Gravity perception in decapped roots of Zea mays

Hillman, Sara; Wilkins, Malcolm B.

doi:10.1007/bf00392726

Cited by 39 publications

(23 citation statements)

References 7 publications

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“…It has been speculated that the amyloplast statoliths act in the statocyte, i.e. the graviperceptive cell, by pressing upon the endoplasmic reticulum (ER) or interact chemically or electrically with the lateral plasmalemma in the horizontally stimulated position (Perbal and Rivi6re 1976;Volkmann and Sievers 1979;Hillman and Wilkins 1982;Sack et al 1984;Wendt and Sievers 1986). Direct contact between the ER and the amyloplasts has not been observed in the root statocyte (Iversen 1974;Moore and McClelen 1985;Stephenson and Hawes 1986).…”

Section: Introductionmentioning

confidence: 98%

Gravitropism and starch statoliths in an Arabidopsis mutant

Sæther¹,

Iversen²

1991

Planta

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The mutant TC 7 of Arabidopsis thaliana (L.) Heynh. has been reported to be starch-free and still exhibit root gravitropism (T. Caspar and B. G. Pickard 1989, Planta 177, 185-197). This is not consistent with the hypothesis that plastid starch has a statolith function in gravity perception. In the present study, initial light microscopy using the same mutant showed apparently starch-free statocytes. However, ultrastructural examination detected residues of amyloplast starch grains in addition to the starch-depleted amyloplasts. Applying a point-counting morphometric method, the starch grains in the individual amyloplasts in the mutant were generally found to occupy more than 20% and in a few cases up to 60% of the amyloplast area. In the wild type (WT) the starch occupied on average 98% of the amyloplast area and appeared as densely packed grains. The amyloplasts occupied 13.9% of the area of the statocyte in the mutant and 23.3% of the statocyte area in the WT. Sedimentation of starch-depleted amyloplasts in the mutant was not detected after 40 min of inversion while in the WT the amyloplasts sedimented at a speed of 6 micrometers h-1. The gravitropic reactivity and the curvature pattern were also examined in the WT and the mutant. The time-courses of root curvature in the WT and the mutant showed that when cultivated under standard conditions for 60 h in darkness, the curvatures were 83 degrees and 44 degrees, respectively, after 25 h of continuous stimulation in the horizontal position. The WT roots curved significantly more rapidly and with a more normal gravitropic pattern than those of the mutant. These results are discussed in relation to the results previously obtained with the mutant and with respect to the starch-statolith hypothesis.

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Section: Introductionmentioning

confidence: 98%

Gravitropism and starch statoliths in an Arabidopsis mutant

Sæther¹,

Iversen²

1991

Planta

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“…Root caps are highly dynamic structures, able to regrow and redifferentiate rapidly when removed or sloughed off as border cells (13,14). Roots sense and respond to gravity by reorienting growth, and the root cap is the site of graviperception (15)(16)(17)(18)(19). Roots also respond to other environmental stimuli, such as light, touch, and water, and there is evidence that the sensing mechanisms for some of these stimuli also reside in root caps (20)(21)(22)(23)(24).…”

mentioning

confidence: 99%

Genetic ablation of root cap cells inArabidopsis

Tsugeki

Fedoroff

1999

Proc. Natl. Acad. Sci. U.S.A.

168

109

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The root cap is increasingly appreciated as a complex and dynamic plant organ. Root caps sense and transmit environmental signals, synthesize and secrete small molecules and macromolecules, and in some species shed metabolically active cells. However, it is not known whether root caps are essential for normal shoot and root development. We report the identification of a root cap-specific promoter and describe its use to genetically ablate root caps by directing root cap-specific expression of a diphtheria toxin A-chain gene. Transgenic toxin-expressing plants are viable and have normal aerial parts but agravitropic roots, implying loss of root cap function. Several cell layers are missing from the transgenic root caps, and the remaining cells are abnormal. Although the radial organization of the roots is normal in toxin-expressing plants, the root tips have fewer cytoplasmically dense cells than do wild-type root tips, suggesting that root meristematic activity is lower in transgenic than in wild-type plants. The roots of transgenic plants have more lateral roots and these are, in turn, more highly branched than those of wild-type plants. Thus, root cap ablation alters root architecture both by inhibiting root meristematic activity and by stimulating lateral root initiation. These observations imply that the root caps contain essential components of the signaling system that determines root architecture.

