristics of the C18O cores in Lupus are similar to those in Ophiuchus North and L 1333, although those in Taurus are found to be different, especially in the line width, virial ratio, and mass spectrum index among the four regions. By comparing the physical properties of the C18O cores with the distribution of YSOs and H13CO+ condensations in Lupus, we have confirmed a trend suggested in previous studies, that star formation preferentially occurs in cores having a small virial ratio, Mvir/Mcore, and a large H2 column density.

A new survey of the LMC has been completed in 2.6 mm carbon monoxide emission with NANTEN. This survey has revealed 107 giant molecular clouds, the first complete sample of giant molecular clouds in a single galaxy at a linear resolution of ∼ 40 pc. The cloud mass ranges from ∼ 6 × 104 to 2 × 106 M⊙, and the total molecular mass has been estimated to be 4–7 × 107 M⊙ for a molecular column density of ≳ 1.0 × 1021 cm-2, corresponding to 5–10% of the atomic mass. The molecular clouds exhibit a good spatial correlation with the youngest stellar clusters whose ages are ≲ 10 Myr, demonstrating that cluster formation is on-going in these clouds. On the other hand, they show little correlation with older clusters or with supernova remnants, suggesting that the molecular clouds are being rapidly dissipated in a several Myrs, probably due to the UV photons of massive stars in clusters.