The Geotropic Curvature in Roots of Norway Spruce (Picea abies) Containing Anthocyanins

Seedlings of Norway spruce (Picea abies L.) have been found to synthesize anthocyanins in the root tips as well as in the hypocotyls upon irradiation with white light when kept at 4°C for 6–8 days. In addition, it has also been found that the elongation and the geotropic curvature of spruce roots are dependent on the light conditions. The course of the geotropic curvature in spruce roots containing anthocyanins has been followed during a period of 5 h, in which the seedlings were geotropically stimulated continuously in the horizontal position. When the stimulation was performed in white light and in darkness at 21°C, significantly larger curvatures were observed in the roots pretreated at 4°C in darkness than in the roots containing anthocyanins. The specific curvature (curvature in degrees per mm elongation), however, was approximately the same in both types of roots stimulated in white light. This was due to a retarded elongation of the roots pretreated with light at 4°C and containing anthocyanins. A smaller difference in elongation rate between roots with and without anthocyanins was observed in the dark than in the light, but even in the dark the anthocyanin-containing roots grew more slowly than roots without anthocyanins. In order to find out if it is the anthocyanin content or the illumination which affects the elongation and geotropic curvature in the roots, a series of similar experiments was performed using cress seedlings grown at 4°C in light or darkness. Roots of cress seedlings cultivated under conditions which would induce anthocyanin formation in spruce roots exhibited the highest geotropic responses both in light and darkness as compared to cress seedlings grown at 4°C in darkness. As in the case of spruce roots an increase in elongation was observed in cress roots illuminated during the geotropic stimulation. These similarities in the behaviour made it relevant to compare the development of the geotropic curvature in cress and spruce roots.     

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

The auxin concentration in roots of Pisum sativum ageotropum was examined by three indirect methods:

• 1) Supply of auxin before geotropic stimulation;
• 2) Lateral placing of the root tip;
• 3) 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.     

The Starch Statolith Hypothesis and the Optimum Angle of Geotropic Stimulation

When roots of cress seedlings (Lepidium sativum L.) are stimulated for 10 min at an angle of 135° (i.e. the root tips are pointing obliquely upward), the resulting geotropic curvatures become larger than after 10 min stimulation at 45°. This well-known behavior has been explained by the better conditions for statoliths, initially located in the floor end of the statocytes, to slide along the cell walls when root tips are pointing upward at 135° than when pointing downward at 45°. Accepting this explanation, one would predict the optimum angle of stimulation to be near 45° when roots had first been kept inverted long enough for their statoliths to accumulate in the opposite end of each functional statocyte. This prediction has been verified in experiments with cress seedlings which were first kept inverted for 16 min, then stimulated for 10 min at given angles, and subsequently rotated parallel to the horizontal axis of the klinostat at 2 rpm. Under these conditions, roots stimulated at 45° curve faster during a 20 to 30 min period on the klinostat than roots stimulated at 135°, but thereafter they stop curving. Roots stimulated at 135°, on the other hand, although initially curving slower than those at 45°, continue curving for at least a whole hour, and attain larger curvatures than the others after 40 min. The optimum shifts from near 45° to near 135° during the course of the klinostat rotation. The behavior of normal and pre-invertcd roots is interpreted as the result of at least two effects: (1) a stimulation due to the movement of amyloplasts, which is enhanced if these are allowed to slide along the cell walls, and (2) a modification of the development of the resulting curvatures by tonic effects, which are inhibitory between stimulation angles 0° and 90°, and absent or enhancing between 90° and 180°.     

Root hydrotropism of an agravitropic pea mutant, ageotropum

We have partially characterized root hydrotropism of an agravitropic pea mutant, ageotropum (from Pisum sativum L. cv. Weibull's Weitor), without interference of gravitropism. Lowering the atmospheric air humidity inhibited root elongation and caused root curvature toward the moisture-saturated substrate in ageotropum pea. Removal of root tips approximately 1.5 mm in length blocked the hydrotropic response. A computer-assisted image analysis showed that the hydrotropic curvature in the roots of ageotropum pea was chiefly due to a greater inhibition of elongation on the humid side than the dry side of the roots. Similarly, gravitropic curvature of Alaska pea roots resulted from inhibition of elongation on the lower side of the horizontally placed roots, while the upper side of the roots maintained a normal growth rate. Gravitropic bending of Alaska pea roots was apparent 30 min after stimulation, whereas differential growth as well as curvature in positive root hydrotropism of ageotropum pea became visible 4–5 h after the continuous hydrostimulation. Application of 2,3,5-triiodobenzoic acid or ethyleneglycol-bis-( β -aminoethylether)-N,N,N',N'-tetraacetic acid was inhibitory to both root hydrotropism of ageotropum pea and root gravitropism of Alaska pea. Some mutual response mechanism for both hydrotropism and gravitropism may exist in roots, although the stimulusperception mechanisms differ from one another.     

