ABSTRACT

Exogenous ethylene inhibited nodulation on the primary and lateral roots of pea, Pisum sativum L. cv Sparkle. Ethylene was more inhibitory to nodule formation than to root growth; nodule number was reduced by half with only 0.07 µL/L ethylene applied continually to the roots for 3 weeks. The inhibition was overcome by treating roots with 1 µM Ag, an inhibitor of ethylene action. Exogenous ethylene also inhibited nodulation on sweet clover (Melilotus alba) and on pea mutants that are hypernodulating or have ineffective nodules. Exogenous ethylene did not decrease the number of infections per centimeter of lateral pea root, but nearly all of the infections were blocked when the infection thread was in the basal epidermal cell or in the outer cortical cells.

INTRODUCTION

Ethylene has been implicated as a regulator in many aspects of plant growth and development, response to stress, and senescence (14). Although several factors such as species, tissue type, and stage of development affect the plant response to ethylene, the concentrations of exogenous ethylene that produce visible symptoms are usually in the range of 0.1 to 1.0 µL/L. For example, the half-maximal response of growth inhibition of etiolated pea roots (Pisum sativum L.) was about 0.34 µL/L (4).

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