| Fish are cold-blooded animals. Growth and development rate of fish relied on species, sex, water temperature, light, DO and p H, in which water temperature played an extremely important role. Rainbow trout(Oncorhynchus mykiss) is a cold-water species of salmonid, which suitable growth temperature in the range of 12°C~18°C. It was more vulnerable to the effects of water temperature changes. In practice, the high temperature is an important threat to aquaculture of rainbow trout, that can easily lead to mass mortality or serious losses in yield of rainbow trout. This study aims to explore the molecular mechanisms of rainbow trout in response to heat stress, in order to provide a basis for optimizing the process of rainbow trout management, and improving the ability of rainbow trout to cope with high temperatures.In this paper, the effects of heat stress on some immunity parameters(COR, CA, RB, SOD, MDA, C3, AKP and LDH) and m RNA expression of the HSP47 gene in different tissues(liver, spleen, head kidney and heart) were investigated in control group(18°C, 0 h), 2, 4, 8 and 12 h after heat-stress(25°C) and heat-stress recovery(18°C, HSR), respectively. The results showed:1. Compared with control group, the heat-stress groups had the following significantly(P<0.05) increased parameters: The content of cortisol(COR) and catecholamine(CA) peaked at 8 h; respiratory burst(RB) activity at 8 and 12 h; serum superoxide dismutase(SOD) activity at 2~12 h; malondialdehyde(MDA) level at 4 and 12 h; complement 3(C3) level at 2 and 12 h; alkaline phosphatase(AKP) activity at 2, 8 and 12 h. However, the activity of lactate dehydrogenase(LDH) in the serum decreased significantly(P<0.05) at 8 h after heat stress. After 6 h heat-stress recovery,COR and SOD level were respectively lower than that of 8 h and 12 h under heat stress(P<0.05), but still significantly higher than that of control group; RB and AKP were remained at the same level as that of 2, 8 and 12 h under heat stress(P>0.05); CA, MDA, C3 and LDH level were recovered to the level of control group(P>0.05). All these results indicated that 25°C heat stress significantly affected the immunity of rainbow trout. The increase of RB, C3 and AKP indicated that heat stress could cause inflammation to rainbow trout. And the high level of COR, CA and MDA after heat stress and the high level in HSR group of AKP indicated that the fish cells were damaged. In the HSR group, CA, MDA, C3 and LDH reduced to the levels of control group, which deduced that rainbow trout could restore normal function gradually under optimal temperature after 25°C heat stress.2. HSP47 m RNA expression responded in a time- and tissue-specific manner to heat stress, which was mainly reflected in the significant up-regulation in all tissues(P<0.05) and greater expression in the liver than the other tissues(P<0.05). Compared with the control group, the HSP47 m RNA level in both the liver and spleen were up-regulated significantly(P<0.05) from 4 h after heat stress, and that in head kidney and heart were up-regulated significantly(P<0.05) from 2 h and 12 h after heat stress, respectively. In the HSR group, the HSP47 m RNA level in all tissues was significantly(P<0.05) higher than that in the control group, but significantly(P<0.05) lower than that in the heat-stress groups, except for the spleen. The result of the HSP47 m RNA expression indicated that heat stress can up-regulate the HSP47 m RNA expression in liver, spleen, head kidney and heart tissues. The up-regulation of HSP47 m RNA can promote cell survival, cellular homeostasis and cellular resistance to external stimulus. But the tissues damage caused by heat stress in rainbow trout is hard to reverse. Hence, even the rainbow trout restored to optimum temperature, it still needs a large number of HSP47 to assist in repairing the damaged tissue and organs. |
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