To meet the growing demand for rice, crops are genetically modified to absorb more sunlight, helping them with increased photosynthetic efficiency. However, this leads to a reduction in healthy seed production. Now, however, scientists have found that the production of unhealthy seeds is due to excess sugar accumulation that affects the plant's seed development. Addressing this issue is crucial for improving crop yields and ensuring a balanced growth-to-seed production ratio for sustainable rice cultivation.
Rice is one of the most consumed grains globally, and with an increase in global population, the demand for rice has significantly risen. To meet this demand, a continuously increasing supply of rice must be maintained. Research aimed at improving crop yield has looked at classical methods for their disease and pest resistance, nutritional value and grain size. While initial efforts have resulted in success, they failed to maximize the crop's ability to fully utilize sunlight for photosynthesis.
Photosynthesis plays a vital role in crop production by helping plants to convert sunlight to energy for the synthesis of their food. With advancements in technology, various methods for improving photosynthesis are being explored, which have resulted in increased biomass and grain production in crops like Arabidopsis, Camelina sativa (false/ wild flax), potato, rice and tobacco. These developments have helped in addressing food security and productivity concerns.
A research team led by Professor Xinxiang Peng from the College of Life Sciences, South China Agricultural University, have conducted extensive research in this area. They investigated two approaches, both of which successfully increased biomass and grain yield. Nonetheless, the team identified a major issue that needed redressal — a decrease in the seed-setting rate (SSR), a crucial factor in rice productivity.
To address this limitation, Prof Peng along with other researchers from South China Agricultural University, Shaoguan University, and the Zhongkai University of Agriculture and Engineering, China, conducted further research on the decreasing trend of SSR. Published in The Crop Journal on 22 October 2024, their latest research presents insights which can help crop breeders achieve better overall rice productivity.
The researchers grew rice seedlings in a greenhouse under controlled conditions and the fields and analyzed various biological parameters that determine pollen fertility, sugar production, and distribution in the crop. They observed excessive photosynthesis buildup that caused sugar accumulation in the crop.
"If we consume too much sugar, it can increase the risk of diabetes. Similarly, we've used the term 'plant diabetes' to describe the overaccumulation of sugars that damages plant cells," explains Peng. "In our study, by enhancing the rice's photosynthetic efficiency, we were able to achieve increased biomass and yield, but reduced pollen fertility and seed-setting."
Previously, the researchers reported improved photosynthesis but with a decrease in the number of healthy seeds in rice.
"This new study further confirmed the earlier finding. The key factor behind the low SSR was low pollen fertility," adds Peng. "This rice variety had lower pollen germination than the widely cultivated variety."
Further analysis revealed that the mature pollen had less starch reserves, and the walls of the pollen were irregularly shaped, which further affirmed the reasons for low pollen germination. Additionally, the rice stored excess sucrose and other sugars in various parts of the plant, making transportation of nutrients within the crop difficult. Sugar was stored in the stems instead of being used for crop development.
While the rice crop offers insights into the challenges of low SSRs, it also demonstrates faster growth and increased biomass accumulation. These findings reveal that an increase in sugar content helps in energy storage within the plant, which is a major reason behind the low SSR.
"This sugar imbalance affects the reproductive parts that produce pollen and makes it less fertile and produces fewer seeds," Peng says. "Our findings offer insights for fellow scientists, particularly crop breeders, on how to effectively harness the genetic yield potential of crops by enhancing photosynthesis in the future."
