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     

Effect of Temperature on Carbohydrate Metabolism in Potato Plants

The effect of temperature on partitioning of newly fixed ¹⁴Cbetween the various carbohydrate fractions was studied in differentplant organs of three potato varieties. Incorporation of ¹⁴Cinto starch in the tubers was reduced at high temperatures,but the amount of labelled sucrose increased. In all varietiesthe incorporation of ¹⁴C into the cell wall components in theapex of the plant and in the stem, as well as its incorporationinto starch in the stem, was increased at high temperatures.The variety Norchip, which was found to be less sensitive tohigh temperature as indicated by carbon translocation to thetubers, was found to be less affected also in terms of ¹⁴C incorporationinto starch in the tubers. We suggest that high temperatureaffects carbon metabolism in the various plant organs and theresulting changes are associated with the change in the partitioningof assimilates between these organs.     

Childhood Association and Sexual Attraction: A Further Test of the Westermarck Hypothesis

A preliminary study of household registration records from Taiwan supports Edward Westermarck's contention that intimate childhood association promotes sexual aversion. Women who are forced to marry a childhood associate bear fewer children than those who marry a stranger. They are also more likely to leave their husband by divorce or avoid him in favor of other men. This evidence suggests that the incest taboo does not prohibit what men's feelings incline them to do, as Westermarck's critics argue, but that it is instead an expression of these feelings, socially unnecessary but psychologically inevitable. [incest taboo, law, China, Taiwan]     

Myxosoma cerebralis: In Vitro Sporulation of the Myxosporidan of Salmonid Whirling Disease

SYNOPSIS. Trophozoites and other pre-spore stages of the myxosporidan Myxosoma cerebralis were taken from infected rainbow trout ( Salmo gairdneri ) and cultured in vitro. Cultures eventually yielded mature spores capable of discharging their polar capsules. This is the first report of culture of a myxosporidan.     

Strong correlation between isoprene emission and gross photosynthetic capacity during leaf phenology of the tropical tree species Hymenaea courbaril with fundamental changes in volatile organic compounds emission composition during early leaf development

Changes of the volatile organic compounds (VOC) emission capacity and composition of different developmental stages of the tropical tree species Hymenaea courbaril were investigated under field conditions at a remote Amazonian rainforest site. The basal emission capacity of isoprene changed considerably over the course of leaf development, from young to mature and to senescent leaves, ultimately spanning a wide range of observed isoprene basal emission capacities from 0.7 to 111.5 µg C g^?1 h^?1 during the course of the year. By adjusting the standard emission factors for individual days, the diel courses of instantaneous isoprene emission rates could nevertheless adequately be modelled by a current isoprene algorithm. The results demonstrate the inadequacy of using one single standard emission factor to represent the VOC emission capacity of tropical vegetation for an entire seasonal cycle. A strong linear correlation between the isoprene emission capacity and the gross photosynthetic capacity (GP_max) covering all developmental stages and seasons was observed. The present results provide evidence that leaf photosynthetic properties may confer a valuable basis to model the seasonal variation of isoprenoid emission capacity; especially in tropical regions where the environmental conditions vary less than in temperate regions. In addition to induction and variability of isoprene emission during early leaf development, considerable amounts of monoterpenes were emitted in a light‐dependent manner exclusively in the period between bud break and leaf maturity. The fundamental change in emission composition during this stage as a consequence of resource availability (supply side control) or as a plant's response to the higher defence demand of young emerging leaves (demand‐side control) is discussed. The finding of a temporary emergence of monoterpene emission may be of general interest in understanding both the ecological functions of isoprenoid production and the regulatory processes involved.