Hypobaria and hypoxia affects growth and phytochemical contents of lettuce

by Nihal C. Rajapakse, Chuanjiu He, Luis Cisneros-Zevallos, Fred T. Davies Jr.

Abstract: The primary objective of this research was to investigate how low pressure (hypobaria) and low oxygen
(hypoxia) affect functional phytochemicals and the nutritional quality of ‘Red Sails’ lettuce (Lactuca
sativa L.). Plants were grown under two levels of total gas pressure (reduced or ambient (25 or 101 kPa,
respectively)) at three levels of O2 partial pressures (low, medium or ambient (6, 12 or 21 kPa,
respectively)). Hypoxia effects on nutritional and functional phytochemicals were more pronounced
than hypobaria effects. Regardless of the total pressure, hypoxia, in general, enhanced leaf anthocyanin
levels, enhanced total phenolic compounds, enhanced carbohydrate concentration and enhanced free
radical scavenging capacity of lettuce but reduced leaf mineral concentration. Hypoxia increased the
ethylene production of plants but ethylene accumulation was not the sole reason for enhanced
anthocyanin production in plants grown under hypoxia. Our results suggest that low oxygen stress
induces the production of protective phytochemicals and the free radical scavenging potential in lettuce,
which may in turn enhance the functional value. However, further human intervention studies are
needed to confirm if enhanced phytochemicals in plants have significant impact in human body.