Growth responses of rice in ammonium-based nutrient solution with variable calcium supply

It is commonly known that calcium promotes NO₃ ^- uptake in many crop species. However, calcium enhancement of NH₄ ⁺ uptake by plants has received little attention. This study aimed to evaluate the effect of Ca supplements on NH₄ ⁺ uptake and plant growth in solution cultured rice. Supplemental Ca applied at vegetative and reproductive phases of plant ontogeny tended to stimulate NH₄ ⁺ absorption, and accordingly resulted in a better straw and grain yield. However, excessively supplied Ca (400 ppm) was detrimental to plant growth. Increases in straw and grain yield observed at Ca levels up to 300 ppm were linked to the Ca-enhanced activities of glutamine synthetase (GS), glutamate synthase (GOGAT), and ribulose 1, 5-bisphosphate carboxylase/oxygenase (Rubisco).     

Cloning, sequence analysis, and expression of a cDNA encoding a plastid-localized heat shock protein in maize

We have cloned and characterized a cDNA encoding a maize (Zea mays L.) heat shock protein (HSP), HSP26. The mRNA of HSP26 is present as a single mRNA species of 1.1 kilobase pairs in size and is detectable when maize seedlings are treated at 40°C but not at 28°C. Accumulation of HSP26 mRNA was detected after 10 minutes of incubation at 40°C, reaching the maximum level after 1 hour. Comparison of the deduced amino acid sequence of maize HSP26 to other HSPs indicated a strong homology to the sequences of two nuclear encoded HSPs that are transported into the chloroplasts during heat shock: pea HSP21 and soybean HSP22. Maize HSP26 was also found to cross-react with anti-pea chloroplast HSP21 antibodies. Because of the sequence homology between maize HSP26, soybean HSP22, and pea HSP21, in vitro chloroplast protein import experiments were conducted. The in vitro synthesized maize HSP26 is specifically imported to the soluble fraction of the chloroplast and processed to a smaller polypeptide. The sequence homology and antibody cross-reactivity between maize HSP26 and pea HSP21 have allowed us to conclude that maize HSP26 is a nuclear-encoded, plastid-localized protein in maize.     

Sucrose synthase in rice plants : growth-associated changes in tissue specific distributions

Different parts of the rice (Oryza sativa L.) plant at different growth stages were analyzed for sucrose synthase (SS) by enzyme activity assay and enzyme-linked immunosorbent assay directly on the extracts or on the eluates from a gel filtration column. On a dry matter basis, the amount of soluble protein and SS activity decreased significantly, but the amount of enzyme protein changed little in growing leaves. In the grain, the SS activity was the highest at the early ripening stage and decreased later, but the amount of SS protein increased with the increase in maturity. In the root, a low activity of SS was detectable only in the tillering but not in other stages. Immunoblotting of SS protein extracted from different parts of rice showed two bands. Elution patterns of crude extracts from a gel filtration column showed the presence of several types of SS protein. Among them, two to three types with larger elution volumes had the SS activity but others with smaller elution volumes (considered as the aggregated forms) had no activity. The SS purified from different parts of the plant showed similar but distinctly different electrophoretic mobilities in a native gel. It has been concluded that different isozymes are expressed in different tissues at different growth stages.     

A major gibberellic Acid-induced barley aleurone cysteine proteinase which digests hordein : purification and characterization

We previously described the purification and characterization of a 37,000 M_r cysteine proteinase, designated EP-A, from gibberellic acid (GA₃)-induced barley (Hordeum vulgare L.) aleurone layers (S Koehler, T-HD Ho [1988] Plant Physiol 87: 95-103). A second, more abundant protease has now been purified from this tissue. This protease, designated EP-B, has an apparent M_r of 30,000 on 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). It resolves into two bands during native isoelectric focusing with pl of 4.6 to 4.7. The analysis of hemoglobin digestion products by both gradient SDS-PAGE and Bio-Gel P2 chromatography, the inhibition of protease activity by E-64, leupeptin, iodoacetate, and p-hydroxymercuribenzoate, and N-terminal amino acid sequence analysis all indicate that EP-B is a cysteine proteinase. The first 22 amino acids at the N terminus of EP-B have been determined, and their sequence is 90% similar to that of EP-A. EP-B has properties similar to EP-A; however, EP-B is much more sensitive to high pH during gel electrophoresis and therefore is not detectable on native activity gels used to detect EP-A. Its pH optimum against azocasein and hemoglobin is 4.5 to 4.6. Both of these proteinases digest hordeins enriched for the B and D fractions into similar peptides of 25,000 to 2,000 M_r as determined by gradient SDS-PAGE.     

