Annals of Botany

Attractive bodies energize ants

Relationships between plants and animals are many and varied. Pollination and seed dispersal are obvious examples but there are others. Thus, Buono et al. of Bel Horizonte, Brazil (pp. 1341–1348) discuss mutualistic relationships in which ants help to protect plants from herbivory by other invertebrate species, i.e. the employment of one type of animal to ward off attacks by other animals. At their most developed, plant–ant relationships involve ants living in or on the plants; such plants are known as myrmecophytes. The ants obtain much of their nutrition from food bodies (FBs) in which proteins, lipids and carbohydrates are deposited. In many of these species, FBs are modified trichomes but they can also be derived from other cell types, including epidermis and parenchyma. There are also forms of plant–ant mutualism in which ‘plants. . . offer food to ants but not shelter’; these plants are classified as myrmecophyles. The production of FBs is known to occur in several angiosperm families but had not been previously seen in the Rhamnaceae. However, Buono et al.’s observations on Hovenia dulcis, a tree that is native to Asia, add that family to the list. The authors observed multi-cellular FBs on the abaxial face, especially alongside the midrib and second- and third-order veins, of leaves in trees of all ages from postseedling (20 cm high) to immediately before the reproductive phase. Ants of the genera Camponotus and Crematogaster were observed visiting the plants, breaking the FBs from the leaves and transporting them away. FBs in this species can be derived from several tissues, including epidermis and parenchyma. The epidermis of the FB does not store nutrients but may act as a protective layer for the nutrient-storing FB parenchyma cells. Analysis of the FBs showed that the main storage compounds are starch and lipids, the latter mainly consisting of glycerin esters of fatty acids, giving a very ‘energy-rich’ mix for the ants.