Detailed analysis of Cucurbita pepo seed coat types and structures with scanning electron microscopy

Discovery of a mutant thin-coated seed phenotype at the end of the 19th century facilitated pumpkin (Cucurbita pepo L.) seed oil production and increased botanic interest in seed coat types and their structures. The main seed coat characteristics were usually analyzed by light and fluorescent microscopy, and more recently, seed coat traits have also been mapped on a C. pepo gene map. The aim of our research was to collect and describe various pumpkin seed types and to analyze, using scanning electron microscopy (SEM), the detailed structure of their seed coats. Seeds of 29 cultivars and landraces were collected and visually evaluated based on seed coat characteristics. Seed samples belonging to different seed types discovered in our collection were transversely sectioned and analyzed by SEM. Twelve seed types were determined, and SEM analysis revealed high variability in their seed coat structures. Using SEM, tissue and cell structures were clearly visible, and novel details of cell and tissue topography were documented. Hypodermal and aerenchyma cells in wild-type seed coats showed fibrous or reticulate secondary cell wall thickening, respectively. In mutant seed types, an absence of different seed coat layers was clearly noted, while the remaining layers were distinctly pronounced. A new completely hull-less seed type was described for the first time. Description of the variability of seed coats in pumpkin was complemented by novel seed coat types, and their structures were analyzed in detail the first time by SEM.