Unearthing the alleviatory mechanisms of hydrogen sulfide in aluminum toxicity in rice.

Hydrogen sulfide (H2S) improves aluminum (Al) resistance in rice, however, the underlying mechanism remains unclear. In the present study, treatment with 30-µM Al significantly inhibited rice root growth and increased the total Al content, apoplastic and cytoplasm Al concentration in the rice roots. However, pretreatment with NaHS (H2S donor) reversed these negative effects. Pretreatment with NaHS significantly increased energy production under Al toxicity conditions, such as by increasing the content of ATP and nonstructural carbohydrates. In addition, NaHS stimulated the AsA-GSH cycle to decrease the peroxidation damage induced by Al toxicity. Pretreatment with NaHS significantly inhibited ethylene emissions in the rice and then inhibited pectin synthesis and increased the pectin methylation degree to reduce cell wall Al deposition. The phytohormones indole-3-acetic and brassinolide were also involved in the alleviation of Al toxicity by H2S. The transcriptome results further confirmed that H2S alleviates Al toxicity by increasing the pathways relating to material and energy metabolism, redox reactions, cell wall components, and signal transduction. These findings improve our understanding of how H2S affects rice responses to Al toxicity, which will facilitate further studies on crop safety.

Berberine versus placebo for the prevention of recurrence of colorectal adenoma: a multicentre, double-blinded, randomised controlled study.

BACKGROUND: Chemoprevention of colorectal adenoma and colorectal cancer remains an important public health goal. The present study aimed to investigate the clinical potential and safety of berberine for prevention of colorectal adenoma recurrence. METHODS: This double-blind, randomised, placebo-controlled trial was done in seven hospital centres across six provinces in China. Individuals aged 18-75 years who had at least one but no more than six histologically confirmed colorectal adenomas that had undergone complete polypectomy within the 6 months before recruitment were recruited and randomly assigned (1:1) to receive berberine (0·3 g twice daily) or placebo tablets via block randomisation (block size of six). Participants were to undergo a first follow-up colonoscopy 1 year after enrolment, and if no colorectal adenomas were detected, a second follow-up colonoscopy at 2 years was planned. The study continued until the last enrolled participant reached the 2-year follow-up point. All participants, investigators, endoscopists, and pathologists were blinded to treatment assignment. The primary efficacy endpoint was the recurrence of adenomas at any follow-up colonoscopy. Analysis was based on modified intention-to-treat, with the full analysis set including all randomised participants who received at least one dose of study medication and who had available efficacy data. The study is registered with ClinicalTrials.gov, number NCT02226185; the trial has ended and this report represents the final analysis. FINDINGS: Between Nov 14, 2014, and Dec 30, 2016, 553 participants were randomly assigned to the berberine group and 555 to the placebo group. The full analysis set consisted of 429 participants in the berberine group and 462 in the placebo group. 155 (36%) participants in the berberine group and 216 (47%) in the placebo group were found to have recurrent adenoma during follow-up (unadjusted relative risk ratio for recurrence 0·77, 95% CI 0·66-0·91; p=0·001). No colorectal cancers were detected during follow-up. The most common adverse event was constipation (six [1%] of 446 patients in the berberine group vs one [<0·5%] of 478 in the placebo group). No serious adverse events were reported. INTERPRETATION: Berberine 0·3 g twice daily was safe and effective in reducing the risk of recurrence of colorectal adenoma and could be an option for chemoprevention after polypectomy. FUNDING: National Natural Science Foundation of China.

Putrescine alleviates aluminum toxicity in rice (Oryza sativa) by reducing cell wall Al contents in an ethylene-dependent manner.

Aluminum (Al3+ ) toxicity in acidic soils limits crop productivity worldwide. In this study, we found that putrescine (PUT) significantly alleviates Al toxicity in rice roots. The addition of 0.1 mM PUT promoted root elongation and reduced the Al content in the root apices of Nipponbare (Nip) and Kasalath (Kas) rice under Al toxicity conditions. Exogenous treatment with PUT reduced the cell wall Al content by reducing polysaccharide (pectin and hemicellulose) levels and pectin methylesterase (PME) activity in roots and decreased the translocation of Al from the external environment to the cytoplasm by downregulating the expression of OsNRAT1, which responsible to encode an Al transporter protein Nrat1 (Nramp aluminum transporter 1). The addition of PUT under Al toxicity conditions significantly inhibited ethylene emissions and suppressed the expression of genes involved in ethylene biosynthesis. Treatment with the ethylene precursor 1-aminocylopropane-1-carboxylic acid (ACC) significantly improved ethylene emission, inhibited root elongation, increased the Al accumulation in root tips and the root cell wall, and increased cell wall pectin and hemicellulose contents in both rice cultivars under Al toxicity conditions. The ethylene biosynthesis antagonist aminoethoxyvinylglycine (AVG, inhibitor of the ACC synthase) had the opposite effect and reduced PME activity. Together, our results show that PUT decreases the cell wall Al contents by suppressing ethylene emissions and decreases the symplastic Al levels by downregulating OsNRAT1 in rice.

Boron reduces cell wall aluminum content in rice (Oryza sativa) roots by decreasing H2O2 accumulation.

When boron (B) deficiency and aluminum (Al) toxicity co-exist in acidic soils, crop productivity is limited. In the current study, we found that 3 µM of B pretreatment significantly enhances rice root elongation under Al toxicity conditions. Pretreatment with B significantly decreases the deposition of Al in rice apoplasts, suppresses the synthesis of cell wall pectin, inhibits cell wall pectin methylesterase (PME) activity and its gene expression, and increases the expression of OsSTAR1 and OsSTAR2, which are responsible for reducing the Al content in the cell walls. In addition, B pretreatment significantly increases OsALS1 expression, thereby facilitating the transfer of Al from the cytoplasm to the vacuoles. However, B pretreatment had no effect on Al uptake and citric acid secretion. Pretreatment with B significantly increases the activity of ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT), thus increasing the elimination rate of H2O2 in rice roots. Co-treatment using B and H2O2 does not increase root growth under Al toxicity conditions; it also improves pectin synthesis, enhances PME activity, and increases Al deposition in root cell walls. However, the co-treatment of B and H2O2 scavenger 4-hydroxy-TEMPO has an opposite effect. The above results indicate that applying B fertilizers in acidic soil can help decrease the side effects of Al toxicity on rice growth.