The Elongation Response of Watermelon Hypocotyls to Indole-3-Acetic Acid: A Comparative Study of Excised Segments and Intact Plants

Carrington, C. M. S. and Esnard, J. 1988. The elongation responseof watermelon hypocotyls to indole-3-acetic acid: a comparativestudy of excised segments and intact plants.—J. exp. Bot39: 441–450. The auxin-growth response along the hypocotyl of Citrullus lanatus(Thumb.) Mansf. seedlings was studied. In excised segments,promotion of elongation was seen in all zones at the concentrationsof IAA used (10–4–10–2 mol m-3). In intactplants, only the most basal zone showed unequivocal IAA-extensionwhile in the most apical zone elongation was inhibited by auxin.This difference between segments and intact plants for apicalzones suggests a modifying effect of the apex and cotyledonson the growth response. Indeed, removal of the apex and colyledonsonly affected elongation in the zones adjacent to the excisionbut only in buffer-treated plants, not auxin-treated plants.Auxin supplied apically to the intact plant only resulted ina short-lived promotion of elongation whereas basally suppliedauxin gave a longer-lasting effect Zonal differences betweenauxin-promoted growth of excised segments suggests that sensitivityto auxin varies in the hypocotyl. The response of intact plantsto auxin was shown to be more complex than in segments. Thus,responses given by segments are poor indicators of auxin activityin intact plants. Key words: IAA, Citrullus lanatus, growth, plant hormone sensitivity     

Studies on the initiation of adventitious roots on mung bean hypocotyl

During the early stages of root induction in hypocotyls of mungbean cuttings, four new peroxidase isoenzymes are formed inthat part of the cutting that produces roots. These isoenzymesare in addition to and different from the three already presentin the hypocotyl. Forty-eight hr is required for the changeto take place from the original three to seven isoenzymes. Thechange in isoenzyme pattern and root initiation itself are retardedwhen streptomycin is applied during the very early stages ofroot induction. However, during the latter part of the first24-hr period after the cutting is made and when some of thenew isoenzymes have already been formed, the rooting processbecomes insensitive to this antibiotic. Cytologically, the occurrenceof cell division is paralleled by the formation of the fournew peroxidase isoenzymes. The delay in the occurrence of celldivision caused by the presence of streptomycin is paralleledby a similar delay in the formation of the four new isoenzymes. (Received November 27, 1970; )     

Structure of the Bark and Clonal Variability in Hevea brasiliensis Muell. Arg. (Willd. ex A. Juss.)

Detailed studies have been made on the structure of the barkof ten Hevea clones and the clonal variabilities with regardto the density and size of ray groups, density of laticifersper row per unit circumference of the tree, diameter of laticifersand the extent of connection between laticifers. Clonal variabilitywas highly significant with regard to the density of ray groups,ray height, ray width in the laticifer layer and the laticifercharacters. The influence of ray characters on the orientationof laticifers and thereby its quantity is discussed. The scopeof using anatomical parameters for clone identification is examined. Hevea brasiliensis, Para rubber tree, laticifers, bark (structure), anatomy, clonal variability, rubber     

METHODS FOR THE STUDY OF BLOWFLY POPULATIONS

The advantages and disadvantages of laboratory-bred material for fly-marking experiments are discussed. Experimental evidence suggests that the tendency to uniformity of history of laboratory-bred blowflies in relation to protein-feeding produces no rhythm, apparent in the first 4 days at least, in their response to protein bait attractants.
The change from insectary environment to field conditions may sometimes result in either a greater or a lower proportionate recapture of a laboratory-bred sample than that for a comparable wild-caught sample. The nature of the difference is apparently associated with the weather conditions of the release area, but may be due to other causes, probably including physiological debilitation of laboratory-maintained strains.     

Distribution, Development and Structure of Resin Ducts in Guayule (Parthenium argentatum Gray)

The distribution, development and structure of resin ducts inguayule (Parthenium argentatum Gray), the second best sourceof natural rubber, have been studied. Resin ducts are widelydistributed in stem, root, leaf, petiole and peduncle. The ductsin the primary tissues are initiated schizogenously and theirfurther development is schizolysigenous. The ducts in the cortexof the root do not have a well-defined epithelium. Ducts developedfrom the vascular cambium are initiated and develop schizogenously.Both resin and rubber are produced in the epithelial cells ofresin ducts. While resin is secreted into the duct lumen, rubberis stored within these cells. Epithelial cells store more thanneighbouring parenchyma cells. Guayule, rubber, resin, ducts, epithelial cells     

Gustatory mechanisms and sugar-feeding in the mosquito, Culiseta inornata

ABSTRACT. Gustatory hairs on the legs and mouthparts of the mosquito, Culiseta inornata , were stimulated with sucrose solutions to determine their role in the finding and consuming of nectar by females. Stimulation of tarsi initiated probing, which continued without subsequent stimulation of tarsal hairs. Turning in response to tarsal stimulation depended on which leg was stimulated. Once gustatory hairs on the labella were stimulated, turning and probing were discontinued. Stimulation of the hairs on the external surface of the labella apparently initiates the labellar opening response, while stimulation of hairs on the oral surface of the labella maintains the labellar response. Electrophysiologically recorded activity of cibarial and pharyngeal pumps was used to assess the influence of the five relevant sets of gustatory hairs on initiation of sucking. None of the sets alone were capable of initiating sucking. Sucking was initiated when the hairs on the oral surface of the labella were stimulated simultaneously with sensory hairs on the tip of the labrum. The gustatory hairs on the oral surface of the labella exerted considerable influence in determining the amount of sugar or water imbibed.     