Prognostic usefulness of certain defined indicators for achieving complete remission and survival of ANLL in adults: proposal of a prognostic scale

Retrospective analysis has included 323 patients with acute nonlymphocytic leukaemia. The comparable patient groups were treated since 1981, according to protocols used by the Polish Acute Leukaemia Group. The prognostic value for achieving complete remission and survival of 67 pre-treatment factors (42 quantitative and 25 qualitative) was evaluated. The most important 9 parameters were scored according to their prognostic value as follows: age, percent of blasts in bone marrow, peripheral blood blast count, morphological subtype, percent of granulocytes in bone marrow, percent of blasts with CD-15 antigen, thrombocyte count, spleen/liver enlargement, CSF protein levels. Proposed scoring system enables classification of ANLL patients to a standard and high risk groups.     

Inward current generated by Na-Ca exchange during the action potential in single atrial cells of the rabbit.

To investigate the underlying ionic mechanism of the late plateau phase of the action potential in rabbit atrium the whole-cell patch-clamp technique with intracellular perfusion was used. We recorded the inward current during repolarizations following a brief 2 ms depolarizing pulse to +40 mV from a holding potential of between -70 and -80 mV. The development of this current coincides with the onset of the late plateau phase of the action potential. Peak activation of the current occurs about 10 ms from the beginning of the depolarizing pulse, and it decays spontaneously with a slow timecourse. Its voltage dependency from -40 mV to +40 mV shows very steep activation (-40 to -20 mV) and shows almost the same maximum magnitude between -10 mV and +40 mV. This behaviour is quite different from that of the calcium current. The inward current and the late plateau phase of the action potential were both abolished by the application of 5 mM EGTA, 1 microM ryanodine and by reducing the Na+ gradient. The fully activated current-voltage relation of the inward current was plotted as the difference current before and after treatment with Ryanodine, Diltiazem, 20 mM Na+ inside or 30% Na+ outside and shows an exponential voltage dependence with the largest magnitude of the current occurring at negative potentials. The current-voltage (I-V) curve was well fitted by the Na-Ca exchange equation, i = A exp (-(1 - r)EF/RT). The results suggest that the inward current contributes to the generation of the late plateau phase of the rabbit atrial action potential, and is activated by intracellular calcium released from the sarcoplasmic reticulum. Sarcoplasmic reticulum calcium release appears to be triggered both by the membrane voltage and by the calcium current. It is concluded that the inward current is generated by Na-Ca exchange.     

Purification, characterization, and amino terminal sequence of xylose reductase from Candida shehatae.

D-Xylose is a major component of the carbohydrates derived from agricultural residues and forest products. Among more than two hundred known xylose-utilizing yeasts, only a few species are known to be able to ferment xylose anaerobically. Candida shehatae is one of such xylose-fermenting yeasts. Xylose reductase (E.C. 1.1.1.21) is a key enzyme responsible for xylose metabolism in xylose-utilizing as well as xylose-fermenting yeasts. In this paper, we report the development of a convenient and reliable procedure for the purification of xylose reductase from C. shehatae to near homogeneity. The amino acid composition and N-terminal sequence of the enzyme have also been analyzed. C. shehatae seems to contain only a single xylose reductase, but the enzyme has a dual coenzyme specificity for both NADPH and NADH. The enzyme is remarkably stable at room temperature and 4 degrees C.     

The channel properties of possible gramicidin dimers

Extending previous work (Sung & Jordan, 1987 a, Biophys. J. 51, 661-672; 1988, Biophys. J.54, 519-526), we describe channel properties of five possible gramicidin dimers by studying dimerization energies and axial electrical potentials. Unlike the head-to-head dimer (the predominant channel former), both tail-to-tail and head-to-tail dimers with the same beta-helical monomer structure as the head-to-head dimer only form four intermonomer hydrogen bonds and are much less stable. Were channels formed from these dimers to be observed, their electrical potential profiles suggest that they should be cation selective, probably conduct less than the head-to-head dimer, have a central cation binding site, bind cations preferentially if crystallizable, and in the case of the head-to-tail dimer, rectify. Like the antiparallel double stranded helical dimer (a possible minor conducting pathway) the parallel double stranded helical dimer has 28 interstrand hydrogen bonds, but its hydrogen bond network is quite distorted and it is much less stable. If it formed, its electrical potential profile suggests that it would be cation selective, bind anions preferentially if crystallizable, rectify, and at high enough voltages, might exhibit a conductance greater than that of the antiparallel form.