Involvement of ethylene in growth induction of stationary tobacco pith tissue in vitro

Abstract

The effects of ethylene on growth initiation of tobacco pith tissue in vitro were investigated. Pith explants were incubated on a double inorganic modified White’s media containing 0.2 mg l⁻¹ kinetin with and without indole-3-acetic acid (IAA) and the ethylene synthesis inhibitor aminooxyacetic acid (AOA). The burst of wound ethylene had no effect on growth initiation, was not affected by the AOA, and decreased to its minimum level during the initial 24 h in culture. Tissue growth was initiated after 72 h and continued on IAA-containing media only. A marked increase in ethylene evolution occurred only in tissues subjected to an IAA-containing medium prior to growth initiation. AOA inhibited this ethylene synthesis and the following growth of the tissues. The initial water uptake by the pith explants occurring even in the absence of IAA was also inhibited by AOA. The metabolic indicators for growth initiation such as enhanced respiration, increased activity of nitrate reductase, and initiation of cathodic isoperoxidases were all inhibited by AOA. It was concluded that the primer function of IAA in growth initiation is via inducing the biosynthesis of a marked ethylene signal, which in the absence of which active growth will not occur. The inhibiting effect of AOA is continuous and a transfer of the pith explants to fresh IAA-containing media did not result in a new ethylene burst nor tissue growth induction. The morphological changes in the tissues and cells during the initial stages of their development on the different media are demonstrated.