Pollen development in male sterile mangosteen (Garcinia mangostana L.) and male fertile seashore mangosteen (Garcinia celebica L.).

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).

Vitrification-based cryopreservation of protocorm-like bodies of an endangered lady's slipper orchid: Paphiopedilum niveum (Rchb.f.) Stein.

BACKGROUND: Paphiopedilum niveum (Rchb.f.) Stein, an endangered lady's slipper orchid, is listed in CITES Appendix I and thus requires conserving. OBJECTIVE: The study aimed to cryopreserve protocorm-like bodies (PLBs) by a vitrification technique. MATERIALS AND METHODS: Four-month-old PLBs were precultured in modified Vacin and Went liquid medium with various sucrose concentrations for 24 h and 5 d with daily increasing sucrose concentrations followed by different exposure times to plant vitrification solution 2 (PVS2). RESULTS: Precultured PLBs in 0.75 M sucrose for 5 d with stepwise increase of sucrose and PVS2 for 90 min provided the highest viability after drying to low moisture content. The cryopreserved PLBs exhibited fewer dark stained nuclei and accumulated starch grains than those of the control. Cryopreserved PLBs had some shrunken epidermal cells, no change in ploidy level, a survival level of 22 % and the regenerated plantlets grew well. CONCLUSION: This study is the first report evaluating the success of cryopreserved PLBs of P. niveum via a vitrification protocol.

Stigma closure and re-opening in Oroxylum indicum (Bignoniaceae): Causes and consequences.

The study of plant responses to touch, particularly the responses of leaves, stems, and roots, has a long history. By contrast, floral responses are relatively unexplored. Stigma closure is common in the Bignoniaceae, but the factors influencing it are not well understood. We investigated factors influencing stigma closure and reopening and its effects on pollen receipt in seven Oroxylum indicum trees near Hat Yai, Thailand. The effects of pressure, conspecific and heterospecific pollen, and pollen load (the amount of pollen deposited) on stigma behavior were examined in 270 flowers (of the total 430 flowers evaluated in the entire study). Pressure alone resulted in faster closure than did conspecific pollination and faster reopening than did heterospecific pollination. Stigmas never reopened after conspecific pollination. Pollen load had no effect on stigma behavior. Stigmas discriminated between conspecific and foreign pollen; they reopened only after pollination with the latter. A manipulative experiment revealed that stigma closure did not affect the number of conspecific pollen grains received. We also counted pollen tubes in styles that were either hand-supplemented with outcross conspecific pollen or open-pollinated. Pollen tube numbers were highest after light pollination (∼900 grains), indicating that interference among pollen grains may occur after pollination with very heavy loads (>6000 grains). Possible fitness consequences of these responses are discussed.