中文摘要：

为了探讨光照、NO3^--N和NH4^＋-N对坛紫菜（Porphyra hahanensis）硝酸还原酶活性（NRA）的影响，在光照和黑暗条件下分别对坛紫菜叶状体进行氮（N）饥饿→氮（N）加富和N加富→N饥饿处理，并测定NRA的变化。结果表明：在N饥饿→N加富过程中，光照下NRA比黑暗中要高；NO3^--N的加富能提高NRA，且在光照下比黑暗中NRA达到最大值的时间要短；而NH4^＋-N与NO3^--N共同对N饥饿藻体加富时NRA没有明显变化，并与NH4^＋-N单独加富无显著差异。另外，对于N加富→N饥饿的处理，在光照下NO3^--N加富和NH4^＋-N与NO3^--N共同加富的NR都能在N饥饿处理后的一段时间内维持较高的活性。这些结果说明：光照和硝酸盐对NRA起正调节作用，而铵盐对NRA起负调节作用，但NRA与体外硝酸盐浓度并不成直接的正相关关系。

英文摘要：

To investigate the effects of light, nitrate （NO3^--N） and ammonium （NH4^＋ -N） on the activity of nitrate reductase （NRA） in the red alga Porphyra haitanensis, thalli were incubated in seawater with different N supply （N-enrichment and N-starvation） in the light or in darkness. The results showed that NRA was higher in the light than in darkness; NRA increased when thalli were incubated in NO3^ --N, and it enhanced faster in the light than in darkness. There was no significant difference of NRA between thalli incubated in seawater enriched by NO3 ^--N and NH4 ^＋-N simultaneously and those enriched by NH4^＋ -N solely. Additionally, NR in light could maintain relative high activity for several hours when thalli were transferred from N-enrichment to N-starvation. It was concluded that light and / or NO3^ - -N increased NRA of Porphyra haitanensis, but NH4^＋ -N restrained it. However, NRA was not in direct proportion to the concentration of NO3^--N in culture.