مروری بر پدیده زندگی بدون آب (anhydrobiosis) در نماتد Aphelenchus avenae Bastian, 1865 (Nematoda: Tylenchomorpha)

The evolution of organisms has been based on the adoption of survival strategies against adverse conditions. Dehydration is one of the most serious stresses for all organisms. Some organisms can persist while losing most of their water content of the body (up to 99%) and stay in a specific biological state for long periods of time until rehydration. This phenomenon is known as anhydrobiosis (life without water) which is actually a type of cryptobiosis (cryptic or hidden life). Cryptobiosis is a generic term for the metabolism of some organisms that do not show any signs of life and whose metabolic activity is difficult to measure and stops reversibly. It is divided into five groups based on the causative factors: cryobiosis (induced by freezing), thermobiosis (low and high temperature), osmobiosis (very high osmolarity), anoxybiosis (lack of oxygen) and anhydrobiosis (lack of water) are classified. Anhydrobiosis is the most common form of cryptobiosis and one of the ways for organisms to counter with drought. Anhydrobiotic organisms are adapted to extremely dry conditions and can survive almost completely after dehydration. Such organisms are found in many different species from unicellular organisms to invertebrates and higher plants. A small number of multicellular eukaryotes can survive without water in their adult stage. The phylum Nematoda encompasses a very diverse group of species and can be found in a variety of habitats. Aphelenchus avenae, as an animal model of anhydrobiosis, has obtained the ability to escape cell death in relative zero humidity for years. This anhydrobiotic nematode resumes its normal metabolic activity in the presence of water. During evolution, A. avenae has developed a plastic genome by genome duplication and has been able to develop molecular systems to protect somatic cells during long-term dehydration. Also, the drought resistance gene that exists in some drought-resistant plants has been identified in this species as well. Of course, A. avenae can only tolerate slow and gradual water loss. Identification of anhydrobiosis-related genes is a major requirement in development of anhydrobiotic engineering, the purpose of which is to confer desiccation tolerance on dehydration-sensitive biological samples (cells, tissues and organs). Successful anhydrobiotic engineering would have multiple applications in agriculture (for example, by rendering plants tolerant to drought), medicine (for example, preservation in the dry state of organs for transplant), and biological control (formulating entomopathogenic nematodes). In this review, we will describe the characteristics of this species and its relationship with anhydrobiosis. Providing solutions such as transferring genes related to anhydrobiosis mechanisms can reduce the effects of drought on agriculture and environment.