Plant Hormone Interaction and Phenolic Metabolism in the Regulation of Russet Spotting in Iceberg Lettuce

Abstract

Russet spotting (RS2) is a physiological disorder that may develop during postharvest transport and storage of iceberg (crisphead) lettuce (Lactuca sativa L.). This disorder is characterized by the appearance along both sides of the midrib of numerous small brown spots that may spread over the leaf blade in severe cases (9). .Exposure to ppm levels of ethylene at storage temperatures around 5°C induces RS development (14). Susceptibility to RS depends on storage temperature, ethylene concentration, oxygen and carbon dioxide levels, maturity, and cultivar (13).Anatomical studies (6, 10) have indicated cell wall thickening and cell discoloration as two major changes associated with RS. These symptoms may start either in the epidermis or in the mesophyll. In advanced stages, the mesophyll cells may collapse and form pit-like depressions. Hyodo et al. (5) found that ethylene induced an increase in PAL activity which suggested the involvement of this enzyme in RS development. We have reported that the application of calcium or 2,4-D inhibited RS development and PAL activity (7). The purpose of this research was to identify the biochemical pathways related to the development of RS symptoms (cell wall thickening and cell discoloration) and the regulation of these pathways by plant hormones, especially ethylene and auxin.

Quality of Cut Lettuce Treated by Heat Shock: Prevention of Enzymatic Browning, Repression of Phenylalanine Ammonia-lyase Activity, and Improvement on Sensory Evaluation during Storage

“…Several studies have described a relationship between the PAL activity in lettuce leaves and browning. [6][7][8] We also showed that inhibitors of the shikimate and phenylpropanoid pathways repressed the browning of cut lettuce and that regulating polyphenol biosynthesis was essential to repress the browning.…”

“…It is well known that PAL is induced by stress such as ethylene or wounding. [6][7][8][9] Cutting lettuce for minimal processing induces a stress in lettuce. On the other hand, the PAL activity of the cut lettuce treated by heat shock was only a little detected during storage.…”

Influence of nutrient sources on growth, yield and economics of organic lettuce production under foothills of eastern Himalayan region

“…The head and leaves are rich in several minerals, vitamins and important source of dietary antioxidants (Ke and Saltveit, 1988;Nicolle et al, 2004). With the increasing awareness on ill effect of chemical faming on human health and environment, the demand of organic lettuce for salad and other preparation is increasing sharply both in domestic and international market.…”

Regulation of Enzymatic Browning of Mung Bean Sprout by Heat-Shock Treatment

“…However, we suppose that phenylalanine ammonia lyase (PAL; EC 4.3.1.24), one of the key enzymes of polyphenol biosynthesis, is induced during cold storage and that the synthesized polyphenols are oxidized by PPO to form a brown pigment. In cut lettuce, the PAL activity is induced by cutting or injury, which leads to the accumulation of phenolic compounds and enzymatic browning during cold storage (Lopez-Galvez et al, 1996;Ke and Saltveit, 1988;Hisaminato et al, 2001). Induction of PAL activity can be repressed by heat-shock treatment to inhibit browning of lettuce (Loaiza-Velarde et al, 1997;Saltveit, 2000;Murata et al, 2004).…”