Heat shock induced changes in exocarp soluble sugars of lemons from two climatic regions

Investigations were conducted to ascertain whether the 55 degreesC heat shock induced changes in soluble sugars of the exocarp (flavedo) of lemons, Citrus limon (L.) Burm. F., derived from two distinct climatic growing regions. The exocarp sugars of coastal- and desert-grown lemons were quantitatively different, but both geographically different lemons responded with sucrose increases to 55 degreesC heat shock of >3 min duration. However, the responses were influenced by fruit maturity and seasonal factors. When comparing the response of coastal- and desert-grown lemons to heat shock treatment, the exocarp sucrose levels were noteworthy. Heat shock significantly increased sucrose level of early-season coastal lemon more than mid- to late-season lemons. In contrast, late-season desert lemon showed a striking response to the heat shock treatment, with a greater increase in sucrose than mid- and early-season lemons. These results suggest a physiological basis for the differential responses to heat treatment of lemons from different geographical regions. The concomitant decreases of glucose and fructose and the sucrose increase with heat shock implied that the sucrose increase may be derived by synthesis from glucose and fructose.