Research projects during 2007

Summer 2007: The use of 15N labeling and photosynthetic CO2 response curves to measure photorespiration under drought conditions in Tall fescue grasses.

Previous studies on tall fescue grasses have shown that the asexual fungus, Neotyphodium ceonophialum, allowed its grass host, tall fescue, to be more drought tolerant and exhibit higher water-use efficiency than plants that have had the fungus eliminated by heat treating the infected seed. Infected plants (E+) were able to maintain higher photosynthetic rates than uninfected plants (E-) plants when stomatal conductance declined under severe drought stress. Plant scientists are proposing that drought tolerance may be improved in E+ grasses in general by an increase in oxidative stress at the cellular level and that phenolics may play a role in this oxidative tolerance while higher ascorbate peroxidase activities may favor H2O2 scavenging. This may imply that E+ plants may have a higher capacity to scavenge for H2O2 and prevent oxygen radicals from forming by employing higher rates of photorespiration which would act as a sink for excess light energy when the carboxylation capacity of Rubisco declines as CO2 concentrations become limiting with stomatal closure under drought conditions.

We used two novel methods to determine if rates of photorespiration in endophyte infected grasses were higher than uninfected tall fescue grasses grown under drought conditions. One method incorporated tracking the assimilation of 15N fertilizer into the leaf amino acid pools over a 24 hour period to see if 15 N was incorporated moreso to the glycine and serine pools under drought conditions. We also used a best-fit non linear model to calculate ratios of oxygenation:carboxylation from A:Ci curves measured with common gas exchange techniques to assess whether the infected plants exhibited higher rates of photosynthesis under drought. This work was funded by the NSF-CRUI grant award (DBI 0330841)

Students, Natalie Grand and Emily Harper worked on this project. Natalie Grand is currently a senior at Hope College and is following her interests in pursuing a medical program in the future. Emily Harper graduated from Hope College in May 2007 and is currently a graduate student in the Department of Cell and Molecular Biology at Michigan State University.

Summer 2007: Comparison of Photosynthesis, transpiration and water-use efficiency between a monocotyledonous and dicotyledonous species growing in the restored prairie community.

This project was an exploratory field study where we investigated how stomatal diversity between a dicot and a monocot species impacted photosynthesis, transpiration and water-use efficiency in a restored prairie community at Pierce Cedar Creek Institute near Hastings, MI. We used common gas exchange measurements collected with the Li-Cor 6400 to compare rates of photosynthesis, stomatal conductance, and transpiration between species. Predawn water potentials were measured using a Scholander pressure bomb to compare the water status among the individual plants at the time of sampling. We also observed stomatal morphology of epidermal peels collected from transplanted individuals in the greenhouse at Hope College. This work was funded by two Pierce Cedar Creek SURF awards.

Elizabeth Weidenhaft and Emily Schuiteman worked on this project. Elizabeth is a sophomore student with the intention of majoring in both Biology and Chemistry and has the aspiration to attend graduate school. Emily is a sophomore student who has the aspiration of becoming a medical doctor.

Fall 2007: Photorespiration in tall fescue grasses with different levels of infection when grown at low and high light levels

This project was a follow up on the summer experiment of 2007 where we found great variability in the infection status of tillers of an individual plant. This time, plants were immunoblotted and the plants were chosen based on three levels of infection status: (1) 100% infection; (2) less than 100 % infection and (3) 0% infection.

We tested to see if photorespiration varied with the infection level of the different infected tall fescue grasses using the best-fit non linear model to calculate ratios of oxygenation:carboxylation from A:Ci curves measured with common gas exchange techniques in a similar way as we did in the summer experiment. This work was supported by the NSF-CRUI grant award (DBI 0330841)

Cindy Reimink and Daniel Hills worked on this project. Cindy Reimink is a senior majoring in both Biology and Chemistry and has the aspiration of attending graduate school in the future. Daniel Hills is a senior majoring in Biology and is interviewing at several medical schools across the country.