Ultrasound application for the decontamination of roselle (Hibiscus sabdariffa L.) seeds: Influence on fungal inhibition and seed quality.

Seed decay is a major problem caused by pathogens that adversely affect seed yield and quality in agricultural production. Herein, the effect of 28 KHz ultrasound treatment for 20, 40 and 60 min and 1.5% sodium hypochlorite solution for 20 min was assessed for the decontamination of roselle (Hibiscus sabdariffa L.) seeds. In addition, seed germination indices, seedling growth traits, total phenolic content and the activity of defense-related enzymes, viz. peroxidase, superoxide dismutase, catalase and malondialdehyde were measured in the treated seeds. An isolate of Fusarium solani was obtained from roselle seeds and identified as the causal agent of roselle seed rot based on morphological and molecular characteristics. After six days of seed storage, the microbial infection caused the highest seed rot in the control seeds on the average of 56.67%, whereas ultrasound treatment for 60 min could remarkably reduce the seed decay by 3.33%. At the end of seed storage, the fungal load showed the highest (7.72 Log CFU ml-1) and lowest (6.99 Log CFU ml-1) rates in the control and ultrasound treatment for 60 min, respectively. Total phenolic content was significantly increased in ultrasound treatment for 60 min compared to control and sodium hypochlorite treatments. Moreover, the activity of peroxidase, superoxide dismutase and catalase was noticeably improved in ultrasound treatment for 60 min. Furthermore, ultrasound treatment did not show any adverse effects on seed germination indices and seedling growth traits of the roselle plants. Overall, ultrasound treatment for 60 min could effectively decrease roselle seed decay and the fungal load without changing seed and seedling quality.

Structural insights into the mechanism of activation of the TRPV1 channel by a membrane-bound tarantula toxin.

Venom toxins are invaluable tools for exploring the structure and mechanisms of ion channels. Here, we solve the structure of double-knot toxin (DkTx), a tarantula toxin that activates the heat-activated TRPV1 channel. We also provide improved structures of TRPV1 with and without the toxin bound, and investigate the interactions of DkTx with the channel and membranes. We find that DkTx binds to the outer edge of the external pore of TRPV1 in a counterclockwise configuration, using a limited protein-protein interface and inserting hydrophobic residues into the bilayer. We also show that DkTx partitions naturally into membranes, with the two lobes exhibiting opposing energetics for membrane partitioning and channel activation. Finally, we find that the toxin disrupts a cluster of hydrophobic residues behind the selectivity filter that are critical for channel activation. Collectively, our findings reveal a novel mode of toxin-channel recognition that has important implications for the mechanism of thermosensation.