Arbuscular mycorrhizal symbiosis enhanced growth and antioxidant metabolism in date palm subjected to long-term drought

Arbuscular mycorrhizal symbiosis can help date palm to cope with the oxidative stress induced by long-term drought due to its capacity to enhance host plant antioxidant defense system. Plant adaptation to water scarcity is mostly the result of existing intrinsic traits. However, mycorrhizal symbiosis is widely believed to provide complementary characteristics that improve host plants protection against the deleterious effect of drought. We previously showed that arbuscular mycorrhizal (AM) date palm seedlings suffered less water stress imposed by short period of water deficiency due to a primary drought avoidance effect by the AM symbiosis related to difference in water and nutrients status between mycorrhizal and non-mycorrhizal plants. The objective of this investigation was to study the impact of long-term drought stress (LTDS, 25 % field capacity) on changes of antioxidant metabolism in non-mycorrhizal and mycorrhizal (colonized with Rhizophagus intraradices or Funneliformis mosseae) date palm seedlings. Obtained results revealed that LTDS induced clear decreases in shoot height (SH), root length (RL) and shoot (SDW) and root (RDW) dry weights. However, AM colonization alleviated the detrimental effect of LTDS on growth performance of date palm seedlings. Moreover, AM colonization mitigated drought-induced oxidative stress by alleviating H2O2 and malondialdehyde (MDA) accumulation and enhancing antioxidant enzymes activities, e.g., catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and guaiacol peroxidase (G-POD). Our results revealed different responses of mycorrhizal seedlings to LTDS depending on AM fungi strains. R. intraradices (Ri) induced the highest SH and RL, the highest SDW and RDW and the highest mycorrhizal dependency. Ri-plants exhibited the lowest MDA and H2O2 contents and the highest CAT, SOD, APX and G-POD activities. Furthermore, Ri-plants showed the lowest oxidative damage and the highest proteins and soluble sugars contents. Thus, AM colonization enhanced date palm strategies involving antioxidant defense system to cope with the LTDS-induced oxidative stress.