Active Oxygen and Freezing Tolerance in Transgenic Plants

Abstract

Winterhardiness is a complex trait involving tolerances to freezing, water deprivation, ice-encasement (severe anoxia), flooding (milder anoxia) and disease. The combination and severity of these stresses that crops must tolerate varies from environment to environment and from year to year. Different crops, even in the same environment, experience different stresses because of their growth habit. For example, a winter annual crop like wheat (Triticum aestivum L.) grows close to the ground and is covered by snow, whereas a woody fruit crop grows above the snow and is not insulated against cold air temperatures. In northern climates, management of our major crops is based on the avoidance of winter injury. For example, a summer annual is grown in these areas instead of a winter annual, i. e. spring wheat is grown instead of winter wheat. Also, production practices for perennial forage crops, such as alfalfa (Medicago sativa L.), include planting before critical seeding dates, harvesting before critical fall harvest dates, leaving shoot growth to hold snow that will insulate the plants over-winter, and grading to improve surface drainage.