Calibration of an extreme-ultraviolet transmission grating spectrometer with synchrotron radiation.

The responsivity of an extreme-ultraviolet transmission grating spectrometer with silicon photodiode detectors was measured with synchrotron radiation. The spectrometer was designed to record the absolute radiation flux in a wavelength bandpass centered at 30 nm. The transmission grating had a period of 200 nm and relatively high efficiencies in the +1 and the -1 diffraction orders that were dispersed on either side of the zero-order beam. Three photodiodes were positioned to measure the signals in the zero order and in the +1 and -1 orders. The photodiodes had aluminum overcoatings that passed the desired wavelength bandpass centered at 30 nm and attenuated higher-order radiation and wavelengths longer than approximately 80 nm. The spectrometer's responsivity, the ratio of the photodiode current to the incident radiation power, was determined as a function of the incident wavelength and the angle of the spectrometer with respect to the incident radiation beam. The spectrometer's responsivity was consistent with the product of the photodiode responsivity and the grating efficiency, both of which were separately measured while removed from the spectrometer.

cDNA and genomic cloning of sugar beet V-type H+-ATPase subunit A and c isoforms: evidence for coordinate expression during plant development and coordinate induction in response to high salinity.

The plant V-type H+-ATPase (V-ATPase) does not only serve basic housekeeping functions but is also involved in stress-induced NaCl sequestration during salinity stress. To address the question whether the same isoforms conferring housekeeping functions are equally involved in the response to high salinity, we have isolated cDNA clones for subunits A and c, as representing the peripheral V1 complex and the membrane-integral V0 complex, respectively, from the halotolerant sugar beet (Beta vulgaris L., diploid variety). RNA blot analysis with gene-specific probes revealed a coordinate expression of the cloned subunit A and c isoforms during plant development and in response to high salinity. Also, in rapidly dividing suspension-cultured cells with 10-fold increased transcript amounts as compared to young leaf tissue, the ratio of transcripts for both genes was similar to the ratio found for transcripts in leaves of different age. We have then isolated partial genomic clones (BVA/70 for Beta V-ATPase 70 kDa subunit; BVA/16-1 for Beta V-ATPase 16 kDa subunit), including the promoter regions. Transcription start mapping revealed long 5'-UTR leader sequences (230 and 172 bases, respectively) for both genes. Both promoters contain putative G-box motifs in similar distance to the TATA boxes. For a quantitative comparison of relative promoter strength, the BVA/70 and BVA/16-1 promoters linked to the luciferase reporter gene (LUC) were delivered to sugar beet suspension-cultured cells by particle bombardment. The BVA/16-1 promoter showed a 1.7-fold higher activity as compared with the BVA/70 promoter. Salt treatment induced an increase of BVA/70 (+70%) and BVA/16-1 (+57%) promoter activities, concomitant with increased transcript amounts. The following sequences have been deposited at the EMBL database X98767: Beta vulgaris V-ATPase subunit A, cDNA clone; X98851, B. vulgaris V-ATPase subunit c isoform 1, cDNA clone; Y11038, B. vulgaris V-ATPase subunit A, partial genomic clone; Y11037, B. vulgaris V-ATPase subunit c isoform 1, partial genomic clone.

Salt stress induces an increased expression of V-type H(+)-ATPase in mature sugar beet leaves.

In the halotolerant sugar beet co-expression of V-ATPase and a vacuolar Na+/H(+)-antiporter provides a mechanism for vacuolar salt sequestration. To analyze salt-induced changes in the expression of the vacuolar H(+)-ATPase (V-ATPase) a partial cDNA of the proton-channel forming subunit c was cloned by RT-PCR. Southern blot analysis indicated a small gene family. In control plants transcript levels were high in roots and young growing leaves but low in fully expanded leaves. In mature leaves salt exposure (400 mM, 48 h) induced a strong increase in subunit c-mRNA. Transcripts for the catalytic subunit A followed a similar developmental and stress-modulated pattern, indicating a coordinate regulation of transcripts for both V-ATPase subunits. Concomittant with the mRNA increases the amount of V-ATPase protein increased as well.

Down-regulation of plant V-type H+ -ATPase genes after light-induced inhibition of growth.

Cell extension growth in the mesocotyl tip of dark-grown Zea mays L. seedlings is dependent on vacuole enlargement and massive flux of ER and Golgi vesicles. Water flow into the expanding vacuole is driven by ion accumulation, which in turn is energized by the vacuolar H+-ATPase (V-ATPase). The V-ATPase energizes the secondary ion transport into the expanding vacuole. As light exposure leads to a strong inhibition of extension growth, the effect of light on transcript levels for subunits A and c of the V-ATPase was analyzed. Partial homologous cDNAs for subunit A and two isoforms of subunit c were cloned by RT-PCR. In dark-grown seedlings transcript levels for both subunits were much higher in the growing mesocotyl tip than in the fully differentiated mesocotyl tissue. Only in the tip region did light exposure lead to a strong and coordinate down-regulation of both mRNAs whereas in the differentiated mesocotyl only a slight decrease was observed. The results indicate that expression of the 'housekeeping' V-type H+-ATPase is strongly regulated in response to growth rate.

Panchromatic spectrograph with supporting monochromatic imagers.

The Arizona Imager/Spectrograph is a set of imaging spectrographs and two-dimensional imagers for space flight. Nine nearly identical spectrographs record wavelengths from 114 to 1090 nm with a resolution of 0.5-1.3 nm. The spatial resolution along the slit is electronically selectable and can reach 192 elements. Twelve passband imagers cover wavelengths in the 160-900-nm range and have fields of view from 2 degrees to 21 degrees . The spectrographs and imagers rely on intensified CCD detectors to achieve substantial capability in an instrument of minimum mass and size. By use of innovative coupling techniques only two CCD's are required to record images from 12 imagers, and single CCD's record spectra from pairs of spectrographs. The fields of view of the spectrographs and imagers are coaligned, and all spectra and images can be exposed simultaneously. A scan platform can rotate the sensor head about two orthogonal axes. The Arizona imager/spectrograph is designed for investigations of the interaction between the Space Shttle and its environment. It is scheduled for flight on a Shuttle subsatellite.