1,721,278 research outputs found
Reactivation on membrane activity from germinated and ungerminated radish seeds
No full textReactivation by polar lipidis of membrane ATPase activity from germinated and ungerminated radish seeds. M. COCUCCI. Centro di Studio del C.N.R. per la Biologia Cellulare e Molecolare
delle Pi ante Istituto di Scienze Botaniche Universita di Milano. The early phases of germination of radish (Raphanus saf;vus L.) seed are cha racterized by the activation of plasmamembrane functions such as K + uptake. acid secretion, transitory increase of negati ve transmembrane potential. T here is evidence suggesting that these functions may depend, in this and in other materials, on the acti vity of a Mg++ , K+ activa ted, dicycJohexylcarbodiimide-sensitive plasmamembrane ATPase. This ATPa ~e activity increases in the membrane fraction in the fi rst 23h of germination (+ 300%).
The removal of polar lipids from membrane preparations by cholate treatment almost completely suppreses the ATPase activity. The subsequent addition of polar Lip ids from radish seeds reconstitutes the ATPase activity. Polar lipids from germinated seeds are more active than that from ungerminated seeds. This data suggest that variation of polar lipids composition of the membrane, during early phases of germination. may be an important factor in determining the rise in ATPase activity duri ng early phases of germination
Calmodulin levels in radish (Raphanus sativus L.) seeds germinating at low calcium availability, induced by EGTA treatments
No full textIncubation of radish (Raphanus sativus L.) seeds in the presence of 1 or 5 mol m(-3) Ca-EGTA, which increased Ca2+ activity in the incubation medium (c. 0.24 or 0.37 mol m-3 at 24 h with respect to c. 0.13 mol m(-3) in the control), did not affect germination, the restoration of K+ net influx, the increase in DNA and RNA levels or protein synthesis. Incubation in 1 mol m(-3) Na-EGTA, which reduced Ca2+ activity in the incubation medium (20 mmol m(-3) at 24 h), decreased the total Ca2+ level in embryo axes (-21%), but only slightly inhibited the increase in fresh weight without affecting the restoration of K+ net influx, the increase in DNA and RNA levels or protein synthesis. In the presence of 5 mol m(-3) Na-EGTA (Ca2+ activity in the incubation medium was 0.6 mmol m(-3)), the decrease in the total Ca2+ level was greater (c. -27%) and the increases in fresh weight, DNA and RNA were inhibited by about 50, 39 and 40%, respectively. These results indicate that increased Ca2+ availability does not affect germination and suggest that the effect of Na-EGTA, at least up to 5 mol m(-3), is a result of an induction of Ca2+ deficiency. The amount and specific activity of calmodulin (CaM) present in the soluble fraction (100 000 g) of radish embryo axes greatly increased during the first 24 h of incubation (c. 5-fold and 7-fold, respectively). This increase was very similar in the Ca-EGTA-treated seeds but was inhibited (c. -38%) by 1 mol m(-3) Na-EGTA, even if the increases in DNA and RNA levels and protein synthesis were not significantly reduced. The lower amount of CaM after 24 h of incubation in 1 mol m(-3) Na-EGTA (c. -30%) was due to a reduction in the fraction of CaM bound to a proteinaceous CaM inhibitor present in radish seeds [M. Cocucci and N. Negrini (1988) Plant Physiology 88, 910-914] and not involved in the metabolic reactivation of the seed. These results suggest that the level of CaM is controlled by Ca2+ availability and that the CaM inhibitor has a role in controlling the amount of Ca-CaM available for the Ca-CaM-dependent enzymes
The effects of oxygen availability on the rate of growth and on RNA and protein metabolism in Rhodotorula gracilis
No full textThe present work deals with the effects of low oxygen availability on the rate of growth
and of RNA and protein synthesis in Rhodotorula gracilis cells growing in a liquid mineralglucose
medium. In these experiments O2 partial pressure in tl.!e medium has been measured
and maintained satisfactorily constant by means of a Clark oxygen electrode. It has been found
that: a) the optimal rate of growth requires O2 partial pressure above 3 mm of Hg; b) lowering
O2 pressure below this value induces a progressive inhibition of growth; c) under conditions
of suboptimal O2 availability (ca. 1 ±0.2 mm Hg) the accumulation of RNA and DNA is
inhibited in an earlier period and to larger extent than protein synthesis. Experiments of
incorporation of 32p orthophosphate into RNA show that the « low O2 » condition is characterized
by a marked inhibition of RNA synthesis, even in the case of relatively short 'pulses' (5 minutes),
while no important changes of the rate RNA breakdown is observed. In fact, the rate of 32p
incorporation into RNA remains practically linear in time for at least 30 minutes. This behaviour
is in contrast with the one observed in this yeast as a consequence of nitrogen or of glucose
starvation; in these cases the block of the net synthesis of RNA appears to correspond rather
to an increased rate of breakdown of the newly formed RNA than to an inhibition at transcription
level
Qualche considerazione a dieci anni dall'entrata in vigore dei nuovi ordinamenti didattici universitari
No full text
Il Contributo della biologia vegetale nella salvaguardia dell'ambiente e della produzione: aspetti biochimici e fisiologici
No full textVariazione del livello di calmodulina durante le prime ore di germinazione dei semi di rapanello
No full textRelationship between the effect of O2 on energy metabolism and RNA synthesis in Rhodotorula gracilis
No full textIn the aerobic yeast Rhodotorula gracilis, a decrease in O2 availability, from saturating conditions (pO2 = 100 mm Hg) to pO2 = 1 mm Hg, causes a decrease in the growth rate accompanied by a fall in the accumulation rate of RNA and, to a lesser extent, of proteins. At pO2 = 1, no relevant changes in the levels of triphosphate nucleotides (ATP, GTP, CTP and UTP) are observed with respect to the controls, while the ADP and AMP levels markedly increase.
The uptake of labelled precursors and qualitative analysis of RNA suggest that the decrease in the RNA accumulation rate at pO2 = 1 is due to a decreased RNA synthesis rate.
This paper examines the mechanism by which low availability of O2 causes a decrease in the RNA synthesis rate even though total triphosphate nucleotide levels remain high
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