CORRELATED BIOCHEMICAL AND ULTRASTRUCTURAL CHANGES IN NITROGEN‐STARVED EUGLENA GRACILIS¹

Abstract

Growth of Euglena gracilis Z Pringsheim under photoheterotrophic conditions in a nitrogen‐deprived medium resulted in progressive loss of chloroplastic material until total bleaching of the cells occurred. Biochemical analysis and ultrastructural observation of the first stages of the starvation process demonstrated an early lag phase (from 0 to 9 h) in which cells increased in size, followed by a period of cell division, apparently supported by the mobilization of some chloroplastic proteins such as the photosynthetic CO2‐fixing enzyme ribulose‐1,5‐bisphosphate carboxylase/oxygenase. The degradation of the enzyme started after 9 h of starvation and was preceded by a transient concentration of this protein in pyrenoidal structures. Protein nitrogen and photosynthetic pigments as well as number of chloroplasts per cell decreased during proliferation through mere distribution among daughter cells. However, after 24 h, when cell division had almost ceased, there was a slow but steady decline of photosynthetic pigments. This was paralleled by observable ultrastructural changes including progressive loss of chloroplast structure and accumulation of paramylon granules and lipid globules in the cytoplasm. These findings reinforce the role of chloroplastic materials as a nitrogen source during starvation of E. gracilis in a carbon‐rich medium. The excess of ribulose‐1,5‐bisphosphate carboxylase/oxygenase acts as a first reservoir that, once exhausted, is superseded by the generalized disassembly of the photosynthetic structures, if the adverse environment persists more than 24 h.

PLASTID MORPHOLOGY, ULTRASTRUCTURE, AND DEVELOPMENT IN COLACIUM AND THE LORICATE EUGLENOPHYTES (EUGLENOPHYCEAE)1

“…Although numerous authors have dealt with plastid development and division in the euglenophytes, they have all used E. gracilis as their study organism (Cook et al 1976, Pelligrini 1980, Ehara et al 1990, García‐Ferris et al 1996). Ours is the first report of plastid division and pyrenoid development in euglenophyte taxa other than E. gracilis , but it appears that many of the phenomena reported for E. gracilis are maintained within euglenophytes with similar type plastids.…”

Heterotrophic cultivation of microalgae: production of metabolites of commercial interest

“…However, limited growth is sometimes possible during periods of nutrient shortage. A proposed mechanism for this phenomenon under nitrogen‐limiting conditions was suggested by García‐Ferris and coworkers using Euglena gracilis as a model. These researchers showed that E. gracilis was able to resume growth after being transferred to a N‐free medium for 15 h (roughly one generation); this resumed growth was feasible due to the reallocation of chloroplastic proteins, such as the photosynthetic CO 2 ‐fixing enzyme ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCO).…”

Growth, photosynthesis, and respiration of Chlorella sorokiniana after N‐starvation. Interactions between light, CO2 and NH4+ supply

“…N-deprivation, by contrast, profoundly affects the chloroplast structure, and causes a time-dependent loss of chloroplast enzymes. In a carbon-rich cellular medium like that of N-starved cells, it was observed that ribulose-1,5-bisphosphate carboxylase/oxygenase and other chloroplast material can serve as an N source for synthesis of other N-compounds (Garcia-Ferris et al 1996).…”