Author ORCID Identifier
https://orcid.org/0000-0002-5660-559X
Date Available
12-11-2025
Year of Publication
2024
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Agriculture, Food and Environment
Department/School/Program
Plant and Soil Sciences
Advisor
Dr. Tomokazu Kawashima
Abstract
Soybeans, which are widely grown in the United States, are used as food, animal feed, and industrial oil. The rise in plant-based diets highlights the high protein content and versatility of soybean. Understanding seed development is crucial for increasing yield. Soybean seed development includes three phases: lag, seed-filling, and maturation. Post-fertilization, the seed undergoes cell division in the lag phase, forming the embryo, endosperm, and seed coat. The embryo absorbs the endosperm and develops into two cotyledons. During the seed-filling phase, cotyledon cells accumulate starch, proteins, and lipids. During maturation, seeds dry out and become quiescent. Studies indicate that the lag phase significantly impacts final seed weight, yet my understanding of soybean seed development, especially its physiological and molecular aspects and environmental interactions, is limited.
I conducted growth chamber experiments where an elevated temperature shift (an 8 °C increase from control) was applied during either the lag or seed-filling phase to observe its effects on seed development. The temperature shift during seed-filling phase did not affect seed weight, but a shift during the lag phase significantly reduced seed weight. The temperature shift during the lag phase did not impact on the lag phase duration but reduced the seed-filling duration and decreased final seed weight, even when plants returned to control temperature. Further, temperature shift during lag phase reduces the number of cotyledon pavement cells indicating that the maximum potential for seed weight is set during the lag phase, and minor environmental changes during this critical period can significantly impact seed weight.
A greenhouse study using soybean cultivars with varying seed weights (two small-seeded and two large-seeded) revealed a significant positive correlation between seed weight and lag phase duration, suggesting a genetic determination of lag phase duration. Further, big-seeded cultivars had more pavement cells on the ventral cotyledon surface than small-seeded ones, implying that a longer lag phase allows for greater cell division in the cotyledons. To validate these observations, I analyzed publicly available RNA-seq data of large- and small-seeded soybeans at the cotyledon stage (final stage of the lag phase). Differential gene expression analysis identified transcripts enriched in either large- or small-seeded soybeans. Mapping these transcripts to specific seed compartments using another seed compartment-specific RNA-seq dataset revealed that seeds of the large-seeded cultivar contained transcripts encoding proteins indicative of continued cell division at the cotyledon stage, with the seed coat containing transcripts related to cell proliferation. By contrast, embryos of the small-seeded cultivar were linked to reserve accumulation processes, and their seed coats exhibited signs of lignification and maturation already at the cotyledon stage. Physiological and molecular data indicate collaborative regulation of seed growth by different seed compartments, with prolonged development in large seeds, marked by a longer lag phase, resulting in more cotyledon cells and increased size.
Next, I studied the effects of two planting dates (May and June) on seed development. Results showed shorter lag and seed-filling phases in June due to different variables like photoperiod and temperature, resulting in lower seed weight in June than in May planting. Our results also revealed that even under field conditions with different planting dates, the lag phase duration is positively correlated with seed weight. These findings highlight the significance of the lag phase in soybean seed development and yield.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2024.445
Funding Information
Netaji Subhas ICAR international fellowship 2020, India 3 years
Recommended Citation
Shivakumar, Ashwini, "Understanding the role of early-stage seed development on final seed weight by linking seed physiology, transcriptomics, and environments in soybean (Glycine max (L.) Merr.)" (2024). Theses and Dissertations--Plant and Soil Sciences. 185.
https://uknowledge.uky.edu/pss_etds/185
