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ROOT GRAVITROPISM: An Experimental Tool to Investigate Basic Cellular and Molecular Processes Underlying Mechanosensing and Signal Transmission in Plants (2002)

Boonsirichai, K. ; Guan, C. ; Chen, R. ; [et al.]

Palo Alto, Calif. : Annual Reviews

Annual Review of Plant Physiology and Plant Molecular Biology 53 (2002), S. 421-447

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ISSN: 1040-2519

Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff

Topics: Biology

Notes: Abstract The ability of plant organs to use gravity as a guide for growth, named gravitropism, has been recognized for over two centuries. This growth response to the environment contributes significantly to the upward growth of shoots and the downward growth of roots commonly observed throughout the plant kingdom. Root gravitropism has received a great deal of attention because there is a physical separation between the primary site for gravity sensing, located in the root cap, and the site of differential growth response, located in the elongation zones (EZs). Hence, this system allows identification and characterization of different phases of gravitropism, including gravity perception, signal transduction, signal transmission, and curvature response. Recent studies support some aspects of an old model for gravity sensing, which postulates that root-cap columellar amyloplasts constitute the susceptors for gravity perception. Such studies have also allowed the identification of several molecules that appear to function as second messengers in gravity signal transduction and of potential signal transducers. Auxin has been implicated as a probable component of the signal that carries the gravitropic information between the gravity-sensing cap and the gravity-responding EZs. This has allowed the identification and characterization of important molecular processes underlying auxin transport and response in plants. New molecular models can be elaborated to explain how the gravity signal transduction pathway might regulate the polarity of auxin transport in roots. Further studies are required to test these models, as well as to study the molecular mechanisms underlying a poorly characterized phase of gravitropism that is independent of an auxin gradient.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1146/annurev.arplant.53.100301.135158

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Thoracic helical CT: influence of subsecond scan time and thin collimation on evaluation of peripheral pulmonary arteries (2000)

Rémy-Jardin, M. ; Baghaie, F. ; Bonnel, F. ; [et al.]

Springer

European radiology 10 (2000), S. 1297-1303

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ISSN: 1432-1084

Keywords: Key words: CT angiography ; Pulmonary arteries ; Pulmonary embolism ; CT technique

Source: Springer Online Journal Archives 1860-2000

Topics: Medicine

Notes: Abstract. The objective of this study was to analyze the influence of collimation on the identification of peripheral pulmonary arteries on helical CT scans. Three hundred sixty of 370 consecutive helical CT angiograms of the pulmonary circulation obtained during an 18-month investigation period were considered as technically acceptable for the detection of acute pulmonary embolism and were retrospectively analyzed. Patients in group A (n = 274) underwent CT with 2-mm collimation and pitch of 2; those in group B (n = 86) underwent CT with 3-mm collimation and pitch 1.7; a 0.75-s rotation time was systematically used. A total of 2160 segmental (six arterial zones per patient) and 2160 subsegmental (six arterial zones per patient) arterial zones were assessed. Whereas the percentage of segmental arteries was not significantly different between group A (86 %) and group B (89 %), the percentage of analyzable subsegmental arteries was greater in group A (65 %) than in group B (43 %) (P 〈 0.001). The causes of inadequately depicted subsegmental arterial zones were partial-volume effects (group A, n = 302; 52 %; group B, n = 197; 67 %; P 〈 0.001), suboptimal enhancement (group A, n = 145; 25 %; group B, n = 43; 15 %; P 〈 0.05), motion artifacts (group A, n = 113; 20 %; group B, n = 30; 10 %), and unincluded arteries (group A, n = 20; 3 %; group B, n = 25; 8 %). Helical CT with 2-mm collimation at 0.75 s per revolution enables marked improvement in the analysis of subsegmental arteries in routine clinical practice.