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Title: Structural mechanics of seed deterioration: Standing the test of time

item Walters, Christina
item Ballesteros, Daniel
item VERTUCCI, VERONICA - University Of Colorado

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2010
Publication Date: 7/6/2010
Citation: Walters, C.T., Ballesteros, D., Vertucci, V. 2011. Structural mechanics of seed deterioration: Standing the test of time. Plant Science. 179:565-573.

Interpretive Summary: Problem: Seeds die during storage without warning. The mechanisms of deterioration are poorly understood and likely combine aspects of biochemistry and physical chemistry. This paper focuses on physical chemical aspects through structural analyses of amorphous solids produced when seeds dry. Accomplishment: The paper reviews past knowledge on mechanisms of seed aging and how water content and temperature influence aging kinetics. These factors also affect structure of seed matrices. This is the first time an engineering approach is used to study the stability of seed structures and link them to seed aging. We demonstrate the feasibility of using thermal mechanical and dynamic mechanical analyses on seeds and use these techniques to detect numerous molecular relaxations that are affected by moisture and temperature. Impact: The physical chemistry of amorphous structures in seeds has long been considered important to their biological integrity. Measurements of seed structural properties are an experimentally accessible method to evaluate the effects of moisture and temperature on seeds and may provide a non-invasive method to predict seed longevity and detect the early effects of seed deterioration.

Technical Abstract: Seeds die unexpectedly during storage and current understanding of seed quality and storage conditions does not allow reliable means to predict or prevent this critical problem. Chemical degradation of seed components likely occurs through oxidative damage, but the rate of these reactions is dominated by properties of seed that are affected by temperature and moisture. These visco-elastic properties contribute to the structure of seeds as amorphous solids. This paper presents the perspective of seed production as an exercise in engineering design for a structure that must persist through time and fluctuating conditions. Structural analyses are engineering tools used to select proper composition of materials and predict their behavior under a range of circumstances and are applicable to measurement of seeds. Thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) measure structural deformation and stress-strain relationships, providing sensitive and universal parameters that detect differences in structural stability in materials with subtle compositional differences or processing methods. When applied to seeds, TMA and DMA techniques provide information consistent with existing information on glass and first order transitions. The depth of additional information obtainable about the behavior of the glass and interactions with lipid structure suggests that these techniques will be able to quantify differences among seed structures that contribute to their tendency to age.