The beetle tree of life reveals that Coleoptera survived end‐Permian mass extinction to diversify during the Cretaceous terrestrial revolution

Here we present a phylogeny of beetles (Insecta: Coleoptera) based on DNA sequence data from eight nuclear genes, including six single‐copy nuclear protein‐coding genes, for 367 species representing 172 of 183 extant families. Our results refine existing knowledge of relationships among major groups of beetles. Strepsiptera was confirmed as sister to Coleoptera and each of the suborders of Coleoptera was recovered as monophyletic. Interrelationships among the suborders, namely Polyphaga (Adephaga (Archostemata, Myxophaga)), in our study differ from previous studies. Adephaga comprised two clades corresponding to Hydradephaga and Geadephaga. The series and superfamilies of Polyphaga were mostly monophyletic. The traditional Cucujoidea were recovered in three distantly related clades. Lymexyloidea was recovered within Tenebrionoidea. Several of the series and superfamilies of Polyphaga received moderate to maximal clade support in most analyses, for example Buprestoidea, Chrysomeloidea, Coccinelloidea, Cucujiformia, Curculionoidea, Dascilloidea, Elateroidea, Histeroidea and Hydrophiloidea. However, many of the relationships within Polyphaga lacked compatible resolution under maximum‐likelihood and Bayesian inference, and/or lacked consistently strong nodal support. Overall, we recovered slightly younger estimated divergence times than previous studies for most groups of beetles. The ordinal split between Coleoptera and Strepsiptera was estimated to have occurred in the Early Permian. Crown Coleoptera appeared in the Late Permian, and only one or two lineages survived the end‐Permian mass extinction, with stem group representatives of all four suborders appearing by the end of the Triassic. The basal split in Polyphaga was estimated to have occurred in the Triassic, with the stem groups of most series and superfamilies originating during the Triassic or Jurassic. Most extant families of beetles were estimated to have Cretaceous origins. Overall, Coleoptera experienced an increase in diversification rate compared to the rest of Neuropteroidea. Furthermore, 10 family‐level clades, all in suborder Polyphaga, were identified as having experienced significant increases in diversification rate. These include most beetle species with phytophagous habits, but also several groups not typically or primarily associated with plants. Most of these groups originated in the Cretaceous, which is also when a majority of the most species‐rich beetle families first appeared. An additional 12 clades showed evidence for significant decreases in diversification rate. These clades are species‐poor in the Modern fauna, but collectively exhibit diverse trophic habits. The apparent success of beetles, as measured by species numbers, may result from their associations with widespread and diverse substrates – especially plants, but also including fungi, wood and leaf litter – but what facilitated these associations in the first place or has allowed these associations to flourish likely varies within and between lineages. Our results provide a uniquely well‐resolved temporal and phylogenetic framework for studying patterns of innovation and diversification in Coleoptera, and a foundation for further sampling and resolution of the beetle tree of life.     

Evaluation of Connectivity Among American Black Bear Populations in Georgia

Habitat fragmentation and loss contribute to isolation of wildlife populations and increased extinction risks for various species, including many large carnivores. We studied a small and isolated population of American black bears (Ursus americanus) that is of conservation concern in central Georgia, USA (i.e., central Georgia bear population [CGBP]). Our goal was to evaluate the potential for demographic and genetic interchange from neighboring bear populations to the CGBP. To evaluate resource selection and movement potential, we used 35,487 global positioning system locations collected every 20 minutes from 2012 to 2014 from 33 male bears in the CGBP. We then developed a step selection function model based on conditional logistic regression. Male bears chose steps that avoided crops, roads, and human developments and were closer to forests and woody wetlands than expected based on availability. We used a geographic information system to simulate 300 bear movement paths from nearby bear populations in northern Florida, northern Georgia, and southern Georgia to estimate the potential for immigration to the CGBP. Only 4 simulated movement paths from the nearby populations intersected the CGBP. The creation of a hypothetical 1-km-wide corridor between the southern Georgia population and the CGBP produced only minor improvements in interchange. Our findings suggest that demographic connectivity between the CGBP and surrounding bear populations may be limited, and coupled with previous works showing genetic isolation in the CGBP, that creation of corridors may have only marginal effects on restoring gene flow, at least in the near term. Management actions such as translocation and the establishment of stepping stone populations may be needed to increase the genetic diversity and demographic stability of bears in the CGBP. © 2021 The Wildlife Society.