Diapause termination and development of encystedArtemiaembryos: roles for nitric oxide and hydrogen peroxide

Abstract

SUMMARYEncysted embryos (cysts) of the brine shrimp Artemia undergo diapause, a state of profound dormancy and enhanced stress tolerance. Upon exposure to the appropriate physical stimulus diapause terminates and embryos resume development. The regulation of diapause termination and post-diapause development is poorly understood at the molecular level, prompting this study on the capacity of hydrogen peroxide (H 2 O 2 ) and nitric oxide (NO) to control these processes. Exposure to H 2 O 2 and NO, the latter generated by the use of three NO generators, promoted cyst development, emergence and hatching, effects nullified by catalase and the NO scavenger 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). The maximal effect of NO and H 2 O 2 on cyst development was achieved by 4 h of exposure to either chemical. NO was effective at a lower concentration than H 2 O 2 but more cysts developed in response to H 2 O 2 . Promotion of development varied with incubation conditions, indicating for the first time a population of Artemia cysts potentially arrested in post-diapause and whose development was activated by either H 2 O 2 or NO. A second cyst sub-population, refractory to hatching after prolonged incubation, was considered to be in diapause, a condition broken by H 2 O 2 but not NO. These observations provide clues to the molecular mechanisms of diapause termination and development in Artemia, while enhancing the organism's value in aquaculture by affording a greater understanding of its growth and physiology.

Stress tolerance during diapause and quiescence of the brine shrimp, Artemia

“…Animals remain in diapause, even in conditions favorable for growth, until a habitat-specific, exogenous signal like desiccation, cold, elevated CO 2 , or light terminates the dormancy, after which growth resumes (Robbins et al 2010). The need for a termination cue differentiates diapause from quiescence, a hypometabolic, stress-tolerant state requiring only return to favorable growth parameters for termination (Drinkwater and Clegg 1991).…”

Artemin, a Diapause-Specific Chaperone, Contributes to the Stress Tolerance of Artemia Cysts and Influences Their Release from Females

“…Initiation is followed by maintenance, with metabolism generally lower and stress resistance higher than in the rest of diapause. Termination, the final phase of diapause, is triggered by species-specific signals including temperature change and desiccation (Clegg and Trotman, 2002;Robbins et al, 2010). If termination takes place in unfavorable conditions, a post-diapause…”

Shell-bound iron dependant nitric oxide synthesis in encysted Artemia parthenogenetica embryos during hydrogen peroxide exposure

“…It is obvious that hematin is actively involved in diapause deactivation in Artemia (Yosefali et al 1999), Diapause termination in Artemia can be achieved through appropriate diapause termination stimuli (for example, light, temperature, hydration, and chemicals), in which cysts undergo variety of catabolic activities to proceed into naupliar development. Hydrogen peroxide (H 2 O 2 ) is well known for its ability to produce greater degree of diapause termination success in Artemia (Van Stappen et al 1998 (Robbins et al 2010). But, it is also emphasized that NO exposure after H 2 O 2 administration helps to sustain the cysts from adverse effect of peroxide exposure.…”