Stylosanthes guianensis (Aublet) Sw. is an important pasture legume in tropical and subtropical countries. Chilling injury of S. guianensis is a serious problem in subtropical cultivated areas. An experiment was conducted under controlled conditions to study the effect of abscisic acid (ABA) on S. guianensis and its relation to antioxidant systems under chilling stress. Stylosanthes guianensis seedlings were sprayed with 10 mg L−1 ABA or water. One day later, the plants were transferred to a 10°C growth chamber and grown for 7 d with a 12‐h photoperiod at 160 μmol m−2 s−1 photosynthetic photon flux density. The chilling treated plants were then rewarmed to 28°C for 2 d. During the 9‐d treatment, a series of enzyme activities, relative water content (RWC), and electrolyte leakage were measured on sampled leaflets. The results showed that chilling increased electrolyte leakage of both water‐ and ABA‐treated plants, while RWC decreased under chilling conditions. ABA‐treated plants had lower electrolyte leakage and higher RWC than those of water‐treated plants. Activities of ascorbate peroxidase (APX) and catalase (CAT) and contents of reduced glutathione (GSH) and ascorbic acid (AsA) were transiently enhanced by ABA treatment before the plants were subject to chilling. ABA‐treated S. guianensis retained higher levels of superoxide dismutase (SOD), APX, GSH, and AsA than water‐treated ones under chilling conditions. The results suggested that ABA‐increased chilling resistance in S. guianensis is partially associated with enhanced scavenging systems.

Comparisons between the theoretical calculations and the experimental observations indicate that eight CO ligands are chemically bonded on the central atom in the singlet state of Sc(CO)8(+) ((1)A1 state of D(4d) symmetry) and the singlet and triplet states of Y(CO)8(+) ((1)A1 state of D(4d) symmetry and (3)A(1g) state of O(h) symmetry). The (1)A1 states of both Sc(CO)8(+) and Y(CO)8(+) have the 18-electron d(10)s(2)p(6) noble gas configuration. In M(CO)9(+) (M = Sc or Y), the ninth CO is weakly adsorbed on the external shell.

Background GC pairs are generally more stable than AT pairs; GC-rich genomes were proposed to be more adapted to high temperatures than AT-rich genomes. Previous studies consistently showed positive correlations between growth temperature and the GC contents of structural RNA genes. However, for the whole genome sequences and the silent sites of the codons in protein-coding genes, the relationship between GC content and growth temperature is in a long-lasting debate. Results With a dataset much larger than previous studies (681 bacteria and 155 archaea with completely assembled genomes), our phylogenetic comparative analyses showed positive correlations between optimal growth temperature (Topt) and GC content both in bacterial and archaeal structural RNA genes and in bacterial whole genome sequences, chromosomal sequences, plasmid sequences, core genes, and accessory genes. However, in the 155 archaea, we did not observe a significant positive correlation of Topt with whole-genome GC content (GCw) or GC content at four-fold degenerate sites. We randomly drew 155 samples from the 681 bacteria for 1000 rounds. In most cases (> 95%), the positive correlations between Topt and genomic GC contents became statistically nonsignificant (P > 0.05). This result suggested that the small sample sizes might account for the lack of positive correlations between growth temperature and genomic GC content in the 155 archaea and the bacterial samples of previous studies. Comparing the GC content among four categories (psychrophiles/psychrotrophiles, mesophiles, thermophiles, and hyperthermophiles) also revealed a positive correlation between GCw and growth temperature in bacteria. By including the GCw of incompletely assembled genomes, we expanded the sample size of archaea to 303. Positive correlations between GCw and Topt appear especially after excluding the halophilic archaea whose GC contents might be strongly shaped by intense UV radiation. Conclusions This study explains the previous contradictory observations and ends a long debate. Prokaryotes growing in high temperatures have higher GC contents. Thermal adaptation is one possible explanation for the positive association. Meanwhile, we propose that the elevated efficiency of DNA repair in response to heat mutagenesis might have the by-product of increasing GC content like that happens in intracellular symbionts and marine bacterioplankton.

The homoleptic heterodinuclear copper-nickel carbonyl anions CuNi(CO)n(-) (n = 2-4) were generated in a pulsed-laser vaporization source and investigated using photoelectron velocity-map imaging spectroscopy. The electron affinities of CuNi(CO)2 (2.15 ± 0.03 eV), CuNi(CO)3 (2.30 ± 0.03 eV), and CuNi(CO)4 (1.90 ± 0.04 eV) were deduced from the photoelectron spectra. Theoretical calculations at the B3LYP level were carried out to elucidate the structures and the electronic properties of CuNi(CO)n(0/1-) (n = 1-4) and to support the experimental observations. Comprehensive comparisons between experiments and calculations suggest that there is a turnover point of the absorption site during the progressive carbonylation process. The carbonyl groups are determined to be preferentially bonded to the nickel atom. When the nickel center satisfies the 18-electron configuration, the copper atom starts to adsorb additional CO molecules. These results will shed light on the bonding mechanisms of the heterometallic carbonyl clusters.