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Data on job performance were collected for 1,053 male (N = 461) and female (N = 592) rubber tappers from nine different estates in Malaysia, and analysed for age, sex and tenure differences. Job performance data were based on output measures derived from production records over a 12-month period. Since the type of terrain varied considerably across plantations, terrain was classified as either ‘hilly’ or ‘undulating’ and the effects of terrain type on performance were also examined. The relationship between age and total output took the form of an inverted U. Partial correlation analyses indicated that tenure, rather than age, was the main determinant of job performance. More experienced rubber tappers were found to perform better than less experienced rubber tappers. Women had significantly higher output levels than did men. Tappers working on estates with predominantly hilly terrains produced significantly higher levels of output than did tappers working on estates with predominantly undulating terrains. Neither sex nor tenure interacted significantly with terrain. These results are discussed in relation to previous research concerned with group differences in job performance.

Studies of sustained attention and controlled visual search suggest that individual differences in energetic arousal are correlated with availability of resources for demanding attentional tasks. However, most of the evidence for this resource hypothesis is derived from studies of single tasks, in which it is difficult to distinguish effects of energy on resource availability from effects on the subject's strategy for allocation of resources across task components. We report a dual-task study of energy and sustained attention, which provides a more powerful test of the hypothesis. High and low energy individuals performed a primary visual vigilance task, in conjunction with either an auditory (n=52) or a visual (n=50) secondary reaction-time task. Primary task stimuli were presented at two levels of stimulus degradation, as a manipulation of resource limitation. No effects of energy were observed when the secondary task was auditory, but the primary task performance of high energy individuals was superior when the secondary task was visual and primary task stimulus discriminability was low. Results are consistent with previous work on energy and single-task performance suggesting that energetic arousal is associated with individual differences in resource availability, but they also illustrate the importance of careful control of task parameters.

Norman Mackworth (1950) demonstrated that amphetamine reduces vigilance decrement. Fifty years on, arousing agents are recognised as important influences on vigilance, but various shortcomings of traditional arousal theories have become apparent. Studies of self-report energetic arousal and vigilance confirm that arousal is a vital component of vigilance research, although arousal effects are contingent upon task demands and other moderating factors. Facilitative effects of arousal on perceptual sensitivity can be accommodated within attentional resource theory. However, it remains unclear whether arousal indexes some basic neural or cognitive capacity, or whether arousal influences ‘functional resources’ rather than basic capacity. Arousal, and other subjective state variables, may be related to effort-regulation strategy or to distraction from internal cognitions and fatigue symptoms. A sound understanding of arousal effects on vigilance is essential for developing practical countermeasures.

Biotin-labelled DNA probes for tandemly repeated sequences have been used in in situ hybridization experiments as chromosome-specific markers in pea. Six of the seven chromosome pairs can be marked at single sites in this way. Translocations from a standard karyotype are revealed as chromosomes that have two hybridization sites, rather than one. By probing a tester set of reciprocal translocation (or interchange) lines, some of the markers can be assigned to chromosomes. The method is rapid and simple and, in the absence of well-resolved chromosome bands, provides a means for clarifying some of the problems in pea cytology.Key words: in situ hybridization, translocations, chromosome markers.

Three experiments were run to test effects of extraversion and self-report arousal on high event rate visual sustained attention tasks in which stimuli were degraded. Such tasks tend to show rapid perceptual sensitivity decrements, attributable to depletion of attentional resources. Across the three experiments, type of discrimination (simultaneous vs successive), type of task (sensory vs cognitive), and signal discriminability were manipulated. Results showed that higher self-report arousal consistently facilitated those sensory and simultaneous cognitive tasks which showed a significant sensitivity decrement. These findings support the hypothesis that increases availability of resources for sustained attention. In contrast, effects of extraversion on performance were inconsistent, and may depend on task-specific processing structures and strategies.

Composition and compilation were examined as two alternative hypotheses relating to ‘cognitive competence’ in older adults. Techniques of molar equivalence–molecular decomposition (ME–MD) and molecular equivalence–molar analysis (ME–MA) were used to investigate performance of experienced (over 100 hours) younger (18–30 years) and older (45–66 years) adults on a word processing task, requiring insertion and deletion of words from passages of text. There was some indication that typing skill may form the basis of a compensatory mechanism. However, differences between ‘good’ and ‘poor’ performers in the older sample supported the position that high levels of complex task skill in older adults are associated with the possession (possibly through maintenance) of high levels of basic cognitive capacities, and are not related to the integration of molecular task components.