The Starch Statolith Hypothesis and the Interaction of Amyloplasts and Endoplasmic Reticulum in Root Geotropism

Roots of cress (Lepidium sativum L, ) seedlings continuouslystimulated at an angle of 135°—root tips pointingobliquely upwards—develop a larger final geotropic curvaturethan roots stimulated at 45° or 90°. This well-knownbehaviour has previously been interpreted as support for thestarch statolith hypothesis. In the present experiments two groups of cress and lettuce (Lactucasativa L.) seedlings were used: (a) the control group in whichthe roots were allowed to curve without adjustment of the stimulationangle, and (b) the test group in which the roots were readjustedat different time intervals to the original stimulation angle.They were stimulated continuously at 45°, 90°, or 135°and the development of root curvatures was followed over a periodof 5–8 h. Initially (1–2 h) the rate of curvature was approximatelythe same for 135° and 90° control and tested cress andlettuce roots. Thereafter the test roots stimulated at 135°followed a linear curvature pattern. Seedlings stimulated at45° and 90° did not show the same linearity in curvaturedevelopment in the test group. The rates of curvature in thetest group were generally higher than in the control group atangles less than 135°. Cress seedlings were examined by light and electron microscopyin order to follow the movement of the cell organelles in thestatocytes. In the statocytes of roots of test seedlings thestarch statoliths were located in the position attained beforethe first readjustment of the stimulation angle. In the statocytesof control roots the starch statoliths followed the curvatureof the root tip sliding along the cell walls and attaining therest position as in normally orientated roots. The behaviour of control and readjusted roots is interpretedas a result of interaction between starch statoliths and endoplasmicreticulum membranes.     

Geotropic Curvatures in Roots of Cress (Lepidium sativum)

Roots of cress growing between two agar slices develop an asymmetry in the extreme root tip region after 10 to 20 min of horizontal stimulation. After prolonged stimulation (exceeding 50 min) the asymmetry disappears and after 3 h the curvature is distributed over the entire growing region. The course of the initial stages in the geotropic curvature has been followed by light microscopy and scanning electron microscopy. — When stimulated at an angle of 135° with the gravitational force, the asymmetry in the root tip is clearly visible after 10 min of stimulation. The asymmetry in the root cap can be explained by a difference in the elongation rate of the epidermal cells on the upper and lower sides of the stimulated root. The disappearance of the asymmetry is followed by a second phase in which there is a differential growth of the cortical cells on the two sides of the elongation zone. The average growth rate of cells in the upper half of the apical region during the first 50 min of continuous stimulation is 1.5 μm per min, while the elongation rate of the entire root is 16.2 μm per min. Only small modifications in the elongation rates were observed when stimulated and unstimulated roots were rotated parallel to the horizontal axis of a klinostat at 2 rpm. The ultimate curvature developed after 50 min is unaffected by stimulation times exceeding the reaction time which for cress roots has been found to be about 5 min. The two phases in the development of geotropic curvature are discussed in view of the statolith theory.     

Orientation and Geotropic Reaction of Seminal Roots of Wheat

The geotropic orientation of seminal roots of wheat has been studied on seedlings grown in five different positions, stationary and on clinostats. The roots perceive a geoinduc-tion before they have emerged from the grain and perform curvatures inside the grain. These are very sharp and transient, the following root growth is straight in any direction unless the positions are shifted. The roots are insensitive to a static gravi-induction but react to a change in gravitation with a geotropic curvature in positive direction. The roots may not reach or reach, or even pass the plumb-line. The orientation of a root depends upon the direction of its initiation and the geotropic curvature attained before the reaction has ceased. There is no nastic component in the reactions. The ‘plagiotropic’ orientation is explained by the limited positive reaction followed by an ageotropic state. Main root and adventitious roots react in the same way. Reactions to later stimuli give likewise limited curvatures which are weaker but of longer duration. — The effect of temperatures from 10°C to 25°C has been studied and compared to the temperature effect on cell elongation. It is concluded that the whole reaction may be explained by the regular auxin effects on cell elongation. No other hormone should be required and no plagiotropic mechanism is necessary.     

