4 – anatomical mechanisms of seed dispersal

Cortical cells within the abscission zone of Nicotiana tabacum flower pedicels were examined to identify cellulases at the fine structural level. A cytochemical method reported by Bal et al. for the ultrastructural localization of cellulase was modified and applied to study cell wall breakdown during ethylene-induced abscission and abscission where pollination was prevented. The deposition of copper (Cu), a precipitate of the Benedict's solution-cellulose sugars reaction, was utilized as a marker to detect cellulase activity in the abscission zone cells. The Cu precipitate was observed principally in the middle lamella region of the cell wall and was also observed in small amounts in the primary and secondary regions of the cell wall. Time-course studies for both ethylene-treated tissue and tissue where pollination was prevented indicated that cellulase activity was at its highest level during advanced stages of abscission. The break strengths of the abscission zone decreased prior to the increase in cell...

Ultrastructural Localization of Cellulase in Abscission Cells of Tobacco Flower Pedicels

Chapter 7 – Phytogerontological Effects of Ethylene

Long before it was established that plant metabolism and growth is regulated and influenced by plant hormones, the action of the plant hormone ethylene on plants was observed and ethylene was recognized as the inducing agent. The first reports on ethylene action date back to 1858, describing plant responses to illuminating gas. At the end of the 19th century a pineapple farmer on the Azores, experimenting with fumes in the greenhouse to kill insects, discovered an earlier flowering of the pineapple plants after this treatment. In the following years the method to induce flowering of pineapple in the greenhouse by fumes became common on the Azores. This was probably the first application of a “plant growth regulator” in agriculture. In a report of 1901, the “triple response” of etiolated pea seedlings (growth inhibition, thickening of the subapical region, horizontal nutation) was observed to occur in the presence of illuminating gas and ethylene was identified as the inducing agent. In 1912 the induction of fruit ripening by ethylene was recognized. The role of ethylene in flower induction of pineapple was established in 1932 (Rodriguez, 1932).

Plant Responses to Ethylene and Ethylene Releasing Compounds

2-Chloroethylphosphonic acid (CEPA) facilitates the separation of the fruit from the pedicel significantly. The application of 2,000 and 4,000 ppm CEPA in four sweet cherry varieties during maturation resulted in the formation of a complete abscission layer in the transition zone between pedicel and fruit. In contrast, in the untreated fruit no abscission layer was evident at maturity. The walls of the cells in the abscission layer contained less total polysaccharides than adjacent cells. Cellulose was partially broken down, and the pectins were degraded. The Ca and Mg content in the cell walls decreased. Thus the same histochemical changes are involved in natural and CEPA induced abscission.

R. Stösser

Papers

Die induktion eines trenngewebes bei früchten von Prunus avium L. durch 2-Chloräthylphosphonsäure