Three studies are reported of individual differences in performance of high event rate vigilance tasks. In each study, measures of attentional resource availability and elementary cognitive components of sustained attention were correlated with vigilance performance. It was predicted that correlates of vigilance should vary with two parameters of the task: the type of target discrimination required (simultaneous or successive) and the type of stimuli used (sensory or symbolic). Speed and accuracy of controlled, resource-demanding visual search predicted overall perceptual sensitivity on three out of four successive tasks used, but only one out of four simultaneous tasks, partially confirming the hypothesis that successive tasks are more strongly resource-limited than simultaneous tasks. Other correlates of overall level vigilance did not appear to vary systematically with task parameters. Few correlates of temporal decrement in perceptual sensitivity were found, possibly for statistical reasons. The data suggest that measures of controlled search may be useful in predicting vigilance on certain real-world tasks, although a substantial part of the variance of vigilance tasks may not be predictable fromts short cognitive tasks.

A cellulose acetate electrophoretic technique has been used to characterise the storage proteins present in pea seeds in order to try and determine the proportions of proteins present which are enriched in sulphur amino-acids. Some of the eight varieties examined were shown to differ in their proportions of the various storage proteins. When the proteins were separated and estimated quantitatively and also characterised by their sub-unit composition, it was shown that cellulose acetate electrophoresis of crude protein extracts or of whole globulins did not give the degree of resolution required. The procedures which have to be undertaken in order to obtain this information are considered, and the difficulties of incorporating them into a plant breeding programme discussed.

Barley anthers from cold pretreated spikes produced no or few calluses when plated with both loculi in contact with the medium (‘flat’). When anthers were plated with only one loculus in contact with the medium (‘up’), a high proportion of the anthers produced calluses. The top loculus of the ‘up’ anthers was most productive. ‘Flat’ anthers, when compared with ‘up’ anthers, were not only slower to produce multicellular pollen grains (MCPs) and microcalluses, but also produced fewer of them and ceased production earlier. The MCPs and microcalluses in ‘flat’ anthers grew more slowly and few developed beyond the 30 cell stage. These results establish the importance of anther orientation for barley anther culture.

The organization of three classes of legumin gene has been studied by exploiting restriction fragment length polymorphisms. Hybridization of cDNA probes, representing different sub-families of legumin gene, to DNA from F2 and F6 plants from selected crosses showed that there was a tight linkage of individual genes within each of two sub-families. One of these sub-families has been mapped to a locus on chromosome 7 close to r, while the other maps to a locus near a on chromosome 1. The results from one of the crosses analyzed indicated that a third class of legumin gene is also linked to a.

In order to detect low copy number sequences in pea using biotin-labelled probes we optimised some aspects of the in situ hybridization technique. We found protoplast preparations to be superior to standard squashes in terms of their signal: noise ratio. Heat and alkali denaturation of chromosomal DNA were both more effective than acid denaturation. A comparison of antibody-fluorochrome and streptavidin-enzyme conjugates showed the streptavidin-alkaline phosphatase conjugate to be the most sensitive detection system. Using the optimised method, we were able to detect a single site for a 13.5 kb legumin gene clone.

The extent of variation in cell mass, and in the size of the cell population of cotyledons has been examined to determine their relative roles in the evolution of variation in seed weight within the genus Vicia. In the 12 species examined there were highly significant correlations between seed weight and cotyledon cell number, and between seed weight and mean cell mass. The extremes differed by a factor of 625 fold in dry seed weight; of this variation, most (140 fold) was attributable to variation in the size of the cell population and only a 4.47-fold change was due to differences in cell mass. The cotyledon cells of all the species, irrespective of their seed weight showed very high levels of replication of their DNA. The implications of these data in terms of the evolution of seed mass in Vicia is considered. There was a constant relationship between cell mass and DNA amount per cell for all species, irrespective of the basic genome size, extent of DNA replication or of the information content of the genome. The basis of this relationship, and its evolutionary implication, is considered.

Variation in cell population size and cell weight in the cotyledons are important factors in determining seed weight in Pisum sativum. The regulation of these parameters as well as that of growth rate has been examined. The use of reciprocal crosses between varieties of contrasting seed size has allowed the recognition of two systems of control-an intrinsic one dependent on the seed's own genotype, and the extrinsic control of the maternal environment. It is shown that the use of particular kinds of crosses can aid in discriminating the separate roles of sinks and sources as determinants of seed size.

