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Efficient and power-scalable laser operation of a vibronic Tm^3+:KLu(WO_4)_2 microchip laser at ∼2.13  μm is demonstrated. In the continuous-wave mode under diode pumping at ∼805  nm, this laser generated 1.17 W at 2109–2133 nm with a slope efficiency of 39%. This emission is related to the coupling of the electronic transitions of Tm^3+ ions with the stretching vibrations of the WOW oxygen bonds in the monoclinic KLu(WO_4)_2 crystal host appearing at ∼379, 406, and 450  cm^−1. The achieved emission wavelength is longer, to our knowledge, than any previously reported laser based on Tm^3+ or Ho^3+ doped double tungstate crystals. Passive Q-switching of the vibronic Tm^3+:KLu(WO_4)_2 laser is realized with a single-walled carbon nanotube (SWCNT) based saturable absorber, representing the longest wavelength in this mode of operation. In this regime, the maximum output power reached 0.70 W at 2131 nm, corresponding to a slope efficiency of 29%. The pulse characteristics were 25 ns/1.1 μJ at the pulse repetition frequency of 0.62 MHz. These are, we believe, the shortest pulses ever achieved in any lanthanide-based laser passively Q-switched by carbon nanostructures. A conventional (purely electronic transition) Tm^3+:KLu(WO_4)_2 microchip laser at 1.92 μm Q-switched by the same SWCNTs generated 40 ns/4.0 μJ pulses corresponding to a peak power of 0.1 kW, which is a record value for this type of laser oscillator, to our knowledge.

A diode-pumped Yb:KLu(WO_4)_2 microchip laser passively Q-switched by a Cr^4+:YAG saturable absorber generated a maximum average output power of 590 mW at 1031 nm with a slope efficiency of 55%. The pulse characteristics were 690 ps/47.6 μJ at a pulse repetition frequency of 12.4 kHz. The output beam had an excellent circular profile with M^2<1.05. Yb:KLu(WO_4)_2 is very promising for ultrathin sub-ns microchip lasers.

Eukaryotic ribosomes are made of two components, four ribosomal RNAs, and approximately 80 ribosomal proteins (r-proteins). The exact number of r-proteins and r-protein genes in higher plants is not known. The strong conservation in eukaryotic r-protein primary sequence allowed us to use the well-characterized rat (Rattus norvegicus) r-protein set to identify orthologues on the five haploid chromosomes of Arabidopsis. By use of the numerous expressed sequence tag (EST) accessions and the complete genomic sequence of this species, we identified 249 genes (including some pseudogenes) corresponding to 80 (32 small subunit and 48 large subunit) cytoplasmic r-protein types. None of the r-protein genes are single copy and most are encoded by three or four expressed genes, indicative of the internal duplication of the Arabidopsis genome. The r-proteins are distributed throughout the genome. Inspection of genes in the vicinity of r-protein gene family members confirms extensive duplications of large chromosome fragments and sheds light on the evolutionary history of the Arabidopsis genome. Examination of large duplicated regions indicated that a significant fraction of the r-protein genes have been either lost from one of the duplicated fragments or inserted after the initial duplication event. Only 52 r-protein genes lack a matching EST accession, and 19 of these contain incomplete open reading frames, confirming that most genes are expressed. Assessment of cognate EST numbers suggests that r-protein gene family members are differentially expressed.

Phosphoglucomutase (PGM) catalyzes the interconversion of glucose (Glc)-1- and Glc-6-phosphate in the synthesis and consumption of sucrose. We isolated two maize (Zea mays L.) cDNAs that encode PGM with 98.5% identity in their deduced amino acid sequence. Southern-blot analysis with genomic DNA from lines with different Pgm1 and Pgm2 genotypes suggested that the cDNAs encode the two known cytosolic PGM isozymes, PGM1 and PGM2. The cytosolic PGMs of maize are distinct from a plastidic PGM of spinach (Spinacia oleracea). The deduced amino acid sequences of the cytosolic PGMs contain the conserved phosphate-transfer catalytic center and the metal-ion-binding site of known prokaryotic and eukaryotic PGMs. PGM mRNA was detectable by RNA-blot analysis in all tissues and organs examined except silk. A reduction in PGM mRNA accumulation was detected in roots deprived of O2 for 24 h, along with reduced synthesis of a PGM identified as a 67-kD phosphoprotein on two-dimensional gels. Therefore, PGM is not one of the so-called "anaerobic polypeptides." Nevertheless, the specific activity of PGM was not significantly affected in roots deprived of O2 for 24 h. We propose that PGM is a stable protein and that existing levels are sufficient to maintain the flux of Glc-1-phosphate into glycolysis under O2 deprivation.

