One of the oldest scientific mysteries of the plant world as to what makes the sunflower track the sun has finally been resolved. This finding has major implications for effective tapping of solar energy. The name sunflower invariably invokes a smile, the bright yellow petals with a contrasting black at the center somehow gives the impression of a smiley the universal emoji on social media.
But to scientists the enigma was how do young buds of the plant track the sun and to what benefit. Sun is the ultimate energy bank for earth and recently the first ‘solar tree’, a solar power generation contraption resembling a tree was inaugurated by Science Minister Harsh Vardhan.
This is part of the current government’s target of ramping up solar energy to generate 100 gigawatts in the next 6 years. It has been always known that sunflower heads follow the sun, a phenomenon called heliotropism in the jargon of scientists. But till now how exactly it happens was unresolved. Now a team six American scientists working at the top notch University of California has found that it is the selective growth of the stem in one direction that makes the sunflower follow the sun. The American team studying the plant has published an elegant paper in the SCIENCE journal last week explaining in detail how this unusual plant phenomenon works and what are its evolutionary advantages to the plant.
The team reports that in the morning the head or the flower plant which is the flower will invariably face east and then it tracks the sun and at night the head re-orients itself by growing in the opposite direction so that once again in the morning the flower faces the sun. This daily rhythm is followed only by the new flowers, once they mature and seeds have been set, the flowers lock themselves in a permanent east facing outlook.
The team reports that young sunflowers track the sun as it moves from east to west because of daily or a circadian rhythm. What’s more, mature sunflowers cease this cycle and face eastward because this behaviour offers an evolutionary advantage with pollinators. While the east-to-west behaviour of maturing sunflowers is well known, the exact mechanism underlying it – be it circadian rhythm or changing osmotic pressure – has been a longstanding mystery.
In a statement, Hagop S Atamian from the University of California at Davies and the lead author who studied the common sunflower, whose botanical name is Helianthus annuus, disrupting its exposure to both sunlight and LED lights. For example, when moved to a growth chamber with constant overhead lighting, the plants maintained their directional rhythms for several days before the pattern deteriorated, suggesting that the plants were relying on a schedule dictated by circadian rhythm.
In maturing sunflowers, the researchers found that cessation of the east-to-west sun-tracking behaviour directly correlated with stem cell growth; in the same way, mutant plants with impaired growth hormones also demonstrated impaired sun-tracking behaviour. In studies, sunflower seedlings were found to respond more strongly to unilateral light in the morning than in the afternoon; the authors suggest that this sensitivity to sunlight from the east causes the plants to eventually shift to face east permanently.
The researchers also grew sunflowers in pots and rotated half of the plants to face west just as the sun was rising. The east-facing half of the potted plants was found to have warmer temperatures than its west-facing counterparts, and was also more likely to attract pollinators. When west-facing sunflowers were warmed with portable heaters, they were more likely to attract pollinators than west-facing sunflowers without artificial warming.
The results show how temperature contributes to the differential attractiveness of east- and west-facing sunflowers to pollinators, the authors report. There are many learnings from this simple piece of research, it cost the authors almost nothing since most of the work was of an observational nature, simply designed experiments has led to resolving a long standing mystery. It is amazing that none of the Indian scientists thought on these lines to conduct experiments that needed only very minimum resources but lead to a big understanding.
By tracking the sun, the sunflower some studies suggest is able to produce 10 per cent more oil simply, similarly the ‘solar tree’ installed at Vardhan’s house is able to tap more sunlight to generate more electricity even though the solar panel are stationary in the current model. The ‘solar power tree’ developed by the science ministry harnesses solar energy for producing electricity with an innovative vertical arrangement of solar cells.
Almost akin to the architecture of a tree, with central trunk and solar panels acting like large leaves. It thus reduces the requirement of land as compared to conventional solar photovoltaic layout, on one hand, while keeping the land character intact on the other. Even the cultivable land can be utilised for solar energy harnessing along with farming at the same time. The innovation finds its viability both in rural and urban areas.
Vardhan noted that in order to produce one megawatt of solar power, it requires about 1.4 hectares of land in the conventional sequential layout of solar panels. Thus, to generate copious quantities of green energy, there will be requirement of thousands of hectares of land. Acquisition of land is a major issue in itself, he added.
Girish Sahni, Director General of the Council of Scientific and Industrial Research (CSIR), says as a future prospect, the ‘solar power tree’ would be developed in a rotatable module, which would have a motorised mechanism to align itself with the movement of the sun during the day. Hence, it would be possible to harness more power over and above the current capacity.
Some learnings it seems from the natural world. This is where the Indian scientists seem to have learnt a lesson from the sunflower plant by applying the knowledge to harvest more solar energy. The sunflower is able to produce upwards of 10 per cent more oil thanks to tracking the sun on the same lines the ‘solar tree’ is able to harvest between 10-15 per cent more electricity.
Vardhan hopes there would soon be plantations of the ‘solar tree’ all over India. In future, the sun facing smiley of the sunflower could help brighten India’s energy prospects.