Germination and growth of sponge gourd (Luffa cylindrica) pollen tubes and FTIR analysis of the pollen tube wall

Emergence of multiple pollen tubes from single pollen grains occurred both in vitro and in vivo in sponge gourd (Luffa cylindrica (L.) Roem). The frequency with which pollen grains produced multiple pollen tubes in vivo (7.2%) was lower than that under in vitro conditions (14.9%). In pollen grains germinated in vitro, the total length of the multiple pollen tubes was greater than that of single pollen tubes, but individual tubes among the multiple tubes did not reach the same length as single tubes. Moreover, the growth of the single pollen tubes continued for a longer period in vitro than that of the multiple tubes. Fluorescence microscopy showed that callose was present throughout the pollen tube wall except in the apical part of growing pollen tubes, and nuclei moved into the longest of the multiple tubes. Results of Fourier transform infrared microspectroscopy indicated that abnormal cell wall components (peaks at 800–1000 cm⁻¹) were more frequent in multiple pollen tubes lacking nuclei, and the pectin content (1733 cm⁻¹) in multiple pollen tubes was much lower than that in single pollen tubes. These findings suggested that there were significant differences in pollen tube growth and wall composition between single and multiple pollen tubes, and that multiple pollen tubes had much less opportunity than single pollen tubes to reach the embryo sac and achieve double fertilization.