The effects of culture medium rigidity on adventitious bud production and tissue vitrification in needle cultures of Sitka spruce [Picea sitchensis (Bong.) Carr.]

Adventitious bud formation on Sitka spruce [ Picca sitchensis (Bong.) Carr.] needle explants was strongly dependent upon the rigidity of the culture medium. In general, of organogenesis was greatest on weak gels and poorest on more rigid gels resulting from increased medium pH or agar strength. There was a significant interaction between agar strength and pH, with the optimum pH for organogenesis declining with increasing agar strength. Poor organogenesis at high agar concentrations was not due to toxic impurities since increased adventitious bud production could be stimulated by decreasing the medium pH whilst maintaining a high agar strength and an agar washing treatment had no significant effect. Although high levels of organogenesis could be sustained on weak gels the resultant adventitious shoots often showed severe vitrification. The frequency of shoots showing vitrification could be reduced by growing the tissues on harder media but this resulted in reduced shoot elongation. Vitrification of needle tissues did not stimulate the formation of adventitious buds in the absence of cytokinins.     

Lignin degradeation by white rot fungi

Abstract. The wood-degrading white-rot fungus Phanerochaete chrysosporium , has been the subject of intensive research in recent years and, based upon isolation of the extracellular enzyme ligninase, major advances have now been made toward elucidating the mechanism by which this fungus degrades lignin. From these developments, a model emerges which could explain the process by which wood-degrading fungi in general, attack lignin.     

The structure and evolution of the spider monkey delta-globin gene

We have isolated the delta-globin gene of the New-World spider monkey, Ateles geoffroyi, and compared its nucleotide sequence with those of other primate delta- and beta-globin genes. Among primate delta-globin genes, the rate of nonsynonymous substitutions is much less than the rate of synonymous substitutions. This suggests that primate delta- globin genes may remain under evolutionary conservation, perhaps because hemoglobin A2 has an as yet unknown physiological importance.      

Biochemical pathways in prokaryotes can be traced backward through evolutionary time

For the first time, a credible prokaryotic phylogenetic tree is being assembled by Woese and others using quantitative sequence analysis of oligonucleotides in the highly conservative rRNA. This provides an evolutionary scale against which the evolutionary steps that led to the arrangement and regulation of contemporary biochemical pathways can be measured. This paper presents an emerging evolutionary picture of aromatic amino acid biosynthesis within a large superfamily assemblage of prokaryotes that is sufficiently developed to illustrate a new perspective that will be applicable to many other biochemical pathways.      

Studies of cereal nematode populations and cereal yields under continuous or intensive culture

In a field experiment on infested sandland from 1955 to 1967, numbers of Heterodera avenae increased only in 1957 and then decreased under both continuous and rotational spring oats (1955-62) and subsequently under spring barley (1963-67). Fluctuations in numbers of Pratylenchus neglectus and Trichodorus primitivus were recorded from 1963 to 1967. Cereal grain yields were generally unsatisfactory, but were consistently higher for cereals grown in rotation rather than continuously. Extra nitrogen fertilizer gave slightly improved yields with higher post-cropping numbers of H. avenae.     

Effects of Incubation Temperature on Crocodiles and the Evolution of Reptilian Oviparity

Crocodylus porosus is a mound-nesting crocodilian in which incubationtemperature influences the rate of embryonic development, theprobability that embryos will survive to hatching, post-hatchinggrowth rates and the probability of hatchlings surviving to2 yr of age. Similar responses have been described in Alligatormississippiensis (Joanen et al., 1987) and C. niloticus (Hutton,1987), and they reflect a suite of "non-sexual" effects of incubationtemperature. Temperature-dependent sex determination allocatessex on the basis of these "non-sexual" effects. In C. porosus,it results in maleness being assigned to embryos with high probabilitiesof surviving and good potential for post-hatching growth. Withinthe limits of survival, effects of the moisture environmenton embryological development rate and hatchling fitness seemminor relative to those of the temperature environment. Reptilian orders have either obligate oviparity (chelonians,crocodilians and rhynchocephalians) or facultative oviparity(squamates), depending on the extent of embryonic developmentwithin the oviducts. The distinction is equally one betweenembryos which are buffered from thermal effects within a female'sbody (facultative oviparity) and those that are not (obligateoviparity). Facultative oviparity and internal thermal bufferingmay be the primitive condition within the Class Reptilia, andthe "shell-less" eggs of extant squamates may reflect the originalamniote egg. Obligate oviparity, which also exists in birds,appears to have been a specialized development, and is a blindend in the evolution of viviparity among vertebrates. The significanceof thermal buffering being lost in obligate oviparous reptilesremains unclear.     

A Dynamic Growth Model of Vegetative Soya Bean Plants: Model Structure and Behaviour under Varying Root Temperature and Nitrogen Concentration

A differential equation model of vegetative growth of the soyabean plant (Glycine max (L.) Merrill cv. ‘Ransom’)was developed to account for plant growth in a phytotron systemunder variation of root temperature and nitrogen concentrationin nutrient solution. The model was tested by comparing modeloutputs with data from four different experiments. Model predictionsagreed fairly well with measured plant performance over a widerange of root temperatures and over a range of nitrogen concentrationsin nutrient solution between 0.5 and 10.0 mmol in the phytotron environment. Sensitivity analyses revealedthat the model was most sensitive to changes in parameters relatingto carbohydrate concentration in the plant and nitrogen uptakerate. Key words: Glycine max (L.) Merrill, dry matter, nitrogen uptake, partitioning, photosynthesis, respiration, sensitivity analysis     

The evolutionary history of the amylase multigene family in Drosophila pseudoobscura

In Drosophila pseudoobscura, the amylase (Amy) multigene family is contained within a series of inversions, or gene arrangements, on the third chromosome. The Standard (ST), Santa Cruz (SC), and Tree Line (TL) inversions are central to the phylogeny of arrangements, and have clusters of other arrangements derived from them. The gene arrangements belonging to each of these three clusters have a characteristic number of Amy genes, ranging from three in ST to two in SC to one in TL. This distribution pattern can reflect a history of either duplications or deletions, although the data available in the past did not permit a decision between these alternatives. We provide unambiguous evidence that three Amy genes were present before the divergence of the ST, SC, and TL arrangements. Thus, the current status of the Amy multigene family is the result of deletions in the TL and SC arrangements, which created three new pseudogenes: TL Amy2-psi, TL Amy3-psi, and SC Amy3- psi. Analysis of pseudogene sequences revealed that, in the SC and ST arrangements, pseudogene evolution has been retarded, most likely due to the homogenization effect of gene conversion. Finally, by determining the original copy number, we have reconstructed the evolutionary history of the Amy multigene family and linked it with the evolution of the central gene arrangements.      

Fluctuating asymmetry and lifetime mating success are correlated in males of the damselfly Coenagrion puella (Odonata: Coenagrionidae)

Abstract.

• 1 The influence of fluctuating asymmetry on lifetime mating success of males of the damselfly Coenagrion puella (Odonata: Coenagrionidae) was investigated. Fluctuating asymmetry was measured as the difference in length of left and right fore and hind wings.
• 2 Males with more symmetrical wings enjoyed higher lifetime mating success.
• 3 Larger males, in contrast to a previous study of this species, also had higher mating success. This may be attributed to differences in the weather conditions prevailing at the time of the studies.