Gibberellins in Embryo-Suspensor of Phaseolus coccineus Seeds at the Heart Stage of Embryo Development

Gibberellins (GAs) in suspensors and embryos of Phaseolus coccineus seeds at the heart stage of embryo development were analyzed by combined gas chromatography-mass spectrometry (GC-MS). From the suspensor four C₁₉-GAs, GA₁, GA₄, GA₅, GA₆, and one C₂₀ GA, GA₄₄, were identified. From the embryo, five C₁₉-GAs GA₁, GA₄, GA₅, GA₆, GA₆₀ and two C₂₀ GAs, GA₁₉ and GA₄₄ were identified. The data, in relation to previous results, suggest a dependence of the embryo on the suspensor during early stages of development.     

Level of Abscisic Acid in Integuments, Nucellus, Endosperm, and Embryo of Peach Seeds (Prunus persica L. cv Springcrest) during Development

Free abscisic acid (ABA) in integuments, nucellus, endosperm, and embryo was determined throughout seed development of peach (Prunus persica L. cv Springcrest). Quantification of ABA was performed using combined high performance liquid chromatography-radioimmunoassay based on a monoclonal antibody raised against free (S)-ABA. In the integuments and endosperm, ABA concentration remained constant during the first 100 days after anthesis and rose in the following days when fresh weight was rapidly decreasing. In the nucellus, the ABA concentration variation pattern paralleled that of tissue growth. ABA concentration in the embryo increased constantly with the growth of the tissues to reach a maximum at the last growth stage. The role of ABA in peach seeds is discussed in relation to the development of the different seed tissues.     

Role of Hydroxyl Radicals in Escherzchza Colz Killing Induced by Hydrogen Peroxide

Escherichia coli lethality by hydrogen peroxide is characterized by two modes of killing. In this paper we have found that hydroxyl radicals (OH -) generated by H₂O₂ and intracellular divalent iron are not involved in the induction of mode one lethality (i.e. cell killing produced by concentrations of H₂O₂ lower than 2.5 mM). In fact, the OH radical scavengers, thiourea, ethanol and dimethyl sulfoxide, and the iron chelator, desferrioxarnine, did not affect the survival of cells exposed to 2.5mM H₂O₂. In addition cell vulnerability to the same H₂O₂ concentration was independent on the intracellular iron content. In contrast, mode two lethality (i.e. cell killing generated by concentrations of H₂O₂ higher than 10mM) was markedly reduced by OH radical scavengers and desferrioxamine and was augmented by increasing the intracellular iron content.

It is concluded that OH. are required for mode two killing of E. coli by hydrogen peroxide.     

NADP+-isocitrate dehydrogenase in germinating cucumber cotyledons: Purification and characterization of a cytosolic isoenzyme

The activity of NADP⁺-dependent isocitrate dehydrogenase (ICDH, EC 1.1.1.42) was investigated during the post-germinative growth of cucumber ( Cucumis sativus L. cv. Marketmore) seedlings. Isoelectric focusing showed the presence of several isoenzymes, two of which represented 70–80% of the total NADP⁺-ICDH activity in cotyledons of seedlings grown in the dark. They had pI values between 4.8 and 5.8. The isoenzyme with higher pI was purified to homogeneity by hydrophobic interaction, affinity, hydroxylapatite and anion exchange chromatography. The purified isoenzyme is a dimeric protein, consisting of two apparently identical 43-kDa subunits. It is specific for NADP⁺, inhibited by ATP and by 2-oxoglutarate, whereas it is not inhibited by citrate, succinate, and glyoxylate. The data indicate that NADP⁺-ICDH from cucumber is structurally similar to ICDHs from other plants, but it shows some peculiar biochemical characteristics.     

