AP Biology class blog for discussing current research in Biology

Tag: chloroplast

How Do Guard Cells Attain Energy?

Ever since we were young, we understood that plants utilize photosynthesis for energy, releasing oxygen in the process. But, we did not learn which parts of the plant actually perform photosynthesis. This is highlighted by guard cells, the cell located in the upper epidermis that controls the concentration of Carbon Dioxide in the plant. So how do they contribute to photosynthesis?

Stomata & Guard Cells

The team of Dr. Boon Leong Lim at HKU wanted to observe the real-time production of ATP and NADPH in the mesophyll cell chloroplasts, which was done by using planta protein sensors in a model plant, Arabidopsis thaliana. This plant is specifically used due to its small genome, short life cycle, simple process to mutagenize, and easily identifiable genes. Shockingly, the Guard Cells Chloroplasts have not detected any ATP or NADPH production whatsoever. Looking for answers, the researchers decided to contact Dr. Diana Santelia, an expert in cell metabolism. Throughout a decade of research and collaboration, they finally have an answer.

Unlike mesophyll cells, photosynthesis in the Guard Cells is inadequately regulated. This is because synthesized sugars from the mesophyll cells are imported into the Guard cells, in which is used ATP production for the opening of the stomata. Additionally, Guard Cells chloroplasts take cytosolic ATP through nucleotide transporters on the chloroplast membrane for starch synthesis throughout the day. At night, though, Guard Cells degrade starch into sugars for the opening of the stomata. Mesophyll Cells, on the other hand, synthesize starch and export sucrose at dawn. Thus, the chloroplasts of Guard Cells ultimately serve as starch storage for the opening of the stomata. Their function is closely linked to that of MCs in order to effectively coordinate CO2 absorption through stomata and CO2 fixation in MCs. 

Although the Guard Cells seem redundant, their role in the overall process of photosynthesis is absolutely necessary. As seen in AP Bio, the stomata are essential for gas exchange for photosynthetic reactions. The stomata’s main role is to take in Carbon Dioxide and release Oxygen, both of which are necessities for the reaction to occur. 

Thank you so much for reading this blog, and let me know what you think in the comments below!

Colorless Coral?

Screen shot 2013-09-24 at 9.51.23 PM on flickr

When one usually thinks of a coral reef they think of bright vibrant colors… this may not be the case anymore. A recent study has found that climate change may be depleting coral of its color. In a process called “bleaching” the color is removed from the coral when the symbiotic algae that provide nutrients to the coral either lose their  photosynthetic pigmentation and their ability to perform photosynthesis or disappear entirely from the coral’s tissue.

While this strange and disturbing phenomenon has been receiving a lot of attention, there is very little concrete knowledge about the exact molecular process that causes the bleaching. Many hypothesized that the bleaching is a result chloroplast damage due to heat stress, which results in the production of toxic, highly reactive oxygen molecules during photosynthesis, they are linking the origin of the heat stress back to climate change.

To test this theory a team of researchers from Carnegie led by Arthur Grossman and accompanied by a few other scientist from Stanford conducted a study that resulted in the surprising discovery that the bleaching occurs when the algae is not performing photosynthesis, while it is surprising the team also concluded that it could be beneficial to aid in the fight against coral decline. “This is surprising since it means that toxic oxygen molecules formed in heat-damaged chloroplasts during photosynthetic reactions during the light are likely not the major culprits that cause bleaching.” (

While their initially theory was incorrect, this research has now motivated further study into the  molecular functions of coral as well as further efforts toward coral preservation.

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