Acquisition of desiccation tolerance by isolated maize embryos exposed to different conditions: the questionable role of endogenous abscisic acid

The effect of exogenous ABA on acquisition of desiccation tolerance has been well documented for the embryos of several species. including maize ( Zea mays L.). It has also been suggested that endogenous ABA plays a role in regulating the same phenomena. To test this hypothesis, endogenous ABA was quantified by radioimmunoassay. Our results show that: (1) during embryogenesis in maize, endogenous ABA increase-concomitantly with the acquisition of desiccation tolerance: (2) ABA deficient embryos of the vp 5 mutant are desiccation intolerant, but tolerance can he induced by exogenous ABA: and (3) desiccation tolerance is acquired if desiccation sensitive embryos undergo a slow drying treatment, during which ABA increases. However, when embryos were preincubated in fluridone to prevent ABA accumulation during slow drying, desiccation tolerance was induced in spite of the low level of endogenous ABA in the embryo. Our results cast doubts on an exclusive role of ABA in the acquisition of desiccation tolerance in maize embryo.     

Affected sib-pair analysis of the GLUT1 glucose transporter gene locus in non-insulin-dependent diabetes mellitus (NIDDM): evidence for no linkage

Despite the strong evidence for a major role played by genetic factors in the aetiology of non-insulin-dependent diabetes mellitus (NIDDM), the genes involved are still unknown. Association studies of candidate genes for the inheritance of NIDDM have so far yielded inconclusive results. Some evidence exists for an association between NIDDM and the glucose transporter gene GLUT1, involved in basal glucose transport, although this has not been confirmed. In the present study we have tested the hypothesis of linkage between NIDDM and the GLUT1 gene, using affected sib-pairs. With this method the concordance observed for a given gene marker is compared with that expected under the assumption of no linkage between that marker and the disease. Fifty-four pedigrees (22 Italians and 32 British), for a total of 82 sibpairs were studied by the affected sib-pair method proposed by Weeks and Lange, using two restriction fragment length polymorphisms (RFLPs) at the GLUT1 locus, the MspI RFLP, at an estimated 0.171 recombination frequency from the GLUT1 gene, and the XbaI RFLP, located within the GLUT1 gene and previously shown to be associated with the disease. Results showed that the MspI marker and NIDDM segregate independently; for the XbaI RFLP, linkage could be shown only if the results were weighted by the allele frequency [f(p) = 1/p], and only in the Italian and the combined (Italian and British) sib-pair groups. Multilocus analysis with both markers was also negative. We conclude that the GLUT1 gene is very unlikely to play a major role in the aetiology of NIDDM, although an accessory role cannot be excluded, and studies of the gene sequence should help to clarify this question.     

The subcellular distribution of glucocorticoid-receptor complexes as studied by chemical crosslinking of intact HTC cells

Treatment of intact HTC cells with glutaraldehyde results in redistribution of glucocorticoid binding sites between cytosolic and nuclear fractions. The decrease in cytosolic receptors and their accumulation at the nuclear level were found to be directly related to the glutaraldehyde concentrations employed in our procedure and inversely related to the cell density of samples. When the data from eleven separate experiments were combined, and analyzed by linear regression of cytosolic and nuclear levels of receptor complexes vs the ratios between the DNA and glutaraldehyde concentration of our samples, two lines were obtained whose intercepts on the ordinate yielded values of cytosolic and nuclear receptors corresponding to 37.5 and 62.5% of the total cellular pool, respectively. When we compared the subcellular redistribution of glucocorticoid receptor to that of the cytosolic enzyme lactate dehydrogenase upon HTC cell crosslinking with glutaraldehyde, we found that the cytosolic and nuclear levels of the enzyme were 53.2 and 46.8% of the total content, respectively. If the subcellular distribution of glucocorticoid receptor is corrected for the artefactual redistribution induced by crosslinking, using the values obtained for lactate dehydrogenase, it can be concluded that glucocorticoid receptors in HTC cells are distributed between cytosol and nuclei in a ratio which is about 2:1. Our findings lend further support to theconclusion that only a portion of glucocorticoid receptor is cytosolic in intact cells.     

Low temperature optical spectroscopy of cobalt-substituted hemocyanin from Carcinus maenas

In this work we report the optical absorption spectra of three cobalt-substituted derivatives of hemocyanin (He) from Carcinus maenas, in the temperature range 300–20 K. The derivatives studied are the mononuclear (Co²⁺)-He with a single cobalt ion in the Cu_A site, the binuclear (Co²⁺)₂-He and the binuclear mixed metal (Co²⁺-Cu¹⁺)-He. At low temperature three main bands are clearly resolved; the temperature dependence of their zeroth, first and second moments sheds light on the stereodynamic properties in the surroundings of the chromophore. Within the limits of the reported analysis, in the binuclear derivatives the motions coupled to the chromophore appear to be essentially harmonic in the whole temperature range investigated; moreover the data are consistent with the presence of an exogenous ligand strongly bound to the two metal ions. For the mononuclear derivative an essentially harmonic behavior is evident only up to 200 K where the data are consistent with the presence of an exogenous ligand much less strongly bound, while at higher temperatures the behavior of the spectra indicates the onset of very large anharmonic contributions to motions, that plausibly involve the above exogenous ligand and, quite likely, the entire active site.Abbreviations He Hemocyanin - M₀ zeroth moment - M₁ first moment - M₂ second moment - (Co^2–)₂-He binuclear bicobalt hemocyanin derivative - (Co²⁺)-He mononuclear monocobalt hemocyanin derivative - (Co²⁺-Cu¹⁺)-He binuclear mixed metals hemocyanin derivative - LFT ligand field theory - CT charge transfer - EPR electronic paramagnetic resonance - XANES X-ray absorption near edge structure Correspondence to: L. Cordone     

