Actomyosin and movement in the angiosperm pollen tube: an interpretation of some recent results

Summary Recent confirmations of the presence of myosin in angiosperm pollen tubes indicate that an energy-transducing actomyosin system is involved in the motility system of the vegetative cells. Myosin has been localised by immunofluorescence on the surfaces of vegetative nuclei and generative cells. It has been shown to be associated with individual amyloplasts in grass pollen, and there are indications that it is present on other particulate bodies in the cytoplasm. The organelles in the leading part of the tube move along separate traffic lanes of acropetal and basipetal polarity, known from electron microscopy and phalloidin labelling to contain numbers of fibrils containing aggregates of actin microfilaments; in older segments the movement can be related to single, uniformly polarised, fibrils. Circulatory flow is maintained at the proximal end by the looping of the fibrils in the grain or at callose plugs. Such loops do not occur at the apex, where entering organelles undergo random movement before becoming associated with basipetal streams. Vegetative nuclei and generative cells interact with several fibrils, and it is suggested that they are held in the leading part of the protoplast in unstable equilibrium between acropetal and basipetal forces. Constantly changing form, especially of the vegetative nucleus, is one consequence of these varying stresses. Possible analogies with the intracellular motility system of the giant cells of the Characeae are noted, and it is suggested that lipid globuli and other nonorganellar bodies may be transported in the pollen tube by association with myosin-bearing membranes similar to those involved in endoplasm movement in the characean cells.     

The relevance of compartmentation for cysteine synthesis in phototrophic organisms

In the vascular plant Arabidopsis thaliana, synthesis of cysteine and its precursors O-acetylserine and sulfide is distributed between the cytosol, chloroplasts, and mitochondria. This compartmentation contributes to regulation of cysteine synthesis. In contrast to Arabidopsis, cysteine synthesis is exclusively restricted to chloroplasts in the unicellular green alga Chlamydomonas reinhardtii. Thus, the question arises, whether specification of compartmentation was driven by multicellularity and specified organs and tissues. The moss Physcomitrella patens colonizes land but is still characterized by a simple morphology compared to vascular plants. It was therefore used as model organism to study evolution of compartmented cysteine synthesis. The presence of O-acetylserine(thiol)lyase (OAS-TL) proteins, which catalyze the final step of cysteine synthesis, in different compartments was applied as criterion. Purification and characterization of native OAS-TL proteins demonstrated the presence of five OAS-TL protein species encoded by two genes in Physcomitrella. At least one of the gene products is dual targeted to plastids and cytosol, as shown by combination of GFP fusion localization studies, purification of chloroplasts, and identification of N termini from native proteins. The bulk of OAS-TL protein is targeted to plastids, whereas there is no evidence for a mitochondrial OAS-TL isoform and only a minor part of OAS-TL protein is localized in the cytosol. This demonstrates that subcellular diversification of cysteine synthesis is already initialized in Physcomitrella but appears to gain relevance later during evolution of vascular plants.     

The relevance of compartmentation for cysteine synthesis in phototrophic organisms

In the vascular plant Arabidopsis thaliana, synthesis of cysteine and its precursors O-acetylserine and sulfide is distributed between the cytosol, chloroplasts, and mitochondria. This compartmentation contributes to regulation of cysteine synthesis. In contrast to Arabidopsis, cysteine synthesis is exclusively restricted to chloroplasts in the unicellular green alga Chlamydomonas reinhardtii. Thus, the question arises, whether specification of compartmentation was driven by multicellularity and specified organs and tissues. The moss Physcomitrella patens colonizes land but is still characterized by a simple morphology compared to vascular plants. It was therefore used as model organism to study evolution of compartmented cysteine synthesis. The presence of O-acetylserine(thiol)lyase (OAS-TL) proteins, which catalyze the final step of cysteine synthesis, in different compartments was applied as criterion. Purification and characterization of native OAS-TL proteins demonstrated the presence of five OAS-TL protein species encoded by two genes in Physcomitrella. At least one of the gene products is dual targeted to plastids and cytosol, as shown by combination of GFP fusion localization studies, purification of chloroplasts, and identification of N termini from native proteins. The bulk of OAS-TL protein is targeted to plastids, whereas there is no evidence for a mitochondrial OAS-TL isoform and only a minor part of OAS-TL protein is localized in the cytosol. This demonstrates that subcellular diversification of cysteine synthesis is already initialized in Physcomitrella but appears to gain relevance later during evolution of vascular plants.     

