Ammonium-induced loss of root gravitropism is related to auxin distribution and TRH1 function, and is uncoupled from the inhibition of root elongation in Arabidopsis

Zou, Na; Li, Baohai; Gao, Dong; Kronzucker, Herbert J.; Shi, Weiming

doi:10.1093/jxb/ers068

Cited by 53 publications

(45 citation statements)

References 47 publications

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“…To assess whether ammonium affected root stem cells, the cellular organization of the stem cell niche was investigated. On day 5, cellular organization of the quiescent center was apparently not affected by ammonium, as assessed by either PI staining or the quiescent center specific marker WOX5::GFP [19] (Figure 4A). Similarly, columella stem cells showed few if any aberrations, as evaluated by several markers, including the enhancer-trap line J2341, which expresses specifically in columella stem cells (Figure 4A), the auxin maximum as revealed by DR5::GUS (Figure 4B), and amyloplast development as revealed by Lugol staining (Figure 4B).…”

Section: Resultsmentioning

confidence: 99%

“…However, Li et al [7] found that neither auxin nor ethylene participated in the ammonium inhibition of root growth as auxin-transport mutants and ethylene-insensitive mutants were still sensitive to ammonium. Zou et al [19] find ammonium induces an agravitropic phenotype in roots, which is related to lateral auxin redistribution and largely independent of inhibitions on root elongation. From this it is clear that further work is required to fully understand the role of auxin in the ammonium induced inhibition of root growth.…”

Section: Introductionmentioning

confidence: 99%

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Ammonium Inhibits Primary Root Growth by Reducing the Length of Meristem and Elongation Zone and Decreasing Elemental Expansion Rate in the Root Apex in Arabidopsis thaliana

et al. 2013

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The inhibitory effect of ammonium on primary root growth has been well documented; however the underlying physiological and molecular mechanisms are still controversial. To avoid ammonium toxicity to shoot growth, we used a vertical two-layer split plate system, in which the upper layer contained nitrate and the lower layer contained ammonium. In this way, nitrogen status was maintained and only the apical part of the root system was exposed to ammonium. Using a kinematic approach, we show here that 1 mM ammonium reduces primary root growth, decreasing both elemental expansion and cell production. Ammonium inhibits the length of elongation zone and the maximum elemental expansion rate. Ammonium also decreases the apparent length of the meristem as well as the number of dividing cells without affecting cell division rate. Moreover, ammonium reduces the number of root cap cells but appears to affect neither the status of root stem cell niche nor the distal auxin maximum at the quiescent center. Ammonium also inhibits root gravitropism and concomitantly down-regulates the expression of two pivotal auxin transporters, AUX1 and PIN2. Insofar as ammonium inhibits root growth rate in AUX1 and PIN2 loss-of-function mutants almost as strongly as in wild type, we conclude that ammonium inhibits root growth and gravitropism by largely distinct pathways.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ammonium Inhibits Primary Root Growth by Reducing the Length of Meristem and Elongation Zone and Decreasing Elemental Expansion Rate in the Root Apex in Arabidopsis thaliana

et al. 2013

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“…Plates were photographed at specified time intervals after gravistimulation with a Nikon COOLPIX800 digital camera (Tokyo, Japan). ImageJ software was used for the measurement of root tip angles as described previously25.…”

Section: Methodsmentioning

confidence: 99%

An improved agar-plate method for studying root growth and response of Arabidopsis thaliana

Ding

Yokawa

et al. 2013

Sci Rep

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Arabidopsis thaliana is a widely used model plant for plant biology research. Under traditional agar-plate culture system (TPG, traditional plant-growing), both plant shoots and roots are exposed to illumination, and roots are grown in sucrose-added medium. This is not a natural environment for the roots and may cause artifact responses. We have developed an improved agar-plate culture system (IPG, improved plant-growing) where shoots are illuminated but roots are grown in darkness without sucrose addition. Compared to TPG, IPG produced plants with significantly less total root length, lateral root length and root hair density, although their primary roots were longer. Root gravitropism, PIN2 (an auxin efflux carrier) abundance, H+ efflux or Ca2+ influx in root apexes, were weaker in IPG-grown roots than those in TPG-grown roots. We conclude that IPG offers a more natural way to study the root growth and response of Arabidopsis thaliana.

