Comparison of Testa Development in Normal and Hull-Less Seeded Strains of Cucurbita pepo L.

Abstract

Testa development was compared in normal and hull-less strains of Cucurbita pepo L. Histochemical studies showed that both normal and hull-less mutant seeds develop a five-zoned testa between 5 and 10 days post-anthesis Because of limited secondary wall development in the epidermis, hypodermis, and sclerenchyma in testae of the hull-less mutant cultivars, individual tissue layers began to compress between 20 days post-anthesis until the seed reached maturity. In the hull-less mutant, complete desiccation of seeds removed from the fruit resulted in complete collapse of the hypodermis, sclerenchyma, and parenchyma. These tissues remain largely intact in normal seeds. Expression of the mutant phenotype was particularly evident in the seed margin where hypodermal tissue normally contributes substantially to overall testa thickness. Analyses of testa composition revealed a marked reduction in lignin (83%), cellulose/hemicelluloses (67%), and protein (54%), and increases in ethanol-soluble material (58%) and lipids (45%) in hull-less mutant strains as compared with normal strains