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Phospholipase A (PLA) is an acyl hydrolase, which hydrolyses phospholipids either at the hydroxyl group of the C1 (phospholipase A1; PLA1) or the C2 atom (PLA2 ). Structurally different enzymes can have this activity. These enzymes are (1) the small (14 kDa) secreted phospholipases A2 (sPLA2) found in fungi, plants and animals; (2) the soluble or secreted patatin-related phospholipases A2 (pPLA2), including the homologous soluble calcium-independent phosholipases A2 (iPLA2) in animals; (3) the cytosolic or calcium-activated phospholipases A2 (cPLA2); (4) the lipase-like phospholipase A1 and (5) the bacterial dimeric phospholipase A2. Since, bacterial phospholipase A2 is not found in plants, it is not discussed here. Both pPLA2 and the homologous iPLA2 hydrolyse in vitro phospholipids at the C1- and C2-position so that the plant enzymes are often called PLA (non-specified A), but indications for PLA2 specificity in vivo exist and hence called pPLA2 here. Although few facts are known about the functions of sPLA2 (four genes in Arabidopsis), there is rapidly accumulating evidence that the pPLA2 in plants (ten genes in Arabidopsis) have function in several signal transduction pathways, such as auxin, pathogen and, perhaps, light signaling. The known localisation of five different enzymes is in the cytosol. Thus, the pPLA2 of plants takes over the function in plant signal transduction, which is fulfilled by the cPLA2 in animal cells. Evidence that the breakdown products, free fatty acid and lysophospholipids are second messengers is fragmentary. The PLA1 group in plants has a preference for hydrolysis of galactolipids and is localised to chloroplasts, so they could be the enzymes to release linolenic acid as a precursor for jasmonate synthesis.

New roles are emerging for nitric oxide (NO) besides senescence and defense. While NO itself is probably used as a chemical weapon in defense, in several examples the biosynthesis of NO is up-regulated so rapidly that a function of NO as a second messenger in signal transduction seems likely. We investigated this postulate with the signal substances cytokinin and polyamines. After polyamine addition to Arabidopsis seedlings, net NO biosynthesis increased with no apparent lag phase, and after zeatin addition, NO increased within 3 min. Thus, the up-regulation of NO levels is faster than activation of gene expression, consistent with our hypothesis of NO being a second messenger. A role for NO in signal transduction constitutes a new finding for both classes of signaling substances – polyamines and cytokinins. Cytokinin–polyamine crosstalk has already been indicated by known overlaps in the physiology of both signals, and the results reported here strengthen the case for this crosstalk. In addition, known multiple functions of polyamines in the physiology of pathogen defense, abiotic stress, hormones, and embryogenesis are already known to involve NO as a mediator. We discuss this new “input” into polyamine physiology.

50 years of Ocean Engineering — the paper presents marine Wonders of the World -offshore structures in extremely harsh environment and deep water, designed to highest technological, economical and ecological standards. German shipyards and subcontractors contributed to this success, especially during the heydays of the North Sea at the end of the seventies. Research and development in special areas stands out for the competitive capacity of the German marine industry, national towing tanks and research institutes.

The search for second messenger systems in signal transduction mechanisms in cells of higher plants has always strongly been influenced by the concepts which had been developped for animal cells. To date, however, the only molecular signal transduction pathway providing a valid working hypothesis for signal transduction in plant cells is the phosphatidylinositol (PI) cycle which, in animals, produces two second messengers, myo-inosito1,1,4,5-trisphosphate (IP3) and diaclyglycerol (DAG) (Berridge 1987; Morse et al. 1989). The function of one of it, IP3, is likely to be the release of Ca2+ from the vacuole and the ER (Schuhmaker and Sze 1987) which would be similar to its function in animal cells. The function of DAG remains unclear because evidence for a DAG-activated protein kinase in plants is still scarce and controversial (Morre et al. 1984; Elliott et al. 1988; Martiny-Baron and Scherer 1989). Our own work originated from our interest in the mechanism of proton transport stimulation in zucchini microsolnes by the platelet-activating factor (PAF) (Scherer 1985) and by auxin (Scherer and Morre 1978; Scherer 1981). The at first bizarre observation of transport stimulation of plant H+-ATPase by an animal lipid

Platelet activating factor (=PAF) stimulates H+ transport in microsomes from zucchini hypocotyl (1) and ATP hydrolysis. The apparent membrane permeability for protons in membrane vesicles is not changed by PAF and in ATP hydrolysis rather vmax than the Km is changed by PAF. PAF stimulation of H+ transport is dependent on the presence of a protein factor which can be removed from the membranes. The properties of PAF-dependent protein factor in DEAE-Sephacel chromatography are very similar to a protein kinase. PAF stimulation of ATP hydrolysis and H+ transport is found in tonoplast and plasma membranes. A possible role for the PAF-dependent factor analogous to animal protein kinase C in plant hormone action is postulated.

