Zeta potential measurements of cell wall preparations from Regnellidium diphyllum and Nymphoides peltata

Abstract. Cell wall particles were prepared from the semi-aquatic plants Regnellidium diphyllum and Nymphoides peltata with minimum disruption to the integrity of the cell wall. The behaviour of freshly-prepared and frozen-thawed particles in a D.C. electric field was monitored with a microscope attached to video recording apparatus. From the respective particles mobility in a well-defined electric field. it was possible to determine their electrostatic potential and consequently estimate the corresponding surface charge density. Experiments were performed in media of different pH and cation concentration (ie, K⁺ Ca²⁺). A significant electronegative potential was found in cell wall preparations of both plants. Freezing and thawing further reduced the electrostatic potential for both plant species in all the media utilized for electrophoresis. A reduction of pH or an increase of the cation concentration was found to neutralize the electrostatic potential in a sigmoidal fashion. Ca²⁺ was more than 10 times more effective than K⁺ at neutralizing the apparent electrostatic potential of the cell wall preparations. Regnellidium was found to have a lower electrostatic potential than Nymphoides , although both responded in a similar manner to the various treatments. The possible relevance of the cell wall electrostatic potential, pH and [Ca²⁺] and particularly their inter-relationship is discussed for the two species of plants in terms of their differing growth responses to the ionic environment of the plant.     

Fine Structure of Phialide and Conidiospore Development in Aspergillus giganteus 'Wehmer'

The conidiophore vesicle is composed of a peripheral regionwhich contains many nuclei and mitochondria and a central regionwhich is densely packed with glycogen granules but containsvery few organelles. The phialides, which arise as sphericalprotuberances from the surface of the vesicle, are bounded bya much thinner wall than that of the vesicle. Nuclei migrateinto the phialides at a comparatively early stage in their development.Septa are present at the proximal ends of mature phialides andalthough pores are present in these septa it is suggested thatthey are too small to permit the ingress of such organellesas nuclei and mitochondria from the vesicle. The developmentof adjacent phialides is well synchronized but the developmentof the vesicle as a whole is not precisely co-ordinated. Eachmature phialide contains a single nucleus, as do the conidiosporeswhich they produce. The first conidiospore produced by a phialidearises as a spherical protrusion from the tapered, thickenedapex of the phialide. The conidiospores are delimited from thephialide by the formation of a cross wall in a manner reminiscentof the process of septation in hyphae. When first formed theconidiospores have a cylindrical shape and they only assumetheir characteristic spherical shape at a later stage in development.