The tropic response of plant roots to oxygen: oxytropism in Pisum sativum L.

Plant roots are known to orient growth through the soil by gravitropism, hydrotropism, and thigmotropism. Recent observations of plant roots that developed in a microgravity environment in space suggested that plant roots may also orient their growth toward oxygen (oxytropism). Using garden pea (Pisum sativum L. cv. Weibul's Apollo) and an agravitropic mutant (cv. Ageotropum), root oxytropism was studied in the controlled environment of a microrhizotron. A series of channels in the microrhizotron allowed establishment of an oxygen gradient of 0.8 mmol · mol⁻¹ · mm⁻¹. Curvature of seedling roots was determined prior to freezing the roots for subsequent spectrophotometric determinations of alcohol dehydrogenase activity. Oxytropic curvature was observed all along the gradient in both cultivars of pea. The normal gravitropic cultivar showed a maximal curvature of 45° after 48 h, while the agravitropic mutant curved to 90°. In each cultivar, the amount of curvature declined as the oxygen concentration decreased, and was linearly related to the root elongation rate. Since oxytropic curvature occurred in roots exposed to oxygen concentrations that were not low enough to induce the hypoxically responsive protein alcohol dehydrogenase, we suspect that the oxygen sensor associated with oxytropism does not control the induction of hypoxic metabolism. Our results indicate that oxygen can play a critical role in determining root orientation as well as impacting root metabolic status. Oxytropism allows roots to avoid oxygen-deprived soil strata and may also be the basis of an auto-avoidance mechanism, decreasing the competition between roots for water and nutrients as well as oxygen. Received: 14 January 1998 / Accepted: 10 February 1998     

Transport and Degradation of Auxin in Relation to Geotropism in Roots of Phaseolus vulgaris

The movement of auxin in Phaseolus vulgaris roots has been examined after injection of IAA^?3H into the basal root/hypocotyl region of intact, dark-grown seedlings. Only a portion of the applied IAA^?3H was transported unchanged to the root tip. The major part of the chromatographed, labelled compounds translocated to the roots was indole-3-acetylaspartic acid (IAAsp) and an unidentified compound running near the front in isopropanol, ammonia, water. The velocity of the auxin transport (7.2 mm per hour) was calculated from scintillation countings of methanol extracts from serial sections of the root. An accumulation of radioactive compounds in the extreme root tip, was observed 5 h after the injection of IAA. The influence of exogenous IAA on the geotropical behaviour of the bean seedling roots was examined. Pretreated roots were stimulated for 5 min in the horizontal position and then rotated parallel to the horizontal axis of the klinostat for 60 or 90 min. The resulting geotropic curvature of IAA-injected and control roots showed significantly different patterns of development. When the stimulation was started 5 h after application of the auxin, the geotropic curvature became larger in roots of the injected plants than in the controls. If, however, the translocation period was extended to 20 h the geotropic curvature was significantly smaller in the roots of the injected plants. The auxin injection did not significally affect the rate of root elongation. The change in geotropical behaviour of the roots is interpreted as a result of the influence of the conversion products of the applied IAA on the geotropical responsiveness.     

Versuche zur Analyse der positiven und der negativen geotropischen Reaktionen von Keimwurzeln

Summary 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.In pea roots the negative movement appears only during a short stage of development. No direct relation exists between the speed of elongation and the appearance of the negative reaction.Primary roots of Zea mays and of Pisum arvense are indifferent to thigmotropic stimuli. The negative movement has, at least in pea roots a smaller mechanically effective force than the positive movement. Therefore the negative reaction does not appear in sand because it cannot overcome the mechanical resistance of the granular medium.In liquid media pea roots react in another way than in air: here the negative reaction begins later, but it has then more influence on the course of the geotropic curvature.The influence of different cations on the geotropic behaviour and on the elongation of the roots can be understood as a combined action of the osmotic effect and of the specific ionic permeability.In pea roots the negative reaction, which appears during the time from 3 to 6 hours after the induction also depends on a definite level of turgor.Primary roots of Zea mays, which grow in a relatively large angle to the vertical line do not lose their geotropic sensibility. They react like plagiotropic organs.In pea roots relations exist between the development of the positive and the negative reaction and the presence of the cotyledons and the tip of the root.Both reactions are induced at the same time by the gravitional stimulus. Their reaction times, however, are different.The root tip is necessary for the induction of both reactions. The negative curvature also appears when the tip is cut off before the end of the reaction time.The course of the geotropic movement of primary roots is compared with the geotropic behaviour of rhizomes. As a possible explanation of both kinds of reactions a two-hormone-hypothesis is discussed.     

