In flowering plants with dry stigmas, pollen hydration involves water movement, which may be facilitated by aquaporins. To explore the possibility underlying this biological process, we identified and characterized a mutant with a T-DNA insertion in PIP2;5, which encodes an aquaporin with water channel activity in the PIP2 subfamily. We monitored the pollination process (pollen hydration, germination, and pollen tube growth) of wild type pollen on stigmas of the mutant and wild type. Pollen hydration was postponed on the stigmas of the mutant, compared with that on wild type stigmas. However, pollen tube germination and growth was unaffected in the mutant. The PIP2;5 protein was located in the cell plasma membrane and was preferentially expressed in the stigma. Based on our results, we concluded that PIP2;5 might play an important role in water movement during pollen hydration.
The roles of mitochondrial respiration in pluripotency remain largely unknown. We show here that mouse ESC mitochondria possess superior respiration capacity compared to somatic cell mitochondria, and oxidative phosphorylation (OXPHOS) generates the majority of cellular ATP in ESCs. Inhibition of OXPHOS results in extensive pluripotency and metabolic gene expression reprogram, leading to disruption of self-renewal and pluripotency. Metabolomics profiling identifies UDP-N-acetylglucosamine (UDP-GlcNAc) as one of the most significantly decreased metabolites in response to OXPHOS inhibition. The loss of ESC identity induced by OXPHOS inhibition can be ameliorated by directly adding GlcNAc both in vitro and in vivo. This work demonstrates that mitochondrial respiration, but not glycolysis, produces the majority of ATP in ESCs, and uncovers a novel mechanism whereby mitochondrial respiration is coupled with the hexosamine biosynthesis pathway to generate UDP-GlcNAc for ESC identity maintenance.
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