Influence of darkness on pigments of Tetraselmis indica (Chlorodendrophyceae, Chlorophyta).

In the photic zone, phytoplankton experience diurnal variation in light intensity. However, prolonged exposure to aphotic condition influences their physiological state. Pigment composition is a useful biomarker to decipher cells physiological state and adaptive response to changing environmental conditions. Chlorophyll, a natural pigment, is biosynthesised even in darkness and studies have shown this ability is determined by genetic characteristics of an organism. The purpose of this study was to examine the influence of darkness on pigments and chlorophyll autofluorescence of Tetraselmis indica. Dark exposure (up to 6 months) had no significant impact on chlorophyll a and b concentration, whereas carotenoids were enhanced. Upon re-illumination pigments gradually recovered to pre-dark phase condition. These adaptive survival strategies of T. indica by altering pigment concentration in response to prolonged darkness are interesting. The absence of loroxanthin and loroxanthin esters in T. indica is reported in a first Tetraselmis species so far. In addition, the evaluation of autofluorescence and cellular chlorophyll concentration pointed out that they are not interdependent in this species. Hence, careful consideration of these two factors is needed when either of them is used as a proxy for other. The results obtained encourage a thorough study of pigment analysis, especially when subjected to darkness, to elucidate potential role in the evolution, chemotaxonomy, and survivability of species.