Understanding of histological and physiological alterations in hull-less seeded pumpkin.

• Histology revealed a collapse of 5 layered structure in the hull-less seed coat. • Protein, amino acid, lipid and starch play no role in producing the hull-less trait. • The cell wall components decreased after 20 DPA in the hull-less seed coats. • A hull-less mutation reduced the lignin deposition in the pumpkin seed coat. • All deviations from the normal pattern of development in seeds occurred at 20 DPA. Pumpkin seeds have great therapeutic value but remain underutilized due to its hulled character. However, a hull-less mutation revolutionized the fate of pumpkin seeds in the oil industry by omitting the decortication process. Therefore, the present research was conducted to understand the histological and physiological changes caused by this mutation in the developing seeds of pumpkin that produces the desired hull-less phenotype. In scanning electronic microscopy, a distinct five cell layered structure was observed in the seed coat of hulled (PCK-1) genotype, which was collapsed in the partially hulled (WT-2046) and the hull-less (PMK-1) genotypes. Also the seed coat layers increased continuously in hulled genotype until maturity; however, these declined after 20 DPA in the other two genotypes. Physiological studies revealed that protein, amino acid, starch and lipid content followed the same trend, but the wall components (pectin, hemicelulose, cellulose and lignin) differed significantly amongst the genotypes. The wall components increased continuously until maturity in the hulled genotype, but decreased after 20 DPA in the partially hulled and hull-less genotypes. Further, the correlation, PCA and cluster analysis also reinforced that the wall components especially the lignin was responsible in maintaining the seed coat structure in the hulled genotype and its reduction poses as a reason for the collapsed seed coat in other two genotypes. Lignin reduction was noticed at 20 DPA in the hull-less genotype and therefore, this stage can be used to identify the gene responsible for lignin synthesis in the seed coats. [ABSTRACT FROM AUTHOR]