Hormonal regulation of the leaf blade movement of Drosera capensis

Several Drosera species show a bending of the leaf blade as a slow reaction to a prey. In Drosera capensis L. this bending is enhanced by a simultaneous application of IAA either to the prey or to the leaf tip, and IAA alone can induce a curvature of the leaf. This curvature is always to the upper side of the leaf independent of the side of IAA application. PCIB (1 m M ), and TIBA (0.1 m M ) inhibit the bending reversibly. The inhibition by ABA (1 m M ) is not reversible. A TIBA barrier between the prey and the tip of the leaf reduces the bending reaction, whereas application of TIBA to the basal part of the leaf has no effect. In the former case 35% of the leaves showed a strong bending just on the apical side of the TIBA barrier. It is concluded that the bending is a consequence of an internal auxin stream from the tip of the leaf to the bending point, induced by the prey.     

Kinetics of indole acetic acid-induced growth in hypocotyl sections of Vigna mdiata

The kinetics of auxin-induced elongation of segments from Vigna radiata (L.) Wilczek hypocotyls have been investigated using auxanometer measurements. Doseresponse curves were established for several well-defined parameters of the growth response. The experimental data revealed that different kinetic parameters were affected differently by increasing auxin concentrations. The dose-response curves are slightly sigmoid for fresh weight, nearly bell-shaped for total elongation or maximal elongation rate, and nearly linear for maximal growth acceleration. The effects of auxin concentration on regulation of growth orientation are discussed.
A biphasic response is observed mainly with segments taken from the middle of the hypocotyl ('C') which exhibit maximal growth rates. Segments from other levels, with lesser growth potentials, exhibit a very weak response. The two successive phases may then require different maturation states. Kinetics of the acceleration curves are very similar all along the hypocotyl and remain very homogeneous with increasing IAA concentrations.     

Temporal morphology and cap formation in Acetabularia--II. Effects of morphactin and auxin

In order to support the hypothesis that circadian rhythms are implicated in cap formation, experiments were undertaken on the possible time-dependency of the effects of (a) a competitive inhibitor of auxins, morphactin and (b) of auxin (IAA). It was found that: (i) the inhibitory effect of morphactin varies dramatically with the time at which the several weeks' treatment was first begun; (ii) the maximum inhibition varies with development and decreases with time; (iii) IAA accelerates cap formation when the algae are submitted to IAA during the exponential growth phase; the effect is time dependent and decreases with time; (iv) IAA first applied on smaller algae has a transient inhibitory effect which is time dependent; (v) anucleate fragments also respond differentially to an IAA treatment begun at several times in the 24-hr cycle, most clearly when newly formed mRNA have been accumulated and (vi) the effect of iAA is not cumulative with that of a LD shift; that of morphactin is not, or only slightly, improved by a LD shift.     

The mechanism of auxin uptake and accumulation in moss protonemata

Protonemata of the moss Funaria hygrometrica Sibth. (L.) show a strong pH dependence for auxin accumulation. IAA uptake is enhanced when the pH of the incubation medium is lowered from 7.6 to 4. In low light intensity grown protonemata (0.56 W m⁻²) a component of IAA uptake could be saturated by IAA; efflux of IAA could be inhibited by 2,3,5-triiodobenzoic acid. This is explained by the presence of influx and efflux carriers for IAA. In protonemata grown at high light intensity (2.00-2.30 W m⁻²) these carriers could not be shown to be present. These results are discussed with regard to the different physiological behavior of moss protonemata grown under different light conditions.     

Modification of the cysteine residues of cytochrome P-450cam with 2-bromoacetamido-4-nitrophenol

The Pseudomonas putida cytochrome P-450 was alkylated with the SH-reagent, 2-bromoacetamido-4-nitrophenol. One out of eight cysteine residues present in the enzyme reacted rapidly while another 3 ～ 4 cysteine residues were gradually alkylated at longer reaction times. The derivative in which the most reactive cysteine residue was labeled with this reagent was hydrolyzed with trypsin and a tryptic peptide isolated. From the amino acid composition and end group analysis of the peptide, the rapidly reacting cysteine residue was shown to be Cys 355. This cysteine residue is probably exposed on the surface and is involved in the dimerization of the enzyme. The amino acid sequence about cysteine 355 shows sequence homology with residues 429–445 of the rat liver cytochrome P-450-LM-2.     

Expression plasmid vectors containing Escherichia coli tryptophan promoter transcriptional units lacking the attenuator

Two DNA fragments which contain the Escherichia coli tryptophan promoter-operator region but lack the attenuator have been used in the construction of a series of pAT153 based plasmids suitable for the regulated expression of foreign genes in E. coli. The first, a 139-bp HhaI fragment includes 59 bp of the trp leader sequence, ending within the “attenuator peptide” coding sequence, eleven codons from the N-terminus. A fusion-type expression plasmid incorporating this fragment has been constructed. The second, a 99-bp HaeIII-TaqI fragment contains no coding sequence but includes the “attenuator peptide” SD site situated 4 bp upstream of the TaqI site. This fragment has been incorporated in expression vectors which result in the direct expression of cloned gene sequences. To further maximise expression, plasmids with directly repeating trp promoter HaeIII-TaqI units have been constructed.     

The use of IAA to overcome interspecific hybrid inviability in reciprocal crosses between Nicotiana tabacum L. and N. repanda Willd.

Summary Flowering hybrid plants were obtained from reciprocal crosses between N. tabacum L. (2n=48) and N. repanda Willd. (2n = 48), in which cross incompatibility and hybrid inviability were manifested. Stylar pollination and ovule culture were used to overcome the cross incompatibility of stylar barriers and ovular death. It was shown that application of 2 mg/l indole-3-acetic acid (IAA) during the growth period, from the fiveto six-leaf stage to the flowering stage, is a useful and easy method to overcome hybrid inviability.     

Stereoselectivity and affinity in molecular pharmacology. III. Structural aspects in the mode of action of natural and synthetic auxins

Analysis of available potency estimates for 35 pairs of enantiomeric arylcarboxylic acids with auxin activity (flax-root-growth inhibition test) revealed extensive correlations between the activity of the more potent and less potent isomers, as well as between the log of the ratio of potencies and the log potency of the more active isomer when structurally similar analogs are compared. 5 structural subgroups were discernible (n, eudismic-affinity quotient (EAQ), r2); (1) arylpropionic acids (6, -0.36, 0.66); (2) 2-naphthoxy-carboxylic acids (6, +1.07, 0.99); (3) 1-naphthoxycarboxylic acids (3, +1.56, 0.96); (4) ortho-substituted phenoxycarboxylic acids (10, +0.97, 0.96) and (5) ortho-unsubstituted phenoxycarboxylic acids (10, +0.56, 0.70). For achiral lower homologs such as auxin itself 3-indolyl-acetic acid (IAA), phenoxyacetic acid and 1-naphthoxyacetic acid, extrapolated potencies were found to agree well with experimental values. On the basis of these observations an auxin receptor is postulated and binding arrangements are described which explain most of the experimental data available. A 3-point attachment when allowed is the only binding mode compatible with the reported data.