Y. Gibon et al., IS GLYCINE BETAINE A NON-COMPATIBLE SOLUTE IN HIGHER-PLANTS THAT DO NOT ACCUMULATE IT, Plant, cell and environment, 20(3), 1997, pp. 329-340
Rape (Brassica napus L. var. oleifera cv. Samourai) leaf discs treated
in vitro in the presence of glycine betaine (GB) exhibited very high
accumulation of GB, suggesting the operation of a specific uptake syst
em. When further subjected to osmotic upshocks by transfer to PEG 6000
media, the typical osmo-induced proline response of the discs was str
ongly inhibited. The level of this inhibition was quantitatively relat
ed to the amount of GB loaded in the tissues. In contrast, the soluble
sugar content increased in GB-treated discs. Surprisingly, viability
tests (i.e. membrane stability and 2,3,5-triphenyltetrazolium chloride
reduction) indicated a destabilizing effect of GB in these tissues. T
his is at variance with the relative compatibility of sucrose and prol
ine. In addition, the protein content was lower in GB-treated discs. T
his could be related to an inhibitory effect on protein synthesis, as
demonstrated by radiolabelling of polypeptides with [S-35] amino acids
. This effect was particularly pronounced on Rubisco large subunit syn
thesis and was still apparent under non-stress conditions. The GB trea
tment was also followed by the induction or up-regulation of a set of
polypeptides, not seen under stress conditions, while the synthesis of
osmo-induced polypeptides was not affected by GB. These novel effects
of GB lead us to discuss the reasons for its incompatibility in leaf
tissues of a non-GB-accumulating species.