Understanding ontogenetic trajectories of indirect defence: ecological and anatomical constraints in the production of extrafloral nectaries.

BACKGROUND AND AIMS: Early ontogenetic stages of myrmecophytic plants are infrequently associated with ants, probably due to constraints on the production of rewards. This study reports for the first time the anatomical and histological limitations constraining the production of extrafloral nectar in young plants, and the implications that the absence of protective ants imposes for plants early during their ontogeny are discussed. METHODS: Juvenile, pre-reproductive and reproductive plants of Turnera velutina were selected in a natural population and their extrafloral nectaries (EFNs) per leaf were quantified. The anatomical and morphological changes in EFNs during plant ontogeny were studied using scanning electron and light microscopy. Extrafloral nectar volume and sugar concentration were determined as well as the number of patrolling ants. KEY RESULTS: Juvenile plants were unable to secrete or contain nectar. Pre-reproductive plants secreted and contained nectar drops, but the highest production was achieved at the reproductive stage when the gland is fully cup-shaped and the secretory epidermis duplicates. No ants were observed in juvenile plants, and reproductive individuals received greater ant patrolling than pre-reproductive individuals. The issue of the mechanism of extrafloral nectar release in T. velutina was solved given that we found an anatomical, transcuticular pore that forms a channel-like structure and allows nectar to flow outward from the gland. CONCLUSIONS: Juvenile stages had no ant protection against herbivores probably due to resource limitation but also due to anatomical constraints. The results are consistent with the growth-differentiation balance hypothesis. As plants age, they increase in size and have larger nutrient-acquiring, photosynthetic and storage capacity, so they are able to invest in defence via specialized organs, such as EFNs. Hence, the more vulnerable juvenile stage should rely on other defensive strategies to reduce the negative impacts of herbivory.

Respuesta in vitro de diferentes biotipos y explantos de Passiflora caerulea L / In vitro response of different biotypes and explants of Passiflora caerulea L

Passiflora caerulea L., al igual que otras especies de la familia Passifloraceae, es utilizada en la medicina popular por sus propiedades antiespasmódicas y para el tratamiento de la ansiedad, el insomnio y el nerviosismo. La belleza de sus flores les otorga valor ornamental, mientras que sus frutos son apreciados por su importancia alimenticia. Se evaluó la respuesta in vitro de diferentes explantos y tres biotipos de P. caerulea: Corral de Bustos (provincia de Córdoba), Zavalla (provincia de Santa Fe) y Neuquén (provincia de Neuquén). Se utilizaron dos tipos de explantos: entrenudos y segmentos nodales, y como medio de cultivo Murashige y Skoog (1962) (MS), suplementado con vitaminas de Gamborg (1976) y 1 mg/L-1 de benciladenina (BA). Las respuestas fueron diferentes según el genotipo y el explanto. Los entrenudos ubicados tanto horizontal como verticalmente en medio de cultivo generaron callos como única respuesta. El biotipo de Neuquén mostró los mayores porcentajes de segmentos nodales con brotes. A través de estudios histológicos se determinó que en medio de cultivo MS con 1 mg/L-1 de BA, los segmentos nodales de P. caerulea originan brotes a partir de las yemas axilares preformadas y raíces que parten de callos en la base de los mismos. En iguales condiciones, los entrenudos originan callo como única respuesta.

As other species of the Passifloraceae family, Passiflora caerulea L. is used in popular medicine for its antispasmodic properties and as a remedy for anxiety, insomnia and nervousness. It is also highly prized for the ornamental value of its beautiful flowers, as well as for the nutritional importance of its fruits. The in vitro response of different explants and three biotypes of P. caerulea: the Corral de Bustos (Province of Córdoba), the Zavalla (Province of Santa Fe) and the Neuquén (Province of Neuquén) genotypes, was evaluated using two types of explants: internodes and nodal segments on Murashige and Skoog (1962) (MS) culture medium supplemented with Gamborg’s vitamins (1976) and 1 mg.L-1 of benzyladenine (BA). There were different responses depending on the genotype and the explant. The internodes placed both horizontally and vertically in the culture medium produced callus as sole response. The Neuquén biotype showed the highest percentages of nodal segments with shoots. Histological tests allowed to establish that in MS culture medium with 1 mg.L-1 of BA, the nodal segments of P. caerulea produce shoots from the preformed axillary buds and roots that develop from the callus situated on its base. Under similar conditions, the internodes produce callus as sole response.