Main results of recent Hungarian family planning studies.

The demographic situation in Hungary is analyzed by presenting results of 5 different surveys on family planning carried out between 1958-1974. During those 16 years the practice of planning the number of children desired grew. In 1958 only 63 out of 100 women planned the number of children at marriage, and in 1974 98% gave an affirmative reply. The number of children planned by women declined from 2.25 in 1958 to 2.05 in 1966, and then increased to 2.19 in 1974. More and more childless married women want to give birth to a child. In early studies, 66-67% desired a child, and in 1974 83% desired a child. The idea of a family size with 2 children has become the rule in Hungary. In 1958 only 76% of the women used birth control; by 1966 the percentage was 84. 37% in 1958, 44% in 1966, and 26% in 1969 used both contraception and induced abortion. By 1972, 42% of the women interviewed had had an abortion. The use of contraception has increased considerably from 58% in 1958 to 75% in 1974. In 1974, 36% of the women using contraception were taking oral pills and only 7% were using the IUD.     

Main results of recent Hungarian family planning studies.

The Hungarian Central Statistical Office has carried out five different sample surveys in the last fifteen years for investigating more closely questions of fertility, family planning and birth control. The study summarizes the main findings. Some of these surveys applied retrospective methods to investigate fertility, family planning and birth control bahaviour of females in the past. Surveys of another type tried to reveal in perspective manner, with longitudinal observation of the couples, changes which took place in family planning and birth control ideas and practice. The main purpose of recent population policy measures was to ensure simple reproduction of the population. As a result of the measures taken in 1974 to increase the number of births the birth-rate went up significantly. This increase (30% as compared to 1973) appeared primarily for the second birth which constitutes 62% of the increment in births in 1974, 31% is accounted for by an 11% increase in the first births. The number of third births rose by 13% and their relative share remained 10%. The number of fourthand further births did not increase and their relative share decreased by 1%. Fertility data of 1974 show that the birth-rate increase was not in line with the intended aim, i.e. it was not the number of third births that increased. The net reproduction coefficient showing long-range growth of the population calculated with birth-rate of 1974, has developed favourably, it was over unity for the first time since 1958 (it was about 1.05). The birth-rate increased in 1974 in every age-group of females. The largest increase (19%) occurred for females 25-34 years old. Though it was 16% also for females under 24. According to a sample survey investigating the number of intended children by married females under 35 it did not increase as compared to data of previous surveys of similiar character. The differences is that the proportion of those who wished to have two children increased, while of those who wished to have one or three and more children decreased. The study deals also with changes in the relative shares of intended children by females under 35 who are now to be married. In the concluding part of the study the femeles' attitude to birth control and changes in this field are discussed.     

Hominid behaviour and the earliest occupation of Europe: an exploration.

The last decade has witnessed a heated debate over the age and the character of the earliest occupation of Europe. This paper addresses two aspects of the debate, one dealing with the chronology of occupation, which is put to use in the second issue, an exploration of the behaviour of the earliest occupants of Europe. The review of the debate on chronology concludes that a short chronology applies to Europe north of the large mountain chains of the Alps and the Pyrenees, where the earliest traces of a human presence date back to about half a million years ago. In this phased-colonisation model, the Mediterranean, and especially Spain, saw an earlier occupation, starting around the end of the Lower Pleistocene. The archaeological record of these first Europeans suggests that from the first presence in northern Europe onwards, regular hunting of large game was common practice among Middle Pleistocene hominids. By situating this archaeological evidence in the context of findings from a range of other disciplines I develop a behavioural scenario which suggests that, at its latest by the Middle Pleistocene, increased forms of social cooperation, exchange of information within larger groups and in general forms of behaviour based on a "release from proximity" had become a standard ingredient of the hominid behavioural repertoire.     

Chitinolytic enzymes: an exploration

Chitin and chitinolytic enzymes are gaining importance for their biotechnological applications. Particularly, chitinases are used in agriculture to control plant pathogens. Chitinases and chitooligomers produced by enzymatic hydrolysis of chitin can also be used in human health care. The success in employing chitinases for different aspects depends on the supply of highly active preparations at reasonable cost. Therefore, the understanding of biochemistry and genetics of chitinolytic enzymes, their phylogenetic relationships and methods of estimation will make them more useful in a variety of processes in near future.     

