Geotropic Response Research Articles

Regulation of Root Growth by Auxin-Ethylene Interaction

A large portion of indoleacetic acid (IAA)-induced inhibition of excised root tips and virtually all such inhibition of intact roots are the result of IAA-dependent ethylene production. Under certain conditions an additional effect of IAA accounts for a small portion of the inhibition of excised root tips. Ethylene production in response to applied IAA is governed by the level of applied auxin found inside the root. Evidence is presented to confirm the participation of ethylene in the geotropic response of roots.

Effect of x-ray irradiation on regeneration and geotropic function of barley root caps.

SummaryRoot-cap regeneration and geotropic function after removal of the differentiated part of the cap were studied in barley roots. Geotropic response was regained when about 35 per cent of the root-cap length was regenerated. The geotropic response progressively increased with increasing length of the differentiated part of the root cap. Irradiation of the root-cap meristem inhibited the regeneration of the root cap. After irradiation in air, the geotropic response of the regenerated root cap decreased with increasing doses. Hypoxic (about 12 p.p.m. of O2 in a gas phase) conditions during irradiation with doses as high as 2400 rads completely protected the function of the partially regenerated root cap. Iodine tests on starch statoliths, and electron micrographs of root-cap cells regenerated from cap initials irradiated in the presence of oxygen, revealed a reduction in the number and size and changes in the chemical composition of starch statoliths in the amyloplasts; but there were no such effects in...

The Geoelectric Effect in Plant Shoots

The development of the geoelectric effect has been followed in Zea coleoptiles with a flowing solution electrode system, and its dependence upon auxin concentration gradients and aerobic metabolism assessed. A symmetrical source of IAA can effectively replace the coleoptile tip in allowing the geo electric potential to occur. The diffusate from coleoptile tips, when applied asymmetrically to the apex of a vertical decapitated coleoptile, generates a potential difference across the coleoptile indistinguishable from that induced by the asymmetrical application of IAA. Asymmetrical application of IAA to vertical Avena and Zea coleoptiles and Helianthus hypocotyls induces closely similar responses. Neither the geoelectric effect nor a geotropic response develops when intact Zea coleoptiles are placed horizontally after being deprived of oxygen, but they both occur when an aerobic atmosphere is restored. The lateral potential difference induced by the asymmetrical applica tion of IAA to the apex of a vertical coleoptile does not occur under anoxic conditions. With a static-drop electrode system and a decapitated Zea coleoptile, a potential difference develops immediately after reorientation of the coleoptile into the horizontal position, and attains a maximum value after about 10 min. This potential difference can be further increased by the asymmetrical application of IAA to the lower half of the apical cut surface of the coleoptile. Our data support the view that both the geoelectric potential and the geotropic response are due to the IAA concentration gradient which arises from the lateral transport of this substance from the upper to the lower half of the horizontal shoot. They also bear out our previous conclusions that the 'geoelectric potential' observed with static-drop electrodes and an intact shoot, is the resultant of two processes. The first is a physical phenomenon arising in the electrodes, or between the electrodes and the plant tissue, and the second arises in the living tissues of the shoot as the result of gravity-induced changes in auxin distribution.

Geotropism and the lateral transport of auxin in the corn mutant amylomaize

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.

THE INFLUENCE OF ACROPETALLY TRANSPORTED INDOLEACETIC ACID ON THE GEOTROPISM OF INTACT PEA ROOTS AND ITS MODIFICATION BY 2, 3, 5-TRIIODOBENZOIC ACID

SUMMARY The geotropic response of horizontal intact pea seedling roots was rapidly influenced by indole-3-acetic acid (IAA), which was applied in narrow rings of lanolin paste a few cm from the apex. The applied auxin thus likely was transported in the acropetal direction in these roots. The influence of IAA was strongly reduced when 2, 3, 5-triiodobenzoic acid (TIBA) was applied to the roots at the apical side of the IAA-ring. When TIBA was applied alone at various distances from the apex of the horizontal roots it also inhibited the geotropic curvature. The transport of auxin in the apical region of horizontal roots probably occurred both in the acropetal and in the basipetal direction.

Elimination of Geotropic Responsiveness in Roots of Cress (Lepidium sativum) by Removal of Statolith Starch

Roots of garden cress (Lepidium sativum L.) seedlings were made starch-free by treatment with gibberellic acid and kinetic for 29 hours at 35°C in the dark. After 3 hours of temperature adaptation at 21°C the starch-depleted roots were unable to respond to gravity, but elongated 0.48 mm por hour. Under the same conditions control roots pretreated in plain water at 21 and at 35°C elongated 0.64 and 0.33 mm per hour, respcetively (at 21°C). When the hormone-treated seedlings were illuminated, their roots reformed starch after 20 to 24 hours; simultaneously the geotropic responsiveness was restored. The results are interpreted in support of the statolith theory.

Effects of 14 MeV neutrons and 300 kVp x-rays on geotropic response and sedimentation velocity of statoliths in barley roots.

