Reddish-brown granules observed within the cytoplasm of generative cells of pollen grains in hymenocallis littoralis (Amaryllidaceae)

Abstract

In some monocotyledonous plants, the generative cell of mature pollen grains possesses small, colored granules within its cytoplasm. However, the identity and origin of these colored granules have been unclear. We unexpectedly found that in Hymenocallis littoralis (Amaryllidaceae), the generative cell of mature pollen grains contained numerous reddish-brown granules. The present investigation was conducted to determine their origin and identity by light and electron microscopy. Most of the generative cells attached to pollen walls were pale red. At this stage, together with small vacuoles, crescent-shaped cavities each encircling some part of the cytoplasm and vacuoles containing cytoplasm appeared within the generative cell cytoplasm. The generative cell detached from the pollen wall and became reddish-brown and spindle shaped in mature pollen. The generative cell contained many small vacuoles. No chromoplasts and few lipid droplets were observed within the cytoplasm. The generative cell entered the pollen tube and divided into two sperm cells, each having many reddish-brown granules. These granules were stainable with neutral red. These results indicate that the reddish-brown granules correspond to small vacuoles and that their formation may commence prior to the detachment of the generative cell from the pollen wall, probably partly in association with autophagy. © 2013 The Japan Mendel Society.