Conopy architecture of Larrea tridentata (DC.) Cov., a desert shrub: foliage orientation and direct beam radiation interception

Summary At sites in the United States, creosote bushes (Larrea tridentata (DC.) Cov.) orient foliage clusters predominantly toward the southeast. Foliage of bushes at the southernmost distribution extreme in Mexico shows no predominant orientation. Clusters at all sites are inclined between 33° and 71° from the horizontal. Inclinations are steeper in the drier and hotter Mojave Desert than in the Chihuahuan Desert. Individual leaflets, though not measured, appear more randomly oriented than foliage clusters. In several populations studied, branches were shorter in the southeastern sectors of the crown, reducing self-shading early in the morning. Measurements of direct beam radiation interception by detached branches, using digital image processing, indicated that foliage clusters oriented toward the southeast exhibited less self-shading during spring mornings than clusters oriented northeast. This effect was not apparent at the summer solstice. This type of canopy architecture may tend to minimize self-shading during the morning hours when conditions are more favorable for photosynthesis, resulting in an improved daily water use efficiency.     

Variable alpha-tocopherol stimulation and protection of glutathione peroxidase activity in established and malignant fibroblasts.

Studies on glutathione (GSH) metabolism in an established baby hamster kidney fibroblast cell line (BHK-21/C13) and in its polyoma virus-transformed counterpart (BHK-21/PyY) have revealed a significant stimulation of intracellular GSH peroxidase (GSHpx) activity (selenium-independent plus selenium-dependent) by alpha-tocopherol supplementation (14 microM). This stimulation was found to be much greater in the transformed cells. Other GSH-requiring enzyme activities (i.e. GSH reductase and GSH S-transferase) were unaltered by alpha-tocopherol treatment, suggesting a degree of specificity in its action on GSHpx. In unsupplemented growth media, the GSHpx activity in both cell lines was significantly decreased by oxidative stress. However, the same stress applied to the alpha-tocopherol-supplemented cells had no effect on the stimulated GSHpx activity, suggesting that some protection was afforded by the alpha-tocopherol.     

The four biochemically distinct species of human interleukin 1 all exhibit similar biologic activities

The supernatants of human monocytes incubated with endotoxin are able to stimulate the proliferation of murine thymocytes in the presence of PHA. This is known as LAF (lymphocyte activating factor) activity and is a characteristic activity of interleukin 1 (IL 1). The LAF activity can be resolved into four major fractions: a 15,000 dalton (pI 7), a 15,000 (pI 5.5), a 35,000 (pI 7), and a 35,000 (pI 5.5) fraction. To determine whether these four fractions shared the other biologic activities ascribed to IL 1, they were compared in a series of bioassays. When standardized with respect to their LAF activities, the four fractions did not differ significantly as mitogens for murine thymocytes, inducers of IL 2, murine or human B cell activators, human chondrocyte or synoviocyte stimulants, or inducers of acute phase proteins in vivo. On the other hand, the samples differed markedly as stimulators of porcine synoviocytes, with the 15,000 dalton (pI 5.5) fraction being the only strongly active fraction. These results are consistent with the hypothesis that all four LAF could be products of a single gene, although the porcine receptor may be able to distinguish between them. If this is the case, all four fractions can properly be termed IL 1.     

Phylogenetic diversification of immunoglobulin genes and the antibody repertoire

Immunoglobulins are encoded by a large multigene system that undergoes somatic rearrangement and additional genetic change during the development of immunoglobulin-producing cells. Inducible antibody and antibody-like responses are found in all vertebrates. However, immunoglobulin possessing disulfide-bonded heavy and light chains and domain-type organization has been described only in representatives of the jawed vertebrates. High degrees of nucleotide and predicted amino acid sequence identity are evident when the segmental elements that constitute the immunoglobulin gene loci in phylogenetically divergent vertebrates are compared. However, the organization of gene loci and the manner in which the independent elements recombine (and diversify) vary markedly among different taxa. One striking pattern of gene organization is the "cluster type" that appears to be restricted to the chondrichthyes (cartilaginous fishes) and limits segmental rearrangement to closely linked elements. This type of gene organization is associated with both heavy- and light-chain gene loci. In some cases, the clusters are "joined" or "partially joined" in the germ line, in effect predetermining or partially predetermining, respectively, the encoded specificities (the assumption being that these are expressed) of the individual loci. By relating the sequences of transcribed gene products to their respective germ-line genes, it is evident that, in some cases, joined-type genes are expressed. This raises a question about the existence and/or nature of allelic exclusion in these species. The extensive variation in gene organization found throughout the vertebrate species may relate directly to the role of intersegmental (V<==>D<==>J) distances in the commitment of the individual antibody-producing cell to a particular genetic specificity. Thus, the evolution of this locus, perhaps more so than that of others, may reflect the interrelationships between genetic organization and function.      

The trace fossils of the Baggy Beds (Upper Devonian) of North Devon,England

The trace fossils of the Baggy Beds are described. They includeTeichichnus cf.rectus Seilacher,Monocraterion cf.tentaculatum Torell,Diplocraterion yoyo sp. nov.,Arenicolites curvatus sp. nov., and other forms insufficiently well preserved for generic assignment. The protrusive and retrusive behaviour pattern ofD. yoyo is interpretated as a response to repeated phases of sedimentation and erosion and as a measure of these.A. curvatus is preserved in two modes: in the position of formation and as eroded tubes in conglomerates. The second reveals that the sediment around the tube was cemented to a thickness equal to the diameter of the tube.