Submitted to: Annals Of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2001
Publication Date: 8/17/2001
Interpretive Summary: The skin covering potato tubers is often easily torn from the tuber surface during harvest. These skinning type wounds increase the spread of disease and development of blemishes that devalue or ruin the marketability of the potatoes. As the skin and related neighboring tissues (periderm) mature the tubers become resistant to skinning; this process is frequently referred to as skin-set. Despite the costliness of the problem of skinning, nothing was known about the physiology associated with the susceptibility to skinning injury or the changes that cause skin-set. We analyzed immature and mature periderm tissues covering tubers that were susceptible and resistant to skinning. We identified a specific layer of cells which interface and connect the skin (phellem) to tough neighboring cells (phelloderm) near the tuber surface. We found that this single layer of interfacing cells (phellogen) is responsible for susceptibility and resistance to skinning because its cell walls are easily fractured in immature periderm, but are toughened and not easily fractured in mature periderm. The fragile nature of these cell walls in immature periderm is marked by their thinness. As the potato tuber periderm matures and becomes resistant to skinning injury, the walls of these cells thicken and become resistant to fracture. Our results refute previous anecdotal theories for skin- set development and reveal the ultastructural and biological basis for susceptibility and resistance to tuber skinning injury during harvest. Currently, we are identifying the biochemical changes and processes responsible for this cell wall thickening and increased strength as part of a strategy to develop technologies to hasten skin-set.
Technical Abstract: Potato tuber (Solanum tuberosum L.) periderm maturation is an important physiological process that directly affects the susceptibility and development of resistance to costly skinning-type wounds at harvest. We have identified the specific types of cells and cellular changes associated with susceptibility and resistance to tuber skinning injury in immature and mature tubers respectively. Epifluorescent microscopic examination of immature tuber periderm (phellem, phellogen and phelloderm cells) from several genetically diverse cultivars has shown that the cellular damage resulting from skinning injury occurs within the phellogen, a meristematic layer of cells which gives rise to neighboring phellem and phelloderm cells. Skinning results in the fracture of radial phellogen cell walls linking the skin (phellem) to the phelloderm. As the tuber periderm matures and resistance to skinning injury develops, the layer of phellogen cells become inactive and the connective radial cell walls of the phellogen become more resistant to fracture. Ultrastructural studies of immature tuber periderm show that radial walls of active phellogen cells are thin and fragile. During periderm maturation, both radial and tangential phellogen cell walls thicken as they strengthen and become resistant to fracture and thereby provide resistance to skinning injury. These results refute previous theories and reveal the biological basis for susceptibility and resistance to tuber skinning.