Macromolecular composition of the propagule wall of Nelumbo Nucifera

The macromolecular constituents of the sclerotic propagule wall of Nelumbo nucifera and seed coat of Nymphaea caerulea were studied using scanning electron- and light microscopy in combination with Curiepoint pyrolysis-gas chromatography-mass spectrometry. In addition, the Nelumbo material was analyzed using solid state ¹³C nuclear magnetic resonance and in-source pyrolysis-mass spectrometry. The sclerotic seed coat of the Nymphaea caerulea revealed the presence of angiosperm lignin-cellulose similar to that found in most sclerotic plant remains. In sharp contrast, the fruit wall plus seed coat of Nelumbo is believed to be composed of a complex of polysaccharides, based on primarily galactose and mannose units, and insoluble tannins, which are suggested to play the same structural role as the lignin-cellulose in the sclerotic seed coat. The distinctive nature of the chemical constituents present in the propagule wall of Nelumbo, supports the systematic distinction of this genus in the separate family Nelumbonaceae. The characteristic chemical composition of the propagule walls of Nelumbo could be an additional factor in favour of a prolonged longevity of these fruits. However, the distinctive composition of polysaccharides and tannins without the presence of lignin is considered to be the main reason for the absence of these propagules in the fossil record, despite their physical resistance.