Functional Characterization of the Pheophytinase Gene, ZjPPH, From Zoysia japonica in Regulating Chlorophyll Degradation and Photosynthesis

Pheophytinase (PPH), the phytol hydrolase, plays important roles in chlorophyll degradation. Nevertheless, little attention has been paid to the PPHs in warm-season grass species; neither its detailed function in photosynthesis has been systematically explored to date. In this study, we isolated ZjPPH from Zoysia japonica, an excellent warm-season turfgrass species. Quantitative real-time PCR analysis and promoter activity characterization revealed that the expression of ZjPPH could be induced by senescence, ABA, and dark induction. Subcellular localization observation proved that ZjPPH was localized in the chloroplasts. Overexpression of ZjPPH accelerated the chlorophyll degradation and rescued the stay-green phenotype of the Arabidopsis pph mutant. Moreover, ZjPPH promoted senescence with the accumulation of ABA and soluble sugar contents, as well as the increased transcriptional level of SAG12 and SAG14. Transmission electron microscopy investigation revealed that ZjPPH caused the decomposition of chloroplasts ultrastructure in stable transformed Arabidopsis. Furthermore, chlorophyll a fluorescence transient measurement analysis suggested that ZjPPH suppressed photosynthesis efficiency by mainly suppressing both photosystem II (PSII) and photosystem I (PSI). In conclusion, ZjPPH plays an important role in chlorophyll degradation and senescence. It could be a valuable target for genetic editing to cultivate new germplasms with stay-green performance and improved photosynthetic efficiency.

A New Benchmark of Charges Storage in Single-Layer Organic Light-Emitting Diodes Based on Electrical and Optical Characteristics

The storage of charges in organic light-emitting diodes (OLEDs) has drawn much attention for its damage to device performance as well as the loss to carriers. Thus, it is essential to address the issue and do further investigation. The traditional approach to storage analysis is mainly based on transient measurement since it is sensitive to transient instead of steady signal. In this paper, we proposed a new benchmark to investigate the single-layer OLEDs capable of stored charges with poly (methyl methacrylate) (PMMA), which is just based on electrical and optical characteristics. Since the stored charges contribute both to luminance and current of the devices with PMMA, the area between them can be taken as a benchmark and evaluated the storage of charges. In our experiment, the areas of 4 nm, 6 nm, 8 nm, and 10 nm PMMA devices are 0.348, 0.554, 0.808, and 0.894, respectively, indicating a higher capability of storage in thicker PMMA. It is exactly in line with the results taken from transient electroluminescence (EL) measurement. Thus, this new benchmark is practical and provides a more accessible approach to investigate the storage of charges in OLEDs.

739SERCA2 Cys674 modification lead to ventricular arrhythmia due to impaired sarcoplasmic reticulum Ca2+ handling

Background Sarcoplasmic reticulum Ca2+-ATPase2 (SERCA2) plays an important role in intracellular Ca2+ handling. Under pathological conditions, oxidative stress leads to irreversible oxidation of Cys674 on SERCA2 which causes intracellular Ca2+ overload. Intracellular Ca2+ overload is known as the cause of ventricular arrhythmia, but the relation between SERCA2 function and ventricular arrhythmia remains unclear. Purpose To investigate the role of Cys674 on SERCA2 in the intracellular Ca2+ handling and the induction of ventricular arrhythmia. Methods We employed SERCA2 Cys674Ser heterozygote knock-in mice (SKI) which mimics oxidative modification of Cys674 on SERCA2. Continuous infusion of angiotensin (ANG) (3mg/kg/day) or distilled water were performed both in wild type mice (WT) and SKI for a week. After 1 week, electrophysiological study and intracellular Ca2+ transient measurement were performed. Results ANG elevated blood pressure and represented cardiac hypertrophy with fibrosis similarly both in WT and SKI. The mRNA expression of calcium/calmodulin-dependent protein kinase-II (CaMKII), ryanodine receptor (RyR) and sodium-calcium exchanger (NCX) was increased in SKI heart compared with WT. QTc interval was prolonged in SKI compared with WT, which was markedly prolonged with ANG infusion. Under programmed electrical stimulation, only SKI with ANG showed high incidence of pacing induced ventricular arrhythmia (0/11 in WT/SKI control, 0/14 in WT with ANG vs. 8/14 in SKI with ANG, P < 0.01). In Ca2+ transient measurement, the peak Ca2+ transient amplitude (F/F0) was decreased (WT: 1.81 vs. SKI: 1.46, P < 0.01) and the time to 50% of cytosolic Ca2+ extrusion (T50) was prolonged (WT: 152.6ms vs. SKI: 202.3ms, P < 0.05) in SKI with ANG, suggesting decreased sarcoplasmic reticulum Ca2+ content and impaired SERCA2 activity in SKI with ANG. Intraperitoneal administration of dantrolene sodium (DAN) which inhibit Ca2+ leakage from RyR receptor normalized decreased F/F0 and prolonged T50 in SKI with ANG (Fig. 1 A, B). DAN also prevented QTc prolongation and decreased the incidence of ventricular arrhythmia in SKI with ANG (8/14 in SKI with ANG vs. 2/13 in SKI with ANG + DAN, P < 0.05) (Fig. 2). Conclusions The loss of thiol on Cys674 under pathological condition resulted in impaired Ca2+ handling and high incidence of ventricular arrhythmia which were ameliorated by inhibition of Ca2+ leakage through RyR. Oxidative modification of Cys674 on SERCA2 might contribute to Ca2+ mishandling and arrhythmogenesis. Abstract Figure.