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.     

Specificity and Reversibility of the Bicarbonate Effect on Hexose Uptake by Maize Root Tips

The inhibition of hexose uptake by bicarbonate ions was investigatedin detail in order to test the specificity and reversibilityof the effect and to compare it with those of other electrolytes.The degree of inhibition was similar at pH 7.0 and pH 8.0. AtpH 4.5 no influence of a high concentration of CO₂ on 3-O-methylglucoseuptake was found. Therefore, the inhibition of hexose uptakeby bicarbonate cannot be explained by consequences of CO₂ influx.The inhibition of sugar absorption by calcium and potassiumions was similar to that exerted by bicarbonate in so far asit was observed at higher pH only. The inhibition exerted bysodium salts of different monovalent weak acids was limitedto lower pH and needed some time to become established or reversed.The bicarbonate effect was independent of time and reversiblewithout a lag phase. Sodium salts of strong mineral monovalentacids did not differ significantly in their effect on sugaruptake. Bicarbonate inhibited phosphate uptake in a similarmanner to hexose uptake but strongly stimulated the absorptionof potassium. The bicarbonate effect is assumed to result froma change in the degree of coupling of secondary active transportto the proton pump. Key words: Inhibition, Transport coupling, pH, Proton pump     

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.     

Edith R. Saunders and floral anatomy: bibliography and index to families she studied

Edith R. Saunders' contributions to floral anatomy are briefly considered. Fourteen of her abstracts and discussions and 49 of her lengthier works are cited. An index to 249 families of angiosperms sensu Airy Shaw (1973) keyed to Saunders' publications is given.     

Challenges of metamorphosis in invertebrate hosts: maintaining parasite resistance across life‐history stages

1. Insects lack the acquired immune system of vertebrates, but there is some evidence that insect immunity can be primed against an encountered pathogen to mitigate the intensity of future infections within a life stage. 2. Many invertebrates have multiple life‐history stages separated by complete metamorphosis, but different life stages can often be infected by the same pathogens, and the potential loss of immune priming during metamorphosis could therefore have detrimental effects on the host. Evidence that invertebrate immune priming can persist through metamorphosis is still missing, and consequently it is unclear how host–parasite interactions change across different life‐history stages in the context of infection history. 3. By experimentally manipulating the infection history of the flour beetle Tribolium confusum, we show that intestinal gregarine parasite infections during the larval stage reduced parasite load in adults, demonstrating that a host‐controlled mechanism for parasite resistance can persist through complete metamorphosis in insects. 4. Infections reduced larval developmental rates and increased host mortality but only during the crucial metamorphic stage, indicating that parasites impact multiple life stages. In general, our results demonstrate that invertebrates can show surprisingly robust immune priming despite dramatic physiological changes and protect hosts across completely different life‐history stages.     

Vacuolar Na/K Exchange, its Occurrence in Root Cells of Hordeum, Atriplex and Zea and its Significance for K/Na Discrimination in Roots

Using excised low-salt roots of barley and Atriplex hortenslsthe transport of endogenous potassium through the xylem vesselswas studied It was enhanced by nitrate and additionally by sodiumions which apparently replaced vacuolar potassium which wasthen available in the symplasm of root cells for transport tothe shoot Vacuolar Na/K exchange also has been investigatedby measurements of longitudinal ion profiles in single rootsof both species. In Atriplex roots a change in the externalsolution from K⁺ to Na⁺ induced an exchange of vacuolar K⁺ forNa⁺, in particular in the subapical root tissues and led toincreased K⁺ transport and loss of K⁺ from the cortex. In inverseexperiments a change from Na⁺ to K⁺ did not induce an exchangeof vacuolar Na⁺; merely in meristematic tissues Na⁺—apparentlyfrom the cytoplasm—was extruded in exchange for K⁺. Inroots of barley seedlings without caryopsis, as in excised roots,a massive exchange of K⁺ for Na⁺ was observed in the continuouspresence of external 1.0 mM Na and 0.2 mM K. This exchange alsowas attributed to the vacuole and was most pronounced in theyoung subapical tissues. It did not occur, however, in the correspondingtissues in roots of fully intact barley seedlings. In these,the young tissues retained a relatively high K/Na ratio alsoin their vacuoles. Similarly, contrasting results were obtainedwith intact and excised roots of Zea mays L. Based on theseresults a scheme of the events that lead to selective cationuptake in intact barley roots is proposed. In this scheme acrucial factor of selectivity is sufficient phloem recirculationof K⁺ by the aid of which K⁺ rich cortical cells are formednear the root tip. When matured these cells are suggested tomaintain a high cytoplasmic K/Na ratio due to K⁺ dependent sodiumextrusion at the plasmalemma and due to recovery of vacuolarK⁺ by Na/K exchange across the tonoplast. Key words: Potassium/Sodium selectivity, Vacuolar exchange, Xylem transport, Hordeum, Zea, Atriplex