Exogenously supplied glycine betaine in spinach and rapeseed leaf discs: compatibility or non-compatibility?

When leaf discs of spinach (Spinacia oleracca cv. Junius) and rapeseed (Bra ssica napus var. oleifera cv. Samourai) were incubated in the light in the presence of glycine betaine (GB), they accumulated GB at a very high level. In comparison with the spinach leaf explants, the uptake of GB by rapeseed tissues was restricted, probably by the destabilizing effects exerted by G B in this plant material, In contrast, the viability of spinach leaf discs, as assessed by their capacity to reduce 2,3,5-triphenyltetrazolium chlorid e (TTC), was not affected, suggesting that the GB taken up was compatible i n the leaf tissues of the CB accumulator. In rapeseed leaf discs treated wi th GB, chlorophyll loss as well as significant changes in polyamine content were induced, leading to a dramatic increase of the putrescine/(spermidine + spermine) ratio, In contrast, this ratio remained constant in the GB tre ated spinach explants, suggesting that spinach has the capacity to stabiliz e polyamine metabolism in the presence of high amounts of GB, The treatment of spinach leaf discs with GB prior to application of osmotic or salt shoc ks provided protection from stress. A weak capacity to accumulate proline u nder stress conditions was partially suppressed, The protein content decrea sed while the free amino acid level increased independently of the presence of GB, It is concluded that GB behaves as a true compatible solute in spin ach, which is a typical GB accumulator, and that GB is damaging when loaded into the leaf tissues of rapeseed, which do not normally accumulate GB.