Distribution and immunolocalization of stachyose synthase in Cucumis melo L.

Indirect evidence for the site of stachyose biosynthesis has been provided by determining the occurrence and distribution of stachyose, raffinose and galactinol, the donor of the galactosyl moiety for stachyose synthesis, in Cucumis melo L. cv. Ranjadew. Studies of enzyme activities for the synthesis of these sugars and their distribution in different plant organs and isolates has led to the conclusion that stachyose is synthesized mainly in mature leaves and seeds. Nevertheless, stachyose-synthase activity varied with leaf age, the developmental stage of a plant, the growing season and the plant cultivar used. No stachyose or stachyose-synthase activity could be detected in isolated mesophyll protoplasts and chloroplasts, whereas both were found in a minor-vein-enriched fraction isolated from mature leaves. The conclusion that stachyose biosynthesis is associated with minor veins was confirmed by immunolocalization of the enzyme. Positive specific immunoreactivity of stachyose synthase with polyclonal anti-stachyose-synthase antibodies, labeled with protein A-gold, was detected in intermediary cells of leaf minor veins. The implication of this local synthesis of the main transport sugar for phloem loading in mature leaves of Cucumis melo is discussed.Abbreviation RUBPCase ribulose-1,5-bisphosphate carboxylase This work was supported by Deutsche Forschungsgemeinschaft. The excellent assistance of Ms. B. Müller in preparing the samples for electron microscopy is gratefully acknowledged. The authors thank Professor H.J. Schneider-Poetsch for anti-RuBPCase antibodies.     

Barley aleurone layer cell protoplasts as a transient expression system

Protoplasts were prepared from barley aleurone layers using Onozuka cellulase digestion and purification through a Percoll gradient. Protoplasts prepared by this procedure had a viability ranging from 60% to 80% during the first two days of culture. They were responsive to gibberellic acid (GA) as measured by the stimulation of -amylase synthesis. The GA stimulation was counteracted by abscisic acid (ABA). In the presence of polyethylene glycol (PEG), the protoplasts took up exogenously added plasmid DNA containing the reporter gene coding for chloramphenicol acetyl transferase (CAT) linked to a 35S promoter from cauliflower mosaic virus (CaMV) or to barley -amylase gene promoters and expressed CAT activity. Therefore, barley aleurone layer protoplasts are suitable for analysis of hormoneresponsive elements in hydrolase genes.     

Regulation of nuclear membrane assembly and maintenance during in vitro maturation of mouse oocytes: role of pyruvate and protein synthesis

Summary In the absence of a suitable energy source, mouse oocytes cultured in vitro resume, but fail to complete, meiotic maturation. However, little is known about the underlying mechanisms leading to this meiotic failure. We utilized pyruvate-deficient medium to test for the role of pyruvate throughout the meiotic maturation process. Germinal vesicle-stage (GV) oocytes underwent germinal vesicle breakdown (GVBD), but failed to form a polar body when cultured continuously in pyruvate-free medium. However, when GV oocytes were preincubated for 4 h in pyruvate-free medium containing dibutyryl cyclic adenosine monophosphate (dbcAMP) and then cultured in pyruvate-free medium, GVBD was markedly inhibited. Preincubation of GV oocytes in dbcAMP and cycloheximide, followed by culture in cycloheximide only, also inhibited GVBD. A longer preincubation period was required in the cycloheximide-dbcAMP case (12 h) than in pyruvate-free-dbcAMP medium situation (4 h). Strikingly, reassembly of the nuclear membrane without polar body formation was observed following GVBD in oocytes continuously cultured in pyruvate-free medium. The reassembled nuclear membrane increased in size with continued culture, and it surrounded partially-decondensed chromatin. Nuclear membrane reassembly also occurred in oocytes which had undergone GVBD during continuous culture in medium containing only cycloheximide. Reformation of nuclear membranes after GVBD was confirmed by electron-microscopic analyses of oocytes cultured in pyruvate-free medium or in the presence of cycloheximide. We conclude that both pyruvate and protein synthesis are required for nuclear membrane disassembly, whereas lack of pyruvate or protein synthesis is associated with interruption of the metaphase state and reassembly of the nuclear membrane. The evidence suggests that assembly and maintenance of an intact nucleus and its disintegration are all amenable to regulation by pyruvate, possibly via mechanism(s) involving protein synthesis.     

