Auxin-induced Changes in Avena Coleoptile Cell Wall Composition

Abstract

Sugar and uronic acid residues were derived from wall polysaccharides of oat (Avena sativa, var. Victory) coleoptiles by means of 2 N trifluoroacetic acid, 72% sulfuric acid, or enzymic hydrolysis. The products of hydrolysis were reduced and acetylated to form alditol acetates which were analyzed using gas chromatography. Time-course studies of auxin-promoted changes in Wiegand and Schrank (31). Seeds were dehulled, placed in distilled water at room temperature for 4 hr, then spread on the surface of distilled water-saturated vermiculite in plastic vegetable crispers with lids. Crispers with seeds were placed in dim red light for 48 hr, then transferred to darkness for 24 hr. Temperature ranged from 22 to 24 C. After a total of 73 to 76 hr, 25-to 30-mm coleoptiles were selected, and the primary leaf was removed. Beginning 3 mm from the tip, a 10-mm section was cut using a double-bladed cutting device. All manipulations were performed in dim green light. After cutting, sections were floated on distilled water for 30 min prior to treatment.Treatment of Sections. Treatments involved incubating 10 to 30 coleoptile sections in the dark in 43-X 20-mm Stender dishes containing 5 or 10 ml of 2.5 mM potassium citrate, pH 5.4. In some experiments, the dishes also contained either 50 mM glucose or 12.5 /M IAA, or both IAA and glucose. The rims of the dishes were coated with petrolatum to prevent evaporation. The dishes were placed in a Dubnoff shaker at 26 C, 60 oscillations per min. After treatment, sections were measured to the nearest 0.1 mm using a 10 x dissecting microscope fitted with an ocular micrometer and stored at -24 C. For a single experiment coleoptile sections from two or three replicates run on different days were pooled for preparation of wall samples and analyses.Preparation of Wail Samples. Wall samples were prepared using a technique adapted from that of Ray (19). Frozen sections were placed between two 10-X 10-cm pieces of plate glass, thawed, then crushed by a force of approximately 0.5 kg per cm2 applied manually. The crushed material was washed into a fritted glass funnel (medium porosity) with 10 ml of distilled water at room temperature. The water was rapidly sucked off, and the water wash was repeated twice more. Five ml of acetone were added to the sample, allowed to stand with occasional swirling for 5 min, and then removed by suction. The acetone extraction was repeated twice more. The residue was then similarly extracted three times, 5 min each, with 5 ml 556 www.plantphysiol.org on May 12, 2018 -Published by Downloaded from

Changes in Biochemical Composition of the Cell Wall of the Cotton Fiber During Development

“…59, 1977 thesis of secondary wall cellulose. Callose is apparently mobilized as a reserve material in pollen (48), and there are other reports in the literature which implicate turnover of noncellulosic glucans of cell walls (14,23,31,34). Callose has also been observed to be deposited behind the tip of growing pollen tubes (18), and it has been suggested that it serves to strengthen the tube wall (48), although the possibility that it turns over has apparently not been explored.…”

“…However, recent data of Klis (25) indicate that when hydroxyproline content is expressed as per cent of the dry weight of cell wall, its content continually increases during cell elongation, but that there is no further increase once the cells have obtained their final length. Also of interest are studies -showing that a specific decrease in noncellulosic glucose, which is accompanied by a roughly compensating increase in cellulose, occurs in the cell wall of Avena coleoptiles elongating in response to auxin in the absence of an external carbon source (31,39), and it has been suggested that changes in noncellulosic wall glucan may be involved in wall loosening (34). cultured in vitro in a synthetic medium supplied with IAA and GA3 (10).…”

Comparison of the Outer and Inner Epidermis

“…Of those wall components that constitute Poaceae cell walls, the (1--3),(1l-4)-f-D-glucans are the prominent polysaccharides undergoing auxin-induced changes. Glucan metabolism has been observed during auxininduced elongation of Avena (16,23), Hordeum (24), Zea (12), and Oryza (26) coleoptiles. Two enzymes, an endo-and an exoglucanase, are involved in the hydrolysis of the polysaccharide in maize (Zea mays L.) coleoptiles (2,9,10).…”

Cell wall and enzyme changes during the graviresponse of the leaf-sheath pulvinus of oat (Avena sativa).

“…Auxin accelerates the loss of f3-D-glucan from walls of excised coleoptile tisues deprived of exogenous sugar (24), but there is no such decrease in glucan content in intact tissues during maximal growth (8) or in excised tissues given sucrose (13). Both auxin and gibberellins act in the graviresponse of the oat pulvinus (4,7,14), indicating that hormone-induced changes in f3-D-glucan content may accompany the graviresponse.…”