Cooperative effect of inositol hexakisphosphate, bezafibrate, and clofibric acid on the spectroscopic properties of the nitric oxide derivative of ferrous human hemoglobin

The cooperative effect of inositol hexakisphosphate (IHP), bezafibrate (BZF), and clofibric acid (CFA) on the spectroscopic (EPR and absorbance) properties of the nitric oxide derivative of ferrous human hemoglobin (HbNO) has been investigated quantitatively. In the presence of IHP, BZF, and CFA, the X-band EPR spectra and the absorption spectra in the Soret region of HbNO display the same basic characteristics described in the presence of 2,3-diphosphoglycerate (2,3-DPG), which have been attributed to a low affinity conformation of the tetramer. Addition to HbNO of two allosteric effectors together (such as IHP and BZF, or IHP and CFA) further stabilizes the low affinity conformation of the ligated hemoprotein (i.e., HbNO). Moreover, in the presence of saturating amounts of IHP, the affinity of BZF and CFA for HbNO increases by about fifteenfold. Likewise, in the presence of both IHP and BZF, as well as in IHP and CFA, the oxygen affinity for ferrous human hemoglobin (Hb) is reduced with respect to that observed in the presence of IHP, BZF, or CFA alone, which in turn is lower than that reported in the absence of any allosteric effector. All the data were obtained at pH 7.0 (in 1.0 × 10⁻¹ M N-[2-hydroxyethyl]piperazine-N′-[2-ethanesulfonic acid]/NaOH buffer system plus 1.0 × 10⁻¹ M NaCl), as well as at 100 K and/or 20°C. The results here reported represent clearcut evidence for the cooperative and specific (i.e., functionally relevant) binding of IHP, BZF, and CFA to Hb.     

Release of cholecystokinin in the central nervous system

The octapeptide cholecystokinin (CCK) is one of the most abundant neuropeptides of the central nervous system. A number of features (for instance heterogeneity of the regional distribution, subcellular localization at the nerve terminal level, calcium-dependent release upon nervous tissue depolarization) support the candidacy of CCK as a neurotransmitter. The reported co-existence of CCK and dopamine in some meso-limbic neurons has led to speculation that the neuropeptide may interact with the catecholamine in neuropsychopathologies linked to dopamine dysfunctions, like schizophrenia. Data from the experimental animals have so far generated conflicting results. It should be noted that the interactions between CCK and dopamine, and, in particular, the effects of CCK and dopamine on each other release, both in vitro and in vivo, have been poorly investigated and would require special attention. Evidence is accumulating that CCK may participate in the expression of anxiety. Indeed antagonists at the central CCK receptors exhibit anxiolytic activity in the laboratory animal. An interesting linkage appears to exist in the brain between 5-hydroxytryptamine (5-HT) and CCK. Activation of 5-HT₃ receptors was found to increase CCK release from rat cortical or nucleus accumbens synaptosomes. Interestingly, antagonists at 5-HT₃ receptors appear to possess anxiolytic activity. Recent studies carried out in conscious unrestrained rats show that the calcium-dependent, tetrodotoxin-sensitive release of CCK-like immunoreactivity evoked in the rat frontal cortex by veratrine infusion can be inhibited by submicromolar concentrations of 5-HT₃ receptor antagonists. It seems legitimate to conclude that 5-HT and CCK interact in the living brain, the former increasing the release of the latter through activation of receptors of the 5-HT₃ type. On the basis of this interaction both 5-HT₃ and CCK receptor antagonists may become novel anxiolytics.     

Rhythmical timing and spatial scattering of foraging in a homer limpet {Patella rustica)

Homing to a more or less permanent scar after each foragingexcursion is a common movement pattern among intertidal gastropodsand chitons; however, details of the timing and spacing of foragingactivity have been investigated only in a few species. The presentstudy analyzes the short-term behavior of the limpet Patellarustica along the Tyrrhenian coast, Italy, using a motographictechnique to assess the fine organization of its foraging duringfavorable periods of sea roughness. P. rustica becomes activeonce the upper midlittoral is well splashed. It alternates foragingexcursions and resting at home with a periodicity slightly longerthan 12 h, suggesting a tidal-diel pattern. However, periodogramanalysis of the sea level oscillations during the study periodsrevealed no such rhythmicity because tidal oscillations werehidden by irregular variations caused by waves. As a resultof this time partitioning, limpets move, on average, less than50% of their potential activity time. Time partitioning maybe highly adaptive in reducing potential risks. Nevertheless,in the absence of clear external driving cues, the significanceof a very regular and apparently tidal pattern, fairly synchronousamong the different specimens, remains to be explained. Theactivity of P. rustica during each excursion is organized intothree parts: the outgoing journey during which grazing activityprogressively increases, a central part characterized by intensegrazing, and the return characterized by fast displacement anda more or less consistent trail following. Limpets head forrandom directions to reach foraging grounds in successive excursions,showing only a slight avoidance of the direction taken duringthe previous outward journey. This pattern produces a spatialscattering of grazing activity, allowing efficient exploitationof grazing areas distributed radially around home during subsequentexcursions.