A comparison has been made of the amount of DNA coding for ribosomal RNA present in a polyploid series of plants of Datura innoxia. The plants which were produced by in vitro culture of pollen grains were haploid, diploid, triploid, tetraploid and hexaploid. In all instances there was a similar proportion of DNA coding for ribosomal RNA. The implications of these results are discussed, and the data compared with that available from other series of plants of different DNA content or ploidy.

1. An abnormal phenotype of six-rowed cultivated barley, having short straw, branching stems and very many nodes was analysed genetically. 2. These characters were due to a single recessive gene with pleiotropic effects, or a complex of genes so tightly linked that no recombinants were found. 3. From a study of ear emergence in the first and later generations of hybrids of this and normal phenotypes, it was shown that normal segregants had very early ear emergence. This earliness is considered in terms of an expression or an interaction of genes in the absence of an inhibitor from the abnormal parent.

1. Considerable controversy exists in relation to the single or doubled nature of the centromeric region of chromosomes at metaphase of mitosis and metaphase II of meiosis. Until comparatively recently it was considered single by most workers, but observations on treated and some untreated material led others to conclude that it was double. 2. Relevant information regarding these two concepts was obtained from observations made on tapetal tissue in the anthers of two intervarietal hybrids ofHordeum vulgare, which revealed numerous cellular and nuclear abnormalities. 3. These abnormalities included-peristent meristematic activity of the cells; polyploid nuclei, uni- and multi-nucleate cells; chromosome stickiness and sticky anaphase bridges, as well as certain abnormal centromeric features such as overcharging of the centromeric chromomeres; divided centromeres at mitotic prophase; precocious repulsion of daughter centromeres. 4. All nuclear and cellular abnormalities were attributed to an upset in the nucleic acid metabolism within the cell. 5. Examples of some of the known effects of the centromere on n. a. organization and of n. a. metabolism on centromeric behaviour are discussed. 6. From a consideration of these effects, and the observed effect of an unusual n. a. metabolism on the centromeres ofH. vulgare chromosomes, it is suggested that whilst most organisms have an undivided centromere at mitotic metaphase and metaphase II of meiosis, others have divided centromeres at these stages, due either to innately differing metabolic activities or to treatment with e.g. c-mitotic substances.

Summary Culturing young hybrid embryos on a synthetic medium proved, in four out of six crosses attempted, to be a successful method of overcoming inter-specific incompatibility within the genus Hordeum. Hybrids of diploid H. vulgare and tetraploid H. bidbosum were studied morphologically and cytologically.

Evidence is presented which contradicts a recent suggestion by Levine and Goodenough that the haploid nucleus of Chlamydomonas reinhardii contains eight chromosomes and that eight of the sixteen known linkage groups may be located within the chloroplast. On the contrary there is direct and indirect evidence that there are sixteen chromosomes located within the nucleus.

1. 1. Studies were made of the UV sensitivity of a series of stages in the cell cycle of synchronous populations of diploid meiotic spores of Chlamydomonas reinhardi . 2. 2. Early stages had sigmoid survival curves, but at successively later stages of development, D Q values were continuously reduced, and the latest stages had exponential survival curves. D O values, though changing only to a minor extent, were at a maximum in mid-cycle. 3. 3. From studies of the effects of various post-irradiation treatments and in particular of the effect of inhibitors of dark-repair processes, it was concluded that much of the variation in stage sensitivity was attributable to different repair activities. Those stages farthest from division had the longest period in which to repair UV lesions, whereas successively later stages had less time and thus exhibited an enhanced sensitivity.

79 mutants of Chlamydomonas reinhardi exhibiting defective cell wall morphogenesis have been induced using N-methyl-N′-nitro-N-nitrosoguanidine (NNG), UV light and ethyl methanesulphoante (EMS). The kinetics of their induction, and their morphology as revealed by electron microscopy, is described. Genetic analysis of 32 randomly chosen mutants indicates the existence of at least 19 loci concerned with the organisation of the cell wall.

SUMMARYFifteen mutant strains of Chlamydomonas reinhardi were isolated which showed defects in some aspect of the process of cell-wall formation. Genetic analyses indicated that most of the mutations were due to single gene changes; two were anomalous in that non-Mendelian segregations were obtained on crossing with other genotypes, and on selfing they frequently gave rise to wild-type phenotypes.Occasional somatic revertants were also obtained from these two strains. On the basis of these analyses it is suggested that there are two levels of control operating in the process of cell wall biogenesis - one concerned with subunit production at the nuclear level and another, possibly concerned with three-dimensional organization, at another level. Electron-microscope analyses of the different mutants showed the mutants to be divided into three main categories: those in which the wall was formed but was not attached to the plasma membrane, those in which the wall was attached to the membrane, and those in which very little wall was formed. In the last class in particular, vesicles containing wall precursors were clearly visible, and were shed through the plasma membrane into the medium.