Movement of Cell Organelles and the Geotropic Curvature in Roots of Norway Spruce (Picea abies)

The geotropic development in roots of Norway spruce [(Picea abies (L.)] H. Karst, has been followed by light and electron microscopy and compared with the movement of cell organelles (statoliths) in the root cap cells. The geotropic curvature develops in two phases: (a) an initial curvature in the root cap region, which results in an asymmetry in the extreme root tip and which appears after about 3 h stimulation in the horizontal position; and (b) the geotropic curvature in the basal parts of the root tip, which after 8 h is distributed over the entire elongation zone. A graphic extrapolation, based on measurements of the root curvatures after various stimulation periods, indicates a presentation time in the range of 8 to 10 min. The root anatomy and ultrastructure have been examined in detail in order to obtain information as to which organelles may act as gravity receptors. The root cap consists of a central core (columella) distinct from the peripheral part. The core contains three to four rows of parenchymatic cells each consisting of 15 to 18 storeys of statocyte cells with possibly mobile cell organelles. Amyloplasts and nuclei have been found to be mobile in the root cap cells, and the movement of both types of organelles has been followed after inversion of the seedlings and stimulation in the horizontal position for various periods of time at 4°C and 21°C. Three-dimensional reconstructions of spruce root cap cells based on serial sectioning and electron microscopy have been performed. These demonstrate that the endoplasmic reticulum (ER)-system and the vacuoles occupy a considerable part of the statocyte cell. For this reason the space available for free movement of single statolith particles is highly restricted.     

Effect of indoleacetic acid,abscisic acid,root tips and coleoptile tips on growth and curvature of maize roots

The effect of externally applied indoleacetic acid (IAA) and abscisic acid (ABA) on the growth of roots of Zea mays L. was measured. Donor blocks of agar with IAA or ABA were placed laterally on the roots and root curvature was measured. When IAA was applied to vertical roots, a curvature directed toward the donor block was observed. This curvature corresponded to a growth inhibition at the side of the root where the donor was applied. When IAA was applied to horizontal roots from the upper side, normal geotropic downward bending was delayed or totally inhibited. The extent of retardation and the inhibition of curvature were found to depend on the concentration of IAA in the donor block. ABA neither induced curvature in vertical roots nor inhibited geotropic curvature in horizontal roots; thus the growth of roots was not inhibited by ABA. However, when, instead of donor blocks, root tips or coleoptile tips were placed onto vertical roots, a curvature of the roots was observed.Abbreviations ABA abscisic acid - IAA 3-indoleacetic acid     

Spatial and temporal changes in endogenous cytokinins in developing pea roots

Germination and seedling establishment follows a distinct pattern which is partly controlled by hormones. Roots have high levels of cytokinins. By quantifying the fluctuations in endogenous cytokinins over time, further insight may be gained into the role of cytokinins during germination and seedling establishment. Radicles were excised from sterile Pisum sativum L. seeds after 30 min and 5 h imbibition. Seedlings germinated on agar were harvested after 1, 3, 6 and 9 days. The roots were divided into the root tip, root free zone, secondary root zone and from day 6, the secondary roots. Samples were purified by various chromatographic methods and endogenous cytokinins detected by LC(+)ES-MS. Benzyladenine levels doubled after 5 h imbibition and then gradually decreased over time. Low concentrations of cis-Zeatin (cZ) type cytokinins were detected in the radicle after 30 min imbibition. After 5 h imbibition, cis-zeatin riboside-5′-monophosphate had greatly increased. The total cytokinin content of the roots increased over time with the ribotides being the predominant conjugates. From day 3 onwards, there was a gradual increase in the free bases, O-glucosides and their ribosylated forms. Mainly N ⁶ -(2-isopentenyl)adenine (iP)-type cytokinins were detected in the root tip, whereas trans-zeatin- (tZ), dihyrozeatin- (DHZ) and iP-type cytokinins were found in the secondary roots and root zone. Cytokinin biosynthesis was only detected after day 6. Biosynthesis of iP and tZ derivatives was quite rapid, whereas biosynthesis of cZ derivatives remained at a low basal level. These fluctuations in cytokinin types and concentrations suggest the cytokinins may be synthesized from various pathways in pea roots.     

