Low pH-Induced Changes of Antioxidant Enzyme and ATPase Activities in the Roots of Rice (<i>Oryza sativa</i> L.) Seedlings

<div><p>Soil acidification is the main problem in the current rice production. Here, the effects of low pH on the root growth, reactive oxygen species metabolism, plasma membrane functions, and the transcript levels of the related genes were investigated in rice seedlings (<i>Oryza sativa</i> L.) in a hydroponic system at pH 3.5, 4.5, and 5.5. There were two hybrid rice cultivars in this trial, including Yongyou 12 (YY12, a japonica hybrid) and Zhongzheyou 1 (ZZY1, an indica hybrid). Higher H⁺ activity markedly decreased root length, the proportion of fine roots, and dry matter production, but induced a significant accumulation of hydrogen peroxide (H₂O₂), and led to serious lipid peroxidation in the roots of the two varieties. The transcript levels of copper/zinc superoxide dismutase 1 (Cu/Zn SOD1), copper/zinc superoxide dismutase 2 (Cu/Zn SOD2), catalase A (CATA) and catalase B (CATB) genes in YY12 and ZZY1 roots were significantly down-regulated after low pH exposure for two weeks. Meanwhile, a significant decrease was observed in the expression of the P-type Ca²⁺-ATPases in roots at pH 3.5. The activities of antioxidant enzymes (SOD, CAT) and plasma membrane (PM) Ca²⁺-ATPase in the two varieties were dramatically inhibited by strong rhizosphere acidification. However, the expression levels of ascorbate peroxidase 1 (APX1) and PM H⁺-ATPase isoform 7 were up-regulated under H⁺ stress compared with the control. Significantly higher activities of APX and PM H⁺-ATPase could contribute to the adaptation of rice roots to low pH.</p></div

H₂O₂ content (A), and MDA content (B) in roots of rice (<i>Oryza sativa</i> L.) grown at three pH levels.

<p>Each value is the mean ± standard error of three replicates. Different letters for each cultivar indicate means that differ significantly (<i>P</i> < 0.05).</p

Proportion of rice (<i>Oryza sativa</i> L. A, YY12; B, ZZY1) root lengths in different diameter classes at three pH levels.

<p>Each value is the mean ± standard error of three replicates. Different letters for each cultivar indicate means that differ significantly (<i>P</i> < 0.05) within a given diameter class.</p

Plasma membrane H⁺-ATPase (A) and Ca²⁺-ATPase (B) activities derived from rice seedling in the roots of rice (<i>Oryza sativa</i> L.) grown at three pH levels.

<p>Each value is the mean ± standard error of three replicates. Different letters for each cultivar indicate means that differ significantly (<i>P</i> < 0.05).</p

Relative expression ratios (ratio of each gene to actin) of genes encoding plasma membrane H⁺-ATPase in the roots of rice (<i>Oryza sativa</i> L.) grown at three pH levels.

<p>Each value is the mean ± standard error of three replicates. Different letters for each cultivar indicate means that differ significantly (P < 0.05).</p

Biomass and root morphology of rice (Oryza sativa L.) seedlings grown at different pH levels.

<p>Note: Each value is the mean ± standard error of three replicates. Different letters for each cultivar indicate means that differ significantly (P < 0.05).</p><p>Biomass and root morphology of rice (Oryza sativa L.) seedlings grown at different pH levels.</p

Comparative Study of the Selective Degradations of Two Enantiomers in the Racemate and an Enriched Concentration of Indoxacarb in Soils

In this study, selective degradations of the two enantiomers of indoxacarb in the concentrate (2.33S/1R) and racemate (1S/1R) are examined. The absolute configurations of indoxacarb enantiomers were determined using X-ray diffraction. The results showed that in two alkaline soils, the <i>S</i>-(+)-indoxacarb was preferentially degraded in both the concentrate and racemate. In one acid soil, the two enantiomers degraded no-selectivity. In another acid soil and one neutral soil, the <i>R</i>-(−)-indoxacarb was preferentially degraded in both the concentrate and racemate. Indoxacarb enantiomers were configurationally stable in the five soils, and no interconversion was observed during the incubation. Because no significant difference in degradation was observed after samples were sterilized, the observed enantioselectivity may be attributed primarily to microbial activity in soils. The results indicate that the selective degradation behavior was the same for both formulations that were tested