Regulation by light and ethanol of the synthesis of the light-harvesting chlorophyll a/b-binding protein of photosystem II in Euglena

Abstract

In dark-grown Euglena, a single 122-kdalton (kDa) precursor to the light-harvesting chlorophyll a/b-binding protein of photosystem II (pLHCPII) was synthesized at a very low rate and LHCPII synthesis was undetectable as determined by pulse-labeling with [(35)S]sulfate and immunoprecipitation with a specific antibody against Euglena LHCPII. Synthesis of a 207-, 161-, 122- and 110-kDa pLHCPII was detected after light exposure, with the 207-kDa pLHCPII being the most abundant pLHCPII synthesized. The rate of synthesis of all four pLHCPIIs and the 25.6-kDa and 27.2-kDa LHCPIIs increased in the first 12-24 h of light exposure and then declined. The maximal rate of LHCPII synthesis in the light was 50-100-fold greater than the rate in darkness. Addition of ethanol at the time of light exposure inhibited LHCPII synthesis, indicating that induction is catabolite-sensitive. The halflife of pLHCPII in the light or in darkness was 20 min. Therefore, the light induction of LHCPII is the result of an increased rate of synthesis rather than a decreased rate of degradation. Transfer of illuminated cells to darkness resulted in an 80% decrease in the rate of pHLCPII synthesis during the first 0.5 h. Illuminated cells returned to darkness continued to synthesize both 207-kDa pLHCPII and LHCPII for at least 5 h. Light exposure or ethanol addition did not increase the level of translatable RNA for LHCPII. The 50-100-fold catabolite-sensitive increase in the rate of LHCPII synthesis in the absence of a concomitant increase in the level of translatable RNA for LHCPII indicates that in Euglena, the synthesis of LHCPII is controlled at the translational rather than at the transcriptional level.

Translational Regulation of the Synthesis of Euglena Fumarase by Light and Ethanol

“…The 50 to 100-fold light induced catabolite repressed increase in the rate ofsynthesis ofLHCPII also occurs in the absence of an increase in the level of translatable RNA coding for Euglena LHCPII (20). In contrast to light induced chloroplast development in higher plants 3Abbreviations: LHCPII, the light harvesting Chl a/b binding protein of PSII; EF-Gchl, chloroplast elongation factor G; EFGmt, mitochondrial elongation factor G; 63 and other algae, it appears that the catabolite repressible photoinduction of Euglena chloroplast development is controlled primarily at the translational rather than at the transcriptional level (2,14,20). In this paper, we show that ethanol and light acting through a nonchloroplast photoreceptor induce the synthesis of fumarase in the absence of an increase in the level of translatable RNA for fumarase.…”

Metabolic Repression of Transcription in Higher Plants

“…In alga1 cells fed with acetate, the glyoxysome, a single membrane-bound organelle, is involved in using acetyl-COA for gluconeogenesis through the glyoxylate cycle (Beevers, 1969;Monroy and Schwartzbach, 1984;Gibbs et al, 1986;Steinbiss and Zetsche, 1986;Rikin and Schwartzbach, 1989). The presence of acetate inhibits the expression of photosynthetic genes under light but activates the expression of glyoxysome enzymes for the metabolism of acetate (Monroy and Schwartzbach, 1984;Gibbs et al, 1986;Steinbiss and Zetsche, 1986;Kindle, 1987;Rikin and Schwartzbach, 1989). These observations suggest that in algae acetate is a more favorable exogenous carbon source than CO, , probably because the utilization of CO, involves the expression of more complex photosynthetic pathways.…”

Dynamics of chlorophyll and paramylon accumulation in Euglena gracilis cells at mixotrophic cultivation

“…Observed decline of chlorophylls after the lag phase and early exponential growth phase is likely consequence of the presence of organic substrate in the medium. It is known that the induction of the synthesis of chlorophyll-containing proteins of light-harvesting complexes is catabolite-sensitive [4,24]. The light intensity 250 µmol•m -2 ·s -1 caused a decrease in chlorophylls content in the cells due to the more intensive process of photodestruction of these pigments [10].…”

“…The addition of ethanol in culture medium of E. gracilis influences on the biochemical composition and the physiological parameters of the cells, because of the using of ethanol as substrate for E. gracilis is under active investigation [4,8,13,20,25]. The physiological effects of ethanol on the cells of E. gracilis are the stimulation of cell respiration, the prevention of losses of mitochondrial enzymes after transition heterotrophic cells on the photoautotrophic cultivation, the repression of light-induced synthesis of chloroplast enzymes and light-harvesting chlorophyll a/b-binding protein of photosystem II [13,24]. Biotechnological value of the cultivation of E. gracilis in the presence of ethanol consist in the increase in the biomass, the stimulation of protein, α-tocopherol and paramylon accumulation in the cells [2,25].…”