The source and lateral transport of growth inhibitors in geotropically stimulated roots of Zea mays and Pisum sativum

Summary The positive geotropic responses of the primary roots of Zea mays and Pisum sativum seedlings depend upon at least one growth inhibiting factor which arises in the root cap and which moves basipetally through the apex into the extending zone. The root apex (as distinct from the cap) and the regions more basal to the extending zone are not sources of growth regulators directly involved in the geotropic response. A difference in the concentration or effectiveness of the inhibitory factor(s) arising in the cap must be established between the upper and lower halves of a horizontal root. Positive geotropic curvature in a horizontal root is attributable, at least in part, to a downward lateral transport of inhibitor(s) from the upper to the lower half of the organ.     

Distribution of Gibberellins and Abscisic Acid in Geotropically Stimulated Vicia faba Roots

The occurrence of gibberellins and abscisic acid (ABA) in extracts of roots of Vicia faba was demonstrated by gas-liquid chromatography (GLC) of the methylated eluates from the relevant zones of thin-layer chromatograms (TLC) of purified extracts. Quantitative determination of the hormone contents in extracts from upper and lower halves of roots which had been kept in the horizontal position for 30 min indicated a redistribution of the hormones during the geotropic stimulation. Gibberellins whose methyl esters appeared at the retention time of methylated gibberellic acid (GA₃), used as a standard, occurred in higher concentration in the upper than in the lower halves (ratio 2.08:1), whereas the concentration of ABA was highest in the lower halves (ratio 3.08:1). The ratio of the hormones in right and left halves of vertical roots was close to 1:1. Indoleacetic acid (IAA) and ABA were found to retard the elongation of roots of Vicia faba and Lepidium during the first 24 h. Additional experiments with Lepidium showed that this retardation occurs within the first hour after application. Low concentrations of GA₃, when applied to germinating seeds just after the radicles had broken the seed coat, stimulated root elongation in Vicia faba within 24 h and in Lepidium within 36 h. When applied to Lepidium seedlings with 20 mm long roots, GA₃ showed a stimulatory trend within the first 2 h, and distinct stimulation in the subsequent hours, particularly at the lowest concentrations, 0.01 and 0.001 mg/1. These results suggest the possibility of a participation of ABA and gibberellins (in addition to IAA) in the development of the positive geotropic curvature.     

Movement of Amyloplasts in the Statocytes of Geotropically Stimulated Roots. The Pre-Inversion Effect

Previously inverted Lepidium roots were placed in a horizontal position and the amyloplasts in the statocytes of the root cap allowed to fall through their entire range of movement across the cell. Under these conditions the amyloplasts first follow a mainly downward course for 6 to 8 min at a speed between 0.5 and 0.8 μm per min. For the next 10 min they move slightly more slowly in a direction away from the apical end of the cell, still sinking somewhat, but without reaching the plasmalemma along the lower wall. Previous experiments have shown that conditions assumed to allow the amyloplasts to slide parallel to the longitudinal cell walls are those that give rise to the largest geotropic curvatures. Such conditions are for instance (1) stimulation at 135° (root tips pointing obliquely upward) and (2) inversion of roots for 16 min followed by stimulation at 45°. Treatments assumed not to permit extensive sliding of the amyloplasts produce smaller geotropic curvatures, namely (3) stimulation at 45° without pre-inversion and (4) inversion followed by stimulation at 135°. The location of the amyloplasts after these four kinds of treatment has now been determined on photomicrographs and the assumptions concerning the paths and extent of sliding of the amyloplasts confirmed. Observations on electron micrographs showed that under all conditions the amyloplasts are separated from the plasmalemma by other organelles, such as ER, nucleus or vacuoles. In roots rotated for 15 min parallel to the horizontal axis of the klinostat at 2 rpm, the amyloplasts are not clumped together as densely as in normal, inverted or stimulated roots, but they are not scattered over the entire cell volume. The statolith function of the amyloplasts is discussed in view of these and other observations.     

