Physiological and metabolic dynamism in mycorrhizal and non-mycorrhizal Oryza sativa (var. Varsha) subjected to Zn and Cd toxicity: a comparative study

Abstract

Arable lands getting contaminated with heavy metals have a very high negative impact on crop plants. The establishment of the mycorrhizal association with crop plants is a sustainable strategy to overcome metal toxicity. The major aim of this study was to analyze mycorrhizae-mediated alterations on the physiology and metabolism of Oryza sativa, as well as the impact of these alterations in the metal tolerance potential of the host on exposure to cadmium (Cd) and zinc (Zn) stresses. For this, 45 d old O. sativa (var. Varsha) plants inoculated with Claroideoglomus claroideum were exposed to 1.95 g Zn kg−1 soil and 0.45 g Cd kg−1 soil. Mycorrhization significantly increased shoot weight, root weight, moisture content, and chlorophyll biosynthesis under Cd and Zn stresses. Mycorrhization mitigated the oxidative stress elicited in O. sativa by the elevated Cd and Zn content, and it aided in maintaining the metabolite’s level and rate of photosynthesis as compared to non-mycorrhizal plants. The circular-shaped unique structures seen as opening on the leaf surface of non-mycorrhizal plants under Zn stress, possibly for the emission of volatile compounds synthesized as a result of Zn stress, have a great chance of leaf tissue destruction. This structural modification was characterized in the case of Zn stress and not in Cd stress and can lead to the reduction of photosynthesis in O. sativa exposed to Zn stress. The reduction in oxidative stress could be correlated to the reduced uptake and transport of Cd and Zn ions in mycorrhizal plants. The exudation of tributyl acetyl citrate, 3-beta-acetoxystigmasta-4,6,22-triene, and linoleic acid from the mycorrhizal roots of rice plants has a crucial role in the stabilization of metal ions. This study proposes mycorrhization as a strategy to strengthen the Cd and Zn stress tolerance level of rice plants by regulating the physiology and metabolomics of the host plant.