Tubulin and Microtubules in the Early Development of the Axolotl and Other Amphibia

SYNOPSIS. Unfertilized eggs of the axolotl, Ambystoma mexicanum,contain a pool of soluble tubulin accumulated during oogenesis.After initiation of cleavage the tubulin pool decreases somewhatand then remains constant through early development. Some propertiesof tubulin alter during development, but at least some of thesechanges are not due to changes in tubulin perse. However, thetubulin in axolotl oocytes, eggs, and embryos differs in someelectrophoretic properties from tubulin in adult axolotl brainand testis. Equivalent differences were observed in Necturusmaculosus tubulins. Heterogeneity of axolotl tubulins was confirmedby peptide mapping: Different patterns of peptides were formedby specific limited proteolysis of soluble tubulin from eggsand testis. The heterogeneity was more marked in the a thanin the ß subunit. Mobilization of soluble tubulininto the mitotic apparatus depends on the functioning of microtubuleorganizing centers after activation of the egg at fertilization.In eggs of the nc mutant axolotl there is a lesion in some stepof activation, one effect of which is that even though the eggscontain an essentially normal pool of tubulin, microtubulesfail to assemble, no mitotic apparatus forms, and embryonicdevelopment does not begin. These eggs can be partially correctedby injection of heterologous microtubule fragments, which elicitthe mobilization of nc tubulin into arrays of microtubules,followed by initiation of cleavage and development to a partialblastula stage. The results of these experiments are discussedin comparison with other reports in the literature about thefunction of microtubule organizing centers during amphibianegg development.     

Grass Leaf Elongation Rate as a Function of Developmental Stage and Temperature: Morphological Analysis and Modelling

Elongation of successive leaves was measured following defoliationof tall fescue plants in controlled environments. Measurementswere made under constant temperatures of 24 °C and 14 °C,and after temperature changes from 24 to 14 °C andvice versa.A morphological analysis of the growing leaf was made from thetime it was 1 mm long until it was fully elongated. The timeelapsed from initiation until the leaf was 1 mm long was estimated.Young leaves less than 1.5 mm long elongated slowly at a constantleaf elongation rate (LER). By extrapolating this LER back toleaf initiation from the apex it was calculated that elongationlasted 42.5 d at 24 °C and 51 d at 14 °C. Lengths ofthe division zone (DZ) and the extension-only zone (E-OZ) increasedto a maximum and then decreased during leaf development. Temperaturechange had an immediate effect on LER but the response varieddepending on the direction of the temperature change. To describethese different features, an empirical model of DZ and E-OZwas designed. Its five parameters were optimized at constanttemperature. The model was then used to simulate the LER ofplants subjected to temperature changes. Instant and lastingeffects of the initial temperature on mean LER in plants transferredfrom 14 to 24 °C andvice versawere well simulated. It wasconcluded that the major reason for differences was due to thegrowth stage (DZ and E-OZ lengths) at which the changes occurredat both temperatures.Copyright 1999 Annals of Botany Company Festuca arundinaceaSchreb., tall fescue, growth zone, division zone.     

A Compartmental Analysis of Abscisic Acid in Roots of Hordeum distichon

An efflux compartmental analysis of abscisic acid (ABA) in barleyroots revealed two compartments of ABA, a fast exchanging one(probably the cytoplasm) containing 3.63 µM ABA and aslowly exchanging compartment (probably the vacuoles) whichcontained 0.39 µM ABA.     

Leg coordination and swimming in an ant, Camponotus americanus

ABSTRACT. Leg movements of Camponotus americanus workers during straight swimming and turning are described herein. Thrust is generated through the different speeds and drag control between power v. return strokes in the forelegs. During the power stroke, femur, tibia and tarsus are straightened and thereby increase resistance; they bend backward during the return stroke. These thrusting legs move in a vertical plane which is similar to their position during walking. The backward stretching mesothoracic and metathoracic legs act, in conjunction with the gaster, as a rudder. Swimming in ants can be derived from walking; the major transformation being a suppression of the rhythmic movements of the middle and hind legs.     

Unusual Multiple Fission in the Gamont of the Larger Foraminiferan Heterostegina depressa*

SYNOPSIS. In the larger foraminiferan, Heterostegina depressa d'Orbigny, new gamonts form directly from adult gamonts by multiple fission. The life of the parent gamont, however, is not always ended by this process. Residual protoplasm which remains inside the parent gamont test during reproduction may grow again and reoccupy the test. Such individuals can add new chambers and are able to reproduce a 2nd time. The oldest individual observed was 32 months of age; it reproduced at 8 months.     

H-Y Antigen in the Teleost

H-Y antigen, presumably the product of mammalian testis-determining genes, has been detected in three species of teleost fish, Xiphophorus maculatus, Haplochromis burtoni , and Oryzias latipes , and in hybrids of the genus Tilapia . In X. maculatus H-Y was most readily detected in YY males, suggesting that a genetic determinant of H-Y antigen expression may exist on the teleost Y-chromosome. Although H-Y was detected in males and not in females in each of the species that we studied, male heterogamety has not been firmly established for H. burtoni . Thus despite the extreme phlyogenetic conservation of H-Y genes and their association with the Y-chromosome, it remains open to question whether H-Y will always be found in the heterogametic sex, and whether serologically defined H-Y antigen plays any part in the differentiation of the teleost gonad.     

Morphological and molecular evidence for a new endemic freshwater crab, Sesarma ayatum sp. n., (Grapsidae, Sesarminae) from eastern Jamaica

Recent morphological studies have shown that the Jamaican mountain stream crab, Sesarma bidentatum Benedict, 1892 (Sensu Abele 1992), consists of several allopatric forms. Three new species have been described from western Jamaica (summarized in Reimer et al. 1998) restricting the range of S. bidentatum to central and eastern Jamaica. In this study we used morphology and genetic markers to further distinguish crab populations from different East Jamaican river systems. Morphological characters such as the shape of male gonopods, front, chelar carpus, and walking legs, as well as mtDNA sequence (16s rRNA gene) comparisons were consistent in the separation of populations of S. bidentatum into two distinct groups. A new species, Sesarma ayatum sp. n., is described with a distribution from easternmost Jamaica to the eastern Blue Mountains.     

Radial transport of salt and water in roots of the common reed (Phragmites australis Trin. ex Steudel)

To understand the root function in salt tolerance, radial salt and water transport were studied using reed plants growing in brackish habitat water with an osmotic pressure (π_M) of 0.63 MPa. Roots bathed in this medium exuded a xylem sap with NaCl as the major osmolyte and did so even at higher salt concentration (π_M up to 1.3 MPa). Exudation was stopped after a small increase of π_M (0.26 MPa) using polyethylene glycol 600 as osmolyte. The endodermis of fine lateral roots was found to be the main barrier to radial solute diffusion on an apoplastic path. Apoplastic salt transfer was proven by rapid replacement of stelar Na⁺ by Li⁺ in an isomolar LiCl medium. Water fluxes did not exert a true solvent drag on NaCl. Xylem sap concentrations of NaCl in basal internodes of transpiring culms were more than five times higher than in medial and upper ones. It was concluded that the radial NaCl flux was mainly diffusion through the apoplast, and radial water transport, because of the resistance of the cell wall matrix to convective mass flow, was confined to the symplast. Radial salt permeation in roots reduced the water stress exerted by the brackish medium.