How pollen and ovule development underlay dioecy in Chloroluma gonocarpa (Sapotaceae)

Abstract

Previous studies have determined that Chloroluma gonocarpa (Sapotaceae), is a species that has cryptic dioecy. This typeof sexual system is characterized by flowers that are morphologically perfect (both sexual whorls are present) but functionallypistillate or staminate (in each type of flower one of the sexual whorls is non-functional). In C. gonocarpa the pistillateflowers present well-developed stigma, functional ovules, and staminodes, while the staminate flowers present a poorlydeveloped stigma, collapsed ovules, and pollen-producing anthers. In angiosperms, the abortion of sexual organs can occurat different stages of development (from pre-meiosis to post-meiosis), that is why we conducted an anatomical analysisof both flower types at various developmental stages. Using light microscopy, we described the processes of sporogenesisand gametogenesis to establish when the staminate flowers lose their pistillate function. To achieve this, we collected,fixed, and processed the flowers following conventional anatomical techniques for observation under a light microscope.Our findings reveal that pollen development occurs only in staminate flowers, while ovule development begins in bothtypes of flowers but ceases in staminate flowers due to post-meiosis abortion. In contrast, normal development continuesin pistillate flowers. These results suggest that dioecy in C. gonocarpa may have arisen from a gynodioecious pathway.