Title: Probing the biology of dry biological systems to address the basis of seed longevity Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: November 20, 2011
Publication Date: N/A
Technical Abstract: Drying cells reduces molecular mobility and slows chemical and physical reactions. As a result, dry biological systems deteriorate slowly. The time course of deterioration in a population of living cells often follows a sigmoidal pattern in which aging is occurring but no changes to viability are observed until a threshold is reached, after which mortality occurs precipitously. The duration of time before the threshold (i.e., longevity) is unpredictable and little is known about the reactions that occur during this period. We have developed a series of tools to probe physical and chemical reactivity within dried seeds. Measurement of lipid crystallization corresponds to triacylglycerol breakdown into more polar compounds, presumably by oxidative reactions. Measurement of volatile emission reveals numerous moisture-dependent and independent reactions including vestiges of glycolysis, lipid peroxidation and volatilization of flavor compounds. Analysis of visco-elastic structure demonstrates how moisture and temperature alter molecular mobility and ultimately affect the kinetics of reactions that occur in the dry state. An array of diverse products is detected in dry seeds, and quantifying any one analyte is insufficient to describe the nature and kinetics of reactions that occur. We interpret this complexity to indicate stochastic degradation of all cell constituents through numerous pathways that ultimately lead to cleavage or cross-linking of biological molecules. The observation that a myriad of byproducts are produced during contemporaneously-occurring degradation introduces the possibility that mortality results from the culmination of multiple damage sites within cells. Consequences of this culminated-damage hypothesis include difficulty both in correlating aging rate with substrate-levels for reactants or byproducts and in ascribing causation to any specific reaction. Variation of longevity among seeds may arise from differences in the regulation of reactivity (likely through molecular mobility mechanisms), extent of redundancy of essential cell machinery or effectiveness of molecular decoys in deflecting damage to cell machinery.