Positive and Negative Messages from Roots Induce Foliar Desiccation and Stomatal Closure in Flooded Pea Plants

Abstract

Flooding the soil for 5–7 d caused partial desiccation in leaves of pea plants (Pisum sativum. L. cv. ‘Sprite’). The injury was associated with anaerobiosis in the soil, a large increase in the permeability of leaf tissue to electrolytes and other substances, a low leaf water content and an increased water saturation deficit (WSD). Desiccating leaves also lacked the capacity to rehydrate in humid atmospheres, a disability expressed as a water resaturation deficit (WRSD). This irreversible injury was preceded during the first 4–5 d of flooding by closure of stomata within 24 h, decreased transpiration, an unusually large leaf water content and small WSD. Leaf water potentials were higher than those in well-drained controls. Also, there was no appreciable WRSD. Leaflets detached from flooded plants during this early phase retained their water more effectively than those from controls when left exposed to the atmosphere for 5 min. Stomatal closure and the associated increase in leaf hydration could be simulated by excising leaves and incubating them with their petioles in open vials of water. Thus, such changes in flooded plants possibly represented a response to a deficiency in the supply of substances that would usually be transported from roots to leaves in healthy plants (negative message). Ion leakage and the associated loss of leaf hydration that occurs when flooding is extended for more than 5 d could not be simulated by isolating the leaves from the roots. Appearance of this symptom depended on leaves remaining attached to flooded root systems, implying that the damage is caused by injurious substances passing upwards (positive message). Both ethylene and ethanol have been eliminated as likely causes, but flooding increased phosphorus in the leaves to concentrations that may be toxic.