Uridine diphosphate glucose metabolism and callose synthesis in cultured pollen tubes of Nicotiana alata Link et Otto

• Published in: Plant physiology (Bethesda) Vol. 105; no. 2; pp. 659 - 670
• Main Authors: Schlupmann, H, Bacic, A, Read, S.M
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Physiologists 01.06.1994
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Carbohydrates; Cultured cells; Cytoplasm; Fundamental and applied biological sciences. Psychology; Glucans; GLUCOSA; GLUCOSE; Metabolism and Enzymology; METABOLISME; METABOLISMO; NICOTIANA; Nucleotides; Plant physiology and development; Plants; POLEN; POLISACARIDOS; POLLEN; Pollen tubes; POLYHOLOSIDE; Radioactive decay; Sexual reproduction; Sugars; URIDINA; URIDINE; Vegetative and sexual reproduction, floral biology, fructification; Radiolabelling; Enzyme; Transferases; Glycosyltransferases; HPLC chromatography; 1,3-β-Glucan synthase; Metabolism; Pollen tube; Cell wall; Callose; Dicotyledones; Angiospermae; Turnover; Nucleotide; Carbohydrate; Hexosyltransferases; Spermatophyta; Solanaceae
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.105.2.659

Membrane preparations from cultured pollen tubes of Nicotiana alata Link et Otto contain a Cal(2+)-independent (1-3)-beta-D-glucan (callose) synthase activity that has a low affinity for UDP-glucose, even when activated by treatment with trypsin (H. Schlupmann, A. Bacic, S.M. Read [1993] Planta 191: 470-481). Therefore, we investigated whether UDP-glucose was a likely substrate for callose synthesis in actively growing pollen tubes. Deposition of (1-3)-beta-glucan occurred at a constant rate, 1.4 to 1.7 nmol glucose min(-1), in tubes from 1 mg of pollen from 3 h after germination; however, the rate of incorporation of radioactivity from exogenous [14C]-sucrose into wall polymers was not constant, but increased until at least 8 h after germination, probably due to decreasing use of internal reserves. UDP-glucose was a prominent ultraviolet-absorbing metabolite in pollen-tube extracts, with 1.6 nmol present in tubes from 1 mg of pollen, giving a calculated cytoplasmic concentration of approximately 3.5 micromolar. Radioactivity from [(14)C]-sucrose was rapidly incorporated into sugar monophosphates and UDP-glucose by the growing tubes, consistent with a turnover time for UDP-glucose of less than 1 min; the specific radioactivity of extracted UDP-[(14)C]glucose was equal to that calculated from the rate of incorporation of [(14)C]sucrose into wall glucans. Large amounts of less metabolically active neutral sugars were also present. The rate of synthesis of (1-3)-beta-glucan by nontrypsin-treated pollen-tube membrane preparations incubated with 3.5 mm UDP-glucose and a beta-glucoside activator was slightly greater than the rate of deposition of (1-3)-beta-glucan by intact pollen tubes. These data are used to assess the physiological significance of proteolytic activation of pollen-tube callose synthase