Morphological studies of rose prickles provide new insights

Prickles are common structures in plants that play a key role in defense against herbivores. In the Rosa genus, prickles are widely present with great diversity in terms of form and density. For cut rose production, prickles represent an important issue, as they can damage the flower and injure workers. Our objectives were to precisely describe the types of prickles that exist in roses, their tissues of origin and their development. We performed a detailed histological analysis of prickle initiation and development in a rose F1 population. Based on the prickle investigation of 110 roses, we proposed the first categorization of prickles in the Rosa genus. They are mainly divided into two categories, nonglandular prickles (NGPs) and glandular prickles (GPs), and subcategories were defined based on the presence/absence of hairs and branches. We demonstrated that NGPs and GPs both originate from multiple cells of the ground meristem beneath the protoderm. For GPs, the gland cells originate from the protoderm of the GP at the early developmental stage. Our findings clearly demonstrate that prickles are not modified trichomes (which originate from the protoderm). These conclusions are different from the current mainstream hypothesis. These results provide a foundation for further studies on prickle initiation and development in plants.