The Responses of Cytochrome Redox State and Energy Metabolism to Dehydration Support a Role for Cytoplasmic Viscosity in Desiccation Tolerance

Abstract

To characterize the depression of metabolism in anhydrobiotes, the redox state of cytochromes and energy metabolism were studied during dehydration of soaked cowpea (Vigna unguiculata) cotyledons and pollens of Typha latifolia and Impatiens glandulifera. Between water contents (WC) of 1.0 and 0.6 g H 2 O/g dry weight (g/g), viscosity as measured by electron spin resonance spectroscopy increased from 0.15 to 0.27 poise. This initial water loss was accompanied by a 50% decrease in respiration rates, whereas the adenylate energy charge remained constant at 0.8, and cytochrome c oxidase (COX) remained fully oxidized. From WC of 0.6 to 0.2 g/g, viscosity increased exponentially. The adenylate energy charge declined to 0.4 in seeds and 0.2 in pollen, whereas COX became progressively reduced. At WC of less than 0.2 g/g, COX remained fully reduced, whereas respiration ceased. When dried under N 2 , COX remained 63% reduced in cotyledons until WC was 0.7 g/g and was fully reduced at 0.2 g/g. During drying under pure O 2 , the pattern of COX reduction was similar to that of air-dried tissues, although the maximum reduction was 70% in dried tissues. Thus, at WC of less than 0.6 g/g, the reduction of COX probably originates from a decreased O 2 availability as a result of the increased viscosity and impeded diffusion. We suggest that viscosity is a valuable parameter to characterize the relation between desiccation and decrease in metabolism. The implications for desiccation tolerance are discussed.

Increasing the rate of drying reduces metabolic imbalance, lipid peroxidation and critical water content in radicles of garden pea (Pisum sativum L.)

“…Following drying of germinating maize seeds, impairment of mitochondrial electron transport chain was marked in the NADH dehydrogenase of NADH-coenzyme Q reductase (complex I) and NADH-cytochrome c reductase (complex IV) and the alternative oxidase (Leprince et al, 1993a;reviewed by Côme and Corbineau, 1996;Leprince and Hoekstra, 1998;Song et al, 2009). In the present investigation, the level of NAD was surprisingly enhanced during drying.…”

“…It has been argued that desiccation differentially affects the activities of various enzymes (Farrant et al, 1985;Leprince et al, 1993a;reviewed by Côme and Corbineau, 1996;Leprince and Hoekstra, 1998;Ntuli et al, 2011) and hence results in metabolic imbalance (Finch-Savage et al, 1993;reviewed by Vertucci and Farrant, 1995;Leprince et al, 2000;Walters et al, 2002;Ntuli et al, 2011). Of particular interest in this regard is respiratory metabolism.…”

Drying Increases Intracellular Partitioning of Amphiphilic Substances into the Lipid Phase

“…0.6 g water g Ϫ1 DW (Leprince and Hoekstra, 1998). From the data obtained it is not completely clear whether the deviation of P from the expected straight line is caused by water-line broadening as a result of increased viscosity, or whether the increased viscosity of the cytoplasm itself promotes partitioning into the more liquid lipid phase.…”

“…4 and 7). Under these conditions there is still freezable water (Buitink et al, 1996), albeit of high viscosity (Leprince and Hoekstra, 1998).…”

Mechanism of endocarp-imposed constraints of germination of Lannea microcarpa seeds

“…If seeds were incubated in water prior to respiration measurements, pieces of wet filter paper were placed at the bottom of the vials to avoid drying of the samples. After 5 h, 40 ml headspace gas samples were taken from the vials and injected into a gas chromatograph (GC) equipped with a catharometer detector as described by Leprince and Hoekstra (1998), which allowed O 2 uptake and CO 2 release to be measured simultaneously. The sensitivity of the GC detection was enhanced by an additional amplifier, connected to an electronic integrator.…”