Due to the increasing frequency of droughts across the world, farmers have become interested in increasing their crop yield under drought conditions. Currently, a portion of lettuce farmers use a cost-effective seed priming technique in which the seeds are soaked in a solution for a twelve hour time period in order to improve the uniformity of emergence and increase their harvest yield.

Silkworm cocoons are comprised of two proteins: hydrophobic silk fibroin and hydrophilic silk sericin. A research article by B. Marelli on the effects of silk fibroin coating as a method for food preservation indicated that silk fibroin may reduce the water transpiration rate, which allows the fruits to retain their water content. Using this concept as inspiration, I primed my seeds in both silk fibroin and silk sericin in order to test whether a hydrophobic or hydrophilic priming solution improves the germination rates of the seeds under drought conditions. Additionally, silk sericin, which is a waste product of the silk fibroin extraction, has been studied as a potential soil conditioner due to its hydrophilic properties. Silk sericin has been shown to increase the length of roots in mulberry trees; therefore, I measured the radicle lengths of all germinated seeds in order to see if sericin-primed seeds have longer, well-established radicles that can theoretically increase surface area for water absorption under drought stress.

My hypothesis was that the silk fibroin primed seeds would have a higher rate of germination than the other primed groups and that the silk sericin primed seeds would have the longest radicles of the other groups.

In my project, Silk Fibroin Seed Priming as a Method for Improving Drought Tolerance of Lactuca sativa, I tested whether priming lettuce seeds in silk fibroin and silk sericin improves the germination rates and radicle lengths of the seeds under both drought stress and normal conditions. The silk fibroin was extracted using the Ajisawa silk fibroin degumming method, which included boiling the silk cocoons in a dilute sodium carbonate solution and solubilizing the dried silk fibers in the Ajisawa reagent, which consists of calcium chloride, ethanol, and water. The seeds are primed by soaking the ethanol-sterilized seeds in the appropriate priming solution for 12 hours. The primed seeds are placed between two pieces of filter paper and are considered to be germinated when at least a 2-millimeter-long radicle emerges from the seed coat. The drought stress is induced through soaking the filter papers with 10% polyethylene glycol (PEG) solution rather than distilled water as it creates an osmotic potential, which mimics drought conditions. The terminal germination count is identified 8 days after the germination procedure is initiated.

The results from my petri-dish germination experiment show that there is a statistically significant difference between the radicle lengths of seeds that were sericin primed in drought conditions compared to the silk fibroin primed seeds group and hydroprimed seed group under drought stress. However, the silk fibroin primed seeds in drought conditions did not have a significantly higher germination rate than the other primed seeds groups, according to an ANOVA test with post-hoc Tukey HSD test. Moreover, the sericin primed seeds in drought had higher germination rates than both the hydroprimed and silk fibroin primed seed groups.

A future study I am interested in pursuing is testing whether a silk fibroin coating of lettuce leaves can increase heat tolerance due to its hydrophobic properties.