We developed a technique to map the availability of sugars and amino acids along live roots in an intact soil-root matrix with native microbial soil flora and fauna present. It will allow us to study interactions between root exudates and soil microorganisms at the fine spatial scale necessary to evaluate mechanisms of nitrogen cycling in the rhizosphere. Erwinia herbicola 299R harboring a promoterless ice nucleation reporter gene, driven by either of two nutrient-responsive promoters, was used as a biosensor. Strain 299RTice exhibits tryptophan-dependent ice nucleation activity, while strain 299R(p61RYice) expresses ice nucleation activity proportional to sucrose concentration in its environment. Both biosensors exhibited up to 100-fold differences in ice nucleation activity in response to varying substrate abundance in culture. The biosensors were introduced into the rhizosphere of the annual grass Avena barbata and, as a control, into bulk soil. Neither strain exhibited significant ice nucleation activity in the bulk soil. Both tryptophan and sucrose were detected in the rhizosphere, but they showed different spatial patterns. Tryptophan was apparently most abundant in soil around roots 12 to 16 cm from the tip, while sucrose was most abundant in soil near the root tip. The largest numbers of bacteria (determined by acridine orange staining and direct microscopy) occurred near root sections with the highest apparent sucrose or tryptophan exudation. High sucrose availability at the root tip is consistent with leakage of photosynthate from immature, rapidly growing root tissues, while tryptophan loss from older root sections may result from lateral root perforation of the root epidermis.

Problematic fossils, extinct taxa of enigmatic morphology that cannot be assigned to a known major group, were once a major issue in palaeontology. A long-favoured solution to the 'problem of the problematica', particularly the 'weird wonders' of the Cambrian Burgess Shale, was to consider them representatives of extinct phyla. A combination of new evidence and modern approaches to phylogenetic analysis has now resolved the affinities of most of these forms. Perhaps the most notable exception is Tullimonstrum gregarium, popularly known as the Tully monster, a large soft-bodied organism from the late Carboniferous Mazon Creek biota (approximately 309-307 million years ago) of Illinois, USA, which was designated the official state fossil of Illinois in 1989. Its phylogenetic position has remained uncertain and it has been compared with nemerteans, polychaetes, gastropods, conodonts, and the stem arthropod Opabinia. Here we review the morphology of Tullimonstrum based on an analysis of more than 1,200 specimens. We find that the anterior proboscis ends in a buccal apparatus containing teeth, the eyes project laterally on a long rigid bar, and the elongate segmented body bears a caudal fin with dorsal and ventral lobes. We describe new evidence for a notochord, cartilaginous arcualia, gill pouches, articulations within the proboscis, and multiple tooth rows adjacent to the mouth. This combination of characters, supported by phylogenetic analysis, identifies Tullimonstrum as a vertebrate, and places it on the stem lineage to lampreys (Petromyzontida). In addition to increasing the known morphological disparity of extinct lampreys, a chordate affinity for T. gregarium resolves the nature of a soft-bodied fossil which has been debated for more than 50 years.

IntroductionMast cells (MCs) and basophils are histamine-containing, metachromatic granulocytes that express the high-affinity IgE receptor, Fc⑀RI, on their surfaces. 1,2 When activated via this receptor, both populations of cells immediately exocytose their granule constituents and then more slowly generate and release cytokines, chemokines, and arachidonic acid metabolites. Thus, these granulocytes play extremely important roles in IgE-mediated inflammatory responses. Although human MCs and basophils are similar in certain aspects, their substantial biochemical and morphologic differences in normal individuals have led to the concept that the 2 populations of cells probably are developmentally unrelated. MCs, for example, reside in tissues and generally possess a centrally positioned, oval nucleus. In contrast, basophils generally reside in the blood and contain a segmented nucleus. The MCs in the lung and skin of most normal individuals contain chymase, carboxypeptidase A, elastase, cathepsin G, and multiple tryptases in their granules. [3][4][5][6][7][8][9][10][11][12][13] Basophils in the peripheral blood of most normal individuals contain cathepsin G and elastase 4 but lack carboxypeptidase A and chymase. 14,15 Tryptase has been detected in normal human basophils. However, in the initial reports, Schwartz and coworkers concluded that normal human MCs contain on average about 250-fold more tryptase protein 16 and about 50 000-fold more tryptase messenger RNA (mRNA) 15 than normal human basophils.Although it was originally thought that the phenotype of a MC was fixed and irreversibly predetermined before its progenitor exited the bone marrow, it is now apparent that human and mouse 26 The developmental relationship between basophils and MCs remains unclear, in part, because no defined biochemical marker has been identified that can distinguish these 2 populations of cells in an animal that can be experimentally manipulated. A population of Fc⑀RI ϩ /metachromatic cells that possesses segmented nuclei is present in the peripheral blood of helminth-infected mice. Because of their location and nuclear profiles, it was originally thought that these mouse cells were basophils; however, recent studies have shown that they are actually senescent MCs trafficking from the jejunum to the spleen. 27 We have described a population of cells with both MC and basophil features in the blood of patients with asthma, allergy, and allergic drug reactions. 28 For personal use only. on May 10, 2018. by guest www.bloodjournal.org From cells resemble normal mature basophils in terms of their peripheral blood location, segmented nuclei, and surface expression of the Bsp-1 epitope. However, they more closely resemble normal mature MCs in terms of their surface expression of CD117 (c-kit) and their granule expression of multiple proteases.In the current study, we present additional biochemical evidence that the unusual population of metachromatic cells we identified in the blood of patients with various allergic disorders belongs in...