Driver stress and related issues influence a number of people and situational interactions. Indeed, in a review of the literature on driving stress, Gulian (1987) found a substantial body of research describing physiological modifications associated with various traffic incidents (e.g., increase in heart rate). Yet few investigations have addressed driver stress from a psychological viewpoint (but see: Stokols, Novaco, Stokols and Campbell, 1978; Hoyos and Kastner, 1987). There is apparently little information regarding coping strategies used by people to deal with driving-induced stress.

Different varieties of peas have different proportions of rDNA in their genomes; there is no obvious correlation between the proportions and seed or leaf size. The rDNA proportions in root tips, seedlings, leaves and in the cotyledon cells of high DNA content, were compared in four varieties. In three, there was no difference between tissues; the fourth showed an amplification of rRNA genes in the cells of high DNA content of the seed cotyledon, and also in the cells of young but not of older leaves. The fourth variety was the one that had the lowest proportion of rDNA of all those examined. Studies of the tissues of hybrids between genotypes with "low" and "high" proportions of rDNA showed that heterozygotes had the "high" value, showing again the occurrence of an amplification phenomenon.

We describe four genomic clones of pea 7S storage protein gene, one of which corresponds to convicilin, and the others to vicilin. Hybridization studies exploiting these clones, and previously identified cDNA clones, have enabled us to define six different loci. Three of these loci have been mapped to positions on chromosome 7.

MANY difficulties and disadvantages are involved in undertaking a programme of improvement of crop plants by the artificial induction of mutations. Among those which have been recognized are (a) the necessity for screening very large populations of plants ; (b) the considerable degree of sterility found in mutant material; (c) the inefficiency of existing mutagens, and (d) in inbreeding forms, the desirability of isolating the frequently male-sterile R 1 generation, to avoid contamination with foreign pollen. The first of these difficulties is less troublesome in certain instances, as for example, when screening seedlings for disease resistance, for large numbers are easily handled. No doubt, for this reason, many reports1 of the successful induction and selection of disease resistant mutants do in fact exist; resistance to Erysiphe graminis f. hordeii in barley, to Puccinia glumarum and Puccinia graminis f. tritici in wheat, and to Puccinia graminis f. avenae in oats, are among the most important.

MICROBIAL cells are potentially attractive sources of protein food, but this usefulness is at present limited, not merely by technical and economic difficulties1–4, but also because the indigestibility of the cell walls limits the extent to which they can be incorporated directly into human food. Indeed it has been suggested that microbial cells5 and the alga Chlorella6 cannot be used in human food without removal of the cell walls. For algae, there are two ways of overcoming this difficulty—either the material can be fed to ruminants, or mechanical, chemical or enzymatic techniques7 can be used for the fractionation and removal of the cell walls. Enzymatic methods are as yet inefficient and, whereas industrial scale production in Czechoslovakia involves mechanical disruption of the algal cells with Ballotini beads, Japanese commercial production involves chemical extraction. Although all these methods are easy and efficient on a laboratory scale, on an industrial scale problems of fractionation are as formidable as those of cultivation2. Furthermore, the cost involved militates against a more general utilization of this food source. There is now evidence that by genetic manipulation it is possible in some instances to overcome these problems posed by the presence of the cell wall.

Examination of data from a set of diallel crosses between a number of inbred lines was used for analysing the genetic control of radiosensitivity in six tomato varieties. The six varities were crossed in all possible combinations, including reciprocals, and the parental and F1 seed were used in the experiments. Seeds were dried and exposed to 28,116 rad of Co60 gamma rays at a rate of 2000 rad/hr. The characters scored were the distance from the apex of one cotyledon to the apex of the other at the 12th day, and the lengths of the 1st and 2nd leaves at the 19th day after sowing. The results showed the response of tomato seeds to radiation to be genetically controlled. The nature of this control was polygeric, with evidence of additivity and dominance. The different varieties had various proportions of dominant and recessive alleles, and dominance and ambidirectional. Pronounced consistent and inconsistent maternal effects influenced the radiation response; these affected dominance values to produce a complex genetic situation. The genetic control of radiosensitivity was different from that of the simple growth characters, though there was some similarity in that both showed maternal effects. There was also evidence that the control ofmore » these characters varied according to whether they were measured in the cotyledon, first or second leaf. Relationships between spontaneous mutation and chromosome breakage, and induced mutation and breakage is discussed. It is concluded that radiosensitivity per se may not be a true character, and that what was measured may be some quite different character, which could control such factors as oxygen tension, metabolic rate, or production of radioprotective substances; and that different levels of expression of this character could result in different levels of radiosensitivity. (H.H.D.)« less

