Rudolf Behl

Induction of a high-capacity nitrate-uptake mechanism in barley roots prompted by nitrate uptake through a constitutive low-capacity mechanism.

Roots of nitrate-starved and nitrate-pretreated seedlings of Hordeum vulgare were used to investigate the induction of a high-capacity uptake mechanism for nitrate. When exposed to 0.2 mmol·l-1KNO3, nitrate-starved roots took up nitrate at a rate of approx. 1 μmol·(g FW)-1·h-1; K+ was absorbed at a rate ten-times higher. Nitrate uptake accelerated after a lag of about 1 h, until it matched the rate of K+ uptake about 4 h later. p-Fluorophenylalanine (FPA), which prevents the synthesis of functioning proteins, suppressed the development of the high-capacity mechanism. Pretreatment of the roots with 0.2 mmol·l-1 Ca(NO3)2 for 24 h established the high-capacity mechanism. Pretreated roots were able to absorb nitrate at high rates immediately upon exposure to 0.2 mmol·l-1KNO3, in the absence or presence of FPA. The high-capacity mechanism, once established, appeared to have a protein turnover as slow as that of the low-capacity mechanism or that of the mechanism involved in the uptake of K+. In contrast, the mechanisms for the transport of nitrate and K+ into the xylem vessels were completely blocked by FPA within 1 h of application, confirming earlier evidence for a rapid turnover of the transport proteins in the xylem parenchyma.Nitrate reduction proceeded at rates which were roughly one-tenth as large as the rates of the respective nitrate-uptake processes, indicating that nitrate-reductase activity was determined by the rate of nitrate uptake and not vice versa.We conclude that the formation of a high-capacity nitrate-uptake mechanism in barley roots occurs in response to nitrate uptake through a constitutive mechanism of low capacity which appears to function as a sensing mechanism for nitrate in the environment of the roots.

Close coupling between extrusion of H+ and uptake of K+ by barley roots

Extrusion of H+ by intact barley (Hordeum vulgare L.) roots was automatically titrated. Simultaneously, uptake of K+ into the roots, transport of K+ through the roots, and (as a residual term) accumulation of K+ within the root tissue were determined. When no monovalent cation was present in the medium the steady rate of H+ release was close to zero. Addition of K+ stimulated H+ extrusion within less than 1 min. The stimulation of H+ release was apparently limited only by the movement of K+ through the apoplast of the roots. The steady rate of H+ extrusion depended on the availability of external K+ and saturated at a K+ concentration of about 100 μmol· dm-3. Half-maximum rates of net K+ uptake and H+ extrusion were reached at a K+ concentration of about 10 μmol·dm-3. With (slowly absorbable) sulfate as the only anion present, the stoichoimetry between H+ release and net K+ uptake was one. In conclusion, the uptake of K+ across the plasmalemma of the cells of the root cortex is electrically coupled to H+ extrusion.

Transport und Stoffwechsel von 2-[14C]Abscisinsäure in Wurzelsegmenten von Phaseolus coccineus L.

SummaryMovement of 2-[14C]ABA through 1.5 cm and 5 cm long root segments of P. coccineus L. was acropetally polarised. The velocity of acropetal transport of [14C]ABA in 1.5 cm long segments was 4–5 mm·h-1. Up to 11 h after the start of incubation [14C]ABA could be extracted unchanged. Beyond this time radioactivity became associated to an unidentified compound, which shows chromatographic qualities similar to those of Milborrows “Metabolite C” (Biochemistry & Physiol. Plant Growth Substances, 1531, Runge Press Ottawa, 1968; and Chem. Comm. 966, 1969).

Die Wirkung von Licht auf den Transport von 2-[14C]Abscisinsäure in Bohnenwurzelsegmenten

Light promotes the acropetal movement of 2-[(14)C]ABA through root segments of Phaseolus coccineus L. The promotion occurs only when the segments are irradited during the transport period. Red light and blue light are as effective as white light. There is no significant promotion when the segments are irradiated with green light or when they are kept in darkness during the transport period after preceding light treatment. Light has no effect on basipetal ABA-transport.SummaryLight promotes the acropetal movement of 2-[14C]ABA through root segments of Phaseolus coccineus L. The promotion occurs only when the segments are irradited during the transport period. Red light and blue light are as effective as white light. There is no significant promotion when the segments are irradiated with green light or when they are kept in darkness during the transport period after preceding light treatment. Light has no effect on basipetal ABA-transport.

