Arabidopsis cryptochrome 1 functions in nitrogen regulation of flowering.

The phenomenon of delayed flowering after the application of nitrogen (N) fertilizer has long been known in agriculture, but the detailed molecular basis for this phenomenon is largely unclear. Here we used a modified method of suppression-subtractive hybridization to identify two key factors involved in N-regulated flowering time control in Arabidopsis thaliana, namely ferredoxin-NADP(+)-oxidoreductase and the blue-light receptor cryptochrome 1 (CRY1). The expression of both genes is induced by low N levels, and their loss-of-function mutants are insensitive to altered N concentration. Low-N conditions increase both NADPH/NADP(+) and ATP/AMP ratios, which in turn affect adenosine monophosphate-activated protein kinase (AMPK) activity. Moreover, our results show that the AMPK activity and nuclear localization are rhythmic and inversely correlated with nuclear CRY1 protein abundance. Low-N conditions increase but high-N conditions decrease the expression of several key components of the central oscillator (e.g., CCA1, LHY, and TOC1) and the flowering output genes (e.g., GI and CO). Taken together, our results suggest that N signaling functions as a modulator of nuclear CRY1 protein abundance, as well as the input signal for the central circadian clock to interfere with the normal flowering process.

Nitric oxide induces monosaccharide accumulation through enzyme S-nitrosylation.

Nitric oxide (NO) is extensively involved in various growth processes and stress responses in plants; however, the regulatory mechanism of NO-modulated cellular sugar metabolism is still largely unknown. Here, we report that NO significantly inhibited monosaccharide catabolism by modulating sugar metabolic enzymes through S-nitrosylation (mainly by oxidizing dihydrolipoamide, a cofactor of pyruvate dehydrogenase). These S-nitrosylation modifications led to a decrease in cellular glycolysis enzymes and ATP synthase activities as well as declines in the content of acetyl coenzyme A, ATP, ADP-glucose and UDP-glucose, which eventually caused polysaccharide-biosynthesis inhibition and monosaccharide accumulation. Plant developmental defects that were caused by high levels of NO included delayed flowering time, retarded root growth and reduced starch granule formation. These phenotypic defects could be mediated by sucrose supplementation, suggesting an essential role of NO-sugar cross-talks in plant growth and development. Our findings suggest that molecular manipulations could be used to improve fruit and vegetable sweetness.

Cytokinins can act as suppressors of nitric oxide in Arabidopsis.

Maintaining nitric oxide (NO) homeostasis is essential for normal plant physiological processes. However, very little is known about the mechanisms of NO modulation in plants. Here, we report a unique mechanism for the catabolism of NO based on the reaction with the plant hormone cytokinin. We screened for NO-insensitive mutants in Arabidopsis and isolated two allelic lines, cnu1-1 and 1-2 (continuous NO-unstressed 1), that were identified as the previously reported altered meristem program 1 (amp1) and as having elevated levels of cytokinins. A double mutant of cnu1-2 and nitric oxide overexpression 1 (nox1) reduced the severity of the phenotypes ascribed to excess NO levels as did treating the nox1 line with trans-zeatin, the predominant form of cytokinin in Arabidopsis. We further showed that peroxinitrite, an active NO derivative, can react with zeatin in vitro, which together with the results in vivo suggests that cytokinins suppress the action of NO most likely through direct interaction between them, leading to the reduction of endogenous NO levels. These results provide insights into NO signaling and regulation of its bioactivity in plants.

[Seasonal divergence in the responses of vegetation growth to PDO in Tibetan Plateau, China]. / 青藏高原植被生长对PDO响应的季节分异.

Regional-scale normalized difference vegetation index (NDVI) derived from satellite remote sensing observations and gridded climate data were used to study the seasonal responses and underlying mechanisms of vegetation growth over Tibetan Plateau to Pacific Decadal Oscillation (PDO) at period of 1982-2015, by performing Spearman correlation analysis and enhanced multivariate regression model: structural equation model (SEM). The results showed that there was significant negative correlation between PDO index and mean growing-season (April-October) NDVI over Tibetan Plateau; however, marked seasonal divergence in the relationship between PDO and vegetation growth existed among different seasons. It characterized with stronger negative correlation between PDO and NDVI in autumn than in summer, and winter PDO had significant effect on consequent summer vegetation growth. Additionally, it showed great divergence in control processes of PDO on vegetation growth among different seasons, with significant control of PDO on both temperature and precipitation in summer, and significant control of PDO on temperature only in autumn.

