Abstract

BackgroundLimited data are available on the responses of reactive oxygen species (ROS) and methylglyoxal (MG) metabolisms to low pH in roots and leaves. In China, quite a few of Citrus are cultivated in acidic soils (pH < 5.0). ‘Xuegan’ (Citrus sinensis) and ‘Sour pummelo’ (Citrus grandis) (C. sinensis were more tolerant to low pH than C. grandis) seedlings were irrigated daily with nutrient solution at a pH of 2.5, 3 or 5 for nine months. Thereafter, we examined low pH effects on growth, and superoxide anion production rate (SAP), malondialdehyde (MDA), MG, antioxidants, and enzymes related to ROS and MG detoxification in roots and leaves in order to (a) test the hypothesis that low pH affected ROS and MG metabolisms more in roots than those of leaves, and (b) understand the roles of ROS and MG metabolisms in Citrus low pH-tolerance and -toxicity.ResultsCompared with control, most of the physiological parameters related to ROS and MG metabolisms were greatly altered at pH 2.5, but almost unaffected at pH 3. In addition to decreased root growth, many fibrous roots became rotten and died at pH 2.5. pH 2.5-induced changes in SAP, the levels of MDA, MG and antioxidants, and the activities of most enzymes related to ROS and MG metabolisms were greater in roots than those of leaves. Impairment of root ascorbate metabolism was the most serious, especially in C. grandis roots. pH 2.5-induced increases in MDA and MG levels in roots and leaves, decreases in the ratios of ascorbate/(ascorbate+dehydroascorbate) in roots and leaves and of reduced glutathione/(reduced+oxidized glutathione) in roots were greater in C. grandis than those in C. sinensis.ConclusionsLow pH affected MG and ROS metabolisms more in roots than those in leaves. The most seriously impaired ascorbate metabolism in roots was suggested to play a role in low pH-induced root death and growth inhibition. Low pH-treated C. sinensis roots and leaves had higher capacity to maintain a balance between ROS and MG production and their removal via detoxification systems than low pH-treated C. grandis ones, thus contribute to the higher acid-tolerance of C. sinensis.

Highlights

  • Limited data are available on the responses of reactive oxygen species (ROS) and methylglyoxal (MG) metabolisms to low pH in roots and leaves

  • We examined low pH effects on growth, and superoxide anion production rate (SAP), MDA, MG, antioxidants, and enzymes related to ROS and MG detoxification in roots and leaves of C. sinensis and C. grandis seedlings differing in low pH-tolerance

  • Low pH effects on seedling growth Compared with pH 5, C. grandis and C. sinensis seedling growth was greatly reduced at pH 2.5, but displayed little changed at pH 3. pH 2.5-induced decreases in root and shoot dry weight (DW) were greater in C. grandis seedlings than those of C. sinensis seedlings

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Summary

Introduction

Limited data are available on the responses of reactive oxygen species (ROS) and methylglyoxal (MG) metabolisms to low pH in roots and leaves. Overproduction and accumulation of reactive oxygen species (ROS) and methylglyoxal (MG) in plant cells in response to abiotic stresses is a common phenomenon [16,17,18,19,20]. Sulfur (S) metabolism, a central pathway for the biosynthesis of S-containing compounds-namely reduced glutathione (GSH), cysteine (Cys) and H2S -plays important roles in plant tolerance to abiotic stresses [16, 25]. The coordinated actions of glyoxalases and antioxidant systems have been suggested to play a role in the alleviation of oxidative stress in plants [17]

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