Calcium distribution during pollen development of Uncaria hirsuta Havil. (Rubiaceae), with special reference to the function of the protruding oncus

Abstract

Calcium distribution in the developing anthers of Uncaria hirsuta was studied with the potassium pyroantimonite method. The amount and distribution of calcium precipitates change along with the developing anthers and pollen grains in U. hirsuta. Calcium distribution is closely correlated with the anther wall differentiation, exine and intine formations. In mature pollen grains, abundant calcium is in intine, protruding onci and nucleus. A generative cell has more calcium than a vegetative cell does. The calcium storage is likely to contribute to pollen germination, and mitosis of the generative cell. Ubisch bodies formed at the same period with the pollen exine development, and some of them are in close contact with the exine. Abundant calcium is present in the Ubisch bodies, protruding onci and tapetum. These results might support the idea that Ubisch bodies and protruding onci participate in calcium transportation during pollen development. The protruding oncus is likely to have function of calcium or other ions transportation, although further experiment and additional data are required to confirm this. The present study also provides confirmatory evidence to the previous knowledge that calcium participates in regulation of cell differentiation, degradation in each layer of anther wall cells, and pollen development.