When it comes to plant rhythms, Stacey Harmer, a professor of plant biology at the University of California, Davis, is hip to the groove.

Harmer is the recipient of the College of Biological Sciences 2016-2017 Faculty Research Award for her work on the circadian clocks of sunflowers.

Her research, which appeared in the August 5, 2016 journal of Science, describes how sunflowers track the sun, beginning each morning with their heads facing east, slowly swinging west throughout the day and then resetting eastward at night.

View an animated video based on Harmer's research

Moving with the sun

“It’s the first example of a plant’s clock modulating growth in a natural environment, and having real repercussions for the plant,” said Harmer, the paper’s senior author.

Hagop Atamian, a postdoctoral researcher in Harmer’s lab, in collaboration with Benjamin Blackman’s lab at the University of Virginia (now at UC Berkeley), carried out a series of experiments with sunflowers in the field, in pots outdoors and in indoor growth chambers.

Two different mechanisms control sunflower stem growth: basic growth from all available light and directed growth which varies depending on whether or not a sunflower’s head is able to move with the sun.

Through time-lapse video, Harmer’s team demonstrated the east side of the stem grows faster during the day, while at night the west side of the stem grows faster.  They identified a number of genes that were expressed at higher levels on the sunward side of the plant during the day, or on the opposite side at night.

With infrared cameras, postdoc Nicky Creux discovered that east-facing sunflowers heated up more quickly in the morning, attracting five times as many pollinating insects compared to west facing plants.

The plants, when staked and unable to move, or faced the wrong way, lost the growth boost that naturally comes with tracking the sun. In addition, they didn’t receive the same level of pollinators, which leads to a decrease in reproductive capabilities.

Recognized by her peers

Based on faculty nominations, the College of Biological Sciences Faculty Research Award is presented annually to acknowledge a single research publication that reflects the exciting, innovative and significant advances in research within the College of Biological Sciences.

“This is a very interesting and groundbreaking paper and answers a century old mystery: why and how sunflowers track the sun,” said Department of Plant Biology chair Savithramma Dinesh-Kumar. “It is remarkable that Dr. Harmer and her colleagues designed experiments in challenging field settings to show that the plants internal clock influences solar tracking to promote growth.”

The Harmer Lab is currently studying how circadian clocks and the environment work together to precisely time flower development in sunflowers. Controlled by internal and external cues, sunflower florets release pollen a few hours after dawn to attract visits from pollinators.  Understanding these factors is important because flowers that release pollen earlier sire more seeds than those flowers that mature later in the morning.

From curiosity to discovery

Plant circadian rhythms have long captivated Harmer, and her research helps to gain a better understanding of the responses that are vital for plants to adapt to their environments.

“The idea that organisms—and even single cells—have internal clocks that accurately measure 24-hour rhythms seemed almost like science fiction,” Harmer said.  “It turns out that many aspects of plant physiology are regulated by these internal timers, which makes plants a great system for studying circadian rhythms.”

Harmer has felt honored that her colleagues were excited by this manuscript. “This represents a new direction for my lab, which makes receiving this award especially gratifying,” she said.

She has studied the molecular basis of circadian rhythms in Arabidopsis thaliana for years, but that work was entirely in the lab. Working with sunflowers adds a new level of complexity through growing the plants outdoors and monitoring their interactions with insects. Integrating plant physiology with genomics continues to provide Harmer with new insights into plant growth and reproduction rhythms.

When it comes to getting research published in scientific journals, Harmer encourages students and budding scientists to work hard, but strategically. “Identify an interesting biological question and figure out the right experiments to generate conceptual advances,” she said. “Ask yourself, will investigating this area lead to new biological insights, or will it simply fill in some details?”

Harmer is a member of the American Society of Plant Biologists and the Society for Research on Biological Rhythms. She was named UC Davis Chancellor’s Fellow in 2011.