Structural anomalies in pollen grains of Dyckia racinae L.B.Sm. (Bromeliaceae)

Abstract

The development of the pollen grains is a complex and regulated process. However, failures in sporogenesis and gametogenesis are common and include cell division errors and multiple structural modifications, culminating usually in abortions or, less frequently, in formation of anomalous pollen grains. These anomalies include altered morphology and functionality and are reported in several species, but are still unexplored in Bromeliaceae, a diverse neotropical family. Thus, this work structurally describes anomalous pollen grains in anthers of Dyckia racinae L.B. Sm., a Bromeliaceae species endemic to Southern Brazil. Mature anthers were processed and analyzed using standard methods for light microscopy. In addition to structurally normal pollen grains, unicellular, geminate, voluminous and aborted pollen grains were structurally described. These morphological alterations include differences in developmental destination, pollen grains with varied sizes, fusions with cytoplasmic communications, morphological alterations in exine and intine and variations in the cytoplasmic content. These anomalies are normally related to developmental disruptions, such as altered programmed cell death in tapetum, associated with cytoplasmic male sterility, for example, which usually leading to extensive abortion of the pollen grains in the anther locules. The structural anomalies described in this study, however, occur in anthers with apparently normal development and were first described for Bromeliaceae. Our results suggest a partial male sterility for this species, an unexplored embryological aspect of pollen grains in this family. Future investigations of ultrastructure and development of the anomalous pollen grains should contribute to a better understanding of the reported anomalies.