Other Tropisms and their Relationship to Gravitropism

Cassab, Gladys I.

doi:10.1002/9780470388297.ch6

Cited by 10 publications

(14 citation statements)

References 62 publications

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“…Herein, there is a promising future on studying root hydrotropism for the development of robust hydrotropic and stress avoidance lines. Most recent hydrotropism studies have been made in the model plant Arabidopsis ( Eapen et al, 2005 ;Cassab, 2008 ;Takahashi et al, 2009 ). Arabidopsis is native to a wide range of environments with varying drought constraints, which suggests large variation in the response of these natural populations to water defi cit.…”

Section: Hydrotropism Playersmentioning

confidence: 99%

“…Drought is a global social and economic problem, which affects several regions on Earth plant roots penetrate the soil in search of water was fi rst considered as the explanation for the downward orientation of roots (Dodart, around 1700, reviewed by Hart, 1990 ). However, studies on hydrotropism have been remarkably limited in comparison with investigations on gravitropism and phototropism ( Eapen et al, 2005 ;Cassab, 2008 ). Indeed, isolation of the fi rst hydrotropic mutants in Arabidopsis thaliana lagged 19 yr and 23 yr, respectively, behind the fi rst accounts of gravitropic and phototropic response mutants ( Eapen et al, 2003 ;Koorneef et al, 1980 ;Olsen et al, 1984 ).…”

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confidence: 99%

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Root hydrotropism: An update

Cassab

Eapen

Campos

2013

American J of Botany

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While water shortage remains the single-most important factor influencing world agriculture, there are very few studies on how plants grow in response to water potential, i.e., hydrotropism. Terrestrial plant roots dwell in the soil, and their ability to grow and explore underground requires many sensors for stimuli such as gravity, humidity gradients, light, mechanical stimulations, temperature, and oxygen. To date, extremely limited information is available on the components of such sensors; however, all of these stimuli are sensed in the root cap. Directional growth of roots is controlled by gravity, which is fixed in direction and intensity. However, other environmental factors, such as water potential gradients, which fluctuate in time, space, direction, and intensity, can act as a signal for modifying the direction of root growth accordingly. Hydrotropism may help roots to obtain water from the soil and at the same time may participate in the establishment of the root system. Current genetic analysis of hydrotropism in Arabidopsis has offered new players, mainly AHR1, NHR1, MIZ1, and MIZ2, which seem to modulate how root caps sense and choose to respond hydrotropically as opposed to other tropic responses. Here we review the mechanism(s) by which these genes and the plant hormones abscisic acid and cytokinins coordinate hydrotropism to counteract the tropic responses to gravitational field, light or touch stimuli. The biological consequence of hydrotropism is also discussed in relation to water stress avoidance.

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Section: Hydrotropism Playersmentioning

confidence: 99%

mentioning

confidence: 99%

Root hydrotropism: An update

Cassab

Eapen

Campos

2013

American J of Botany

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“…PHOT1 locates to the plant-root synapses in the root transition zone, 89 indicating that auxin-secreting sensory synapses unify portions of the separate networks of gravi-and phototropism. Root hydrotropism 90 has also had a long history of study 17 and is now a maturing field for the further understanding of sensorymotoric circuits in plants. We will not discuss here any of the other tropisms listed in Box 2: Gladys Cassab has adequately summarized these topics recently.…”

Section: The Darwins' 'Root-brain' Hypothesismentioning

confidence: 99%

The ‘root-brain’ hypothesis of Charles and Francis Darwin

Baluška

Mancuso

Volkmann

et al. 2009

Plant Signaling & Behavior

124

108

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This year celebrates the 200(th) aniversary of the birth of Charles Darwin, best known for his theory of evolution summarized in On the Origin of Species. Less well known is that, in the second half of his life, Darwin's major scientific focus turned towards plants. He wrote several books on plants, the next-to-last of which, The Power of Movement of Plants, published together with his son Francis, opened plants to a new view. Here we amplify the final sentence of this book in which the Darwins proposed that: "It is hardly an exaggeration to say that the tip of the radicle thus endowed [with sensitivity] and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements." This sentence conveys two important messages: first, that the root apex may be considered to be a 'brain-like' organ endowed with a sensitivity which controls its navigation through soil; second, that the root apex represents the anterior end of the plant body. In this article, we discuss both these statements.

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“…Overall root system depth determines the efficiency of exploration for shallow resources such as phosphorous (Lynch and Brown 1997) and deep resources such as water (Ho et al 2005(Ho et al , 2004. The differential growth of roots directed by a moisture gradient is called hydrotropism, a long-recognized, but not well-understood, plant behavior (Cassab 2008;Darwin 1881). Perception of moisture gradients, as other stimuli (gravity, obstacles, light, nutrients, etc.…”

Section: Introductionmentioning

confidence: 99%

Accumulation of High Levels of ABA Regulates the Pleiotropic Response of the nhr1 Arabidopsis Mutant

et al. 2009

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Plants have evolved a variety of mechanisms for responding to environmental cues, which allows them to survive in the presence of limited resources or environmental stresses. One of the most significant growth adaptations plants have attained is tropism, a growth response that involves bending of plant organs toward or away from a stimulus. Roots exhibit hydrotropism in response to moisture gradients, which is thought to be critical in acquiring water and establishing their stand in the soil. However, the mechanism underlying hydrotropism remains unsolved. Here, we report that the no hydrotropic response (nhr1) mutant of Arabidopsis, which is impaired in hydrotropism, is tolerant to drought. The no hydrotropic response phenotype of nhr1 was repressed by AbamineSG, an inhibitor of abscisic acid (ABA) biosynthesis, indicating that ABA negatively regulates hydrotropism. Furthermore, the content of ABA was higher in nhr1 compared to those of wild type (wt). However, the higher ABA levels in nhr1 plants were not due to higher transcript levels of 9-cisepoxycarotenoid dioxygenase (NCED3), since these were diminished compared to those of wt. Our results indicated that the root hydrotropic response of the nhr1 mutant is modulated by ABA and that the higher ABA levels of the mutant might confer it drought resistance.

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Other Tropisms and their Relationship to Gravitropism

Cited by 10 publications

References 62 publications

Root hydrotropism: An update

Root hydrotropism: An update

The ‘root-brain’ hypothesis of Charles and Francis Darwin

Accumulation of High Levels of ABA Regulates the Pleiotropic Response of the nhr1 Arabidopsis Mutant

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