Cellular specifiCity of the gravitropic motor response in roots

Evans, Michael L.; Ishikawa, Hideo

doi:10.1007/pl00008099

Cited by 41 publications

(15 citation statements)

References 44 publications

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“…Similar wobbles consistently resulted when relative elongation rate was calculated directly from groups of points along the velocity profile. The smaller peaks that formed the wobbling shape of the relative elongation curve may coincide with specialized physiological zones, such as the so-called distal elongation zone, that are sensitive to hormonal and environmental stimuli Evans, 1993, 1995;Evans and Ishikawa, 1997;Mullen et al, 1998). The wobbles could alternatively reflect the mechanics of the growth process as cells leave the meristem and enter the rapid elongation zone via an abrupt transition.…”

Section: Discussionmentioning

confidence: 99%

Regulation of Root Elongation under Phosphorus Stress Involves Changes in Ethylene Responsiveness

et al. 2003

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We characterized the growth of the primary root of Arabidopsis under phosphorus sufficiency (1 mm phosphate) and deficiency (1 m phosphate), focusing on the role of ethylene. We quantified the spatial profile of relative elongation with a novel method based on image processing, as well as the production rates of cortical cells, trichoblasts, and atrichoblasts. Phosphorus deficiency moderately decreased the maximal rate of relative elongation, shortened the growth zone, and decreased the production rate of both epidermal cell types but not of cortical cells. Inhibiting ethylene production (with aminoethoxyvinyl-glycine) or action (with 1-methylcyclopropene) increased elongation in high phosphorus and decreased it in low phosphorus. That these effects were specific to ethylene was confirmed by negating the effect of inhibited ethylene production with simultaneous treatment with an ethylene precursor (1-aminocyclopropane-1-carboxylic acid). Under both phosphorus regimes, ethylene regulated the maximal rate of relative elongation rather than the size of the growth zone. In addition, inhibiting ethylene action in high versus low phosphorus elicited opposite responses for the position of root hair initiation and for the production rates of cortex cells and atrichoblasts. We conclude that the root system acclimates to phosphorus deficiency by changing the signal transduction pathway connecting ethylene levels to growth and division.Plant root systems display an array of physiological, morphological, and architectural responses to low phosphorus availability. These responses enhance the ability of the root to explore the soil and include changes in branching patterns, in elongation rate, and in root hair length and density (Bates and Lynch, 1996;Bonser et al., 1996;Borch et al., 1999; Lynch and Brown, 2001; Ma et al., 2001a). These changes accompany changes in biochemical and metabolic processes and both together presumably represent adaptive responses to assist growth during phosphorus deficiency. In particular, the growth of root hairs and their response to phosphorus availability is important in the acquisition of this highly immobile nutrient (Lewis and Quirk, 1967;Bhat and Nye, 1974;Gahoonia and Nielsen, 1997; Lynch, 2000a, 2000b; Ma et al., 2001b).In response to low phosphorus, adaptive changes in roots may be mediated through the plant hormone ethylene. Both phosphorus deficiency and ethylene cause similar changes in root systems, such as aerenchyma formation, altered root growth angle, and stimulated root hair development (He et al., 1992;Lynch and Brown, 1997;Borch et al., 1999; Lynch and Brown, 2001). In bean (Phaseolus vulgaris), ethylene inhibits root elongation in phosphorus-sufficient conditions but maintains elongation under phosphorus deficiency (Borch et al., 1999). This finding suggests that roots respond to phosphorus stress by changing ethylene signal transduction pathways involved in regulating growth.In this report, we focus on the role of ethylene in mediating growth responses to low phosphoru...

