Biodiversity Science ›› 2007, Vol. 15 ›› Issue (6): 639-644.doi: 10.1360/biodiv.070214

Special Issue: Studies on Plant–Pollinator Interaction

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The relation between stigma position and receptivity in two flexistylous gingers

Min Liu1, 2, Shan Sun1, Qing-jun Li1*   

  1. 1 Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303
    2 Graduate University of the Chinese Academy of Sciences, Beijing 100049
  • Online:2007-11-20

Flexistyly is a unique sexual dimorphic system found in Amomum and Alpinia species of the ginger family (Zingiberaceae). The populations of flexistylous species have two phenotypes, named an anaflexistylous morph and a cataflexistylous morph, and all individuals of both morphs separate their male and female functions spatio-temporally. We conducted manipulated pollinations and pollen tube growth experiments on Alpinia blepharocalyx and A. galanga to detect the manner of separation of male and female functions within the individual and its adaptive significance. The results showed that the outcrossing rates of manipulated and natural pollination in the cata-morph did not differ significantly (P>0.05). However, the number of seeds per fruit of manipulated cata-morphs was significantly lower (P<0.01) than that of control individuals, perhaps due to the inbreeding depression caused by ovule discounting. Pollen tube growth experiments showed that, when stigma were located at the receptive position (ana-morph in AM, cata-morph in PM), stigma provided appropriate conditions (had stigmatic secretion) for pollen grain germination, and pollen tubes penetrated into the style within 2 hours after pollination, regardless treatment of selfing or outcrossing. However, when stigma were beyond the anther (ana-morph in PM, cata-morph in AM, without stigmatic secretion), it usually took 6–10 hours for pollen germination and pollen tube penetration. Pollen tubes, however, could reach the ovary within 24 hours under both treatments. Hand-pollination also showed that pollen grains of anaflexistylous flowers have matured before the dehiscence of pollen sacs. Our research suggests that flexistyly is a floral dimorphism comprising reciprocal mobile herkogamy and heterodichog-amy. Heterodichogamy encourages outcrossing, meanwhile reciprocal curvatures of stigmas play a role of reducing interference between male and female functions.

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