SummaryThe effects of 300 kVp x-rays and 14 MeV neutrons on the geotropic response and the sedimentation of statoliths in the statocytes of barley roots have been studied. 24 hours after irradiation with 100 rads of x-rays or 60 rads of 14 MeV neutrons in air, the geotropic response was inhibited by 25 and 15 per cent, respectively. Higher doses up to 800 rads of x-rays or 220 rads of neutrons had no greater effect. Irradiation in the absence of oxygen did not affect the geotropic response, and a slight enhancement was observed. Sedimentation of statoliths was slowed down after irradiation in air and speeded up after irradiation in the absence of oxygen. The hypothesis is put forward that the effects of radiation on geotropic response are due to the changes in the viscosity of the protoplasm; irradiation in air increases the viscosity; whereas irradiation in the absence of oxygen decreases it. Mechanisms for the effects of radiation on the viscosity of the protoplasm are suggested.

Auxin transport in roots

Light promotes the net acropetal movement of (14)C through 6-mm subapical segments of dark-grown roots of Zea mays supplied at their basal ends with 1 μM IAA-1-(14)C in agar blocks. This promotion occurs only when the segments are irradiated during the transport period, and both red and blue light appear to be as effective as white light at the radiant flux densities used in this investigation. The promotion is not found if the segments are pretreated with light and then returned to darkness before the trasport of IAA-1-(14)C is determined. The very slight basipetal movement of (14)C through the segments supplied with an apical source of IAA-1-(14)C is unaffected by light.Only one radioactive substance is found in the apical receiver blocks. This substance has an Rf virtually identical to those of the stock solution of IAA incorporated into the donor block and of unlabelled IAA. The movement of radioactivity into the receiver blocks through, the illuminated segments therefore appears to reflect the movement of IAA. Light thus increases the acropetal movement of IAA through the Zea root segment.The primary roots of Zea mays var. Giant Horse Tooth seedlings grown in total darkness do not exhibit a positive geotropic response. When the seed is orientated with the embryo uppermost the radicle grows out horizontally. On exposure to light, however, the roots bend down. This reaction appears about 3-9 hours after the onset of illumination, and white, red and blue light appear to be equally effective at the flux densities employed in this study. Green light in the spectral band between 510-530 nm did not appear to induce this positive geotropic responsiveness.

GEOTROPIC CURVATURE OF AVENA COLEOPTILES IN SOLUTIONS OF VARIOUS OSMOTIC VALUES

Isolated Avena coleoptiles are placed with their bases in mannitol solutions of various osmotic values. In this way the water uptake is inhibited. The coleoptiles are irradiated with red light and turned through 90 °. Considerable geotropic curvatures are developed in solutions which prevent growth to a large extent. Red light enhances the geotropic response also under these conditions, but a red, far-red reversal of the red effect does not take place. The tips of the horizontal coleoptiles appear not to reach the vertical position, but end up growing at a constant angle to the vertical.

Further Studies of Factors Which Influence Xyleborus spp. Emergence and Attack of Theobroma cacao12

The largest numbers of Xyleborus ferrugineus (F.) emerged daily from brood logs between 5 and 6 PM. This peak in emergence was correlated with the daily period when light intensity reached zero as registered by a light meter. Peak daily emergence of X. posticus Eichhoff occurred between 2 and 3 PM. The light intensity usually started its decline to darkness during this interval each day. Flight of beetles from brood logs was random with regard to wind direction when wind velocities were below about 1 mile per hour, but approximately 80% of flying beetles were carried by the wind when its velocity exceeded 1 mile per hour. Diesel oil-treated logs attained peak attractiveness to beetles in field conditions 2 days after the logs were cut and treated. Consecutive daily increases in beetle attacks on untreated logs in field conditions began at 9 days after the logs were cut, and peak attractiveness occurred at 18 days. Treated and untreated logs sustained a similar total number of attacks. Attacks were concentrated in the basal (lower) bark-covered portion of each log, apparently as a result of a positive geotropic response by the beetles. There was no real difference in the susceptibility of logs of cacao clones U.F. 650 and U.F. 613 to beetle attack.

THE SIGNIFICANCE OF THE ROOT CAP FOR GEOTROPISM

The geotropic curvature of pea roots decapitated at 0.3 or 0.4 mm was retarded and no positive geotropic response occurred when the roots were decapitated at 0.5 mm or more. The elongation of the roots was not affected by these decapitations. Caffeic acid and 2,4-dichlorophenol, when applied to the root cap, inhibited the geotropic curvature initially, probably because these compounds decreased the lateral distribution of the auxin in the root cap. 2,3,5-Triiodobenzoic acid, when applied to the root cap prevented the geotropic curvature almost completely. None of these treatments altered the elongation of the roots. It is concluded from the results presented in this and a previous paper (Konings 1967) that the part of the root cap between 0.2 and 0.5 mm from the apex, where the starch-containing columella cells are localized, controls both geotropism and the lateral distribution of auxin.

