Abstract
Aquatic organisms are exposed to a wide range of salinity, which could critically affect their survival and growth. However, their survival and growth response to salinity stress remain unclear. This study evaluates the growth response and intracellular proline accumulation of green algae, Scenedesmus quadricauda, isolated from brackish water, against dissolved salts stress with N and P enrichment. We tested a hypothesis that nutrient enrichment can relieve the dissolved salts stress of algae by accumulating intracellular proline, thereby improving survival and growth. Four levels of salinity (0, 3, 6, 12 psu) were experimentally manipulated with four levels of nutrient stoichiometry (N:P ratio = 2, 5, 10, 20) at constant N (1 mgN/L) or P levels (0.05 and 0.5 mgP/L). In each set of experiments, growth rate and intracellular proline content were measured in triplicate. The highest level of salinity inhibited the growth rate of S. quadricauda, regardless of the nutrient levels. However, with nutrient enrichment, the alga showed tolerance to dissolved salts, reflecting intracellular proline synthesis. Proline accumulation was most prominent at the highest salinity level, and its maximum value appeared at the highest N:P ratio (i.e., highest N level) in all salinity treatments, regardless of P levels. Therefore, the effects of P and N on algal response to salt stress differ.
Highlights
These results indicate that proline synthesis in high salinity level higher than 6 and N:P ratio of 20
These results indicate that proline synthesis in salt high stress is likely promoted by increasing
This study showed that nutrient enrichment could relieve the adverse effects of dissolved salts stress on a green alga S. quadricauda by promoting cell growth and proline synthesis, with differential role of N and P
Summary
Freshwater and estuarine environments experience a wide range of variations in salinity, and the residing organisms have to undergo physiological adaptation to overcome dissolved salts stress. Biota physiologically respond to environmental stress in diverse ways [9], one of which is proline synthesis and accumulation [10,11,12]. Various terrestrial and aquatic organisms (e.g., plants, bacteria, and protozoa) synthesize proline in response to environmental stress [2,12,16]. Algae synthesize proline in response to various environmental stresses such as drought, UV irradiation, high temperature, exposure to heavy metals, oxidative stress, and high salinity [11]. In biological adaptation to environmental stress, proline accumulation could be a major mechanism by which organisms protect
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