Free l-amino acids and d-aspartate content in the nervous system of Cephalopoda. A comparative study

We have determined the content of free l-amino acids and d-aspartate in the nervous tissue of three representative cephalopods: Sepia officinalis, Octopus vulgaris, and Loligo vulgaris, and the optic lobes of adult and embryo Sepia officinalis. Taurine is the most abundant amino acid in the cephalopod nervous tissue. Its content amounts to more than 50% of the total free amino acids. The other most concentrated amino acids are Glu, Ala, Asp, and GABA. High concentrations of d-aspartate were found in the nervous tissue of all cephalopods examined (7–12 μmol/g wet tissue) which represents 50–80% of the total aspartate (d + l), depending on the animal. Among the various regions of the brain of Octopus vulgaris, d-aspartate was found to be evenly distributed in the various regions of the brain. In nerve tissue of Sepia officinalis, there is no significant difference in the pattern of free l-amino acids, in particular of the d-aspartate concentration, between adults and embryos, except for GABA, Gly, His and Thr. This suggests that d-aspartate in nerve tissue of the Cephalopoda is of endogenous origin and not a product of accumulation from exogenous sources. From a comparative study of the content of d-aspartate in the nervous tissue of different animals, we found that protostomia contain a significantly higher amount than deuterostomia. Thus, d-aspartate could be a criterion to distinguish the protostomia phyla from the deuterostomia phyla.     

Action of Cystine in the Cytotoxic Response of Escherichia Coli Cells Exposed to Hydrogen Peroxide

Cystine markedly enhanced the cytotoxic response of Escherichia coli cells to concentrations of hydrogen peroxide resulting in mode one killing, but displayed little effect in mode two killed cells. The effect of cystine was concentration-dependent over a range of 5-50 μM and did not further increase at higher levels. Cystine had similar effects in other bacterial systems.

In order to sensitize the cells to the oxidative injury, the amino acid must be present during exposure to the oxidant since no enhancement of the cytotoxic response can be observed in cystine pre-loaded cells. In addition, no further enhancement of cytotoxicity could be detected when cystine was added before and left during challenge with the oxidant. The enhancing effect of cystine on oxidative injury of E. coli cells appears to be directly mediated by the amino acid and in fact cysteic acid, the most likely oxidation product, had no effect on the killing of bacterial cells elicited by hydrogen peroxide. Other disulfide compounds such as oxidized glutathione, cystamine and dithionitrobenzoic acid only slightly increased the susceptibility of bacteria to the oxidant. The effect of the disulfides was not concentration-dependent over a range of 200-800 μM and was statistically significant only for cystamine.

Taken together, these results indicate that cystine markedly increases the cytotoxic response of bacteria to hydrogen peroxide and suggest that the amino acid might impair the cellular defence machinery against hydrogen peroxide. This effect may involve a thiol-disulfide exchange reaction at the cell membrane level.     

Gibberellins in suspensor,embryo and integument from very young seeds of Phaseolus coccineus L.

Endogenous gibberellins (GAs) were extracted from suspensor, embryo and integument of very young seeds of Phaseolus coccineus L. and detected by combined gas chromatography-mass spectrometry (GC-MS). Results show the presence of one C₂₀-GA, GA₄₄ and five C₁₉-GAs in the suspensor: GA₁, GA₄, GA₅, GA₆ and GA₈, and four C₁₉-GAs in the integument: GA₁, GA₅, GA₆ and GA₈. Only traces of GA₁ and GA₅ were identified in the embryo. A compound structurally related to GAs was identified as tetrahydroxy-Kauranoic acid in suspensor, integument and, only in trace amounts, in the embryo.     

A radiochemical assay for N-acetyl-L-aspartate amidohydrolase (EC 3.5.1.15) and its occurrence in the tissues of the chicken

A simple and rapid radiochemical method for the determination of N-acetyl-L-aspartic acid amidohydrolase (EC 3.5.1.15) activity using ion exchange chromatography has been developed. The activity of this enzyme in the developing brain and some non-nervous tissues of the chicken has been determined. No activity of the enzyme could be detected in the brains of chick embroys prior to 14 days of gestation; activities gradually increased thereafter to adult levels which are about 60% of that found in the adult rat. In non-nervous system tissues of the adult chicken, activities varied from high levels in the kidney to low levels in heart and breast muscle. Treatment of the homogenates of the adult tissues with a detergent significantly increased the enzyme activity, suggesting that a portion of the enzyme is membrane bound.