Pea (Pisum sativum L.) tendril-surface changes are correlated with changesin functional development

A scanning electron microscope (SEM) developmental study of tendrils of bot h conventional (Improved Laxton's Progress) and semileafless (Curly) cultiv ars of Pisum sativum was carried out in order to ascertain if there were ch anges in surface features that correlated with tendril functional developme nt and to identify any potential thigmotropic receptors. These results were also compared with leaflet, rachis, and petiole surfaces at comparable dev elopmental stages. Tendrils from the two cultivars did not differ, nor were positional differences found among tendrils from the same leaf. A number o f dome-shaped protrusions were present on the dorsal tip cells of tendrils. These protrusions bear a superficial resemblance to the tactile bleps repo rted for other tendril species. However, they are unlikely to play any role in the thigmotropic response since they are not located at the site of gre atest thigmotropic sensitivity and are also present on leaflet tips. A dist inct pattern of epidermal ridges was found on the tendrils that changes fro m interwoven during the young expanding phase, to primarily radial when thi gmotropic, to nearly absent at maturity. The composition of these structure s was determined, with transmission electron microscopy (TEM), to be wall m aterial and cuticle. Ridges were also variably present on the other cylindr ical organs. These ridges may be related to the requirement by tendrils for directional wall extension during coiling and to similar requirements in r achides and petioles for rapid extension during leaflet unfolding and growt h.