The time course of the induction of callose in wounded pea roots

Summary Initial study indicated that much callose is produced in pea root tissues during the preparation of fresh hand-cut sections or during conventional fixation in formalin-acetic acid-alcohol, glutaraldehyde or acrolein. In contrast, there is little callose in freeze-substituted tissues and this is mostly in sieve tubes and considered endogenous. Freeze-substitution was subsequently used to monitor wound-induced callose development in the various tissues of pea roots. This development was fastest in the phloem, first detected 1 minute post-wounding and complete by 3 hours. In some parenchyma cells full development was delayed by 20 hours. By 100 hours, wound callose was no longer detectable in parenchyma cells but remained undiminished in the phloem. The implications of these results for all studies involving callose localization are discussed.Abbreviations C callose - FAA formalin-acetic acid-alcohol - GMA glycol methacrylate - P phloem - PAS periodic acid-Schiffs - PF phloem fibres - PP pith parenchyma - PW post-wounding