J Syst Evol ›› 2015, Vol. 53 ›› Issue (2): 166-178.DOI: 10.1111/jse.12142

• Research Articles • Previous Articles     Next Articles

Distyly and cryptic heteromorphic self-incompatibility in Mussaenda macrophylla (Rubiaceae)

Xiao-Qin Wu1 , Pei-Xing Li1,3, Xiao-Fang Deng1,2, and Dian-Xiang Zhang1 *   

  1. 1Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China
    2State Academy of Forestry Administration, Beijing, China
    3University of Chinese Academy of Sciences, Beijing, China
  • Received:2014-01-13 Accepted:2014-12-25 Online:2015-03-05 Published:2015-03-25

Abstract: Typical distylous species display both reciprocal herkogamy and heteromorphic incompatibility, which exclude self- and intramorph pollination and accordingly promote intermorph pollination. Here we explore an unusual distylous flower associated with self- and intramorph compatibility in Mussaenda macrophylla Wall. The species did not exhibit a precise reciprocal herkogamy, and the populations studied had a slight bias in favor of the short-styled morph (S-morph). In addition, pollen tube growth in intermorph pollination was faster than either in intramorph or self-pollination, indicating that cryptic heteromorphic self-incompatibility occurred in M. macrophylla. Specifically, pollen tube growth rates after legitimate and illegitimate pollination were much more highly differentiated in long-styled morph (L-morph) than in S-morph, which might be attributed to the increased de-esterified pectin in the tip of L-morph pollen tube wall in comparison with S-morph. Transmission electron microscopic observation revealed illegitimate self-pollinated pollen tubes of two morphs were seriously degraded with the large autolysosome-like vacuoles in cytoplasm of L-morph pollen tube but accumulating small vacuoles in that of S-morph pollen tube, suggesting that incompatible pollen tubes might undergo autophagic programmed cell death except self-incompatible S-morph pollen tubes. Our results indicate that M. macrophylla is morphologically distylous with a cryptic heteromorphic self-incompatibility breeding system, which functions differently in S-morph with self-pollination compared with other illegitimate pollination.

Key words: cryptic self-incompatibility, distyly, Mussaenda macrophylla, pollen tube growth, Rubiaceae