Architectural Diversity of the Cuticle and Epidermis of Native and Hybrid Tomato Fruit Genotypes and the Relation to Polygalacturonase Expression

Abstract

The tomato (Solanum lycopersicum L.) fruit has been widely studied because of its high consumption, nutritional value, and well-characterized genome. It also represents a good model for studying the structure and function of the cuticle, a protective film that is deposited on the surface of outer epidermal cell walls, and affects the integrity and firmness of the fruit, and, therefore, its commercialization. To evaluate the differences in their structure and function, we characterized the morphology of the cuticle and the epidermis and their relationship to firmness, brightness, weight loss, and transcript levels of polygalacturonase (PGA) in four hybrid genotypes and four native genotypes of different origins, shapes, and colors. Our results show a different architecture of the epidermis and cell wall among the genotypes. Native genotypes showed irregular-shaped epidermal cells and a thicker epidermis. Anticlinal pegs were also present to only one-third of the depth of the epidermal cells. The hybrid fruit surface was smoother compared to native genotypes, and it was associated with a higher level of brightness and a less weight loss. A negative correlation between firmness and PGA transcript levels was found. The chartreuse yellow genotype was the firmest, and it had the lowest levels of PGA expression. Meanwhile, the black genotype displayed the lowest weight loss and stem scar diameter. Our results suggest that several morphological features of the cuticle and epidermis have been modified through selection of the tomato fruit, altering quality parameters, such as weight loss and firmness.