Determination of the rate of 18F-labeled water movement to the leaf and its association with water relations in acid soil-tolerant rice varieties

Abstract

The visual symptoms of damage by acid sulfate soil look quite similar to those due to soil moisture deficit. The present paper is to confirm if acid soil-tolerance is associated with drought tolerance in terms of leaf water potential, transpiration, and dry matter production. Seedlings of seven acid soil-tolerant (acid-tolerant), and three acid soil-intolerant varieties (acid-intolerant) were subjected to low pH conditions (pH 3.8) for 48 hours. The rate of water uptake was determined continuously by measuring radioactivity in the collar part (target area) of rice leaves exposed to 18F-labeled water (18F-water) using a Positron Emitting Tracer Imaging System (PETIS). The PETIS measurement showed that the radioactivity in the target position of leaves of acid-tolerant varieties increased faster than that of the intolerant varieties after the 18F-water was applied into the vial. In the plants subjected to low pH conditions, the transpiration rate (Tr) and leaf water potential (Ψ) decreased in both acid-tolerant and intolerant varieties. However, the extent of reduction was less in the acid-tolerant varieties than in the intolerant ones. Moreover, the dry matter production rate of the acid-tolerant varieties was significantly higher than that of the acid-intolerant ones in the low pH conditions. This study clearly shows that 18F-water uptake in a leaf was higher, and water relations were also better maintained in the acid-tolerant varieties compared with intolerant ones, resulting in higher growth rate in the acid-tolerant varieties, when plants were exposed to the acid solution conditions. We conclude that acid soil-tolerance is closely associated with leaf water relations in rice plants.