Growth and Geotropic Responses of Avena Coleoptiles to 4‐Amino‐3,5,6‐Trichloropicolinic Acid

AbstractThe elongation and geotropic responses of coleoptile sections of Avena sativa L. to various concentrations of 4‐amino‐3,5,6‐trichloropicolinic acid (Tordon) proved to be qualitatively similar to those previously reported for 2,3,6‐trichlorobenzoic acid (TCBA). Tordon stimulated growth in a range of concentrations from 1 × 10−6 to 1 × 10−4M but higher concentrations were inhibitory. Geotropic curvature was extensively depressed by 1 × 10−5 and 1 × 10−4M Tordon, concentrations which accelerated elongation. A similar differential effect has been reported for TCBA and other auxins. Several other picolinic acids and related compounds were tested, but only very slight responses were noted.

Experiments in the analysis of the positive and the negative geotropic reactions of primary roots

In the present work the influence of moist air, of sand and of several solutions on the geotropic behaviour of primary roots is studied. The course of the geotropic movement is the result of a concerted action of positive and negative reactions the intensity and duration of which differ in roots of various species.

A Theory for Circumnutations in Helianthus annuus

AbstractA theory is given for circumnutations in plants, especially hypocotyls of Helianthus annuus, which were used as experimental materialThe theory is based on the lateral auxin transport, which arises when a gravitational force component acts on the plant. With a suitable time delay between stimulus and response, oscillations or circumnutations should arise. It is possible to describe these oscillation phenomena by the solutions of a differential equation, derived in this paper. The time delay has a central role in this equation.The time delay is assumed to be identical with the geotropic reaction time for the hypocotyls. The ratio between the periodic time for the circumnutations and the reaction time for geotropic curvatures was found to be approximately constant in the temperature region investigated (namely 15–40°C), which supports the theory. Different methods of recording the circumnutations were used, 8 mm film camera technique being the most frequently employed.The introduction of a weighting function for describing the plants “memory” of the stimulation makes it possible to relate the periodic time of the circumnutations to the reaction time for geotropic curvatures. The necessity of this weighting function as well as of the time delay in the equations is emphasized. An explanation of the “Fünfphasen‐bewegungen”, reported in the literature, is presented.

Geotropic Response of Coleoptiles under Anaerobic Conditions1

Coleoptiles of Avena sativa and Zea mays do not develop a geotropic response under anaerobic conditions.

An Explanation of the Inhibition of Root Growth Caused by Indole-3-Acetic Acid

Low concentrations of indole-3-acetic acid inhibit the growth of pea root sections by inducing the formation of the growth regulator, ethylene gas. Ethylene is produced within 15 to 30 minutes after indole-3-acetic acid is applied and roots begin to swell immediately after they are exposed to the gas. Carbon dioxide competitively inhibits ethylene action in roots, impedes their geotropic response, and partially reinstates auxin inhibited growth. It is concluded that ethylene participates in the geotropic response of roots, but not that of stems.

Effects of morphactin on the negative geotropic response and leaf senescence

Effects of morphactin on the negative geotropic response and leaf senescence

Relations entre la structure chimique de quelques acides arylphtalamiques et leur action sur la reponse geotropique de racines

The intention of the authors has been to determine whether the conception of a potential cycle as formulated by Dodds, to explain the pharmacological activity of stilboestrol, and as illustrated by the immunologic studies of Erlenmeyer, could foreshadow the activity of structurally related analogues of N-(chromannyl-6)-phtalamic acid on the geotropic response of lentil roots. In fact, the activity of N-(alkyloxy-4-phenyl)-phtalamic acids increases with the number of atoms of the carbon side chain, but from 2 carbon atoms onwards their activity is greater than that of N-(chromannyl-6)-phtalamic acid.

Alteration in the Geotropic Response of Allium Seedlings by Growth Regulators

AbstractIndoleacetic acid (1AA) brings about a striking alteration in the normal geotropic response in the seedlings of onion and several other species of Allium. The seedlings which are normally positively geotropic, become ageotropic. Besides IAA several other auxins like IBA, NAA and 2,4‐D also showed a similar response. An anti‐auxin like triiodobenzoic acid (TIBA) enhanced the auxin‐effect instead of reversing it. A marked enhancement of the auxin‐effect was also brought about when sucrose (in the culture medium) was replaced by L‐arabinose which appeared to act synergistically with the auxin.

A Comparison between Geotropism and Geoelectric Effect in Pisum sativum and Its Mutant ageotropum

AbstractThe auxin concentration in roots of Pisum sativum ageotropum was examined by three indirect methods: Supply of auxin before geotropic stimulation; Lateral placing of the root tip; Inhibiting the auxin transport in half of the root. All the results indicated supraoptimal auxin concentration.When decapitated ageotropum roots were supplied with 1.5 mm long tips from normal Pisum roots their geotropic reactivity was almost restored.The geoelectric potential of stems of Pisum sativum and its mutant ageotropum was measured. In ageotropum stems the geoelectric potential was less and the geotropic reaction appeared later than in the normal stems.