The calcium dependence of auxin action in roots.
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Calcium↗
Biomedical subjects
K H Hasenstein
Publications and source records attributed to K H Hasenstein.
Cell wall pH and auxin transport velocity.
According to the chemiosmotic polar diffusion hypothesis, auxin pulse velocity and basal secretion should increase with decreasing cell wall pH. Experiments were designed to test this prediction. Avena coleoptile sections were preincubated in either fusicoccin (FC), cycloheximide, pH 4.0, or pH 8.0 buffer and subsequently their polar transport capacities were determined. Relative to controls, FC enhanced auxin (IAA) uptake while CHI and pH 8.0 buffer reduced IAA uptake. Nevertheless, FC reduced IAA pulse velocity while cycloheximide increased velocity. Additional experiments showed that delivery of auxin to receivers is enhanced by increased receiver pH. This phenomenon was overcome by a pretreatment of the tissue with IAA. Our data suggest that while acidic wall pH values facilitate cellular IAA uptake, they do not enhance pulse velocity or basal secretion. These findings are inconsistent with the chemiosmotic hypothesis for auxin transport.
Avena↗
Purification and identification of ABA-binding proteins and antibody preparation.
Maize root membranes were extracted and the solubilized proteins were affinity-purified using an ABA-BSA-Sepharose 4B matrix. The retained proteins were eluted with 4M urea or 10(-4)M ABA. ABA could elute the binding proteins but other phytohormones, such as IAA or GA3, could not. ABA binding activity was detected in ABA- and urea-elute fractions using competitive ELISA block tests and [3H]ABA binding assays. Scatchard analysis showed an apparent K(d) of 4.8 nM for the ABA binding activity of the protein. When ABA or urea eluate was loaded on a concanavalin-A-Sepharose column, the fraction eluted with 0.2 M methyl alpha-mannopyranoside still showed ABA binding activity, suggesting that ABA binding proteins are glycoproteins. Polyclonal antibodies against ABA binding proteins were raised using as immunogen ABA or urea eluate from the ABA-BSA-Sepharose column. The resulting antibodies not only recognized 56 kDa binding proteins but also blocked the binding of ABA to an ABA-specific antibody, indicating properties similar to anti-idiotypic antibodies. The purified antibodies will be suitable to purify and characterize putative ABA receptors.
Abscisic Acid↗