The Influence of Gravity on the Formation of Amyloplasts in Columella Cells of Zea mays L

Abstract

MATERIALS AND METHODSFlight Hardware. Flight hardware consisted of four concentrically sealed bags of heat-sealable Kapak plastic (Fisher Scientific, Springfield, NJ). The innermost bag measured approximately 10 x 10 cm and contained approximately 100 ml of 2% (v/v) glutaraldehyde in 0.05 M sodium cacodylate buffer (pH 6.9). This 'fixative bag' was placed inside a 'growth chamber' bag measuring approximately 25 x 30 cm containing the plant material (see below) and inflated to near capacity with air. This bag was then sealed inside two other Kapak bags. We launched 12 of these bags, each containing 2 to 6 seeds. Ground controls were also grown in Kapak bags.Plant Material. Seeds of Zea mays cv Bear Hybrid (Custom Farm Seed Co., Momence, IL) were soaked in distilled H2O for 8 h, placed against moist pieces of filter paper, and loaded into the growth chamber bag of the flight hardware. Due to loading restrictions, imbibed seeds were loaded onto the orbiter Columbia 13 h before launch. We used data from a temperature recorder in the flight locker to ensure that controls were grown at the same temperature (±2°C) as flight-grown seedlings. Plants were grown in darkness throughout the experiment.Protocol on Orbit. Our experiment was terminated after approximately 4.8 d on orbit. Mission Specialist Franklin ChangDiaz ruptured the inner fixative bag of glutaraldehyde and kneeded its contents into the growth chamber bag, thereby submerging the seedlings in fixative.Microscopy and Morphometry. Preparation of tissue for microscopical observation was as described previously (8). We examined randomly selected columella cells from random radial sections of 8 caps of primary roots of flight-grown seedlings and Earth-grown controls. Methods of sample randomization, point counting, and calculating relative and absolute volumes were as described by Steer (15). The formula Pt = [(0.453)(1-Vv)/ (Vv)(E2)(Vv)] was used to determine the total number of points (Pt) necessary to obtain relative volumes (Vv) with relative errors (E) less than 5% (18). Morphometric analyses were facilitated by use ofthe MORPHO computer program ofVodopich and Moore (16). Student's t test (14) was used to determine the significance level of differences between means. Differences with probability (P) levels >5% were considered insignificant. RESULTS AND DISCUSSIONThe influence of microgravity on the dimensions and volumes of columella cells of primary roots of Z. mays is shown in Table I. Table II

O-Acetylation of Plant Cell Wall Polysaccharides

“…There are several pieces of evidence that O -acetylation of wall polysaccharides in plants occurs in the endomembrane system, most likely the Golgi apparatus, where non-cellulosic polysaccharides are synthesized (Moore et al, 1986; Scheible and Pauly, 2004). First, O -acetylated XyG can be isolated from intact microsomes of Arabidopsis confirming that O -acetylation occurs prior to deposition of the wall polysaccharide in the apoplast (Obel et al, 2009).…”

Golgi-Mediated Synthesis and Secretion of Matrix Polysaccharides of the Primary Cell Wall of Higher Plants

“…Quantitative immunolabeling experiments using antibodies recognizing either the XyG backbone (anti-XG antibodies: Moore et al, 1986; Lynch and Staehelin, 1992) or an α- l -Fuc p -(1-2)-β- d -Gal p epitope of XyG side chains in sycamore cultured cells have shown that the epitopes localize to trans cisternae and the TGN (Zhang and Staehelin, 1992). These data suggested that the synthesis of XyG occurs exclusively in late compartments of the Golgi and that no precursor forms of XyG are made in cis and medial cisternae.…”

Architecture and permeability of post-cytokinesis plasmodesmata lacking cytoplasmic sleeves

“…To analyse the ultrastructural organisation of plasmodesmata during tissue 129 differentiation, we first focused on Arabidopsis root tip columella (COL), a tissue 130 involved in gravitropism and soil excavation [41][42][43] . COL cells offered excellent 131 plasmodesmata preservation after cryo-fixation and freeze-subtitution but also 132 unequivocal traceability of cell lineage where plasmodesmata modification from early 133 formation to later maturation stages can be easily traced.…”