The Role of Free Indole-3-acetic Acid (IAA) Levels, IAA Transport, and Sucrose Transport in the High Temperature Inhibition of Primary Root Development in Pea (Pisum sativum L. cv. Alaska)

Abstract

Growth of Alaska pea (Pisum sativum L.) at high temperature results in general inhibition of the root system. As part of a study on the effects of temperature on developmental timing, we tested the possibility that reductions in free indole-3-acetic acid (IAA) levels, IAA transport, or sucrose transport might be responsible for inhibition of primary roots. Seedlings were grown at 25 and 32°C. For transport studies, pea cotyledons were inoculated with 3 H-sucrose and 14 C-IAA. Free endogenous IAA in tips of pea primary roots was determined at three stages of development by gas chromatography-mass spectrometry (GC-MS) using a 13 C-IAA internal standard. Differences in mean free IAA concentration between temperature treatments were not significant during the early stages of development (28 to 58 ng/g FW). IAA concentration increased significantly in root tips during the late stage at both temperatures (108-165 ng/g FW) when elongation was declining. Differences in sucrose and IAA transport rates between temperatures were minor. Differences at each temperature over time were consistent with stage-specific growth patterns. Neither transport failure nor differences in free IAA level appear responsible for developmental inhibition of pea primary roots. Results suggest that pea primary root inhibition at high temperature is not due to heat-induced stress on transport systems but rather to shifting of developmental timing.