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Hydration, protons and onset of physiological activities in maize seeds
Author(s) -
Bruni Fabio,
Leopold A. Carl
Publication year - 1991
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1991.tb08744.x
Subject(s) - endosperm , conductivity , enthalpy , percolation (cognitive psychology) , thermodynamics , chemistry , materials science , chemical physics , biochemistry , physics , biology , neuroscience
Dry maize ( Zea mays L.) seed components, namely, embryo and endosperm, provide model materials for studies on water‐dependent mechanisms in cellular function. We explored the thermodynamics of hydration for both tissues, along with their dielectric behavior, as a function of water content. In addition, we evaluated the direct current (DC) conductivity due to water protons. Our data on embryo tissue show large enthalpic and entropic peaks at water content [h, in g H 2 O (g dry sampie) −1 ] around 0.08 g g −1 , indicating very tight binding and ordering of water molecules. With increasing water content both enthalpy and entropy decrease, and the completion of primary hydration requires h ∼ 0.26 g g −1 . Data for endosperm tissue show the absence of such an enthalpic peak and a reduced degree of ordering for h < 0.10 g g −1 . The DC protonic conductivity shows explosive growth above a threshold hydration level h c = 0.082 g g −1 and h c = 0.12 g g −1 , for embryo and endosperm, respectively. Protonic conduction can be considered within the framework of a percolation modell characterized by a hydration threshold and by a power law increase in conductivity with further hydration. The critical exponent of the power law is in agreement with theory for a two‐dimensional percolative process. This percolative water‐assisted behavior reflects the presence of an extended network of water molecules adsorbed on the surface of proteins and/or membranes inside cells. We consider this percolative protonic conduction as being a prerequisite to respiration processes.