Self-Programming Machines (II): Network of Self-Programming Machines Driving an Ashby Homeostat

The progress in artificial intelligence enables us to conceive adaptive systems whose characteristics are nearer and nearer to those of living beings. These characteristics though depend on ingenious choices by the designer of these systems: Initial conditions, parameters, optimisation functions, gradient and measure of fitness within the environment. Nevertheless, in living systems which are non-finalist, there are no programmers or designers to conceive of such ingenious choices. Our paper "Self-Programming Machines (I)" presents a non-finalist model since initial states and functions are randomly chosen at the beginning and once and for all. In spite of the fact that they are non-finalist, these machines always stabilise at fixed points when they are connected to an external process. This paper studies the dynamics of a mono-layered network of self-programming machines driving a real device. "the Ashby homeostat", and shows the striking properties of such networks. This system stabilises only at fixed points even if it is subjected to small perturbations or intentional breakdowns such as a reversal of power supply or disconnection of one or several motors. Real and simulated experiences are compared and theoretical results are demonstrated.     

Organisms as Functional Machines: A Connectivity Explanation

Living organisms exist as a complex set of levels of organizationarranged in a pattern of strong ordering with none of theselevels being more important than others for a full understandingof life. Central to biological strong ordering is the organismallevel. Individual organisms are of special interest to biologistsbecause they are relevant to all biological processes regardlessof the operational level of the process. This is especiallytrue for investigations of the morphological-physiological propertiesof organisms. For such studies, living organisms must be consideredas complex machines with all of the sophisticated integrationand multifarious interactions of component parts typical ofcomplex systems. Understanding of the properties of any individualfeature in an organism depends as much, or possibly even more,on an appreciation of its connections and interactions withother features of that organism than on an understanding ofits intrinsic attributes. Learning the connectivity skills,including the modes of thinking, needed to comprehend the integrationof diverse components of any complex system requires a differenttraining than that needed to determine the detailed attributesof individual parts; both are necessary, however, to achieveproper advances in biological knowledge. Case studies of severalvertebrate features will be used to illustrate types of interactionswhich exist between structural/functional attributes, and howtheir recognition can lead to new and interesting questions.This feeling for the organism may be the major factor separatingthose biologists who are able to make important discoveriesfrom those who will only provide the subsequent, less excitingdetails of normal science.     

Bluegill growth as modified by plant density: an exploration of underlying mechanisms

Summary Bluegill (Lepomis macrochira) growth varies inconsistently with plant density. In laboratory and field experiments, we explored mechanisms underlying bluegill growth as a function of plant and invertebrate density. In the laboratory, bluegills captured more chironomids (Chironomus riparius) than damselflies (Enallagma spp. and Ischnura spp.), but energy intake per time spent searching did not differ between damselfly and chironomid treatments. From laboratory data, we described prey encounter rates as functions of plant and invertebrate density. In Clark Lake, Ohio, we created 0.05-ha mesocosms of inshore vegetation to generate macrophyte densities of 125, 270, and 385 stems/m² of Potamogeton and Ceratophyllum and added 46-mm bluegill (1/m²). In these mesocosms, invertebrate density increased as a function of macrophyte density. Combining this function with encounter rate functions derived from laboratory data, we predicted that bluegill growth should peak at a high macrophyte density, greater than 1000 stems/m², even though growth should change only slightly beyond 100 stems/m². Consistent with our predictions, bluegills did not grow differentially, nor did their use of different prey taxa differ, across macrophyte densities in the field. Bluegills preferred chironomid pupae, which were relatively few in numbers but vulnerable to predation, whereas more cryptic, chironomid larvae, which were associated with vegetation but were relatively abundant, were eaten as encountered. Bluegills avoided physid snails, which were abundant. Contrary to previous work, vegetation did not influence growth or diet of bluegill beyond relatively low densities owing to the interaction between capture probabilities and macroinvertebrate densities.The unit is sponsored jointly by the United States Fish and Wildlife Service, Ohio Department of Natural Resources, The Ohio State University, and The Wildlife Management Institute