Is Xylem Embolism and Refilling Involved in the Rapid Wilting and Recovery of Plants Following Root Cooling and Rewarming?

Abstract

Rapid wilting and subsequent rapid recovery of the shoots of plants whose roots are cooled and rewarmed (first described by Sachs, 1860^[23]), has been investigated by cryoscanning electron microscopy. Squash plants began to wilt within 5 min and were completely wilted 1 h after their roots were placed in nutrient solution at 4°C. Recovery began in 5 min and was complete by 45 min when the roots were returned to solution at 22°C. Some stomata on the abaxial leaf surface remained fully or partially open in the wilted plants and transpiration continued at a low level. Both control and wilted plants had the same proportion (60%) of large root vessels partially or totally gas-filled, showing that the supply of water was not limited by the reduction of axial hydraulic conductance due to vessel embolism. However, only 10% of these embolized vessels in the wilted plants contained any liquid, compared to ∼80% of similar vessels in control and recovered plants. This is visual evidence of reduced radial hydraulic conductance into the vessels in the cold roots, and that this reduced conductance, together with still open-stomata, produces wilting. These effects were reversed by rewarming.

Key words

Chilling - cryo-microscopy - Cucurbita maxima Duchesne - root hydraulic conductance - root cooling - transpiration - xylem vessel embolism - wilting