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“…In contrast to the numerous studies of root graviresponsiveness of Ig (4,(7)(8)(9)(10)13) is the absence of reliable data for the influence of gravity on the structure of amyloplasts and columella cells. This absence of data is understandable, however, since (a) such investigations require growing controls in microgravity, and (b) clinostats have been shown to be of dubious value for mimicking microgravity (2).…”

mentioning

confidence: 95%

“…(c) Removal of amyloplast starch from columella cells abolishes root graviresponsiveness (6). (d) Decapped roots are not graviresponsive (4,7). The resumption of graviresponsiveness by these roots correlates positively with the differentiation and sedimentation of amyloplasts in cells of their tips (4).…”

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confidence: 99%

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The Influence of Gravity on the Formation of Amyloplasts in Columella Cells of Zea mays L

Moore¹,

Fondren²,

Koon³

et al. 1986

Plant Physiol.

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MATERIALS AND METHODSFlight Hardware. Flight hardware consisted of four concentrically sealed bags of heat-sealable Kapak plastic (Fisher Scientific, Springfield, NJ). The innermost bag measured approximately 10 x 10 cm and contained approximately 100 ml of 2% (v/v) glutaraldehyde in 0.05 M sodium cacodylate buffer (pH 6.9). This 'fixative bag' was placed inside a 'growth chamber' bag measuring approximately 25 x 30 cm containing the plant material (see below) and inflated to near capacity with air. This bag was then sealed inside two other Kapak bags. We launched 12 of these bags, each containing 2 to 6 seeds. Ground controls were also grown in Kapak bags.Plant Material. Seeds of Zea mays cv Bear Hybrid (Custom Farm Seed Co., Momence, IL) were soaked in distilled H2O for 8 h, placed against moist pieces of filter paper, and loaded into the growth chamber bag of the flight hardware. Due to loading restrictions, imbibed seeds were loaded onto the orbiter Columbia 13 h before launch. We used data from a temperature recorder in the flight locker to ensure that controls were grown at the same temperature (±2°C) as flight-grown seedlings. Plants were grown in darkness throughout the experiment.Protocol on Orbit. Our experiment was terminated after approximately 4.8 d on orbit. Mission Specialist Franklin ChangDiaz ruptured the inner fixative bag of glutaraldehyde and kneeded its contents into the growth chamber bag, thereby submerging the seedlings in fixative.Microscopy and Morphometry. Preparation of tissue for microscopical observation was as described previously (8). We examined randomly selected columella cells from random radial sections of 8 caps of primary roots of flight-grown seedlings and Earth-grown controls. Methods of sample randomization, point counting, and calculating relative and absolute volumes were as described by Steer (15). The formula Pt = [(0.453)(1-Vv)/ (Vv)(E2)(Vv)] was used to determine the total number of points (Pt) necessary to obtain relative volumes (Vv) with relative errors (E) less than 5% (18). Morphometric analyses were facilitated by use ofthe MORPHO computer program ofVodopich and Moore (16). Student's t test (14) was used to determine the significance level of differences between means. Differences with probability (P) levels >5% were considered insignificant. RESULTS AND DISCUSSIONThe influence of microgravity on the dimensions and volumes of columella cells of primary roots of Z. mays is shown in Table I. Table II

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Gravity perception in decapped roots of Zea mays

Cited by 39 publications

References 7 publications

Gravitropism and starch statoliths in an Arabidopsis mutant

Gravitropism and starch statoliths in an Arabidopsis mutant

Genetic ablation of root cap cells inArabidopsis

The Influence of Gravity on the Formation of Amyloplasts in Columella Cells of Zea mays L

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