Sieve Element of Impatiens sultanii

Abstract

A Study of wound reaction of the metaphloem of the stem by white-light, fluorescence, and electron microscopy provides evidence for the structure of mature sieve elements in the intact plant. Starch grains usually are retained in plastids which are located against the lateral walls of sieve elements and concentrated at both ends of each cell. Slime plugs and dense connecting strands in the sieve plates seem to result from reactions to cutting or penetration of the killing agent; after appropriate methods of killing, the contents of a connecting strand may be only slightly denser, if any, than the milieu on either side of the sieve plate. A strange accumulation of slime, consisting of streamers directed toward the wound surface from each sieve plate, occurred in tissue boiled immediately after incision of the phloem. Callose is present in sieve elements of intact plants when the tissue is killed within 4 seconds after injury. Callose is accumulated in response to wounding in added amounts, but only after 5 minutes or more and only within about 15 sieve elements from the wound. Quantities of callose sufficient for plugging the sieve plate accumulate after 30 minutes or more. Sieve-plate callose and deposits on the nearby lateral walls produce a cup-shaped mass which is called a cup deposit.