Abstract Detail

From canonical to new model systems: The future of plant development

Gladish, Daniel [1], Saito, Susumu [2], Niki, Teruo [3].

Vacuolar granules in the root tips of Zea mays var. amylacea: new puzzle, classical solutions.

Maize (Zea mays) has for decades been a frequent subject of experimentation, probably because of its ease of handling, robust growth habits, and high economic value as a crop. The large size and dependable growth of its primary root has made it a popular subject for root studies. We recently evaluated for research purposes a Peruvian cultivar of the Z. mays subspecies amylacea that produces seeds of extraordinary size (2 cm dia.). The seeds produce primary roots of very large size (1+ mm dia.) that grow very rapidly (ca. 40 mm/d). Z. mays var. amylacea seeds were germinated in vermiculite at 20° C for 4-5 d. Root tips were embedded in Technovit 7100 after 4% paraformaldehyde fixation and alcohol dehydration, then thinsectioned and stained with toluidine blue "O" at pH 7.2. Preliminary observations by light microscopy (LM) of the ultrastructure of cells of the rapidly growing primary meristem tissues revealed that newly formed small (1-2 µm) vacuoles occasionally contained densely granular objects. Therefore, a systematic examination of primary root apical meristems was undertaken using LM. "Granules" were most commonly found between 500 and 1500 µm from the dermatogen layer. Closer to the tip granules were mainly in cells concentrically surrounding developing metaxylem vessel elements. Farther from the tip they were found in the pericycle, endodermis, and the inner layerof cortical cells. Transmission electron microscopy (TEM) showed that the granules were electron-dense aggregates of what appeared to be polysomes that assembled in the cytosol and then invaginated into a nearby growing vacuole as a membrane-bound inclusion. A histochemical approach was used to evaluate the hypothesis that the granules were filled with polysomes. Root tips were embedded in Technovit 8100 resin containing 5% butoxyethanol and thinsectioned. The sections were variously treated with Proteinase K, RNase A, both (in alternate order), or neither. They were then stained variously with toluidine blue "O" (0.1%, pH 7.2 or 10, 5 min at 45° C), coomassie brilliant blue R250 ca. 17% in glacial acetic acid:ethanol (1:3; 30 min), or methyl green-pyronin (solution by manufacturer, 20 min at 45° C). The addition of butoxyethanol to this newly developed resin allowed penetration by the enzymes. Consistent with the hypothesis, following enzyme treatment the specific histochemical properties of the stains permitted the diagnosis that the granules were very dense aggregates of RNA and protein. The function of the granules and their fate remain to be discovered.

Broader Impacts:

1 - MIAMI UNIVERSITY, Botany, 544 MOSLER HALL, 1601 UNIVERSITY BLVD, HAMILTON, OH, 45011, USA
2 - Takushoku University, Cell Technology, Tatemachi 815-1,Hachioji, Tokyo Prefecture, Japan
3 - BIOTECH DEPT/FAC OF ENGINEER, TATE-MACHI 815-1 HACHIOJI-SHI, TOKYO, N/A, 193, Japan

Keywords:
Zea mays var amylacea
primary root apical meristem
vacuolar granule.

Presentation Type: Symposium or Colloquium Presentation
Session: SY10
Location: Delaware A/Hyatt
Date: Wednesday, July 11th, 2012
Time: 4:45 PM
Number: SY10008
Abstract ID:830