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Laser Doppler flux (LDF) was determined at the forefoot in 17 healthy volunteers and 16 patients with mild peripheral arterial occlusive disease. LDF was assessed simultaneously by two probes, one was unheated and the other was run with a probe holder temperature of 37 degrees C. During occlusion of the venous circulation a decrease between 43 and 61% was recorded in both groups and at both temperatures. When the leg was elevated there was an increase of about 60% in unheated skin; at 37 degrees C LDF was impaired significantly in patients. During leg dependency LDF decreased in 15 of the volunteers by 44 and 50% which is the result of the physiological vasoconstrictor response. In patients there was a decrease in unheated skin in 12 cases, in heated skin only in 8 cases. When pure oxygen was inhaled, LDF was unchanged in probands, but increased in patients when measured at 37 degrees C. Reactive hyperaemia flow was about three times higher in unheated skin than in heated skin. Reproducibility was best during leg elevation and was more reliable for measurements at 37 degrees C. Rhythmical variations had a frequency of about 4 cycles/min in healthy subjects and 2.6 cycles/min in patients. As a rule, in both groups frequencies at 37 degrees C were higher as compared with unheated skin. Patients had lower frequencies than probands at both temperatures. During intraarterial application of two differently acting drugs quite different reactions of LDF could be recorded. Measurements of LDF at 37 degrees C made differences between patients with PAOD and healthy volunteers more obvious. Moreover, vasomotional changes in skin blood flow could better be studied at this temperature.

In an effort to examine the specificity of the auxin transport system, the movement of a variety of growth substances and of auxin analogues through corn coleoptile sections was measured in both the basipetal and acropetal directions. In contrast to the basipetal, polar transport of the auxins indoleacetic acid (IAA) and 2,4-dichlorophenoxyacetic acid, no such movement was found for benzoic acid or for gibberellin A1. A comparison of the α- and β-isomers of naphthaleneacetic acid showed that the growth-active α-form is transported, but not the inactive β-analogue. Both the dextro (+) and leavo (-) isomer of 3-indole-2-methylacetic acid showed the basipetal movement characteristic of IAA, the dextro isomer being more readily transported than the (-)-form. In this instance, too, the transport was roughtly proportional to the growth promoting activity. The antiauxin p-chlorophenoxyisobutyric acid inhibited auxin transport as it inhibited auxin-induced growth. These results agree with the hypothesis that processes involved in auxin transport are closely linked to or even identical with the primary auxin action.

Plasma membrane-rich fractions were prepared from maize coleoptiles by low-shear homogenization and differential and sucrose-gradient centrifugation. Plasma membrane fragments were identified using a specific cytochemical stain based on phosphotungstic acid prepared in chromic acid. In a comparison of 10 different cell fractions of varying plasma membrane content, the N-1-napthylphthalamic-acid (NPA)-binding activity of the fractions was directly proportional to the content of plasma membrane. The NPA binding appears to be strong K M between 10(-8) and 10(-7) M) but non-covalent. NPA is known to inhibit auxin transport efficiently and quickly. Thus, the results are consistent with the localization of auxin transport sites at the plasma membrane of plant cells.

Within 20 min of its application, auxin enhances the transport processes that move auxin molecules through coleoptile tissue. The effect was observed after treatment with indoleacetic acid and α-naphthaleneacetic acid, but not with growth-inactive auxin analogues.

Wild-type corn coleoptiles showed an initial downward bending upon transfer from the vertical to the horizontal position. Strong upward curvature started only 15-30 min after the begin of horizontal exposure.Little, if any at all, initial downward geotropic bending was found with amylomaize coleoptiles at 1 X g. With stronger stimuli (10 or 20 X g) the amylomaize mutant reacted initially strongly in the "wrong" direction, i.e. opposite to the later response.When wild-type coleoptiles had been symmetrically prestimulated for 60 min with alternating 2-min horizontal exposures from opposite sides, no initial downward bending occurred if the plane of horizontal exposure was maintained from pretreatment to the continuous horizontal stimulation of the test. If, however, the coleoptiles were rotated 90° around their long axis between pretreatment and test, the initial downward bending reaction developed as in the non-prestimulated controls. Thus changes in reactivity remained localized to the site of stimulation.Following the same pretreatments used for the curvature measurements, lateral (3)H-IAA transport was measured in coleoptile segments for 10 or 12.5 min. The auxin distribution found was strikingly parallel to the bending for all pretreatments.The dependence of reaction pattern on the duration of prestimulation in the same plane was tested. The function indicates a "half life" of 10-20 min for the change in sensitivity. The findings are discussed in view of a model of overstimulation and adaptation.

The early time course (0-30 min) of the action of auxin (3-indoleacetic acid) on the elongation of segments from corn coleptiles was studied, using a high-resolution continuous recording technique. Two different effects of auxin were observed: (1) After addition of low auxin concentrations (2 x 10(-7)M) to 4-mm sections, a very rapid (2-3 min) enhancement of elongation was found. Similar early responses were seen following the addition of low concentrations of the methyl ester of indoleacetic acid. (2) Following a large step-up in the auxin level (10(-5), 10(-4), or 10(-3)M), a rapid transient decrease was observed one to three minutes after the addition of indoleacetic acid. It lasted 10-15 minutes at which time the steady rate of auxin-promoted elongation became evident. Similar kinetic patterns of auxin effects other than on elongation and the implications of the findings on hypotheses of the primary action of auxin are discussed.

