Mycorrhizas alter sucrose and proline metabolism in trifoliate orange exposed to drought stress

Hui-Hui Wu,Qiu-Dan Ni,Ying-Ning Zou,Mohammed Mahabubur Rahman,Qiang-Sheng Wu

doi:10.1038/srep42389

Hui-Hui Wu, Qiu-Dan Ni + Show 3 more

Open Access

https://doi.org/10.1038/srep42389

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Abstract

Arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in plants, whereas little is known regarding AMF contribution to sucrose and proline metabolisms under drought stress (DS). In this study, Funneliformis mosseae and Paraglomus occultum were inoculated into trifoliate orange (Poncirus trifoliata) under well watered and DS. Although the 71-days DS notably (P < 0.05) inhibited mycorrhizal colonization, AMF seedlings showed significantly (P < 0.05) higher plant growth performance and leaf relative water content, regardless of soil water status. AMF inoculation significantly (P < 0.05) increased leaf sucrose, glucose and fructose concentration under DS, accompanied with a significant increase of leaf sucrose phosphate synthase, neutral invertase, and net activity of sucrose-metabolized enzymes and a decrease in leaf acid invertase and sucrose synthase activity. AMF inoculation produced no change in leaf ornithine-δ-aminotransferase activity, but significantly (P < 0.05) increased leaf proline dehydrogenase activity and significantly (P < 0.05) decreased leaf both Δ1-pyrroline-5-carboxylate reductase and Δ1-pyrroline-5-carboxylate synthetase activity, resulting in lower proline accumulation in AMF plants under DS. Our results therefore suggest that AMF strongly altered leaf sucrose and proline metabolism through regulating sucrose- and proline-metabolized enzyme activities, which is important for osmotic adjustment of the host plant.

Highlights

Arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in plants, whereas little is known regarding AMF contribution to sucrose and proline metabolisms under drought stress (DS)
Mycorrhizal colonization was not observed in roots of non-AMF seedlings regardless of well watered (WW) and DS
The negative effects of drought stress on root AMF colonization might be due to the germination of spores and the spread of hyphae in soils being inhibited by DS21,27

Summary

Introduction

Arbuscular mycorrhizal fungi (AMF) can enhance drought tolerance in plants, whereas little is known regarding AMF contribution to sucrose and proline metabolisms under drought stress (DS). AMF inoculation produced no change in leaf ornithine-δ-aminotransferase activity, but significantly (P < 0.05) increased leaf proline dehydrogenase activity and significantly (P < 0.05) decreased leaf both Δ1-pyrroline-5-carboxylate reductase and Δ1-pyrroline-5-carboxylate synthetase activity, resulting in lower proline accumulation in AMF plants under DS. The mechanisms about AMF-enhanced drought tolerance of host plants are poorly known, though possible mechanisms include direct water and nutrient uptake via extraradical hyphae, better root system architecture, enhancement of antioxidant defense systems, and greater osmotic adjustment[3,5]. Mycorrhizal inoculation did not affect AI activities, but increased SS activities 40 days after seed germination[15] Such changes in sugar accumulation and sucrose-metabolized enzyme activities under mycorrhization highlight AMF’s ability in OA to enhance drought tolerance of host plants. The effect of AMF on proline metabolism is still not fully understood

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