Effects of Arbuscular Mycorrhizal Fungi on Watermelon Growth, Elemental Uptake, Antioxidant, and Photosystem II Activities and Stress-Response Gene Expressions Under Salinity-Alkalinity Stresses.

Lin Ye,Zhirong Zou,Encai Bao,Kai Cao,Xia Zhao

doi:10.3389/fpls.2019.00863

Abstract

Salinity-alkalinity stress has caused severe environment problems that negatively impact the growth and development of watermelon (Citrullus lanatus L.). In this study, watermelon seedlings were inoculated with the arbuscular mycorrhizal fungi (AMF) Funneliformis mosseae to investigate its effect on watermelon growth and development. The main measurements included morphological traits, elemental and water uptake, the level of reactive oxygen species, antioxidant enzyme and photosynthesis activities, and relative expression levels of stress response genes. Under salinity-alkalinity stresses, watermelon morphological traits, elemental and water uptake were all significantly alleviated after incubation with AMF. Antioxidant abilities of watermelon were significantly improved after incubation with AMF in salinity-alkalinity stresses. Under normal conditions, all photosynthesis related parameters were significantly increased after incubation of AMF. In contrast, they were all significantly reduced under salinity-alkalinity stresses and were all significantly alleviated after incubation of AMF. Salinity-alkalinity stresses impacted the chloroplast structure and AMF significantly alleviated these damages. Under salinity-alkalinity stresses, the relative expression level of RBCL was significantly reduced and was significantly alleviated after AMF treatment. The relative expression level of PPH was significantly increased and was further significantly reduced after AMF treatment. For the relative expression levels of antioxidant response related genes Cu-Zn SOD, CAT, APX, GR, their relative expression levels were significantly increased and were further significantly increased after AMF treatment. Our study demonstrated the beneficial effects of AMF under salinity-alkalinity stresses, which could be implicated in the management of watermelon cultivation under salinity-alkalinity regions.

Highlights

Soil salinization and alkalization have become major contributing factors to the ever increasing areas of land degradation worldwide, in arid and semi-arid areas (Al-Karaki, 2006; Aragüés et al, 2015)
We aim to investigate the effects of arbuscular mycorrhizal fungi (AMF) under salinity-alkalinity stresses on: (1) watermelon morphological development and elemental uptake; (2) the chlorophyll content, fluorescence, and ultrastructure as well the super oxidant species and antioxidant enzyme activities; (3) the relative expression levels of some important antioxidant response related genes, such as Cu-Zn subunit-superoxide dismutase (Cu-Zn SOD), catalase (CAT), cytoplasmic ascorbate peroxidase (APX), and cytoplasmic glutathione reductase (GR)
When there was no salinity-alkalinity stress, AMF treatment had no significant influence on the activities of the enzymes aforementioned (Figure 3). These results revealed that watermelon seedlings inoculated with AMF grown under salinity-alkalinity conditions improved the tolerance to salinity-alkalinity stresses

Summary

Introduction

Soil salinization and alkalization have become major contributing factors to the ever increasing areas of land degradation worldwide, in arid and semi-arid areas (Al-Karaki, 2006; Aragüés et al, 2015). The production of reactive oxygen species (ROS) is an important indicator for plants under salinity-alkalinity stress conditions (Noctor et al, 2014). High levels of ROS severely destroy cell membranes and impact a wide range of essential macro-molecules, such as photosynthetic pigments, proteins and DNA (Noctor et al, 2014; Li et al, 2017; Cao et al, 2018; Abdel Latef et al, 2019). The accumulation of ROS species is significantly increased (Li et al, 2017). Over accumulation of ROS inhibits the photosynthetic related enzyme activities and destroys the photosynthetic apparatus within the cell (Allakhverdiev et al, 2008)

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Methods

Results