Two Types of Water Passages in Okra Hypocotyls

Abrasion of okra hypocotyl segments with carborundum enhances the rate of water uptake into segments, while it decreases the response to auxin. Incubation of abraded segments in buffer recovers the decreased response to auxin. In abraded segments, mercuric chloride is found to inhibit auxin-induced cell elongation. When abraded segments were soaked in 0.3 M sorbitol, they maintained the ability to shrink in the presence of mercury. In contrast, when abraded segments were soaked in a 0.1 M sorbitol solution, mercury completely suppressed osmotic shrinkage. These results suggest that water flows through at least two types of passages; One, which is resistant to mercury, requires a high osmotic pressure such as that provided by 0.3 M sorbitol. The other, which is vulnerable to mercury, requires a low osmotic pressure for water to pass through it.