Gravitropism in tip-growing cells

Braun, Markus

doi:10.1007/pl00008098

Cited by 51 publications

(21 citation statements)

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“…The initiation of the positive gravitropic responses of characean rhizoids and the negative gravitropic response of protonemata were shown to depend on the sedimentation of statoliths (for review, see Braun, 1997). The actomyosin system plays an important, but different role in the positioning and the sedimentation of the statoliths in both cell types (Buchen et al, 1993;Braun, 1996aBraun, , 1996b.…”

Section: Discussionmentioning

confidence: 99%

“…The ER aggregate represents the structural center of the Spitzenkö rper and is suggested to be essential for controlling the tip-high calcium gradient (Braun and Richter, 1999). Furthermore, it may play a crucial role in the mechanism of tip growth and the regulation of the statoliths-induced reorientation of positively gravitropic rhizoids and negatively gravitropic protonemata (Braun, 1996b(Braun, , 1997Sievers et al, 1996). Based on the localization of spectrin-like epitopes in gravistimulated or drugtreated cells, conclusions are drawn on the possible function of spectrin-like proteins in the mechanism of gravity-oriented tip growth.…”

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confidence: 99%

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Association of Spectrin-Like Proteins with the Actin-Organized Aggregate of Endoplasmic Reticulum in the Spitzenkörper of Gravitropically Tip-Growing Plant Cells

Braun

2001

Plant Physiology

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Spectrin-like epitopes were immunochemically detected and immunofluorescently localized in gravitropically tip-growing rhizoids and protonemata of characean algae. Antiserum against spectrin from chicken erythrocytes showed cross-reactivity with rhizoid proteins at molecular masses of about 170 and 195 kD. Confocal microscopy revealed a distinct spherical labeling of spectrin-like proteins in the apices of both cell types tightly associated with an apical actin array and a specific subdomain of endoplasmic reticulum (ER), the ER aggregate. The presence of spectrin-like epitopes, the ER aggregate, and the actin cytoskeleton are strictly correlated with active tip growth. Application of cytochalasin D and A23187 has shown that interfering with actin or with the calcium gradient, which cause the disintegration of the ER aggregate and abolish tip growth, inhibits labeling of spectrin-like proteins. At the beginning of the graviresponse in rhizoids the labeling of spectrin-like proteins remained in its symmetrical position at the cell tip, but was clearly displaced to the upper flank in gravistimulated protonemata. These findings support the hypothesis that a displacement of the Spitzenkö rper is required for the negative gravitropic response in protonemata, but not for the positive gravitropic response in rhizoids. It is evident that the actin/spectrin system plays a role in maintaining the organization of the ER aggregate and represents an essential part in the mechanism of gravitropic tip growth.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Association of Spectrin-Like Proteins with the Actin-Organized Aggregate of Endoplasmic Reticulum in the Spitzenkörper of Gravitropically Tip-Growing Plant Cells

Braun

2001

Plant Physiology

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“…In positively gravitropic (downward-growing) rhizoids, the gravitropic signaling pathway is short and all steps occur within the tip region of a single cell. Gravity susception is accomplished by the gravity-induced sedimentation of statoliths, small vacuoles containing BaSO 4 crystals, onto the lower subapical cell flank (for review, see Sievers et al, 1996;Braun, 1997). There is unambiguous evidence that the actin cytoskeleton plays an essential role in the early processes of gravity sensing.…”

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How to Activate a Plant Gravireceptor. Early Mechanisms of Gravity Sensing Studied in Characean Rhizoids during Parabolic Flights

et al. 2005

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Early processes underlying plant gravity sensing were investigated in rhizoids of Chara globularis under microgravity conditions provided by parabolic flights of the A300-Zero-G aircraft and of sounding rockets. By applying centrifugal forces during the microgravity phases of sounding rocket flights, lateral accelerations of 0.14g, but not of 0.05g, resulted in a displacement of statoliths. Settling of statoliths onto the subapical plasma membrane initiated the gravitropic response. Since actin controls the positioning of statoliths and restricts sedimentation of statoliths in these cells, it can be calculated that lateral actomyosin forces in a range of 2 3 10 214 N act on statoliths to keep them in place. These forces represent the threshold value that has to be exceeded by any lateral acceleration stimulus for statolith sedimentation and gravisensing to occur. When rhizoids were gravistimulated during parabolic plane flights, the curvature angles of the flight samples, whose sedimented statoliths became weightless for 22 s during the 31 microgravity phases, were not different from those of in-flight 1g controls. However, in ground control experiments, curvature responses were drastically reduced when the contact of statoliths with the plasma membrane was intermittently interrupted by inverting gravistimulated cells for less than 10 s. Increasing the weight of sedimented statoliths by lateral centrifugation did not enhance the gravitropic response. These results provide evidence that graviperception in characean rhizoids requires contact of statoliths with membrane-bound receptor molecules rather than pressure or tension exerted by the weight of statoliths.

