Incorporation of [3H]sucrose after the resorption of nectar from the spur of Platanthera chlorantha (Custer) Rchb.

Abstract

Platanthera chlorantha (Custer) Rchb., a moth-pollinated orchid, secretes abundant nectar. Sucrose incorporation following the resorption of nectar from the spurs of the pollinated and unpollinated flowers of P. chlorantha was investigated. The study was carried out using 3H-labelled sucrose and microautoradiography. In this orchid species, nectar was secreted and accumulated in the spur. Inside the spur, the epidermis developed numerous unicellular secretory hairs engaged in nectar secretion and resorption. Nectar resorption occurred near the end of anthesis. Following pollination, sucrose from the resorbed nectar was incorporated into starch accumulated in parenchyma cells of developing capsules. Additionally, radioactivity in the cell walls of parenchyma and ovules was also observed. The label was not detected either in the gynoecium of unpollinated flowers or in tuberous roots of all plants investigated. Therefore, the results demonstrate that carbohydrates reclaimed from uncollected nectar in pollinated flowers of P. chlorantha are next utilized inside the adjacent maturing fruits.Key words: Platanthera chlorantha, Orchidaceae, nectar resorption, nectary spur, microautoradiography, pollination.