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Section: Discussionmentioning

confidence: 99%

Regulation of Root Elongation under Phosphorus Stress Involves Changes in Ethylene Responsiveness

et al. 2003

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“…There, an auxin response machinery converts the auxin gradient signal into a differential cellular growth responsible for the gravitropic curvature (for review, see Masson et al, 2002), although an auxin gradientindependent phase may contribute to the early curvature response that occurs in the root distal elongation zone (Evans and Ishikawa, 1997;Wolverton et al, 2002).…”

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confidence: 99%

The ARG1-LIKE2 Gene of Arabidopsis Functions in a Gravity Signal Transduction Pathway That Is Genetically Distinct from the PGM Pathway

et al. 2003

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The arl2 mutants of Arabidopsis display altered root and hypocotyl gravitropism, whereas their inflorescence stems are fully gravitropic. Interestingly, mutant roots respond like the wild type to phytohormones and an inhibitor of polar auxin transport. Also, their cap columella cells accumulate starch similarly to wild-type cells, and mutant hypocotyls display strong phototropic responses to lateral light stimulation. The ARL2 gene encodes a DnaJ-like protein similar to ARG1, another protein previously implicated in gravity signal transduction in Arabidopsis seedlings. ARL2 is expressed at low levels in all organs of seedlings and plants. arl2-1 arg1-2 double mutant roots display kinetics of gravitropism similar to those of single mutants. However, double mutants carrying both arl2-1 and pgm-1 (a mutation in the starch-biosynthetic gene PHOSPHOGLUCOMUTASE) at the homozygous state display a more pronounced root gravitropic defect than the single mutants. On the other hand, seedlings with a null mutation in ARL1, a paralog of ARG1 and ARL2, behave similarly to the wild type in gravitropism and other related assays. Taken together, the results suggest that ARG1 and ARL2 function in the same gravity signal transduction pathway in the hypocotyl and root of Arabidopsis seedlings, distinct from the pathway involving PGM.Gravity is one of the environmental cues that guides plant organs' growth. Most plant organs are characterized by a specific gravity set point angle, which defines their preferential growth vector relative to gravity (Firn and Digby, 1997). In young Arabidopsis seedlings, shoots grow upward, displaying negative gravitropism, whereas roots grow downward, toward the center of gravity (positive gravitropism; Bullen et al., 1990;Boonsirichai et al., 2002).Gravity perception by dicot organs involves primarily the sedimentation of amyloplasts within specialized cells (statocytes) located in the columella region of the root cap and in the starch sheath, which constitutes the endodermis of hypocotyls and inflorescence stems (Kiss et al., 1996;Kuznetsov and Hasenstein, 1996;Blancaflor et al., 1998; Weise et al., 2000). In shoots, sedimentable amyloplasts and the curvature response to gravistimulation occur along the elongation zone (for review, see Masson et al., 2002). After amyloplast sedimentation, signals are likely transduced within the endodermal cells, and physiological signals are transported laterally to affect elongation of cortical and epidermal cells. In roots, sites of gravity perception and curvature response may be physically separated (Poff and Martin, 1989). Hence, physiological signals resulting from activation of the gravity signal transduction pathway should be transported from the root cap columella to the elongation zones where the gravitropic curvature is initiated (for review, see Boonsirichai et al., 2002).Auxin is a physiological signal that has been shown to mediate the gravitropic response (for review, see Masson et al., 2002). In gravistimulated roots, auxin is redistributed asymmet...

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“…1) are the sites of gravisensing. Once gravity is perceived, this signal is communicated to the elongation zone, where differential growth occurs (Selker and Sievers, 1987;Ishikawa et al, 1991;Ishikawa and Evans, 1993; for review, see Masson, 1995;Evans and Ishikawa, 1997;Chen et al, 1999).…”

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Changes in Cytosolic pH within Arabidopsis Root Columella Cells Play a Key Role in the Early Signaling Pathway for Root Gravitropism

1999

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Cellular specifiCity of the gravitropic motor response in roots

Cited by 41 publications

References 44 publications

Regulation of Root Elongation under Phosphorus Stress Involves Changes in Ethylene Responsiveness

Regulation of Root Elongation under Phosphorus Stress Involves Changes in Ethylene Responsiveness

The ARG1-LIKE2 Gene of Arabidopsis Functions in a Gravity Signal Transduction Pathway That Is Genetically Distinct from the PGM Pathway

Changes in Cytosolic pH within Arabidopsis Root Columella Cells Play a Key Role in the Early Signaling Pathway for Root Gravitropism

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