Carbon Translocation in the Tomato: Effects of Fruit Temperature on Carbon Metabolism and the Rate of Translocation

The effects of fruit temperature on the rate of carbon translocationand on the contents of the major carbon metabolites in the experimentalfruits were investigated. Carbon import, which was inverselyproportional to fruit size, was inhibited by fruit cooling (5°Cand enhanced by fruit warming (35°C) when compared withcontrols (25°C); furthermore, there was net export of carbonfrom the largest cooled fruits. The carbon translocation rateswere related both to the rates of accumulation or depletionof starch and insoluble residue and to the concentration ofsucrose in the fruit. The possible dependence of the rate oftranslocation on a gradient of sucrose concentration betweensource and sink is discussed.     

Concanavalin A binds of purified prolyl hydroxylase and partially inhibits its enzymic activity.

Prolyl hydroxylase [(EC 1.14.11.2; prolyl-glycyl peptide, 2-oxoglutarate dioxygenase (4-hydroxylating)] was electrophoresed on polyacrylamide gels and the enzyme in the gels was shown to bind [acetyl-³H]concanavalin A. The enzyme-lectin complex was dissociated by treating the gel with methyl α-D-mannopyranoside, a sugar known to inhibit binding of concanavalin A to glycoproteins. Furthermore, prolyl hydroxylase activity was partially inhibited by concanavalin A when the enzyme was assayed in the absence of bovine serum albumin, a protein which enhances enzymic activity. The inhibition of enzyme activity was prevented by sugars known to react with concanavalin A.     

The Relationship Between the Rates of Carbon Transport and of Photosynthesis in Tomato Leaves

The rate of carbon transport based on the carbon balance overa 6-h period from a mature tomato leaf was measured overa rangeof net photosynthetic rates from 0.1 to 4.9 mg C dm^–2h^–1 under light flux densities from 4 to 140 W m^–2.A proportional relationship was demonstrated between the rateof carbon transport and carbon fixation when the carbon fixationrate was higher than 2 mg C dm^–2 h^–1.Below a carbonfixation rate of 1 mg C dm^–2 h^–1, the rate of carbonexport was maintained at 1 mg C dm^–2 h^–1 at theexpense of the breakdown of starch. A highly significant correlationwas observed between sucrose concentration and the rate of carbontransport. The sucrose concentration in the leaf appears tobe the factor controlling carbon export.     

大鼠延髓腹外侧部微量注射心房钠尿肽的心血管效应

在麻醉大鼠观察了延髓腹外侧部的谷氨酸敏感区(GSA)应用ANP对血压和心率的影响。在GSA应用α-hANP,血压和心率明显降低。低浓度的APⅢ(10~(-6)mol/L)仅引起血压减低而不伴有心率减慢效应,而高浓度的APⅢ对血压和心率均有抑制效应。这些结果提示,ANP可能具有抑制延髓交感中枢作用并可能作为动脉压力感受器中枢通路的一种化学递质或调质。     

Optical spectroscopic characterization of single tryptophan mutants of chicken skeletal troponin C: evidence for interdomain interaction.

The effects of metal ion binding on the optical spectroscopic properties and temperature stability of two single tryptophan mutants of chicken skeletal TnC, F78W and F154W, have been examined. The absence of tyrosine and other tryptophan residues allowed the unambiguous assignment of the spectral signal from the introduced Trp residue. Changes in the molar ellipticity values in the far-UV CD spectra of the mutant proteins on metal ion binding were similar to those of wild-type TnC suggesting that the introduction of the Trp residue had no effect on the total secondary structure content. The fluorescence and near-UV absorbance data reveal that, in the apo state, Trp-78 is buried while Trp-154 is exposed to solvent. Additionally, the highly resolved (1)L(b) band of Trp-78 seen in the near-UV absorbance and CD spectra of the apo state of F78W suggest that this residue is likely in a rigid molecular environment. In the calcium-saturated state, Trp-154 becomes buried while the solvent accessibility of Trp-78 increases. The fluorescence emission and near-UV CD of Trp-78 in the N-terminal domain were sensitive to calcium binding at the C-terminal domain sites. Measurements of the temperature stability reveal that events occurring in the N-terminal domain affect the stability of the C-terminal domain and vice versa. This, coupled with the titration data, strongly suggests that there are interactions between the N- and C-terminal domains of TnC.     

Identification of a novel alternative splicing variant of RGS5 mRNA in human ocular tissues

Regulator of G protein signaling (RGS) proteins act as GTPase-activating proteins (GAPs) for Galpha subunits and negatively regulate G protein-coupled receptor signaling. Using RGS5 gene-specific RT-PCR, we have identified a novel alternative splicing variant of RGS5 mRNA in human ocular tissues. The alternative splicing of RGS5 mRNA occurred at position +44 (GenBank NM_003617), spliced out 174 bp (+44 to +218 bp) of the coding region, and encoded an RGS5s protein with a 108 amino acid N-terminal deletion. This study is the first to document alternative splicing of an RGS5 gene. We therefore studied RGS5 and RGS5s mRNA distribution in human tissues. In the eye, RGS5s was found to be highly expressed in the ciliary body and trabecular meshwork. It was also expressed in the kidney, brain, spleen, skeletal muscle and small intestine, but was not detectable in the liver, lung, heart. RGS5s was not found in monkey and rat ocular tissues, indicating species specificity for the eye. Comparing the recombinant RGS5 and RGS5s expression in HEK293/EBNA cells, RGS5s was present almost exclusively in the cytosolic fraction, whereas RGS5 was present in both membrane and cytosolic fractions. The data suggest that the N-terminal of RGS5 may be important for protein translocation to the cell membrane. Both RGS5 and RGS5s antagonized the rapid phosphorylation of p44/42 MAP kinase induced by Galphai coupled cannibinoid receptor-1 activation. RGS5, but not RGS5s, inhibited the Ca2+ signaling initiated by activation of Galphaq coupled angiotensin II receptors (AT1) and prostaglandin FP receptors. Cotransfection of RGS5s with RGS5 resulted in the blockade of RGS5 actions with respect to inhibition of the signal transduction initiated by activation of both AT1 and FP receptor, suggesting that RGS5s may contain functional domains that compete with RGS5 in the regulation of the Galphaq coupled AT1 and FP receptors. The unique expression pattern, cellular localization and functions of RGS5s suggest that RGS5s may play a critical role in the regulation of intracellular signaling pathways.     

Sugar cane buds as an efficient explant for plantlet regeneration

An efficient and reproducible protocol for regeneration of plantlets at a high frequency was developed by using sugar cane buds. Disinfected buds were firstly submerged in ethanol sodium hypochlorite solution with 0.1 % polyvinylpyrrolidone, 1.5 % ascorbic acid and 1.75 % citric acid as antioxidants and subsequently treated with solution of agrimicin:captan (1:1). The upper stalk segment was better to obtain bud in vitro culture compared to lower segments. The medium for induction of multiple shoots consisted of Murashige and Skoog basal medium (MS) supplemented with 2 mg dm⁻³ thidiazuron and 1 mg dm⁻³ naphthalene acetic acid. An average of 24 shoots per bud was obtained for cv. Mex 68-P23 within four weeks and 29 shoots for cv. MY 55-14 within six weeks. Indole-3-butyric acid induced more roots in both cultivars compared to the untreated plantlets. Plantlets transferred to soil showed normal growth with up to four axilliary buds in each node. It was concluded that the germplasm obtained through the above mentioned technique generated stalks with more buds in each node which would give farmers more vegetative material for plantations in field with 100 % germination.This research was funded by Fundacion Produce Chiapas A.C. (Mexico).