It has been customary to introduce any discussion on the mitochondrion by summing up its functions as the energy center of the cell. Because of the extensive reviews and symposia in this field in recent years such an introduction would be repetitious and will therefore be omitted. — The relative ease by which mitochondria can be isolated from various cells and the considerable purity of such fractions permitted an analysis of the overall functions of mitochondria and the extrapolation of these results, on a statistical basis, to a single mitochondrion. Further fragmentation of isolated mitochondria into sub-units that carry segments of the functional activity of the whole organelle significantly contributed to the understanding of this complex system. With the discovery of morphologic sub-units, using high resolution electron microscopic techniques, a stage is approached where the inextricable connection between structure and function becomes a tangible reality rather than a cliche, so widely used by biologists. — Concentration on the basic aspects of mitochondrial organization and the ingenuity and industriousness by which this approach is pursued have somewhat diverted our attention from problems faced at a higher level of organization. I am referring to such questions as the origin and fate of individual mitochondria, structural and biochemical variations within a cell and in various cells in an organ, intracellular interactions of mitochondria with other cell organelles, or in other words, the problems in which mitochondria with their structural and morphologic facets are viewed from cell and organ physiologic points of view. Here the potentialities of in situ techniques, including histochemical staining methods, are obvious. — The program of this symposium intends to reflect the two levels of operation at which investigations of mitochondrial systems are pursued. One refers to the basic problem of molecular organization. The other approach, including the use of histochemical techniques, is not refined at present to a molecular level of organization, but it nevertheless offers other parameters for the understanding of the biology of mitochondria. — In the followings Dr. Andre will discuss the general morphology of mitochondria. Dr. Stoeckenius will review the evidence for the existence of morphologic sub-units. Dr. Siebert will focus on some biochemical aspects of mitochondria structure. Drs. Bahr and Zeitler will deal with the problems of origin and fate of mitochondria, in general, while Dr. Luck will present evidence indicating that mitochondrial populations increase by division of existing mitochondria and that the mitochondrial mass is augmented by addition of new units to the existing frame-work. Drs. Farber and Morrison’s and Dr. Barrnett’s talks should provide us with the critical understanding of the potentialities of the in situ staining techniques. Finally, Dr. Balogh assumed the difficult task of discussing how histochemical technics may contribute to the investigation of organ physiologic problems.

In principle there are no fundamental differences between the effects of kallikrein and of the kinins on the cardiovascular system. Kallikrein does not act directly on the responsive tissues which initiate changes in the circulation but affects them through the liberation of kinins. The release of kinins from kallikrein is brought about by enzymatic processes which take varying periods of time, lasting but a few seconds. For this reason the onset of all reactions to kallikrein is somewhat delayed in comparison to that elicited by kinins In addition, the reactions to kallikrein fade away more slowly than those resulting from kinins, because the latter are rapidly inactivated by enzymes.

Unter dem Begriff Symbiose seien in diesem Zusammenhang lediglich solche Einrichtungen verstanden, die Buchner schon seit vielen Jahren als Endosymbiosen bezeichnet hat und bei denen pflanzliche Mikroorganismen wie Hefen oder Bakterien innerhalb bestimmter, genau um-rissener Zellen oder Zellbezirke des tierischen Wirtsorganismus leben. Derartige symbiontische Einrichtungen sind im Tierreich nicht besonders selten, erreichen aber ihre groβte Verbreitung bei den Insekten. Die Symbionten haben eine ganz spezielle physiologische Bedeutung und durften wohl in den allermeisten Fallen zur Produktion von Vitaminen herangezogen werden. Aus diesem Grund ist es nicht verwunderlich, daβ nur diejenigen Insekten Symbionten besitzen, die eine sehr einseitige, spezialisierte Ernahrung haben. Es gehoren hierher alle pflanzensaft- und blut-saugenden Insekten sowie auch Horn-, Zellulosefresser usw. Symbionten finden sich aber nur dort, wo auch die Larve dieselbe Nahrung aufnimmt. So hat zwar eine Laus Symbionten, ein Floh dagegen nicht.