ABSTRACT
Mangosteen (Garcinia mangostana L.) is an economically important tropical fruit, yet the reproductive biology of this dioecious plant is complex. Male trees are not known, and female trees have sterile anthers leading to apomixis. We hypothesized that pollen abortion in mangosteen is due to altered tapetum activity during microgametogenesis. Developmental events at the cellular and sub-cellular levels during pollen development in G. mangostana were therefore examined and compared with seashore mangosteen (G. celebica L.), a closely related species with fertile anthers. In G. mangostana, the microspore mother cell had disorganized cytoplasm, including lack of Golgi apparatus and its vesicles, as well as abnormal callose wall accumulation. Globular droplets, which resembled orbicules or Ubisch bodies, were abundant in the locule, including pre-Ubisch bodies found along the tapetal plasma membrane. The tapetum of G. mangostana underwent cell death earlier than the fertile G. celebica, and during the premature death, the mitochondria had dramatically altered shapes. Low accumulation of starch in collapsed microspore mother cells and tetrad cell remnants also suggested that altered cell metabolism is related to pollen abortion in mangosteen. The present results demonstrate the importance of coordinated development between the tapetum and microspores in pollen development and provide new insights into male sterility in mangosteen (G. mangostana).