Alcohol dehydrogenase-1 (ADH1) synthesis in O2-deprived roots of maize (Zea mays L.) results from induced transcription and selective translation of ADH1 mRNA. The effect of ADH1 mRNA sequences on message stability and translation was studied in protoplasts of the maize cell line P3377.5' capped and 3' polyadenylated mRNA constructs containing the firefly gene (luc) for luciferase (LUC) or the Escherichia coli gene (uidA) for beta-glucuronidase (GUS) coding region were synthesized in vitro and electroporated into protoplasts that were cultured at 40 or 5% O2. A LUC mRNA with a 17-nucleotide polylinker 5' untranslated region (UTR) was expressed 10-fold higher under aerobic conditions than under hypoxic conditions. Expression of five chimeric ADH1-GUS mRNAs was measured relative to this LUC mRNA. An mRNA containing the 5'-UTR and the first 18 codons of adh1 in a translational fusion with the GUS coding region and followed by the 3'-UTR of adh1 was expressed 57-fold higher at 5% O2. Progressive deletion of adh1 5'-UTR and coding sequences reduced expression of the GUS-mRNA at 5% O2, but had little impact on expression of 40% O2. Enhancement of expression in hypoxic protoplasts conferred by the adh1 5'-UTR and the first 26 codons decreased more than 3-fold when the adh1 3'-UTR was removed. In addition, the adh1 3'-UTR slightly inhibited expression in aerobic protoplasts. The physical half-lives of the GUS and LUC mRNAs were similar under both anaerobic and hypoxic conditions, indicating that expression levels were largely independent of mRNA stability. Thus, both adh1 5' and 3' mRNA sequences are required for enhanced translation in protoplasts under O2 deprivation.

Variation in mitochondrial genome organization and expression between male fertile and sterile nuclear-cytoplasmic combinations of sorghum has been examined. Cytoplasmic genotypes were classified into eleven groups on the basis of restriction endonuclease digestion of mitochondrial DNA (mtDNA) and five groups on the basis of mitochondrial translation products. These cytoplasms were further characterized by hybridization of specific gene probes to Southern blots of EcoRI digested mtDNA, and identification of the fragment location of four mitochondrial genes. Variation was observed in the genomic location and copy number of the F1 ATPase a-subunit gene, as well as the genomic location and gene product of the cytochrome c oxidase subunit I gene. The effect of nuclear genotype on mitochondrial genome organization, expression and the presence of two linear plasmid-like mtDNA molecules was examined. Our results indicate that nuclear-mitochondrial interactions are required for regulation of mitochondrial gene expression. When a cytoplasm is transferred from its natural to a foreign nuclear background some changes in the products of in organello mitochondrial protein synthesis occur. In a number of cytoplasmic genotypes these changes correlate with the expression of cytoplasmic male sterile phenotype, suggesting a possible molecular basis for this mutation.

The effect of O2 deprivation on the activities of RNases and levels of total cellular RNA and ribosomes in seedling roots of maize (Zea mays L.) was investigated. Sodium dodecyl sulfate-polyacrylamide gels containing RNA were used to distinguish RNase isoenzymes by apparent molecular mass. Since O2 deprivation causes a decrease in cytosolic pH from approximately pH 7.4 to 6.4 and an elevation in cytosolic Ca2+, RNase levels were examined in the physiological range of cytosolic pH and in the presence of Ca2+, Mg2+, Zn2+, ethylenediaminetetracetate, or ethyleneglycol-bis([beta]-aminoethyl ether)-N,N[prime]-tetraacetic acid. The activity of a number of RNases present in aerobic roots was reduced in response to O2 deprivation. Several RNases with a pH optimum of 6.4 were rapidly down-regulated by O2 deprivation. Spectrophotometric assay of extracts revealed that RNase activity was higher at pH 6.4 than at 7.2, and ethylenediaminetetracetate-insensitive RNase activity decreased in response to O2 deprivation. The decrease in RNase activity was correlated with no loss of total cellular RNA or ribosomes, despite a 4-fold decrease in run-on transcription of rRNA in isolated nuclei. Regulation of RNase activity may facilitate the conservation of nontranslating ribosomes and poorly translated mRNAs during O2 deprivation.

We determined that ribosomes of seedling roots of maize (Zea mays L.) contain the acidic phosphoproteins (P-proteins) known to form a flexible lateral stalk structure of the 60S subunit of eukaryotic ribosomes. The P-protein stalk, composed of P0, P1, and P2, interacts with elongation factors, mRNA, and tRNA during translation. Acidic proteins of 13 to 15.5 kD were released as a complex from ribosomes with 0.4 M NH4Cl/50% ethanol. Protein and cDNA sequence analysis confirmed that maize ribosomes contain one type of P1, two types of P2, and a fourth and novel P1/P2-type protein. This novel P-protein, designated P3, has the conserved C terminus of P1 and P2. P1, P2, and P3 are similar in deduced mass (11.4-12.2 kD) and isoelectric point (4.1-4.3). A 35.5- to 36-kD acidic protein was released at low levels from ribosomes with 1.0 M NH4Cl/50% ethanol and identified as P0. Labeling of roots with [32P]inorganic phosphate confirmed the in vivo phosphorylation of the P-proteins. Flooding caused dynamic changes in the P-protein complex, which affected the potential of ribosome-associated kinases and casein kinase II to phosphorylate the P-proteins. We discuss possible alterations of the ribosomal P-protein complex and consider that these changes may be involved in the selective translation of mRNA in flooded roots.