Background: Multiple functions of nitric oxide (NO) in organisms and itsspecial function and role in the atmosphere were investigated. In this study, marine microalga culture-mediumNO concentrations were detected and studied in order to find the laws governing NO release by marinemicroalgae and relevant material was collected for discussion on the production mechanisms. Material/Methods:NO concentrations in culture media of the marine microalgae Platymonas subcordiformis, Skeletonema costatum,and Gymnodinium sp. were detected and other media parameters, such as nutrients concentrations, Chl-a,alga cell density, and pH, were also measured concurrently. Results: The NO concentrations in culturemedia of the marine microalgae Platymonas subcordiformis, Skeletonema costatum, and Gymnodinium sp. weredetected and found to be about 10[sup]-8>/sup.-10[sup]-9[/sup] mol/l. The relationships between NO and nutrients and NOand pH were discussed. It was found that "NO" could serve as the message factor of microalga growth status.Experiments showed that factors affecting alga growth, such as trace elements, light, temperature, andsalinity, all affected the culture-medium NO concentration. At the same time, an environmental stimuluscould give rise to sudden NO peaks, with NO being a signal molecule of marine microalga stress response.Conclusions: These results indicated that low concentrations of NO were produced by marine phytoplankton(microalgae) under the condition of normal growth. NO is a message factor of microalga growth and isalso a signal molecule of stress response.

Keywords: Chlorophyta - metabolism, Culture Media, Diatoms - metabolism, Dinoflagellida - metabolism, Eukaryota - metabolism, Hydrogen-Ion Concentration, Models, Biological, Nitric Oxide - biosynthesis, Phytoplankton - metabolism, Plant Growth Regulators - pharmacology, Salicylic Acid - pharmacology, Trace Elements - pharmacology