487  2000 American Society for Photobiology 0031-8655/00 $5.00+0.00 Photochemistry and Photobiology, 2000, 71(4): 487–492 Changes in Hemolymph Glutathione Status After Variation in Photoperiod and Light-irradiance in Crayfish Procambarus clarkii and Procambarus digueti Julio Prieto-Sagredo 1 , Ine ´ s Ricalde-Recchia 1 , Marı ´a Elena Dura ´ n-Lizarraga 1 , Marı ´a Eugenia Gonsebatt 2 and Marı ´a Luisa Fanjul-Moles* 1 1 Lab. Neurofisiologı ´a Comparada, Facultad de Ciencias, UNAM, Mexico and 2 Departamento de Gene ´ tica y Toxicologı ´a Ambiental, Instituto de Investigaciones Biome ´ dicas, UNAM, Mexico Received 4 November 1999; accepted 9 January 2000 ABSTRACT This work studied the effect of light-stressors, irradiance and photoperiod length on the status of hemolymph glu- tathione in two species of crayfish, Procambarus clarkii and Procambarus digueti. Adult animals of each species were submitted to two experimental approaches: (1) two batches of each species were placed under low or high light irradiant conditions of light–dark (LD) 24 h cycles of two different photoperiod lengths, one normal LD 12: 12 and one extreme LD 20:4 low and high irradiance for 10 weeks. Time-dependent light changes on hemolymph glutathione concentration were determined throughout the entire experimental period; and (2) three batches of the two species were submitted to independent treat- ments consisting of the same LD 12:12 cycles of high and low irradiance and 20:4 high-irradiance LD cycles. Re- duced and oxidized glutathione hemolymph concentra- tions were determined and total glutathione was calcu- lated. In addition midgut glutathione reductase activity in both species was determined. The two species showed different hemolymph glutathione reactivity and glutathi- one status for the two light parameters. Dissimilar re- sponses of both species, as well as the rate of mortality of P. digueti represent specific differences in the meta- bolic responses, as well as tolerance to photo-oxidative stress produced by light. The role of glutathione in the tolerance of crayfish to photo-oxidative stress is dis- cussed. INTRODUCTION The crayfish of species Procambarus clarkii and Procam- barus digueti show different resistance to light-stress, de- pending on dissimilar adaptive abilities that imply a certain metabolic depression. This is expressed in P. clarkii by strat- egies that help overcome the decreasing oxygen consumption caused by light-stressors, the shift from aerobic to anaerobic *To whom correspondence should be addressed at: Lab. Neurofi- siologı ´a Comparada, Ap. Postal 41630, Me ´xico DF 11000, Mex- ico. Fax: 56-82-10-86; e-mail: mfajul@netmex.com pathways and a decrease of activity (1). Light irradiation and exercise are both factors that determine reactive oxygen spe- cies (ROS)² in mammals, thus producing oxidative stress (2–4). Since ROS originate with oxygen as a reactant, a de- crease in these reactive species should be expected under hypoxic conditions. However, studies have documented the production of ROS during anoxia, as well as the antioxidant mechanisms that control and prevent the formation of ROS (5–7), reporting differences between aerobic and facultative anaerobic organisms, vertebrates and invertebrates. The most important of the nonenzymatic antioxidants is the tripeptide -glutamyl-cystein-1-glycin or reduced glutathione (GSH), seemingly ubiquitous in animal cells. When GSH is present, any ROS will be instantly quenched with the immediate for- mation of oxidized glutathione (GSSG) that is subsequently enzymatically reduced by glutathione reductase (GR) to re- store GSH. In vertebrates, GSH originates from different or- gans; particularly from the liver that releases it into blood plasma, which in turn transfers it to various tissues. It has been proposed that plasma GSH can protect cells from ox- idative damage (8), and that higher concentration of blood GSH, as a response to repeated oxidative stress, is an indi- cator of increasing tolerance to environmental stress (9). In Crustacea, small concentrations of this thiol in the hemo- lymph were reported a long time ago (10). Recently, Almar et al. (11) observed changes in the midgut gland GSH con- centrations of P. clarkii exposed to toxic stress, but its role during the light-dependent generation of ROS has not been explored. There are no reports to our knowledge of the he- molymph GSH status, neither in crayfish nor in Crustacea that are exposed to environmental stress. However, the dy- namics of this system could be a good indicator of the mech- anisms allowing the different species of this group to cope with the changing environmental stresses. These changes may modify the animal’s oxygen availability and consump- tion, as studied here regarding the case of light. Hence, the objective of the current study was to investi- gate whether the glutathione status in hemolymph is corre- ² Abbreviations: ANOVA, analysis of variance; GR, glutathione re- ductase; GSH, reduced glutathione; GSSH, oxidized glutathione; GSH-t, total GSH; LD, light–dark; OPT, o-phthalaldehyde; ROS, reactive oxygen species; SE, standard error.