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41.
Vacuolar Na/K Exchange, its Occurrence in Root Cells of Hordeum, Atriplex and Zea and its Significance for K/Na Discrimination in Roots 总被引:1,自引:0,他引:1
JESCHKE WOLF DIETER; STELTER WILFRIED; REISING BERND; BEHL RUDOLF 《Journal of experimental botany》1983,34(8):964-979
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 cytoplasmwas 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 相似文献
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43.
WILFRIED WESTHEIDE 《Zoologica scripta》1990,19(2):165-167
A syllid species new to science is described from intertidal sandy sediments on the cast coast of India, for which a new genus is erected: Psammosyllis aliceae gen. et sp.n. Incorporation into either the Eusyllinae or the Exogoninae is unresolved, because it possesses characters of both of these poorly defined subfamilies. 相似文献
44.
A new hesionid. Sinohesione genitaliphora gen. et sp. n., is described from intertidal sandy sediments of Hainan Island, China. It differs from hitherto known hesionids by the presence of external genital organs in both sexes. In the males there is one pair of sae-like appendages, each bearing a tube-shaped penis, on chaetiger 10. In the females the paired sae-shaped organs are situated on chaetiger 12. Reconstructions of semi- and ultrathin sections show that a long, heavily coiled sperm duct opens at the tip of each penis. The duct opens with a ciliated funnel into a seminal vesicle in chaetiger 9. Prominent gland cells surround the sperm duct for the most part. The female genital organs each have two openings; one of which leads to a blind ending seminal receptacle. The other is the external pore of a ciliated oviduct that originates as an open funnel in the coelom of chaetiger 10. The functional and phylogenetic significance of these structures is discussed. 相似文献
45.
DIEKMANN WILFRIED; HEDRICH RAINER; RASCHKE KLAUS; ROBINSON DAVID G. 《Journal of experimental botany》1993,44(10):1569-1577
Guard cell protoplasts were prepared from young leaves of peaplants. Under hypertonic conditions they shrink and large numbersof endocytotic (osmocytotic) vacuoles are formedby invagination of the plasma membrane. In thin section theseare indistinguishable from other small vacuoles (mini-vacuoles)which are formed by fragmentation of the large central vacuole.However, the two types of vacuole can be individually recognizedby labelling the central vacuole with neutral red and by performingthe osmotic shrinkage with fluorochromes such as Lucifer Yellow-CHor Cascade Blue present in the extracellular medium. Osmocytoticvacuoles do not fuse with the plasma membrane nor with the mini-vacuolesduring a subsequent swelling phase. After several hours, osmocytosedLucifer Yellow gradually leaks out of the endocytotic vacuoleswhen protoplasts are returned to hypotonic conditions. Thisleakage is not prevented by probenecid at concentrations (2050mmol m3) which do not give rise to pathological changesin protoplast ultrastructure. In order to determine the relevanceof these observations to the situation in planta, intact guardcells in epidermal strips were first allowed to accumulate neutralred in their vacuoles and then subjected to osmotic shrinkagein the presence of external Lucifer Yellow. Osmocytotic vacuoleswere not formed, although the production of mini-vacuoles wasfrequently observed. Key words: Guard cell protoplasts, fluid phase markers, Pisum sativum, probenecid, osmocytosis, shrinkage-swelling cycles 相似文献
46.
Role of Copper Binding, Absorption, and Translocation in Copper Tolerance of Agrostis gigantea Roth 总被引:3,自引:0,他引:3
The capacity of roots to accumulate and retain copper was examinedin two clones of Agrostis gigantea which differ in their toleranceto excess copper. Root elongation growth in the non-tolerantclone was completely inhibited by 16 mmol m3 Cu whereas40 mmol m3 was required for inhibition in the tolerantclone. The amount of readily exchangeable copper was greaterin roots of the tolerant clone than in the non-tolerant clone.The higher capacity for binding copper did not prevent the entryof copper into the cells of intact or excised roots of the tolerantclone. Roots of both clones contained similar amounts of copperafter removal of the readily exchangeable fraction. More copperwas translocated to the shoots of the tolerant than the non-tolerantclone. The explanation of copper tolerance in Agrostis giganteamust be sought in areas other than those of differences in grosscopper absorption and retention by roots. 相似文献