The role of the root cap in the response of the primary roots of Zea mays L. seedlings to white light and to gravity

Wilkins, H. D.; Wain, R. L.

doi:10.1007/bf00390700

Cited by 53 publications

(20 citation statements)

References 18 publications

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“…As previously reported for several plant species (6,9,13,20) and in particular for some varieties of maize (16,17,20,26,35), the exposure of both LG 11 and Orla 264 root segments to light enhanced their ability to respond to gravity (see Fig. 1 AB).…”

Section: Discussionsupporting

confidence: 80%

“…On the other hand, the role of the cap cells in the geogreactivity of roots seems to be similar to their role in the growth response to light (17,20,35). Growth inhibitors produced in the cap on exposure to light (27) can be used by the root to produce curvature in response to gravitational stimulation in darkness, i.e., under conditions in which dark-exposed roots do not normally respond to gravity (21,35). Using two maize varieties-Kelvedon33, which requires light for georeaction, and Anjou 210, which does not-and exchanging their root caps has shown that the curvature of the root stumps is only related to the biological nature of the cap (16,17).…”

mentioning

confidence: 94%

“…The sensitivity of the root to light is essentially in the root cap where growth-inhibiting substances are formed or released in response to light (10, 14-22, 32, 34). On the other hand, the role of the cap cells in the geogreactivity of roots seems to be similar to their role in the growth response to light (17,20,35). Growth inhibitors produced in the cap on exposure to light (27) can be used by the root to produce curvature in response to gravitational stimulation in darkness, i.e., under conditions in which dark-exposed roots do not normally respond to gravity (21,35).…”

mentioning

confidence: 95%

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Effect of the light on adenine nucleotide content of georeacting maize roots

Steck¹,

Pilet²

1979

Plant and Cell Physiology

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Apical segments from maize roots of LG 11 and Orla 264 varieties georeacted, at least for the first few hours, only in light, while those of the Anjou 210 variety were georeactive both in light and darkness. The energy charge in the apical end of the two light geo-sensitive (LG and Orla) maize roots significantly increased in the light. In contrast, in Anjou root tips, the energy charge was already high in the dark and did not change significantly after light exposure. The time course of light-induced changes in adenine nucleotide contents in root tips was compared with varietal differences in georeactivity in light and darkness. The present data corroborate the hypothesis that a high energy state in the root tip is a prerequisite for the expression of the root reaction to gravity.

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Section: Discussionsupporting

confidence: 80%

mentioning

confidence: 94%

mentioning

confidence: 95%

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Effect of the light on adenine nucleotide content of georeacting maize roots

Steck¹,

Pilet²

1979

Plant and Cell Physiology

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“…The root cap is apparently the site of photoperception both for this change in gravitropism (14,15,25,26) and a general growth inhibition (16,26 broad band R,4 and determined the reciprocity characteristics and FR reversibility for this phenomenon. The ultimate aim is to elucidate the photobiology that governs directional growth of roots underground.…”

Section: Introductionmentioning

confidence: 99%

Photobiology of Diagravitropic Maize Roots

Mandoli

Tepperman²,

Huala³

et al. 1984

Plant Physiol.

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Light-induced modification of gravitropism in etiolated roots of Zea nays cv Bear x W38 is a low fluence response mediated by phytochrome. This cultivar has a threshold of 10-' mol m2 and becomes saturated with 10-2 mol m-2 of red light. The maximum light-mediated response of 32 degrees downward from horizontal occurs in roots 10 to 30 millimeters in length, 120 to 165 minutes after irradiation. Reciprocity is valid from 2 to at least 9,000 seconds and the response can be about 90% reversed by far red light. Photoreversibility is lost ('escape' occurs) about 20 minutes after red irradiation but appears to be regained 60 to 80 minutes later. A red light-induced (or synchronized) nutation in the apparent curvature rather than unusual escape characteristics may explain these results.Many roots are diagravitropic in darkness and change their response to gravity, becoming more orthogravitropic when exposed to light (2; review 24). The root cap is apparently the site of photoperception both for this change in gravitropism (14,15,25,26) and a general growth inhibition (16,26 broad band R,4 and determined the reciprocity characteristics and FR reversibility for this phenomenon. The ultimate aim is to elucidate the photobiology that governs directional growth of roots underground.MATERIAIS AND METHODS Zea mays (Bear x W38) caryopses were planted, imbibed, and grown in rows. Two rolls of modeling clay (Little Sculptor, 3M Co.) were positioned along the edges of a 1.5 x 17 cm black Plexiglas strip and about 20 maize caryopses were pressed into the clay so that all the embryos faced upward and in one direction. Each row was partially covered with water and imbibed in absolute darkness for at least 4 h. Styrofoam blocks, covered with absorbent paper (Kimpac, Kimberley-Clark) were placed inside opaque plastic boxes and the bottom of the boxes filled with deionized H20. The paper acted as a water wick for the duration of growth and treatment of the roots. Individual rows of imbibed seeds were placed into a rectangular groove which had been precut from a long edge of the styrofoam block, and the seedlings allowed to grow in the dark (95% humidity, 26C) for 2 d so that the roots grew out over the edge of the styrofoam block and above the water soaked paper. All manipulations were done in the absence of any light.Two-d-old roots were irradiated from above with broad band R or FR according to Mandoli and Briggs (10). After irradiation, seeds were grown for an additional time in the dark and then harvested in white light. Excised roots were arranged on lucite sheets and photocopied. Root lengths and angles were measured with a computerized digitizer (10). All experiments were done three times with 20 to 40 roots per datum point. SE per datum point rarely exceeded ±4°(e.g. Fig.

