A dramatic increase of chlorophyll (Chl) degradation occurs during senescence of vegetative plant organs and fruit ripening. Although the biochemical pathway of Chl degradation has long been proposed, little is known about its regulatory mechanism. Identification of Chl degradation-disturbed mutants and subsequently isolation of responsible genes would greatly facilitate the elucidation of the regulation of Chl degradation. Here, we describe a nonyellowing mutant of Arabidopsis (Arabidopsis thaliana), nye1-1, in which 50% Chl was retained, compared to less than 10% in the wild type (Columbia-0), at the end of a 6-d dark incubation. Nevertheless, neither photosynthesis-nor senescence-associated process was significantly affected in nye1-1. Characteristically, a significant reduction in pheophorbide a oxygenase activity was detected in nye1-1. However, no detectable accumulation of either chlorophyllide a or pheophorbide a was observed. Reciprocal crossings revealed that the mutant phenotype was caused by a monogenic semidominant nuclear mutation. We have identified AtNYE1 by positional cloning. Dozens of its putative orthologs, predominantly appearing in higher plant species, were identified, some of which have been associated with Chl degradation in a few crop species. Quantitative polymerase chain reaction analysis showed that AtNYE1 was drastically induced by senescence signals. Constitutive overexpression of AtNYE1 could result in either pale-yellow true leaves or even albino seedlings. These results collectively indicate that NYE1 plays an important regulatory role in Chl degradation during senescence by modulating pheophorbide a oxygenase activity.

Brassinosteroids (BRs) play an essential role in plant growth and development, and have been implicated in many physiological responses. However, little is known about the role of BRs in the plant response to oxidative stress. In this study, we identified a novel insertion allele (det2-9) of the DET2 gene in Arabidopsis based on molecular, physiological and genetic approaches. We found that the det2 mutant exhibited an enhanced resistance to oxidative stress. The enhanced oxidative stress resistance in det2 plants was correlated with a constitutive increase in superoxide dismutase (SOD) activity and increased transcript levels of the defence gene catalase (CAT). To our knowledge, these results demonstrate, for the first time, that loss-of-function mutations in the DET2 gene lead to an enhanced oxidative stress resistance in Arabidopsis. A general explanation is that the long-term BR deficiency in the det2 mutant results in a constant in vivo physiological stress that, in turn, activates the constitutive expression of some defence genes and, consequently, the activities of related enzymes.

Lipotoxicity plays a vital role in development and progression of type 2 diabetes. Prolonged elevation of free fatty acids especially the palmitate leads to pancreatic β-cell dysfunction and apoptosis. Curcumin (diferuloylmethane), a polyphenol from the curry spice turmeric, is considered to be a broadly cytoprotective agent. The present study was designed to determine the protective effect of curcumin on palmitate-induced apoptosis in β-cells and investigate underlying mechanisms. Our results showed that curcumin improved cell viability and enhanced glucose-induced insulin secretory function in MIN6 pancreatic β-cells. Palmitate incubation evoked chromatin condensation, DNA nick end labeling and activation of caspase-3 and -9. Curcumin treatment inhibited palmitate-induced apoptosis, relieved mitochondrial depolarization and up-regulated Bcl-2/Bax ratio. Palmitate induced the generation of reactive oxygen species and inhibited activities of antioxidant enzymes, which could be neutralized by curcumin treatment. Moreover, curcumin could promote rapid phosphorylation of Akt and nuclear exclusion of FoxO1 in MIN6 cells under lipotoxic condition. Phosphatidylinositol 3-kinase and Akt specific inhibitors abolished the anti-lipotoxic effect of curcumin and stimulated FoxO1 nuclear translocation. These findings suggested that curcumin protected MIN6 pancreatic β-Cells against apoptosis through activation of Akt, inhibition of nuclear translocation of FoxO1 and mitochondrial survival pathway.

A B S T R A C TLung carcinogenesis is a complex process in an unregulated inflammatory environment.Curcumin has been extensively investigated as a multi-target anti-tumor and antiinflammation compound. In this paper, we demonstrate a novel inflammation-related mechanism for curcumin-induced inhibition of lung tumor growth. We found that neutrophil elastase, an important regulator of inflammatory processes, directly triggered tumor cell proliferation in human lung adenocarcinoma A549 cells, and curcumin could completely suppress the excess tumor proliferation induced by neutrophil elastase. a1-antitrypsin is synthesized by tumor cells and is the natural inhibitor of neutrophil elastase.We found that curcumin counteracted the decrease of a1-antitrypsin induced by neutrophil elastase by inducing the promoter activity of a1-antitrypsin and promoting its expression in A549 cells. The inhibition of neutrophil elastase-induced proliferation by curcumin was dependent on the PI3K/Akt pathway. Knockdown of a1-antitrypsin by siRNA further enhanced the tumor cell proliferation induced by neutrophil elastase and significantly blocked the anti-proliferation effect of curcumin against neutrophil elastase. Curcumin remarkably inhibited the primary tumor growth of Lewis lung carcinoma (LLC) in C57BL/6 mice. We further showed that curcumin upregulated the level of a1-antitrypsin in primary tumor tissue by promoting its local expression, and the protein level of neutrophil elastase in tumor tissue was obviously decreased in mice treated with curcumin. Overall, our results suggest that neutrophil elastase and a1-antitrypsin play important roles in modulating lung tumor proliferation in inflammatory microenvironment and curcumin inhibits neutrophil elastase-induced tumor proliferation via upregulating a1-antitrypsin expression in vitro and in vivo.