Analogues of vertebrate natriuretic peptides (NPs) present in plants, termed plant natriuretic peptides (PNPs), comprise a novel class of hormones that systemically affect salt and water balance and responses to plant pathogens. Several lines of evidence indicate that Arabidopsis thaliana PNP (AtPNP-A) affects cellular redox homeostasis, which is also typical for the signaling of its vertebrate analogues, but the molecular mechanism(s) of this effect remains elusive. Here we report identification of catalase 2 (CAT2), an antioxidant enzyme, as an interactor of AtPNP-A. The full-length AtPNP-A recombinant protein and the biologically active fragment of AtPNP-A bind specifically to CAT2 in surface plasmon resonance (SPR) analyses, while a biologically inactive scrambled peptide does not. In vivo bimolecular fluorescence complementation (BiFC) showed that CAT2 interacts with AtPNP-A in chloroplasts. Furthermore, CAT2 activity is lower in homozygous atpnp-a knockdown compared with wild type plants, and atpnp-a knockdown plants phenocopy CAT2 -deficient plants in their sensitivity to elevated H 2 O 2 , which is consistent with a direct modulatory effect of the PNP on the activity of CAT2 and hence H 2 O 2 homeostasis. Our work underlines the critical role of AtPNP-A in modulating the activity of CAT2 and highlights a mechanism of fine-tuning plant responses to adverse conditions by PNPs.

ObjectivesTo evaluate methods for the pre-treatment verification of volumetric modulated arc therapy (VMAT) based on the percentage gamma passing rate (%GP) and its correlation and sensitivity with percentage dosimetric errors (%DE).MethodsA total of 25 patients with prostate cancer and 15 with endometrial cancer were analysed. The %GP values of 2D and 3D verifications with different acceptance criteria (1%/1 mm, 2%/2 mm, and 3%/3 mm) were obtained using OmniPro and Compass. The %DE was calculated using a planned dose volume histogram (DVH) created in Monaco's treatment planning system (TPS), which relates radiation dose to tissue and the patient's predicted dose volume histogram in Compass. Statistical correlation between %GP and %DE was verified using Pearson's correlation coefficient. Sensitivity was calculated based on the receiver operating characteristics (ROC) curve. Plans were calculated using Collapsed Cone Convolution and the Monte Carlo algorithm.ResultsThe t-test results of the planned and estimated DVH showed that the mean values were comparable (P > 0.05). For the 3%/3 mm criterion, the average %GP was acceptable for the prostate and endometrial cancer groups, with average rates of 99.68 ± 0.49% and 99.03 ± 0.59% for 2D and 99.86 ± 0.39% and 99.53 ± 0.44% for 3D, respectively. The number of correlations was poor for all analysed data. The mean Pearson's R-values for prostate and endometrial cancer were < 0.45 and < 0.43, respectively. The area under the ROC curve for the prostate and endometrial cancer groups, was lower than 0.667.ConclusionsAnalysis of the %GP versus %DE values revealed only weak correlations between 2D and 3D verifications. DVH results obtained using the Compass system will be helpful in confirming that the analysed plans respect dosimetric constraints.