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“…Although these cell-types are attached to a multicellular organism, tip-growing cell type is discussed in this section as a term of "singlecell-system" because graviperception and graviresponse occur in the same cell type. The positively gravitropic Chara rhizoids are tube-like cells, in which cytoskeletal elements are involved for maintaining structural polarity, positioning of statoliths and tip-growing response [16,45,46]. The negatively gravitropic bending of Chara protonemata is hypothesized to be based on different properties of actin cytoskeleton in a similar way.…”

Section: Graviresponses In Unicellular Plants or Plant Systemsmentioning

confidence: 99%

Gravistimulated Effects in Plants

Schnabl¹

2002

Astrobiology

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Plant growth and development are affected by a lot of different environmental abiotic factors such as light, temperature and water supply. Immediately upon germination another physical stimulus, gravity, strongly influences the growth of plant organs, root and shoot, in order to ensure their correct orientation in space and the survival of the young seedling. Since plants have evolved under the constant stimulus of gravity, its presence is one of the most important prerequisites for their growth and spatial orientation. Because of the importance of gravity it is astonishing that sensitivity to the gravitational vector, the mechanisms of graviperception and gravisresponse which are still partially controversially discussed, are unclear up to now. Indeed, we know that the framework of the plant body is disturbed without the permanent g-vector, its physiological balance is disrupted. But we do not know the way the gravitational force as an abiotic signal is translated into gravity-dependent phenomena and definite plant structures maintaining adaptive strategies for survival. The biological effects of gravity (studies under microgravity) would be easier understood if this abiotic factor could be reduced or minimized as other common environmental parameters can be modified in order to study their effects on plant differentiation and growth.Since we have no ways to reduce the gravity vector on our planet without inducing stress, we may only speculate on the strategies of plant adaptation mechanisms during the evolution. Leaving the original life space, the water environment, and occupying the land environment 400 million years ago, the plants have been forced to adapt to the new conditions characterized by missing convection. Thereby land-plants were affected by a force 1000 times bigger than in water. The local orientated plants had to optimize their life conditions with respect to water balance, to nutrition, to mechanical problems and to reproduction changing the typical horizontal orientated vegetative thallus into the upright orientated plant body, the cormus. This statically local orientated life way resulted in a high adaptation strategy to environmental factors (Fig. 19.1). In order to overcome mechanical problems induced by the deficiency of the convection, the collapse of the plant cormus had to be avoided by the formation of tissues, delivering special structural rigidity, such as the deposition of lignin in the secondary wall. The supply of water, minerals and nutrition materials had to be organized by the development of a system for the conduction of water and minerals from the soil via the roots in the rest of the plants (xylem) and for the transport of the products of photosynthesis from the leaves throughout the plant (phloem). The total vessels are known as the vascular bundles. Moreover, the plants had to develop suitable nutrition sources, resulting in the formation of leaves which are able to fix CO2 and to store carbohydrates. The shoot functions as the mediator between root and leaves. Other

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Gravitropism in tip-growing cells

Cited by 51 publications

References 47 publications

Association of Spectrin-Like Proteins with the Actin-Organized Aggregate of Endoplasmic Reticulum in the Spitzenkörper of Gravitropically Tip-Growing Plant Cells

Association of Spectrin-Like Proteins with the Actin-Organized Aggregate of Endoplasmic Reticulum in the Spitzenkörper of Gravitropically Tip-Growing Plant Cells

How to Activate a Plant Gravireceptor. Early Mechanisms of Gravity Sensing Studied in Characean Rhizoids during Parabolic Flights

Gravistimulated Effects in Plants

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