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“…These findings indicate clearly that the cap inhibitors control root geotropism (37,45,48,49). One of these growth regulators could be abscisic acid (ABA), which strongly inhibits root elongation (23,24,26) and seems to have the same effects on root growth as the capinhibiting substances (32)(33)(34)46). Kundu and Audus (19,20) detected the presence of a cap inhibitor, the chromatographic properties of which were similar to those of ABA.…”

mentioning

confidence: 86%

Abscisic acid effect on the DNA microgradients of decapped maize roots

1978

Plant and Cell Physiology

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Longitudinal and transversal total DNA gradients were analysed in 42-/*m thin sections of maize root tips. The optimum DNA concentration was found in the apex (quiescent centre and meristem). It significantly increased after removal of the root cap, which can be considered an essential source of abscisic acid (ABA). When the caps were taken off and agar blocks containing ABA were immediately placed on the apical cut sections, the total DNA level in the root apex decreased gready. ABA regulation of cellular and nuclear behaviour is discussed. Key words: ABA -Apex -Cap -DNA -Maize -Meristem -Nuclear behaviour -Nucleic acid -Root.Geosensitivity in roots is lost after removal of the cap (9,17,18,27,28), but is regained after a few hours, which is considered the georecovery time (17,27, 31). It has been assumed that the georecovery time is directly related to the formation of a new root cap (2,12,17). Decapping does indeed stimulate the cells of the quiescent centre to divide to form a new cap (3,13). However, it has been clearly demonstrated that georecovery precedes cap reformation by many hours (3, 4). Consequently, georecovery is not related to regeneration of the cap. During the ageotropic period of the decapped roots, some ultrastructural changes in the cells of the apex have been reported (5-7) and the formation of some amyloplasts has been observed (7). It is quite clear now that the cap imposes quiescence on cells at the pole of the root. As expected, removing the cap stimulates the cells of the quiescent centre and the meristem to grow and divide (3,5). This was also clearly demonstrated by Clowes (11): he cut off the distal half of the cap and, 5 hr later, observed that the average rate of cell division had declined in the cap initials but increased in the quiescent centre and the apex cells.On the other hand, the cap is the source of growth inhibitors (15, 29) which move basipetally (30,41). For horizontally placed roots, downward transport of these inhibiting substances occurs inside the apex (33, 36) and their level is greater in the lower than the upper half of the cap (56", 37, 41, 47). These findings indicate clearly that the cap inhibitors control root geotropism (37,45,48,49). One of these growth regulators could be abscisic acid (ABA), which strongly inhibits root elongation (23,24,26) and seems to have the same effects on root growth as the capinhibiting substances (32)(33)(34)46). Kundu and Audus (19,20) detected the presence of a cap inhibitor, the chromatographic properties of which were similar to those of 1475

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The role of the root cap in the response of the primary roots of Zea mays L. seedlings to white light and to gravity

Cited by 53 publications

References 18 publications

Effect of the light on adenine nucleotide content of georeacting maize roots

Effect of the light on adenine nucleotide content of georeacting maize roots

Photobiology of Diagravitropic Maize Roots

Abscisic acid effect on the DNA microgradients of decapped maize roots

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