Introduction
Ribulose-1,5-bisphosphate carboxylase/oxygenase, also known as Rubisco, is the most prevalent enzyme found on the planet and is involved in one of the quintessential processes of life, photosynthesis. Therefore, its impact on agriculture and ecology is significant. Rubisco is one of the key components of the Calvin cycle in photosynthesis. It fixes carbon from carbon dioxide into a usable compound for the production of metabolic sugars necessary for plant function. The gene for the large sub-unit, RBCL, of rubisco is found in the chloroplasts. One area of study is the effect of water availability on Rubisco levels and therefore, on the plant’s ability to photosynthesize. Studies done by Sherrard and Maherali have shown that plants that receive very little water, such as plants accustomed to drought, have decreased metabolic rates (1). Thus, it is likely that Rubisco has been decreased as well. In addition, plants that are well watered can adapt and change their rate of photosynthesis. In another study done by Barrios, Murguia, and Nobel on Agave tequiliana, the agave plant had varying rates of carbon dioxide uptake with the highest uptake during the rainy season. Carbon dioxide uptake correlates with higher photosynthetic rate and hence, high rubisco levels (2).
In order to further study the effects of water on Rubisco levels, three types of plants were chosen based on their water requirement. The first plant chosen was Portulaca oleracea or purslane (Fig 1). Purslane is native to India and the Middle East and was speculated to have arrived in North America around the 15th century. It is now commonly known as a weed. Because of its desert origins purslane is drought resistant and does not require much water to grow (3).
Fig 1. Portulaca oleracea
The second plant chosen is from the genus Lavandula or lavender (Fig 2). Lavender is a common garden plant that is used for potpourris, scented oils, and attractive flowers. It is considered a mesophyte or a plant that thrives in moderate climates. Though it has origins in Africa, India, and the Mediterranean, most of the forms found in America are cultivated and have become adapted to the moderate climate and would not likely be able to survive such conditions now (4).
Fig 2. Lavandula
The final plant is Pistia stratiotes or water lettuce (Fig 3). It is an aquatic species and requires a constant water supply. It grows all over America floating on top of the water’s surface. It can be considered a weed because it can block major water ways and reduce the biodiversity (5).
Fig 3. Pistia stratiotes
Real time PCR and Western Blot analysis were used to determine the amount of RBCL gene and rubisco protein. It was predicted that the purslane would contain the least Rubisco, both at the DNA level and the protein level, since it is accustomed to an arid environment and thus has a slow metabolism. The lavender, on the other hand, would most likely have more Rubisco since it lives in a rainier climate and the water lettuce would have the greatest amount of Rubisco at both levels since it has a constant supply of water allowing a higher rate of photosynthesis.
Acknowledgements
2. Pimienta-Barrios, Eulogio, Robles-Murguia, Celia, and Nobel, Park S. "Net CO2 uptake for Agave tequilana in a warm and a temperate environment." Biotropica 33(2001): 312-318.
3. "Common Purslane." How to Manage Pests. Aug 2007. UC IPM. 2 Oct 2007 <http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7461.html>.
4. "Lavender." University of Maryland Medical Center. 01/17/2007. University of Maryland. 2 Oct 2007 <http://www.umm.edu/altmed/articles/lavender-000260.htm>.
5. "Aquatic, Wetland and Invasive Plant." University of Florida, Center for Aquatic and Invasive Plants. University of Florida. 2 Oct 2007 <http://aquat1.ifas.ufl.edu/>.
Fig. 1 courtesy of http://www.wildgardenseed.com/product_info.php?cPath=49&products_id=136
Fig. 2 courtesy of http://www.sherryspaessentials.com/lavenderchamomile.html
Fig. 3 courtesy of http://sfrc.ufl.edu/4h/waterlettuce/lettuce.htm
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