ABSTRACT
Molybdenum (Mo) is an important trace element for higher plants and plays an important regulatory role in developmental processes, photosynthesis, nitrogen (N) metabolism, hormone signaling, and stress tolerance. Molybdenum is an important element for more than 40 enzymes, four of which have been extensively studied in plants and include nitrate reductase (NR), and nitrogenase which is involved in nitrogen fixation and assimilation, respectively, xanthine dehydrogenase/oxidase (XDH), which plays an important role in purine catabolism, aldehyde oxidase (AO), which plays an essential part in the synthesis of indole-3 acetic acid (IAA), abscisic acid (ABA), and sulfite oxidase (SO) which has a role in sulfur metabolism. Molybdenum application increased the synthesis of nitric oxide (NO) through regulating NR and NO as a signal molecule regulates a series of growth modules including primary root growth, root meristem growth, root hair development, and lateral root formation. Therefore, it could be speculated that Mo application might improve root system growth through NO accumulation 326and NR regulation. Molybdate is the dominant form of Mo available to plants. Although Mo participates in various redox reactions, it is required at very low levels and the required amount of Mo is considered to be one of the lowest among the essential micronutrients. There are several possible ways by which Mo could enhance the development of stress tolerance in plant cells; Mo may increase the anti-oxidative defense by increasing the activity of the anti-oxidative enzymes. Molybdenum also activates AO and thereby increasing the ABA content. ABA accumulation can trigger bZIP transcription factors (TFs) and downstream stress signaling.
