Histological changes during maturation in male and female cones of the cycad Zamia furfuracea and their significance in relation to pollination biology

Abstract

Abstract The cycad Zamia furfuracea L. Fil. is pollinated by a curculionid beetle, Rhopalotria mollis Sharp which completes its life cycle in male cones of the cycad, and effectively pollinatcs female cones. ldioblasts within parenchyma in both male and female cones appear to contain toxic compounds, including at least one neurotoxin, 2-amino-3-(methylamino) propanoic acid (BMAA), and a toxic glycoside, methylazoxymethanol-β-primeveroside (macrozamin). Idioblasts appear structurally unmodified in male cones throughout the period of pollen maturation, and feeding weevils consume much of the starch-rich microsporophyll parenchyma tissue, including idioblasts. During this activity no appreciable change in morphology or staining reactions of male-cone idioblasts is detectable. Prior to pollen receptivity, female-cone idioblasts resemble those of male cones. Thereafter, many female-cone idioblasts show marked changes in morphology and content not caused by the weevils themselves. Idioblast changes in female cones are probably associated with the defence of female cone resources against predation by animals, including pollinating weevils, and may relate to mobilization of toxins. Absence of similar morphological changes in male-cone idioblasts is correlated with toxin sequestration, enabling the pollinator to breed and feed without intoxication.