Potentiation of Lateral Root Induction by Root Initials in Isolated Flax Roots

Goldacre, P. L.

doi:10.1071/bi9590388

Cited by 37 publications

(13 citation statements)

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“…An alternative option is that for operation of the second growth control point no founder cell formation is needed. Experiments showing that practically all pericycle cells in the xylem radii participated in LRP formation (Goldacre, 1959;Blakely et al, 1982;Laskowski et al, 1995) indicate such a possibility. In contrast with other tissues in the root differentiation zone, pericycle cells do not endoreduplicate (Blakely and Evans, 1979).…”

Section: Discussionmentioning

confidence: 99%

Pericycle Cell Proliferation and Lateral Root Initiation in Arabidopsis

et al. 2000

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In contrast with other cells generated by the root apical meristem in Arabidopsis, pericycle cells adjacent to the protoxylem poles of the vascular cylinder continue to cycle without interruption during passage through the elongation and differentiation zones. However, only some of the dividing pericycle cells are committed to the asymmetric, formative divisions that give rise to lateral root primordia (LRPs). This was demonstrated by direct observation and mapping of mitotic figures, cell-length measurements, and the histochemical analysis of a cyclin-GUS fusion protein in pericycle cells. The estimated duration of a pericycle cell cycle in the root apical meristem was similar to the interval between cell displacement from the meristem and the initiation of LRP formation. Developmentally controlled LRP initiation occurs early, 3 to 8 mm from the root tip. Thus the first growth control point in lateral root formation is defined by the initiation of primordia in stochastic patterns by cells passing through the elongation and young differentiation zones, up to where lateral roots begin to emerge from the primary root. Therefore, the first growth control point is not restricted to a narrow developmental window. We propose that late LRP initiation is developmentally unrelated to the root apical meristem and is operated by a second growth control point that can be activated by environmental cues. The observation that pericycle cells divide and lateral root primordia form without intervening mitotic quiescence suggests that lateral organ formation in roots and shoots might not be as fundamentally different as previously thought.

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Section: Discussionmentioning

confidence: 99%

Pericycle Cell Proliferation and Lateral Root Initiation in Arabidopsis

et al. 2000

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“…Goldacre (8) obtained evidence for the production of a cytokinin-like substance by the dividing cells of unemerged root initials in isolated flax roots, and proposed that cytokinin production may be a normal accompaniment of cell division. Furthermore, Torrey (35) suggested that the quiescent zone may be the site of highest cytokinin concentration in the root SIN ROOTS 159 tip.…”

Section: Discussionmentioning

confidence: 99%

Cytokinins in Seedling Roots of Pea

1972

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The natural occurrence of cytokinins existing both in a free form and as a constituent of transfer RNA was examined in serial segments of young seedling roots of pea. Purified ethanol extracts of root apices were resolved into four factors capable of inducing soybean callus tissue proliferation. The most active factor was identified as zeatin or some closely related compound; it produced polyploid divisions and tracheary element differentiation when tested on cultured pea root segments. 2Abbreviations: IPA: 6-(3-methyl-2-butenylamino)-9-,3-D-ribofuranosylpurine or isopentenyladenosine; 2iP: 6-(3-methyl-2-butenylamino)purine or isopentenyladenine; ZR: 6-(4-hydroxy-3-methyl-2-cisbutenylamino)-9-,8-Dribofuranyosylpurine or zeatin ribonucleoside; Z: 6-(4-hydroxy-3-methyl-2-transbutenylamino)purine or zeatin. Extraction of Free Cytokinins. Immediately after harvesting, the different fractions of pea root segments were immersed separately in precooled absolute ethanol at -72 C. The frozen segments were collected by filtration on Whatman No. 1 filter paper and homogenized in an all-glass homogenizer in cold 80% (v/v) ethanol. The homogenized tissue was extracted for 3 hr in two portions of 80% ethanol and centrifuged at 10,000g for 15 min at 4 C. The original absolute ethanol fraction and the two 80% ethanol extracts were combined and the alcohol evaporated in vacuo. The water phase was adjusted to pH 8.0 and extracted with three equal volumes of 1-butanol which were then combined and taken to dryness in vacuo. The residue was redissolved in about 100 ml of water and adjusted to pH 2.0 with concentrated H2SO,. Fifteen milliliters of cold saturated AgNO, solution were added, and the mixture constantly was stirred for 12 hr at 4 C and centrifuged at 7000g for 15 min. The precipitate was washed with cold 2% AgNO, solution and stirred with 20 ml of 0.2 N HCl at 50 C for 30 min before being centrifuged at 7000g. This procedure was repeated twice. The combined acidic supernatants were adjusted to pH 2.5 with concentrated NaOH and percolated through a Dowex 50W-X8, H+ (200-400 mesh) column, 1.0 cm X 25.0 cm, which was then washed with 100 ml of water and eluted with 300 ml 3 N NH,OH. The eluate was evaporated in vacuo to about 50 ml and extracted at pH 8.0 with three equal volumes of 1-butanol which were combined and taken to dryness in vacuo. The resulting residue was dissolved in 80% ethanol and applied as a streak on Whatman No. 1 paper and developed with solvent system A, 1-butanol-acetic acid-water (12: 3:5 v/v). In addition, the following solvents were employed: B: 30 mM borate buffer at pH 8.4; C: ethyl methyl ketone saturated with water; D: l-butanol-1 N ammonium hydroxide (10:7 v/v); E: 1-butanol saturated with water. Each chromatogram was thoroughly air dried and cut into 10 equal RF strips and eluted with 80% ethanol. The eluates were reduced in volume and tested for cytokinin activity using the soybean callus bioassay.

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“…Pecket (1957aPecket ( , 1957b has presented evidence of a factor other than auxin involved in lateral root formation in peas. Goldacre (1959) suggested that root primordia might produce a cytokinin, which would interact with auxin to induce cell division in the pericycle, and Torrey (1962) found that kinetin stimulated branching in isolated pea roots. In cultured radish roots the production of an endogenous cytokinin by primordia might be expected to stimulate the formation of a multiseriate pericyclic zone, as applied BA does.…”

Section: Department Of Agronomy and Range Science University Of Calimentioning

confidence: 99%