The involvement of NtFtsZ2-1 gene in the regulation of chloroplast division and expansion in tobacco.

Chloroplasts are a vital group of organelles of plants, yet the molecular mechanisms associated with their division remain poorly understood. Recent studies have revealed that the FtsZ protein, known as a key component in prokaryotic cell division, is involved in chloroplast division process. The NtFtsZ2-1 gene was isolated from Nicotiana tabacum by RT-PCR, and the sense and antisense expression plasmids were used to examine the function of NtFtsZ2-1 gene in transgenic tobacco. Light and confocal observations revealed that the normal chloroplast division process was severely disrupted in transgenic plants with enhanced or reduced expression of NtFtsZ2-1 gene. These chloroplasts were abnormally larger in size and fewer in number compared with that of the wild-type tobacco. But the total chloroplast plan area per mesophyll cell was conserved in sense, antisense and wild type tobaccos. Analyses of electron micrographs and chlorophyll content of different transgenic plants showed that constitutively enhancing or inhibiting the expression of NtFtsZ2-1 gene had no direct influence on the ultrastructure and photosynthetic ability of chloroplasts. Basing on these results, we suggest that NtFtsZ2-1 gene is involved in chloroplast division and expansion; the fluctuation of NtFtsZ2-1 expression level would alter normal chloroplast number and size in plant cells. In addition, the similarities of ultrastructure and photosynthetic ability of chloroplasts among sense, antisense and wild type tobaccos implies that a special mechanism regulate the relationship between chloroplast number and size to maximize photosynthetic rate.

[Effect of Dissolved Humic Acid on Thyroid Receptor Antagonistic Activity of Zinc in Aquatic Environment].

A rapid recombinant human thyroid (hTR) gene yeast bioassay was used to evaluate the effect of dissolved humic acid on thyroid receptor antagonistic activity of ZnCl2.The concentration of bio-available zinc after its reaction with dissolved humic acids was measured by anodic stripping voltammetry (ASV).Furthermore,the reaction mechanism of humic acid and zinc was investigated by three-dimensional excitation-emission matrix fluorescence spectroscopy (3DEEM).The results revealed that ZnCl2 demonstrated strong thyroid receptor antagonistic activity,and the concentration inhibiting 20% of the maximum effect of ZnCl2 was 1.70×10-5 mol·L-1.The thyroid receptor antagonistic activity of ZnCl2 was reduced by 30%-50% after the reaction of dissolved humic acids.The results of ASV showed that the concentration of bio-available zinc was decreased after the reaction of dissolved humic acids,the result was similar to that of bioassay test.The thyroid receptor antagonistic activity of the mixed solution of humic acid and ZnCl2 was increased after UV radiation treatment,however it was still lower than the antagonistic activity induced by ZnCl2.The results of 3DEEM showed that ZnCl2 could reduce the fluorescence peak intensity of humic acid,which could intuitively characterize the interaction between humic acid and ZnCl2.The above results can provide basic data and theoretical support for zinc toxicity study in aquatic environment and the establishment of water quality criteria for znic.

[Cloning and expression in E.coli of Chlamydomonas reinhardtii CrFtsZ3 gene].

FtsZ protein plays a key role in the division of bacteria and chloroplast. To investigate the evolution of the chloroplast dividing apparatus, cloning and molecular characterization of a second chloroplast division gene, CrFtsZ3, from Chlamydomonas reinhardtii is performed. As there are two ftsZ genes in Chlamydomonas reinhardtii, duplication and divergence of the ftsZ genes might occur in an early stage before the emergence of green algae during the course of plant evolution. Sequence analysis showed that CrFtsZ3 gene had significant sequence homology with other ftsZs. It encoded a precursor of 479 amino acid residues with a putative transit peptide in its N-terminal. To study the function of CrFtsZ3, a recombinant plasmid expressing the full length CrFtsZ3/EGFP fusion protein was constructed. By using IPTG inducing, overexpression of CrFtsZ3/EGFP in E.coli was achieved, and this overexpression blocked cell division and resulted in filament formation. GFP-derived fluorescence showed regularly spaced dots along the bacterial filaments. This suggests that CrFtsZ3 could still recognize the signals of cell division site in E.coli and could take part in the process of bacterial division.