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Title: Volatile emission in dry seeds as a way to probe chemical reactions during initial asymptomatic deterioration

Author
item MIRA, SARA - Universidad Politécnica De Madrid
item Hill, Lisa
item GONZALEZ-BENITO, M. ELENA - Universidad Politécnica De Madrid
item IBANEZ, MIGUEL - Universidad Politécnica De Madrid
item Walters, Christina

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2016
Publication Date: 6/1/2016
Citation: Mira, S., Hill, L.M., Gonzalez-Benito, M., Ibanez, M.A., Walters, C.T. 2016. Volatile emission in dry seeds as a way to probe chemical reactions during initial asymptomatic deterioration. Journal of Experimental Botany. 67(6):1783-1793.

Interpretive Summary: The goal of this work was to understand the biochemistry that occurs in seeds so that we can understand why dry seeds eventually die during storage. Cells in dry seeds are not fluid like most living cells, making typical biochemical techniques unusable. Instead, we monitored biochemistry by sampling the air space within seed storage containers in a modified “breathalyser” test. These tests characterize small molecules called volatile organic compounds (VOC) released during chemical reactions. Seeds emit products of fermentation (e.g., ethanol, methanol, acetone and acetaldehyde) when they are stored at high relative humidity, which causes seeds to die rapidly. These reactions could also be measured in very dry seeds that are intrinsically short lived. In contrast, fermentation is not detected in longer-living seeds at low relative humidity, and reactions seem to be limited to oxidation of food reserves.

Technical Abstract: The nature and kinetics of reactions in dry seeds determines how long they survive. We used gas chromatography to assay volatile organic compounds (VOC) emitted from seeds of three unrelated species as a means to non-invasively probe chemical changes during very dry, dry and humid (15, 33 and 75% RH, respectively) storage. VOC emitted from seeds stored at 75% RH reflected fermentation-type reactions, with methanol and ethanol being predominant in Lactuca sativa and Carum carvi, and acetaldehyde and acetone being predominant in Eruca vesicaria. Dried C. carvi seeds continued to emit fermentation products under dry and very dry conditions, though at slower rates compared to seeds stored at 75% RH. In contrast, drying caused a switch in VOC in L. sativa and E. vesicaria seeds towards higher emission of pentane and hexanal, molecules considered to be byproducts from peroxidation of polyunsaturated fatty acids. Longevity correlated best with the rate of fermentation-type reactions and appeared unrelated to the rate of lipid peroxidation. Emission of VOC decreased when seed species were mixed together, indicating that seeds adsorbed VOC. Absorption of VOC did not appear to damage seeds, as longevity was not impacted in seed mixtures. Collectively, the work shows similarity among species in the types of reactions that occur in dry seeds, but high diversity in the substrates, hence the byproducts, of the reactions. Moreover, the work suggests that the most abundant VOC arise from degradation of storage reserves within seed cells, and that these reactions and their byproducts are not, in themselves, damaging.