The role of hydrogen peroxide in chitosan-induced resistance to osmotic stress in rice (Oryza sativa L.)

Chitosan is a biopolymer with multiple agricultural applications. The objective of this research was to identify the mechanism required for the chitosan response. Chitosan clearly induced resistance to osmotic stress (a surrogate for drought stress) in the ‘Leung Pratew 123’ (‘LPT123’) rice (Oryza sativa L. ‘Leung Pratew123’) by enhancing plant growth and maintenance of the photosynthetic pigments during osmotic stress, but not in the derived mutated line, LPT123-TC171. Hydrogen peroxide (H₂O₂) was increased after osmotic stress in both lines, but higher levels were found in the LPT123 cultivar. Chitosan application did not affect the H₂O₂ or glutathione content under the osmotic stress condition in the LPT123 cultivar, but decreased H₂O₂ accumulation in the LPT123-TC171 line. The 20-fold lower glutathione level in the LPT123 cultivar suggested a low glutathione-ascorbate cycle activity that would lead to the higher H₂O₂ levels. Whereas, the chitosan-mediated reduction in glutathione levels in the LPT123-TC171 line during osmotic stress suggested a higher glutathione-ascorbate cycle activity leading to low H₂O₂ levels. Additionally, a higher peroxidase and catalase activity following chitosan treatment of the LPT123-TC171 line supports the lower observed H₂O₂ level. The lipid peroxidation after osmotic stress was decreased by chitosan treatment in LPT123, but not in LPT123-TC171. The exogenous H₂O₂ application with chitosan treatment in LPT123-TC171 could enhance plant growth during osmotic stress. It is concluded that the limited H₂O₂ level, the signal molecule for chitosan responses in the LPT123-TC171 line, resulted in no beneficial effects of chitosan application for osmotic stress. Therefore, H₂O₂ is proposed to be one of the key components for plant growth stimulation during osmotic (drought) stress by chitosan.     

Protection of renal function by green tea extract during Plasmodium berghei infection

Impairment of renal function from oxidative stress during malaria infection is one of the leading causes of death in endemic areas. Since blood urea nitrogen and creatinine levels in plasma can be used as markers for monitoring renal damage, this study investigated the effect of green tea extract on reduction of blood urea nitrogen and creatinine levels during malaria infection using Plasmodium berghei ANKA infected mice as in vivo model. For in vivo testing, ICR mice were infected with 1 × 10⁷ parasitized erythrocytes and green tea extract was subsequently administered orally twice a day for 10 consecutive days. Parasitemia was estimated by standard microscopy, and blood urea nitrogen and creatinine levels in plasma were also measured. It was found that parasitemia kept increasing until animal death, and is strongly correlated with high blood urea nitrogen and creatinine. The highest levels of blood urea nitrogen and creatinine in plasma were found on day 10 after infection. However, blood urea nitrogen and creatinine levels in plasma were reduced and decreased significantly (p < 0.01) in green tea extract treated mice, compared with untreated group. It can be concluded that green tea extract can protect and maintain renal function during malaria infection, and this extract can be developed for use as a supplement and combination therapy.     

Anti-inflammatory cyclohexenyl chalcone derivatives in Boesenbergia pandurata.

The cyclohexenyl chalcone derivative [(-)-hydroxypanduratin A], together with the previously known panduratin A, sakuranetin, pinostrobin, pinocembrin, and dihydro-5,6-dehydrokawain were isolated from the chloroform extract of the red rhizome variety of Boesenbergia pandurata (Robx.) Schltr. [currently known as Boesenbergia rotunda (L.) Mansf., Kulturpfl.]. Their structures were assigned on the basis of their spectroscopic data. (-)-Hydroxypanduratin A and (-)-panduratin A showed significant topical anti-inflammatory activity in the assay of TPA-induced ear edema in rats.     

Expression levels of genes involved in metal homeostasis,physiological adaptation,and growth characteristics of rice (Oryza sativa L.) genotypes under Fe and/or Al toxicity

Acid sulphate soil contains high amounts of iron (Fe) and aluminum (Al), and their contamination has been reported as major problems, especially in rainfed and irrigated lowland paddy fields. Rice is sensitive to Fe and Al grown in acid soil (pH < 5.5), leading to growth inhibition and grain yield loss. The objective of this study was to evaluate Fe and/or Al uptake, translocation, physiological adaptation, metal toxicity, and growth inhibition in rice genotypes grown in acid soil. Fe and Al in the root tissues of all rice genotypes were enriched depending on the exogenous application of either Fe or Al in the soil solution, leading to root growth inhibition, especially in the KDML105 genotype. Expression level of OsYSL1 in KDML105 was increased in relation to metal uptake into root tissues, whereas OsVIT2 was downregulated, leading to Fe (50.3 mg g⁻¹ DW or 13.1 folds over the control) and Al (4.8 mg g⁻¹ DW or 2.2 folds over the control) translocation to leaf tissues. Consequently, leaf greenness (SPAD), net photosynthetic rate (P_n), stomatal conductance (g_s), and transpiration rate (E) in the leaf tissues of genotype KDML105 under Fe + Al toxicity significantly declined by 28.4%, 35.3%, 55.6%, and 51.6% over the control, respectively. In Azucena (AZU; Fe/Al tolerant), there was a rapid uptake of Fe and Al by OsYSL1 expression in the root tissues, but a limited secretion into vacuole organelles by OsVIT2, leading to a maintenance of low level of toxicity driven by an enhanced accumulation of glutathione together with downregulation of OsGR expression level. In addition, Fe and Al restrictions in the root tissues of genotype RD35 were evident; therefore, crop stress index (CSI) of Fe + Al–treated plants was the maximum, leading to an inhibition of g_s (53.6% over the control) and E (49.0% over the control). Consequently, free proline, total phenolic compounds, and ascorbic acid in the leaf tissues of rice under Fe + Al toxicity significantly increased by 3.2, 1.2, and 1.5 folds over the control, respectively, indicating their functions in non-enzymatic antioxidant defense. Moreover, physiological parameters including leaf temperature (T_leaf) increment, high level of CSI (>0.6), SPAD reduction, photon yield of PSII (Φ_PSII) diminution, P_n, g_s, and E inhibition in rice genotype IR64 (Fe/Al-sensitive) under Fe + Al treatment were clearly demonstrated as good indicators of metal-induced toxicity. Our results on Fe- and/or Al-tolerant screening to find out the candidate genotypes will contribute to present screening and breeding efforts, which in turn help increase rice production in the Fe/Al-contaminated acid soil under lowland conditions.