In Situ and in Vitro Binding of Natriuretic Peptide Hormones in Tradescantia multiflora

Abstract: An increasing body of evidence suggests that in plants, as in vertebrates, biologically active natriuretic peptide (NP) hormones play an important role in the regulation of the osmotic and ionic balance. The evidence includes isolation and immunoaffinity purification of biologically active natriuretic peptide analogues (irPNP) from ivy that promoted stomatal opening and specifically, rapidly and transiently increased cGMP levels in root conductive tissue. In this study we demonstrate that I¹²⁵-rat atrial natriuretic peptide (rANP) binds to plasma membranes from leaf and stem tissue of Tradescantia multiflora and importantly, both unlabelled rANP and irPNP can competitively displace that binding. In addition, tissue section autoradiography reveals specific in situ binding of I¹²⁵-rANP to leaf and stem tissue. The findings are consistent with the presence of a biologically active NP system in plants and suggest that NPs signal through a dedicated receptor system.     

The effect of water-miscible solvents on the Δ1-dehydrogenase activity of free and PAAH-entrapped Arthrobacter simplex

Summary The effect of water-miscible cosolvents on biotransformations of poorly water-soluble substrates by immobilized cells was investigated, using ¹-dehydrogenation of hydrocortisone by Arthrobacter simplex as a model. Criteria for solvent selection on the basis of retention of enzymic activity were postulated and tested. Diols were considered to be the most suitable group of solvents. Substrate solubility increased tenfold in 30% (v/v) ethylene glycol, but reaction rates were significantly slower in such solutions. This was mainly caused by a decrease of oxygen solubility in the presence of the cosolvent and conformational changes imposed on the intracellular enzyme by cosolvent molecules penetrating the cell. The inhibition could be eliminated by the addition of an artificial electron acceptor, phenazine methosulphate (PMS). Reaction rates faster than those for substrate suspensions (no cosolvent added) could thus be achieved. Immobilization of Arthrobacter simplex in cross-linked polyacrylamide hydrazide gave high retentions of activity. PMS exhibited toxic effects on the entrapped cells, leading to reduced activity after extended use.     

Serial reconstruction and behaviour during cytokinesis of the chondriome ofProrocentrum minimum (Pavillard) Schiller (Pyrrhophyta)

Summary Serial reconstruction of the chondriome of vegetative cells ofProrocentrum minimum (Pavillard) Schiller has revealed a major reticulated mitochondrion and several small satellite mitochondria. During cytokinesis the major portion of the chondriome splits passively with the cell. The significance of this structure and division mechanism is discussed.