Comparison of salt- and heat-induced alterations of protein synthesis in the cyanobacterium Synechocystis sp. PCC 6803

Protein synthesis of the cyanobacterium Synechocystis spec. PCC 6803 decreases after a 684 mM NaCl salt shock. Qualitative changes were observed during the shock and the subsequent adaptation process using one-dimensional polyacrylamide electrophoresis. Proteins of apparent molecular masses of 13.0, 14.2, 16.6, 20.0, 21.0, 23.0, 33.0, 47.0, 52.0, 65.0 and 72.0 kDa are synthesized at enhanced rates after salt stress. The proteins of 14.2, 21.1 and 52.0 kDa are transiently induced during the first hours of the adaptation phase, while the other proteins are also synthesized at enhanced rates in salt-adapted cells. The proteins of 14.2, 23.0, 33.0 and 65.0 kDa are also induced by heat shock (43°C). Heat shock proteins of about 88.0, 75.0, 58.0, 17.5 and 13.8 kDa, in contrast, are induced by heat shock but not by salt. Two-dimensional polyacrylamide electrophoresis showed that the induced salt and heat shock proteins in some cases consisted of isoforms of different isoelectric points.Abbreviations IP isoelectric point - PAGE polyacrylamide gel electrophoresis - PMSF phenylmethylsulfonyl fluoride     

Utilization of alpha-ketoglutarate as a precursor for transmitter glutamate in cultured cerebellar granule cells

Alpha-ketoglutarate together with an amino group donor (alanine) was shown to be able to serve as a precursor for the glutamate pool which is released by potassium-induced depolarization (i.e., transmitter glutamate) in cerebellar granule cells. However, these compounds could not be utilized as precursors for intracellular glutamate or for release of transmitter aspartate. The formation of transmitter glutamate was inhibited by the transamination inhibitor aminooxyacetic acid but not by phenylsuccinate, an inhibitor of the dicarboxylate carrier in the mitochondrial membrane. Both of these inhibitors have previously been found to inhibit synthesis of transmitter glutamate from glutamine. The results support the hypothesis that alpha-ketoglutarate and alanine undergo transamination in the cytosol to form pyruvate and glutamate, and that this glutamate pool is available for transmitter release of glutamate but does not constitute the major intracellular pool of glutamate.     

Models of seasonal growth of the equatorial carp Labeo dussumieri in response to the river flood cycle

Synopsis The phenology of Labeo dussumieri, an omnivorous carp common to South Asia, was investigated in a population inhabiting a flood plain anabranch of the Mahaweli Ganga, Sri Lanka. The Mahaweli Ganga exhibited a bimodal discharge pattern typical of many equatorial rivers, with a minor peak during the S.W. monsoon and a major peak during the N.E. monsoon. Seasonal changes in several lotic variables were measured in an attempt to correlate changes in environmental conditions to reproduction and growth in L. dussumieri. The onset of gonad recrudescence and spawning were synchronized with the increased river discharge during the S.W. and N.E. monsoons: gonad development followed one monsoonal discharge peak and spawning took place at the beginning of the other. Most fish spawned at the beginning of the major discharge peak in October and November, following the September dry season. Increased discharge was concomitant with a fall in temperature, light intensity, pH and conductivity. Growth was shown to be seasonal, exhibiting an annual bimodal pattern with peaks coincident with S.W. and N.E. monsoonal rains. Seasonal changes in growth were expressed by two models in terms of: (a) change of somatic weight or fork length with time, (b) change of specific growth rate in response to river discharge, modified by somatic weight. Gonad recrudescence and spawning stress did not appear to influence growth rate.     

Physiological roles of animal succinate thiokinases Specific association of the guanine nucleotide-linked enzyme with haem biosynthesis

The discovery of two distinct succinate thiokinases in mammalian tissues, one (G-STK) specific for GDP/GTP and the other (A-STK) for ADP/ATP, poses the question of their differential metabolic roles. Evidence has suggested that the A-STK functions in the citric acid cycle in the direction of succinyl-CoA breakdown (and ATP formation) whereas one role of the G-STK appears to be the re-cycling of succinate to succinyl-CoA (at the expense of GTP) for the purpose of ketone body activation. A third metabolic participation of succinyl-CoA is in haem biosynthesis. This communication shows that in chemically induced hepatic porphyria, when the demand for succinyl-CoA is increased, it is the level of G-STK only which is elevated, that of A-STK being unaffected. The results implicate G-STK in the provision of succinyl-CoA for haem biosynthesis, a conclusion which is further supported by the observation of a high G-STK/A-STK ratio in bone marrow.