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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.

Exposure of cucumber seedlings (Cucumis sativus L.) to chilling temperature resulted in injuries such as increased leakage of cellular materials, loss of water and wilting. In addition, the development of the seedlings after the exposure to chilling was impaired. Abscisic acid applied to the seedlings prior to chilling significantly ameliorated these injuries.

Tobacco plants (Nicotiana rustica L.) pre-exposed to leaf dehydration, mineral deprivation, salination, or B033-toxicity exhibited increased resistance to subzero temperature and to reduced oxygen in the root medium. The stressed plants all showed an elevated content of leaf abscisic acid. Upon transfer of mineral deprived and salinated plants to prestress conditions, a decline in leaf abscisic acid content to prestress levels took place together with a loss of the increased resistance to subzero temperature and to deprivation of root oxygen. Treatment with abscisic acid by direct application to the leaves or by addition to the root medium improved leaf resistance to subzero temperature and to deprivation of root oxygen. A common hormone-regulation mechanism involving abscisic acid is suggested for this phenomenon of "cross-adaptation" by which a given stress confers increased resistance to other, apparently unrelated stresses.The concept of cross-adaptation (2) holds that exposure of an organism to a given adverse environment modifies its response to other adverse factors. Examples of cross-adaptation covering the entire biological spectrum have been reported (1,2,4,7). The phenomenon is widely recognized in plants. Levitt (5) Response to this stress was determined by measuring leaf WSD 4 hr after imposing the lack in root aeration.Recovery treatment was imposed by transferring the plants from the stressing environment back to aerated half-Hoagland solution used in the prestress period and as the control.

ABSTRACrCotyledons of cotton (Gossypium hirsutum L.) seedlings grown under a photoperiod of 12 hour darkness and 12 hour light showed daily oscillations in ethylene evolution. The rate of ethylene evolution began to increase toward the end of the dark period and reached a maximum rate during the first third ofthe light period, then it declined and remained low until shortly before the end of the dark period. The oscillations in ethylene evolution occurred in young, mature, and old cotyledons (7 to 21 day old). These oscillations in ethylene evolution seemed to be endogenously controlled since they continued even when the photoperiod was inverted. Moreover, in continuous light the oscillations in ethylene evolution persisted, but with shorter intervals between the maximal points of ethylene evolution. In continuous darkness the oscillations in ethylene evolution disappeared. The conversion of 13,4-'4Cmethionine into 14C] ethylene followed the oscillations in ethylene evolution in the regular as well as the inverted photoperiod. On the other hand, the conversion of applied 1-aminocyclopropane-1-carboxylic acid into ethylene did not follow the oscillations in ethylene evolution, but was affected directly by the light conditions. Always, light decreased and darkness increased the conversion of applied 1-aminocyclopropane-1-carboxylic acid into ethylene. It is concluded that in the biosynthetic pathway of ethylene the conversion of 1-aminocyclopropane-1-carboxylic acid into ethylene is directly affected by light while an earlier step is controlled by an endogenous rhythm.Many plant processes are controlled by endogenous rhythms (12). There are several reports of daily changes in the level of plant hormones, e.g. cytokinin levels in poplar leaves (11), ABA levels in sorghum and pearl millet leaves (10, 13), and phaseic acid in sorghum leaves (13). The daily changes in ABA levels were only partially related to the leaf water potential. Recently, Lecoq et al. (16) showed that in soybean leaves the oscillations in ABA level persisted in continuous light, indicating that such ABA levels were endogenously controlled. Daily changes in ethylene evolution were found in leaves of several species (7,15) and in cotton fruits ( 17). El-Beltagy et al. (7) showed that these oscillations were not related to changes in the leaf water saturation deficit or stomatal aperture but were endogenously controlled, since they occurred also in continuous light or darkness.In in ethylene evolution in cotton seedlings mainly in relation to its biosynthesis. MATERUILS AND METHODSCotton (Gossypium hirsutum L.) seeds were germinated and grown for 7 d in plastic pots (12.5 cm in diameter, 12 cm in height) filled with peat, and irrigated with water. The seedlings were grown in growth chambers at 29°C under photoperiods which were specified for each experiment. The light (200 sE m-2 s ') source was a combination of regular incandescent light and fluorescent light (F48T1 8-CW-VHO, Sylvania).The production of ethylene was measured in detached cotyledo...