Ultrastructure and movements of cell structures in normal pea and an ageotropic mutant

The pea mutant (Pisum sativum ageotropum) and the normal pea (P. sativum cv. Sabel) were compared in order to see if there were any differences in root anatomy or submorphology which could explain the presumed ageotropic behaviour of the mutant. In both types the root cap consists of a central core (columella) distinct from the peripheral part. The core contains five to six rows of columella cells, each consisting of 10 to 16 storeys of statocytes. The ultrastructure of the columella cells in the two types is very similar; the main difference is confined to the distribution of rough endoplasmic reticulum (ER), which in the mutant statocytes is evenly distributed throughout the cell, while in the normal pea statocytes it is mainly concentrated in the distal part at the “floor” of the cell. Using light micrographs, the movement of amyloplasts and nuclei have been followed in detail during a 40 min inversion period. The pattern of movement of the amyloplasts is apparently identical in the two types and the distances moved during the inversion period are 39 μm and 44 μm in the normal and mutant statocytes, respectively. The nucleus has not been observed to move in normal pea; a slight rearrangement of the nucleus position can be observed during the period 30 to 40 min after the start of inversion of the mutant. Based on magnified electron micrographs of the statocytes a morphometrical analysis was made of five cell structures – amyloplasts, nuclei, mitochondria, vacuoles and ER – which appeared to be freely movable or redistributable under the influence of the gravitational force.     

The Optimum Angle of Geotropic Stimulation and its Relation to the Starch Statolith Hypothesis

Roots which are turned from their normal direction to directions at various angles with the plumb line develop the largest geotropic curvatures during a subsequent klinostat rotation period when the stimulation angle is well above the horizontal. In experiments with roots of Lepidium sativum L., the optimum is located at 120 to 140° when the stimulation time is between 2 and 15 min. If this fact is to be explained by the movements of amyloplasts in the root cap cells, one would expect roots which bad been kept inverted before the stimulation (so that the moveable amyloplasts are accumulated in the opposite end of the cells) to show an optimum angle well below 90°. — Pre-inversion of the roots did suppress the curvatures produced by stimulation at angles larger than 90° when measured after 10 to 30 min of klinostat rotation. This suppression may be taken as a support for the starch statolith hypothesis, since the amyloplasts in pre-inverted roots placed at angles exceeding 90° have a restricted opportunity to slide along the cell walls compared to non-inverted roots placed at the same angles. In pre-inverted roots measured after a period of klinostat rotation, however, no optimum was found at angles below 90°. When the stimulation time was 3.75 min, the response curves were nearly symmetrical about 90°. Stimulation for 15 min, on the other hand, resulted in curvatures which were much larger (although suppressed in comparison with non-inverted roots) when the stimulation angle was 165° than when it was 15°. During the 15 min stimulation period itself, however, pre-inverted roots curved 0.3° when stimulated at 15, but only 3.4° at 165°. This small difference was very highly significant and is in agreement with the starch statolith hypothesis insofar as the amyloplasts in pre-inverted roots placed at 15° have the greatest opportunity to slide along the cell walls. The lack of further development (and the actual decrease) of their curvatures during the subsequent klinostat rotation must then be due to other, depressing, factors, summarily designated as tonic. At angles above 90°, the tonic factors are either absent or even enhancing. Tbe tonic effects cannot be explained by amyloplast movements.     

New Gene Crt(Curly Roots) Controlling Pea (Pisum sativum L.) Root Development

Using ethyl methane sulfonate (EMS) treatment of the seeds ofline SGE, a new mutant of pea (Pisum sativum L.) with alterationsin root development was obtained. The mutant phenotype dependson the density of the growth substrate: on sand (a high densitysubstrate) the mutant forms a small compact curly root systemwhereas on vermiculite (a low density substrate) differencesbetween the root systems of the mutant and wild type plantsare less pronounced. Genetic analysis revealed that the mutantcarries a mutation in a new pea gene designedcrt (curly roots).Gene crt has been localized in pea linkage group V. The mutantline named SGEcrt showed increased sensitivity to exogenousauxin and an increased concentration of endogenous indole-3-aceticacid (IAA) in comparison with the wild type line SGE. Copyright2000 Annals of Botany Company Pisum sativum L., root development, garden pea mutant, curly roots, auxin, environmental stimulus response