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Antibody to the Euglena light-harvesting chlorophyll a/b binding protein of photosystem II (LHCPII) immunoprecipitated 207-, 161-, 122-, and 110-kDa proteins from total Euglena proteins pulse-labeled for 10 min with [35S]sulfate. The 25.6-and 27.2-kDa LHCPII were barely detectable in the immunoprecipitate. During a 40-min chase with unlabeled sulfate, the amount of radioactivity in the high molecular mass proteins decreased, and the amount of radioactivity in the 25.6-and 27.2-kDa LHCPII increased with kinetics consistent with a precursor-product relationship. The half-life of the high molecular mass proteins was :20 min. The major proteins immunoprecipitated from a nuclease-treated rabbit reticulocyte cell-free translation system programmed with Euglena whole cell or poly(A)+ RNA had molecular masses corresponding to the molecular masses of the proteins immunoprecipitated from the pulse-labeled in vivo translation products. RNAs of 6.6 and 8.3 kilobases were the only Euglena whole cell and poly(A) + RNAs that hybridized to a 0.7-kilobase EcoR-l-BamHI fragment of plasmid pAB165, which contains a portion of the coding sequence for Arabidopsis LHCPII. RNAs of this size are more than sufficient to code for proteins of 207 kDa. Taken together, these findings demonstrate that the LHCPIIs of Euglena are initially synthesized as slowly processed precursors with molecular masses of 207, 161, 122, and 110 kDa.Chloroplast biogenesis requires the coordinated expression of the nuclear and chloroplast genomes. Nuclear-coded chloroplast-localized proteins are synthesized on cytoplasmic ribosomes as higher molecular mass precursors (reviewed in ref. 1). These precursors contain an amino-terminal extension called the transit sequence, which can range in size from 3.5 to 15 kDa (1). The transit sequence enables the precursor to bind to specific receptors on the chloroplast envelope (2), to be transported through the envelope into the chloroplast stroma, and to be localized within the proper intrachloroplast compartment (3). The transit sequence is proteolytically removed by a specific chloroplast protease (4) in what appears to be at least a two-step process (5, 6). Although transit peptides do not have a common amino acid sequence, specific conserved domains required for uptake and processing have been identified (1, 7).The light-harvesting chlorophyll a/b binding proteins of photosystem II (LHCPIIs) are the major protein component of the light-harvesting chlorophyll protein complex. They are nuclear-coded proteins that are synthesized as precursors (pLHCPIIs) about 5 kDa larger than the mature protein (reviewed in refs. 1 and 7-10). The amino-terminal portion of the LHCPII is thought to be responsible for grana stacking (11). In both green algae and plants, the LHCPIIs represent a heterogenous mixture of immunologically related proteins ranging in size from 20 to 30 kDa (12, 13).The identified nuclear genes coding for LHCPII comprise a multigene family containing from 3 to 20 members depending on the species studied (9...

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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.

Fluctuations in fatty acid composition were examined in cotton (Cossypium hirsutum 1. cv Deltapine 50) leaves during light-dark cycles of 1 2 1 2 h and under continuous light and were correlated to the rhythmic changes in chilling (5°C) resistance (CR) and heat (53°C) resistance (HR). l h e chilling-resistant and chilling-sensitive phases developed in the dark or the light period, respectively, and this rhythm persisted under continuous light for three cycles. The heat-resistant phase developed in the light period and an additional peak of HR occurred in the middle of the dark period. Under continuous light, only one peak of HR developed, lasting from the middle of the subjective night to the middle of the subjective day. The amounts of palmitic and oleic acids were constant during the light-dark cycle and under continuous light, but those of linoleic and linolenic acids fluctuated, attaining a high level in the middle of the dark period or the subjective night, and a low level in the middle of the light period or the subjective day. A low temperature of 2O'C induced CR and affected changes in fatty acid composition similar to those that occurred during the daily CR phase. A high temperature of 40°C induced HR but did not affect changes in fatty acid composition. The results in their entirety show that the CR that develops rhythmically as well as the low-temperature-induced CR coincide with increased levels of polyunsaturated fatty acids.No correlation is found between changes in fatty acid composition and the HR that develops rhythmically or the high-temperatureinduced HR.