Lokalisation des akropetalen Transports von 2-[14C]Abscisinsäure in Wurzeln von Phaseolus coccineus L. und Hinweise für einen Radialtransport von ABA zwischen Zentralzylinder und Rindenzylinder

SummaryAcropetal polarity of ABA-transport in roots of runner beans is found to be located strictly in the stele. ABA movement in the cortex is very slow and unpolar. Experiments on partly decorticated and desteled roots gave evidence for a radial ABA-transport between the stele and cortex. Thus an ABA distribution quotient stele/cortex of 12/1 (expressed on tissue volume basis) is established after 9 h ABA incubation. The radial ABA-translocation is strongly inhibited at low temperature.Acropetal polarity of ABA-transport in roots of runner beans is found to be located strictly in the stele. ABA movement in the cortex is very slow and unpolar. Experiments on partly decorticated and desteled roots gave evidence for a radial ABA-transport between the stele and cortex. Thus an ABA distribution quotient stele/cortex of 12/1 (expressed on tissue volume basis) is established after 9 h ABA incubation. The radial ABA-translocation is strongly inhibited at low temperature.

Lokalisation des akropetalen Transports von 2-[14C]Abscisinsure in Wurzeln von Phaseolus coccineus L. und Hinweise fr einen Radialtransport von ABA zwischen Zentralzylinder und Rindenzylinder@@@Localisation of acropetal transport of 2-[14C]abscisic acid in roots of Phaseolus coccineus L. and evidence for a radial ABA-translocation between stele and cortex

SummaryAcropetal polarity of ABA-transport in roots of runner beans is found to be located strictly in the stele. ABA movement in the cortex is very slow and unpolar. Experiments on partly decorticated and desteled roots gave evidence for a radial ABA-transport between the stele and cortex. Thus an ABA distribution quotient stele/cortex of 12/1 (expressed on tissue volume basis) is established after 9 h ABA incubation. The radial ABA-translocation is strongly inhibited at low temperature.Acropetal polarity of ABA-transport in roots of runner beans is found to be located strictly in the stele. ABA movement in the cortex is very slow and unpolar. Experiments on partly decorticated and desteled roots gave evidence for a radial ABA-transport between the stele and cortex. Thus an ABA distribution quotient stele/cortex of 12/1 (expressed on tissue volume basis) is established after 9 h ABA incubation. The radial ABA-translocation is strongly inhibited at low temperature.

Die Wirkung von Licht auf den Transport von 2-[14C]Abscisinsure in Bohnenwurzelsegmenten@@@Effect of light on transport of 2-[14C]abscisic acid through root segments of runner beans

Light promotes the acropetal movement of 2-[(14)C]ABA through root segments of Phaseolus coccineus L. The promotion occurs only when the segments are irradited during the transport period. Red light and blue light are as effective as white light. There is no significant promotion when the segments are irradiated with green light or when they are kept in darkness during the transport period after preceding light treatment. Light has no effect on basipetal ABA-transport.SummaryLight promotes the acropetal movement of 2-[14C]ABA through root segments of Phaseolus coccineus L. The promotion occurs only when the segments are irradited during the transport period. Red light and blue light are as effective as white light. There is no significant promotion when the segments are irradiated with green light or when they are kept in darkness during the transport period after preceding light treatment. Light has no effect on basipetal ABA-transport.

Transport und Stoffwechsel von 2-[14C]Abscisinsure in Wurzelsegmenten von Phaseolus coccineus L.@@@Transport and metabolism of 2-[14C]abscisic acid in root segments of Phaseolus coccineus L.

SummaryMovement of 2-[14C]ABA through 1.5 cm and 5 cm long root segments of P. coccineus L. was acropetally polarised. The velocity of acropetal transport of [14C]ABA in 1.5 cm long segments was 4–5 mm·h-1. Up to 11 h after the start of incubation [14C]ABA could be extracted unchanged. Beyond this time radioactivity became associated to an unidentified compound, which shows chromatographic qualities similar to those of Milborrows “Metabolite C” (Biochemistry & Physiol. Plant Growth Substances, 1531, Runge Press Ottawa, 1968; and Chem. Comm. 966, 1969).