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“…The resulting shallower root system is thought to aid the plant in mining the generally nutrient rich upper regions of the soil. Ammonium also inhibits gravitropic response (Zou et al, 2012), and in a screen for NH 4 + -sensitive gravitropic mutants, Zou et al (2013) isolated an allele of ARG1, leading to a model where NH 4 + could modulate gravitropic response through ARG1-dependent effects on auxin transport. In such studies it remains critical to separate specific effects on tropic bending from more general effects on growth rate.…”

Section: Auxin and The Regulation Of Growthmentioning

confidence: 99%

“…Reduced rates of tropic reorientation could then simply reflect slower overall growth. However, in the case of NH 4 + , it is the interaction with auxin rather than any confounding effect of altered growth rate that is thought to be the principal reason for the inhibition of gravitropic response (Zou et al, 2012(Zou et al, , 2013.…”

Section: Auxin and The Regulation Of Growthmentioning

confidence: 99%

Gravitropic Signaling in Plants

Gilroy

Swanson

2014

Encyclopedia of Life Sciences

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The direction of gravity represents a fundamental signal that plants use to shape their growth and development. In the simplest description of this phenomenon, roots grow down and shoots grow up; however, closer examination reveals that different plant organs such as the individual branches of a tree, maintain different angles to gravity, their ‘gravitropic set‐point angle’. When displaced from this orientation, plant organs have the ability to redirect growth to regain their preferred angle through the process of gravitropism. The starch‐statolith hypothesis describes the cellular mechanism whereby plants can sense the direction of gravity and so regulate growth in response to this signal. The sedimentation of dense starch‐filled amyloplasts within specialised sensory cells is thought to generate an as yet undefined directional biochemical signal. This signalling system then modulates transport of the plant hormone auxin resulting in its accumulation and the localisation of growth that leads to the gravitropic response. Key Concepts: Plants sense the direction of gravity and regulate growth of roots and shoots using this information. Directional growth in response to gravity is known as gravitropism. Different organs can use gravitropism to maintain different genetically defined angles, or gravitropic set‐point angles, relative to the gravity vector. Sensing the direction of gravity is achieved by dense starch‐filled amyloplasts sedimenting in specialised sensory cells, called statocytes. The statocytes are the columella cells of the root cap and the endodermal cells in the shoot. Sedimentation of amyloplasts generates an initial biochemical signal within the statocytes that has yet to be defined. Signalling within the statocytes triggers redistribution of transporters for the hormone auxin to the plasma membrane on the lower side of the cell. Asymmetrical activity of auxin transport causes this hormone to accumulate on the lower side of the root or shoot. Auxin promotes cell elongation in shoots and inhibits this process in roots. Differential cell elongation between one side of an organ and the other causes the root to bend downwards and the shoot upwards.

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Ammonium-induced loss of root gravitropism is related to auxin distribution and TRH1 function, and is uncoupled from the inhibition of root elongation in Arabidopsis

Cited by 53 publications

References 47 publications

Ammonium Inhibits Primary Root Growth by Reducing the Length of Meristem and Elongation Zone and Decreasing Elemental Expansion Rate in the Root Apex in Arabidopsis thaliana

Ammonium Inhibits Primary Root Growth by Reducing the Length of Meristem and Elongation Zone and Decreasing Elemental Expansion Rate in the Root Apex in Arabidopsis thaliana

An improved agar-plate method for studying root growth and response of Arabidopsis thaliana

Gravitropic Signaling in Plants

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