Metabolic dysfunction and unabated respiration precede the loss of membrane integrity during dehydration of germinating radicles

This study shows that dehydration induces imbalanced metabolism before loss of membrane integrity in desiccation-sensitive germinated radicles. Using a photoacoustic detection system, responses of CO2 emission and fermentatio n to drying were analyzed non-invasively in desiccation-tolerant and -intol erant radicles of cucumber (Cucumis sativa) and pea (Pisum sativum). Surviv al after drying and a membrane integrity assay showed that desiccation tole rance was present during early imbibition and lost in germinated radicles. However, tolerance could be re-induced in germinated cucumber radicles by i ncubation in polyethylene glycol before drying. Tolerant and polyethylene g lycol (PEG)-induced tolerant radicles exhibited a much-reduced CO2 producti on before dehydration compared with desiccation-sensitive radicles. This di fference was maintained during dehydration. In desiccation-sensitive tissue s, dehydration induced an increase in the emission of acetaldehyde and etha nol that peaked well before the loss of membrane integrity. Acetaldehyde em ission from sensitive radicles was significantly reduced when dehydration o ccurred in 50% O-2 instead of air. Acetaldehyde/ethanol were not detected i n dehydrating tolerant radicles of either species or in polyethylene glycol -induced tolerant cucumber radicles. Thus, a balance between down-regulatio n of metabolism during drying and O-2 availability appears to be associated with desiccation tolerance. Using Fourier transform infrared spectroscopy, acetaldehyde was found to disturb the phase behavior of phospholipid vesic les, suggesting that the products resulting from imbalanced metabolism in s eeds may aggravate membrane damage induced by dehydration.