Movement of radioactive auxins was analysed in corn coleoptile sections. The results support the idea that processes involved in the transport of indoleacetic acid (IAA) are specific for growth-promoting auxins.Inhibition of IAA transport by triiodobenzoic acid is caused by a reversible block of the exit; the auxin held back remains in the transport pool. The observed increase in immobilization may be a secondary effect caused by the increased concentration of free IAA in the tissue.Auxin molecules are most likely transported by anon-covalent mechanism. IAA and naphthaleneacetic acid (NAA) move through the cell and exit as free molecules. A search for a transient auxin complex, chaseable as required for any transport carrier intermediate, yielded negative results. No(18)O was lost from NAA labeled with(18)O in the carboxyl group during transport of the auxin through coleoptile tissue.After application of IAA to auxin-depleted tissue, the transport rate undergoes oscillations with a period length of ca. 25 min.The movement of the auxin 2.4-dichlorophenoxyacetic acid which is usually sluggish, increased several times if some IAA was added. Auxin, thus, stimulates its own transport.A model is discussed in which auxin-binding to the plasma membrane and reversible changes of membrane conformation may provide a basis for active secretion and for the observed cooperativity.

In coleoptiles of the amylomaize corn mutant (AM), the amyloplasts are much reduced in size in comparison with the wild type corn (WT), permitting a comparison of geotropic responsiveness as related to lateral displacement of amyloplasts and lateral transport of auxin. The amyloplasts of AM showed 30-40% lesser lateral redistribution in response to horizontal exposure in comparison with WT. With geotropic stimulation, the lateral transport of auxin in the direction of growth was 40-80% less, and the geotropic curvature by the coleoptiles was also significantly less in the mutant as compared with WT. These correlations support the hypothesis that the starch plastids serve as gravity sensors in the geotropic responses of coleoptiles.

Auxin transport was studied in coleoptile sections that were stimulated geotropically. The early time course of auxin-transport asymmetry was measured. An initial phase in which more IAA was delivered into the receptor for the upper half was found after 5 min of horizontal exposure. After about 15 min this was followed by the expected known asymmetry in which more auxin flows in the lower side of the coleoptile. Upon return of the coleoptile to a vertical position, this asymmetry disappeared within 30 min.Earlier correlations of geosensitivity of the auxin transport system with sedimentation of amyloplasts in comparisons of wild type corn and an amylomaize mutant were confirmed and extended. It was also shown that, in contrast to the geotropic effect, phototropically induced lateral auxin asymmetry was not significantly different in wild type and amylomaize. Eleven other single-gene endosperm starch mutants of corn were compared to their corresponding normals. In all pairs, if a difference in geosensitivity of lateral auxin transport was present, it was correlated with a parallel difference in amyloplast sedimentation: e.g., sugary 1 ("67") had an amyloplast asymmetry index of 0.32 and a 13% gravity effect on auxin transport; the paired wild-type had both a greater amyloplast asymmetry (0.61) and a greater gravity effect on transport (23%).Correlations between gravity effects on auxin transport and amyloplasts were also shown in comparisons of apical and basal sections of corn, oat and Sorghum coleoptiles.Further results, confirming the increased effect of centrifugal acceleration greater than 1xg on lateral auxin transport and on curvature, are in agreement with the hypothesis that the pressure exerted by amyloplasts, acting as statoliths, locally stimulates the auxin transport system in the individual cells.

Inversion of corn coleoptile sections resulted in a 10-20% inhibition of basipetal transport of 3-indoleacetic acid (IAA) and a more pronounced inhibition (20-50%) of the transport of 1-naphthaleneacetic acid (NAA).The effect of inversion on basipetal NAA transport was compared in wild-type corn and in the amylomaize mutant which contains smaller and slower sedimenting amyloplasts: the gravity induced inhibition was higher in the wild type coleoptiles (27% versus 9%).In wild type the inhibitory effect on basipetal NAA transport appeared within less than 30 min after inversion; then the effect remained relatively constant over at least 2 hr of transport. When the sections were returned to the upright position the transport rate increased, reaching the level of upright controls within 30 min.An effect of gravity on lateral transport of NAA was also demonstrated and shown to be expressed within 10 min after placing the tissue horizontally.When basipetal transport was tested in the direction of gravity and/or centrifugal acceleration, auxin movement incrased with increasing acceleration. Transport against centrifugal acceleration (10 x g) was less than transport of control sections (inverted at 1 x g).The results agree with the hypothesis that starch statoliths act by a pressure mechanism on the membrane transport system of auxin.

When low concentrations (e.g. 10(-6) M) of labelled 3-indoleacetic acid ((14)C-IAA) or α-naphthaleneacetic acid ((14)C-NAA) are added in vitro to homogenates of corn coleoptiles, radioactivity is reversibly bound to pelletable particles. From the saturation kinetics of the binding it is possible to estimate an apparent K M between 10(-6) M and 10(-5) M and a concentration of specific sites of 10(-7)-10(-6) M per tissue volume.The binding is auxin-specific. Among many compounds tested, only auxins and such auxin analogues that are known to interact directly with auxin in transport and/or growth were found to interfere with this binding. For instance, the growth-active D-dichlorophenoxyisopropionic acid at 10(-4) M inhibits (14)C-NAA binding more than the less active L-isomer.The auxin-binding fractions are practically free of DNA and cytochrome-C oxidase and contain binding sites for 1-naphthylphthalamic acid. The results are discussed in context with the hyothesis-derived mainly from physiological data-that auxin receptors are localized at the plasma membrane.