Physiological responses of the green alga Dunaliella parva (Volvocales, Chlorophyta) to controlled incremental changes in the N source

Abstract

This work is aimed at obtaining information on the acclimation processes of the green flagellate Dunaliella parva Lerche to gradual changes in the N source from NO3– to NH4+, in continuous cultures. Photosynthesis, dark respiration, and light-independent carbon fixation (LICF) rates, chlorophyll a fluorescence, RUBISCO and phosphoenolpyruvate carboxylase (PEPc) activities, plasmalemma electrical potential difference, cell volume, and absolute or relative amounts of major cell constituents were measured. Two phases characterised the response to the transition from NO3– to NH4+: (1) an initial phase in which photosynthesis and anaplerosis were stimulated and protein increased; (2) a subsequent phase in which most parameters reached new values that were close to those at the beginning of the experiment (100% NO3–). The only exceptions were PEPc activity and LICF, whose rates remained at least 2-fold higher than at 100% NO3–, when NH4+ was the sole N source. The results are indicative of a tendency to re-establish homeostasis, after an initial perturbation of the intracellular composition. The roles of different metabolic processes during acclimation are discussed.

Impact of environmental conditions on photosynthesis, growth and carbon allocation strategies of hypersaline species of Dunaliella

“…The importance of this anaplerotic enzyme in the detoxification of the cellular environment by excess NH 4 + is consistent with the overall physiological patterns of high NH 4 + grown cells (Giordano and Bowes, 1997). PEPC is not only up-regulated in cells acclimated to growth in NH 4 + , but it also appears pivotal in the short term (minutes to hours) and medium term (hours to few days; = from one to a few generations) responses to changes in N-source (Giordano et al, 2007). This activity is in fact among the few physiological parameters that do not respond homeostatically (sensu Montechiaro et al, 2006) to a transition from NO 3 -to NH 4 + , but is present at a higher level in the presence of incremental amounts of NH 4 + , compared to when NO 3 -is the sole N-source.…”

FOURIER TRANSFORM INFRARED SPECTROSCOPY OF MICROALGAE AS A NOVEL TOOL FOR BIODIVERSITY STUDIES, SPECIES IDENTIFICATION, AND THE ASSESSMENT OF WATER QUALITY1

“…For instance, D. parva , C. marina , and P. autumnale showed no change in their FTIR spectra after transfer to NH 4 + ; the stability of the macromolecular pools of P. autumnale and D. parva to environmental perturbations has been previously reported in the literature (Montechiaro et al. 2006, Giordano et al. 2007).…”

“…The FTIR signature of algal cells is affected by their nutritional status (Giordano et al. 2001, 2007, Heraud et al.…”

Macromolecular Response of Individual Algal Cells to Nutrient and Atrazine Mixtures within Biofilms

“…If N, P, and other micronutrients are available, these LMW compounds are further transformed into proteins and other growth-related macromolecules. Otherwise, LMW compounds are increasingly converted into carbohydrates or lipids as an energy reserve [10,19,20,33].…”