Ovule abortion in white clover (Trifolium repens L.)

Plants of white clover ( Trifolium repens L.) cv. Olwen were grown in an open glasshouse maintained at a mean temperature of 20^oC and ovule growth and seed production measured. Differences in the rate of growth of ovules within ovaries were observed as early as 2 days after pollination. Ovules reached a maximum size after 8 days with the smallest only half the size of the largest. After 8 days, the smallest ovules became flaccid and shrivelled. Ovule position within the ovary had little effect on the frequency of seed set and although there was an apparently higher probability that central ovules produced a seed than those nearer the peduncle or style this was not statistically significant. Inflorescence position and floret position on the inflorescence had a significant effect on the number of seeds per floret and seed weight; the first formed inflorescences and the first florets to be pollinated on each inflorescence had more seeds per floret and heavier seeds and fewer florets with no seed than later pollinated florets. There were also differences between florets within the same whorl. The role of a number of factors which may influence floret site utilisation are discussed.     

The diversification of South American murid rodents: evidence from mitochondrial DNA sequence data for the akodontine tribe

Phylogenetic relationships based on 801 base pairs (bp) of the mitochondrial cytochrome b gene are examined for eight genera and 28 species of the akodontine tribe of South American murid rodents. The akodontine tribe comprises some 35% of the total diversity of the subfamily Sigmodontinae, but the current taxonomy at virtually all levels is uncertain because of inadequate generic diagnoses and assessments of variation and trends in traditional morphological characters. Monophyly of the tribe cannot be resolved by the sequence data, based on comparisons to outgroup taxa in three other tribes (Oryzomyini, Phyllotini, and Thomasomyini). However, highly corroborated monophyletic units within the group are obtained in a variety of both parsimony and distance analyses. These include a redefined and numerically dominant genus Akodon (with Microxus and Hypsimys as synonyms), Bolomys, Lenoxus, Oxymycterus, and a strongly supported assemblage that includes the central Andean Chroeomys and 'Akodon' andinus and the southern Abrothrix, 'Akodon' olivaceus, and the long-clawed mice of the genera Notiomys, Geoxus, and Chelemys. Sequence divergence within species is typically less than 5%, although levels can reach 10% for some highly polytypic forms. Divergence among genera within the tribe reaches 35% in corrected estimates, a level that is as great as that among representatives of different tribes. Changes in the current classification of akodontines are suggested based on these data, and the timing and place of origin of the tribe and its radiation is discussed.     

Human TRP-1 Has Tyrosine Hydroxylase but no DOPA Oxidase Activity

Human TRP-1 has been immunopurified from normal human melanocytes cultured from black neonatal subjects and used to investigate the catalytic function of TRP-1 for the two substrates, L-tyrosine and L-DOPA. Immunopurified TRP-1 did not demonstrate DOPA staining on SDS/PAGE nor DOPA oxidase (DO) activity with either routine or modified assays. The purified TRP-1 also demonstrated no tyrosine hydroxylase (TH) activity using the routine Pomerantz assay. However, there was apparent TH activity exhibited by immunopurified TRP-1 under conditions with low tyrosine concentration (≤0.8 μCi/ml of ³H-tyrosine), prolonged incubation time (i.e., overnight) and in the absence of the cofactor L-DOPA. Using these latter specific conditions, TH activity was also detected in cell lysates from a tyrosinase-negative albino melanocyte line which exhibited no TH activity with the routine Pomerantz assay. In addition, TH activity under low substrate assay conditions was not exhibited in a melanocyte line derived from a TRP-1 deficient, Brown albino individual. However, the absence of TH in this Brown albino cell line could be compensated for by the addition of L-DOPA to the assay. These results suggested that TRP-1 has some tyrosine hydroxylase but no DOPA oxidase activity. We propose that one function of TRP-1 is to modulate tyrosinase activity by making DOPA available as a cofactor to perpetuate the initial steps in melanogenesis.     

Description of a New Species of Microsporidia from Muscidifurax raptor (Hymenoptera: Pteromalidae), a Pupal Parasitoid of Muscoid Flies

ABSTRACT. A microsporidian parasite, Nosema muscidifuracis n. sp., has been found in Muscidifurax raptor , a parasitoid of muscoid flies. Stages of the parasite developed in direct contact with the host cell cytoplasm and were detected in midgut epithelium, Malpighian tubules, ovaries (including oocytes) and fat body of larvae and adults. Spores were also detected within eggs deposited on the host. Light and electron microscopy revealed a developmental cycle with diplokaryotic stages dividing by binary fission and disporous sporulation sequences producing diplokaryotic spores of three morphological classes, differing significantly only in length of the polar filament. Two of the classes were found in larvae, pupae and adults. One of these, with about five turns in the coiled polar filament, is presumed to be responsible for transmission from cell to cell within the host (autoinfection) and the other, with about 10 turns, responsible for transmission from host to host. A third class, with about 15 turns in the polar filament, was found in eggs of M. raptor . It is, presumably, either involved in initiation and spread of the infection at eclosion or is responsible for horizontal transmission to a new host individual when eggs are cannibalized.     

Mechanism of Isoxaben Tolerance in Agrostis palustris var. Penncross

Previous work has demonstrated that isoxaben tolerant mutantsof Arabidopsis thaliana var. Columbia are most likely alteredat the site of isoxaben binding. The salient question becomeswhether or not species selectivity to this herbicide might alsobe a result of differential target site binding. Grasses aregenerally more tolerant to isoxaben than dicots. In this communicationwe show that Agrostis palustris var. Penncross, a grass, is83-fold more tolerant in a soil incorporation test and 170-foldmore tolerant to inhibition of glucose incorporation into cellulosethan is Arabidopsis, a dicot. Cell wall fractionation of Agrostisshows a specific effect on cellulose biosynthesis. At most,5-fold of the 170-fold tolerance exhibited by Agrostis in termsof cellulose biosynthesis can be attributed to decreased isoxabenuptake under the test conditions. Furthermore, Agrostis is unableto metabolize isoxaben to any significant degree. Therefore,we suggest that the major portion of the tolerance in Agrostismight be due to differences in isoxaben binding. Key words: Isoxaben, cellulose, Arabidopsis, Agrostis, herbicide tolerance