Summary(1) The radiosensitivity of soaked barley seeds was directly dependent on their stage of development in relation to the cell cycle.(2) At any given stage of development there was a pronounced oxygen effect, but no effect of irradiation temperature in the range 2° to 20°c. There was no evidence of any temperature-dependent recovery process.(3) Similar responses were obtained when radiobiological damage was measured in terms of induced mutation, sterility, or growth inhibition.

Among a series of mutants regulating wall formation, two exhibit both Mendelian and non-Mendelian segregation patterns on crossing with wild type. In addition each, on crossing with an identical mutant, frequently gives wild type and pseudo-wild type forms. Diploid wild types can be generated by fusing two identical haploid mutants. The results of genetic analyses indicated that extra-nuclear information is involved in the regulation of wall formation; this is usually stable in vegetative cells but can be renewed at the diploid spore stage. The degree of autonomy of the extra-nuclear system is considered, and the possibility of its being ultimately based on nuclear information discussed.

The nuclear DNA content of prophase nuclei in root tips of two cultivars and two primitive lines of Pisum sativum and of Pisum fulvum have been determined, using a scanning microdensitometer. The nuclear DNA contents differed significantly between the genotypes investigated but there was no correlation with their supposed phylogenetic positions.A loss of 73% of the DNA from cells of aseptically cultured excised pea roots has been recently reported (Abbott, 1971). In marked contrast to this claim, our measurements of the nuclear 4C DNA content of root tip meristematic cells have shown that there is no significant loss in excised roots compared with attached roots.

THE V by leaf-marking allele in Trifolium repens results in the production of a phenotype characterized by the presence of a broken white V surmounted by a yellow tip (Fig. 1a). A separation of the two parts by crossing-over has never been reported. There are eleven known alleles at this locus1, of which v determining the absence, is recessive to all alleles determining the presence of a mark. Most compounds not involving v exhibit mosaic dominance2.

The survival of cells exposed at a high or a low dose rate to60 Co γ-radiation, under well-oxygenated and hypoxic conditions, is compared for three strains of Chlamydomonas reinhardi differing in repair activity. In oxygen a dose-rate effect is found in all strains, but in hypoxia the mitigating effect of protracted irradiation is observed only in those strains having a certain type of repair activity. Differences in dose-rate and dose-fractionation effects observed under hypoxic conditions in mammalian and plant cells are considered in relation to possible differential repair activity.

It has now been well established that many actively metabolizing cells which have suffered damage after exposure to sparsely ionizing radiation have the capacity to repair at least some part of this damage. This capacity for recovery has been clearly demonstrated in the numerous dose fractionation experiments that have been undertaken in recent years, especially in those using asynchronous populations of mammalian cells cultured in vitro. In these experiments it has been shown that, under optimal conditions of growth, survival following exposure to fractionated doses improves in comparison with that obtained from the same dose given as an acute treatment, as the interval between doses increases. Beyond a certain point further increases in the time interval lead to a decrease in survival, but with yet longer intervals, survival once more increases (1, 2). A similar pattern has been observed also in Saccharomyces (3). Recovery processes now seem to be of general occurrence, having been reported in a green alga (4), a protozoan (5), and a higher plant (6), as well as in mammalian systems in vivo (7, 8). The pattern of response obtained in vitro in the asynchronous mammalian systems has been interpreted by Elkind et al. (9) as follows: the initial increase in survival is due to an intracellular recovery process, and the later fluctuations are due to the progression of surviving cells through stages having different inherent sensitivities. This interpretation has now been supported by the results of dose fractionation experiments using synchronous mammalian cell systems grown in vitro (10, 11). Many details of the interpretation, however, remain to be elucidated; for example, it has not been possible to determine whether recovery is associated solely with changes in the shoulder of the survival curve, or whether changes also occur in Do-that is, changes other than those associated with cell progression. Furthermore, the patterns of recovery of cells irradiated in different stages of the cell cycle have not been accurately assessed. To answer these questions it is essential to obtain full survival curve parameters in a synchronous system after dose fractionation. These problems have been studied by using synchronous populations of diploid cells of the green alga Chlamydomonas reinhardi.