Morphological studies of developingRubusprickles suggest that they are modified glandular trichomes

Prickles are defined as outgrowths of epidermal tissues and can provide a simple developmental system for the study of the control of cell proliferation and growth. Setting the stage for future studies on gene regulation in the genus Rubus (brambles), a detailed analysis and staging series of prickle development in Rubus idaeus subsp. idaeus L. (red raspberry) is presented and compared with Rubus L. subsp. rubus Watson (blackberry) and Rosa hybrida L. 'Radtko' (rose). Morphological measurements from light and scanning electron micrographs were used to subdivide prickle development into four stages. Our studies indicate that raspberry and rose prickles are modified glandular trichomes continuing to grow and eventually hardening into their final prickle morphologies as outgrowths of epidermal tissue. Although glandular trichomes seem to be involved in blackberry prickle development, our studies indicate that these prickles do not follow the same developmental progression as raspberry, suggesting a potential evolutionary deviation from what is commonly seen in raspberry and rose.