Abstract

Darwin famously referred to the origin of flowering plants (angiosperms) as an ‘abominable mystery’. Flowering plants are the most diverse group of land plants, and the ability to vary floral traits has been key to their success. One such floral innovation is the nectar spur (a tubular outgrowth of the petal which may contain nectar). Nectar spurs protect nectar from the environment and also enhance pollinator specificity, pollination efficiency and reproductive success. Despite their ecological importance, much is still unknown about the development and morphogenesis of spurs as there are no conventional model plant species which possess a nectar spur.

This project aims to probe the morphological and molecular basis of nectar spur outgrowth. To understand the basis of nectar spur outgrowth, a species which possesses a nectar spur (Linaria vulgaris) was compared to a closely related species which does not (Antirrhinum majus). A comparative transcriptome (the sum of all of the genes which are expressed by cells at that time point) was performed in order to give a global view of the genes involved in spur development and produce new candidate genes which may be involved in spur outgrowth in Linaria. Nectar spur length can be highly variable. Control of variation in nectar spur length was also investigated, focusing on two closely related species which have extremely long and short spurs respectively. A morphological characterisation was undertaken (recording cell number and cell length across a range of developmental stages) to determine whether the difference in spur length between the species is due to cell expansion or cell division. We found that primarily cell number and therefore cell division drives an increase in spur length in Linaria. This contrasts with previous studies in Aquilegia which have found that variation of nectar spur length is due to directed cell expansion over a longer timeframe. These data suggest that spurs may have evolved in different systems by disparate mechanisms.