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ANN H. SZYSZKO BESSEMARIE L. PRAZAK CHARLES F. EHRET WILLIAM J. EISLER JOHN J. WILLE 《The Journal of eukaryotic microbiology》1968,15(4):781-785
SYNOPSIS. A multi-unit automatic sampling device for investigation of microbial growth under a wide variety of conditions is described. The kinetics of asynchronous population growth for batch cultures of Tetrahymena pyriformis (W) at several temperatures show that there are 2 distinct growth phases: an exponential ultradian growth phase that is strongly temperature dependent and a non-stationary growth phase, the infradian phase, that shows little or no temperature dependence over the range from 15–27 C. 相似文献
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Salt Stress Causes Acceleration of Purine Catabolism and Inhibition of Pyrimidine Salvage in Zea mays Root Tips 总被引:1,自引:0,他引:1
PETERSON TODD A.; LOVATT CAROL J.; NIEMAN RICHARD H. 《Journal of experimental botany》1988,39(10):1389-1395
Nucleotide metabolism was studied in apical 5.0 mm root tipsof corn plants (Zea mays L., cv. Pioneer 3906) hydroponicallycultured for 7 d and then salinized for 19 d at a rate calculatedto reduce the osmotic potential (o) of the solutions by O.1MPad1 to a final o = -0.4 MPa. Saline treatments withtwo different molar ratios of Ca2+/Na+ were employed, viz.,003 (2.5 mol m3 CaCl2 + 86.5 mol m3 NaCl)for the NaCl treatment and 0.73 (31.5 mol m3 CaCl2 +43.1 mol m3 NaCl) for the NaCl + CaCl2 treatment. Bothsalt treatments reduced root growth by more than 30%. The capacityof roots to provide purine nucleotides either by de novo synthesisor by re-utilization of existing bases, e.g. salvage of hypoxanthineto adenine nucleotides, was not affected by either salt treatment.However, catabolism of hypoxanthine was accelerated more than3.5-fold by both salt treatments, demonstrating an increasedcapacity for purine catabolism which would shift the normal1: 1 ratio of synthesis: degradation of purine nucleotides observedfor the roots of healthy control plants to less than 0.2 duringsalt stress. The ratio of pyrimidine nucleotide synthesis: degradationwas also reduced. In this case, the unfavourable shift towardnucleotide degradation resulted because both salt treatmentsreduced salvage capacity by more than 25%, but had no compensatingeffect on de novo synthesis or catabolism of pyrimidines. Key words: Salinity, osmotic potential, nucleotide metabolism 相似文献
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Cytokinin was found to be a controlling or limiting factor invessel regeneration around a wound in internodes of Coleus blumeiBenth. in which the endogenous cytokinin level was minimized.The cytokinin was applied in aqueous solution to the base ofexcised, mature internodes that had an active vascular cambium.Each internode also received IAA in lanolin at its apical end.Under low (0.1 %, w/w) or high (10%, w/w) auxin concentrations,the control internodes (without exogenous cytokinin) exhibitedsmall amounts of vessel regeneration. At appropriate concentrationszeatin, kinetin and 6-benzylamino-purine (BAP) induced a significantincrease in vessel regeneration around the wound. The threecytokinins also induced novel patterns of supplementary regenerationfurther from the wound surface. Kinetin and BAP showed the strongestpromoting effect at 5 and 10 µg ml1, while zeatinwas most effective at 20 µg ml1. At a low (0.1%) auxin level zeatin was the most effective cytokinin, whereaskinetin was the most effective one at high (1 %) auxin. An inhibitoryeffect on vessel regeneration was observed at the highest kinetinconcentration tested (50 µg ml1). The regenerationof vessels induced by cytokinin was very polar. Many more regeneratedvessel members differentiated below the wound than above it,and the regeneration process proceeded acropetally from thebase of the internode to its upper parts. Our results implya basipetal polar increase in cambium responsiveness along thestem axis from internode 5 to 7. The possible significance ofsuch a basipetal increase in cambium sensitivity in wood formationin trees is discussed. Auxin, Coleus blumei, cytokinin, vascular differentiation, vessel regeneration, wound xylem 相似文献