The biosynthesis of the chlorophyll a/b binding protein associated with photosystem II (LHC-II) was characterized during light-induced greening of etiolated barley (Hordeum vulgare [L.] cv Boone), maize (Zea mays [L.] Pioneer 3148), pea (Pisum sativum [L.] cv Progress 9), and soybean (Glycine max [L.] Merr. cv Ransom 2). Northern blot analysis revealed that pea LHC-II mRNA was present in dark-grown seedlings and accumulated rapidly within 1 hour following illumination with white light. In contrast, the accumulation of LHC-II mRNA was delayed in barley and soybean until 2 to 4 hours after illumination began. Single radial immunodiffusion analysis revealed that LHC-II polypeptides began to accumulate in all species between 4 and 8 hours although the protein was present in detectable levels at earlier times in certain species. In a pattern similar to the LHC-II protein accumulation, chlorophyll accumulated at increased rates between 4 and 8 hours of greening in all species following an initial delay. The absence of coordination between LHC-II mRNA and LHC-II protein accumulation that was clearly observed in pea suggested that transcription is not the factor that limits LHC-II complex formation during chloroplast development. The accumulation of chlorophyll and LHC-II protein appeared to coincide suggesting that chlorophyll biosynthesis may be a factor that limits LHC-II complex formation.
The influence of various colors of soil cover (mulch) on the farred/red (FR/R) ratio in upwardly reflected light and on concentrations of chlorophyll (Chi) and light-harvesting Chi protein were measured under field conditions. The FR/R ratios above green surfaces were higher than over white surfaces. Even though plants (Gossypium hirsutum L. cv PD-1) were grown in full sunlight, those that received higher FR/R ratios in upwardly reflected light were taller and had thinner leaves with higher concentrations of Chi and LHC-11. A controlled environment experiment showed FR/R control of Chi and LHC-11 concentrations. The results illustrate the importance of spectral distribution of reflected light on plant growth and a potential means of altering the chemistry of leaf crops under field conditions. survival among the perceived competition (1 1, 12). For example, plants in higher-density populations receive higher FR/R ratios and develop longer stems, a characteristic that increases the probability of keeping some leaves in sunlight.Since plants respond to the FR/R ratio and they cannot discern the source of an altered ratio, variously colored soils and soil surface covers (mulches) have been studied to determine effects on spectral distribution of upwardly reflected light and the associated effects on plant development (15). The spectral distribution of upwardly reflected light (particularly the FR/R ratio) can influence photosynthate partitioning, which alters shoot/root ratios and the amount of nodulation of soybean (Glycine max L.) (10) as well as the fruit yield of tomatoes (Lycopersicon esculentum Mill.) (5). The present research was undertaken to study the influence of the FR/R ratio in upwardly reflected light on Chl and LHC-II content under field conditions. Controlled environment studies have shown that the ratio ofFR' relative to R light acts through the phytochrome system to regulate stem elongation (6); leaf shape, thickness, and Chl concentration (16)
LHC-II3 is the major light harvesting Chl-protein complex present in thylakoid membranes of chloroplasts (29). LHC-II proteins are encoded by nuclear genes (8,9,15) that are organized into gene families (9,25,30). The regulation of ' Cooperative investigations ofthe U.S. Department ofAgriculture,
Genomic DNA from three Clostridium difficile strains was analyzed by PCR for DNA sequences encoding toxin A (tcdA) and toxin B (tcdB). Toxigenic control strain VPI 10463 possessed tcdA, tcdB, and an open reading frame (tcdE) between these two genes, whereas nontoxigenic control strain 85 lacked each of these genetic determinants. However, strain M90, also a nontoxigenic strain, was found to possess tcdA, tcdB, and tcdE. Normally the presence of toxin genes is associated with toxigenicity. Analysis of tcdA and tcdB mRNA revealed toxin gene transcription in strains VPI 10463, 23 (a mildly toxigenic strain), and M90, but not in strain 85. However, for strain M90, tcdA and tcdB mRNA was at the lower limit of detection, whereas mRNAs encoding tcdA and tcdB were easily detected in strains VPI 10463 and 23. Low levels of toxin gene transcription is the probable cause of M90's lack of toxigenicity.
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