Xiang Wang is a graduate student in Dr. Rajeev Arora's lab currently pursuing his Ph.D. degree. Xiang was born in Wuhan (central China), Hubei Province, China. He obtained his B.S. degree in June 2002 from Huazhong Agricultural University in Agronomy, and M.S. degree in June 2005 from Chengdu Institute of Biology at the Chinese Academy of Sciences in Ecology. In January 2006, Xiang enrolled in the Ph.D. program (Horticulture) at Iowa State University.
Rhododendrons are important landscape plants, many of which are broad-leaf evergreens. Overwintering broad-leaf rhododendrons typically experience a combination of freezing temperatures and high light in their natural habitats in winter as understory plants. Since at freezing temperatures, enzymatic reactions of photosynthesis are deactivated while light harvesting is not affected, rhododendron leaves are exposed to excess photon flux which can be damaging to PSII reaction centers causing photoinhibition. Higher plants have evolved several mechanisms to protect them from, or ameliorate injurious effects of, excess photon flux. My research objective is to understand physiological, anatomical, and/or biochemical mechanisms of photoprotection strategies employed by overwintering evergreen Rhododendron.
For my first experiment, I have used two contrasting Rhododendron species: R. catawbiense shows thermonastic leaf movement (leaf curling and drooping under freezing temperatures) and is substantially more freeze-tolerant while R. ponticum does not exhibit thermonasty and is relatively less cold-hardy. The overall objective of this work is to compare leaf anatomy of these species in context of their putative role in photoprotection. The preliminary data published recently (left panel below; Wang et al., 2008) indicate that the two species had significantly different leaf anatomies. There is one layer of upper epidermis and three layers of palisade mesophyll in R. catawbiense compared to two distinct layers of upper epidermis and two layers of palisade mesophyll in R. ponticum (right panel below). The additional layer of upper epidermis in R. ponticum while a thicker cuticle with a large amount of wax deposits (data not shown here) and extra palisade layer in R. catawbiense might represent structural adaptations for reducing light penetration in the leaves during winter when leaf photochemistry is generally sluggish. This paper also implicates differences in the opening area of stomatal aperture in the two species together with the contrasting thermonasty behavior in their response to winter desiccation. For more details, please refer to the publication below.
The second component of my research, i.e. investigation of the biochemical and molecular basis of
photoprotection strategies is currently underway. STAY TUNED......
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