Exocytosis Precedes and Predicts the Increase in Growth in Oscillating Pollen Tubes

• Published in: The Plant cell 2009-10, Vol.21 (10), p.3026-3040
• Main Authors: McKenna, Sylvester T, Kunkel, Joseph G, Bosch, Maurice, Rounds, Caleb M, Vidali, Luis, Winship, Lawrence J, Hepler, Peter K
• Format: Article
• Language: English
• Subjects: Carboxylic Ester Hydrolases - genetics; Carboxylic Ester Hydrolases - metabolism; Cell growth; Cell Wall - metabolism; Cell walls; Exocytosis; Exocytosis - genetics; Exocytosis - physiology; Fluorescence; Fringe; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; Iodides; Lilium - genetics; Lilium - growth & development; Lilium - metabolism; Memory interference; Molecular Sequence Data; Nicotiana - genetics; Nicotiana - growth & development; Nicotiana - metabolism; Plant cells; Plants; Pollen; Pollen Tube - genetics; Pollen Tube - growth & development; Pollen Tube - metabolism; Pollen tubes; Secretion; Statistical analysis; Tobacco
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.109.069260

We examined exocytosis during oscillatory growth in lily (Lilium formosanum and Lilium longiflorum) and tobacco (Nicotiana tabacum) pollen tubes using three markers: (1) changes in cell wall thickness by Nomarski differential interference contrast (DIC), (2) changes in apical cell wall fluorescence in cells stained with propidium iodide (PI), and (3) changes in apical wall fluorescence in cells expressing tobacco pectin methyl esterase fused to green fluorescent protein (PME-GFP). Using PI fluorescence, we quantified oscillatory changes in the amount of wall material from both lily and tobacco pollen tubes. Measurement of wall thickness by DIC was only possible with lily due to limitations of microscope resolution. PME-GFP, a direct marker for exocytosis, only provides information in tobacco because its expression in lily causes growth inhibition and cell death. We show that exocytosis in pollen tubes oscillates and leads the increase in growth rate; the mean phase difference between exocytosis and growth is -98° ± 3° in lily and -124° ± 4° in tobacco. Statistical analyses reveal that the anticipatory increase in wall material predicts, to a high degree, the rate and extent of the subsequent growth surge. Exocytosis emerges as a prime candidate for the initiation and regulation of oscillatory pollen tube growth.