Involvement of polyamines in the interacting effects of low temperature and mineral supply on Pringlea antiscorbutica (Kerguelen cabbage) seedlings

Pringlea antiscorbutica, which is the sole endemic crucifer in the subantarctic zone, undergoes seedling development in a harsh and cold environment. Since, at the mature stage, this species exhibits several adaptations linked to cold tolerance such as high polyamine levels, potential adaptations and polyamine response were investigated in seedlings. In order to assess the specificity of responses, P. antiscorbutica was compared with Arabidopsis thaliana, which is characterized by a life cycle preventing cold exposure at seedling stage. P. antiscorbutica and A. thaliana seedlings were found to have strikingly contrasted responses to temperature changes and to mineral nutrition. Whereas A. thaliana seedlings showed the typical growth arrest of chilling-sensitive plants, P. antiscorbutica seedlings showed optimal root growth at low temperature (5/10 degrees C) and temperate conditions caused the early arrest of root growth. Cold tolerance was associated with increased levels of polyamines or with maintenance of high levels of polyamines. Comparison of both species showed that polyamine levels could be a significant marker of chilling tolerance in seedlings. Treatments with varying mineral supply showed a positive relationship between root growth rate and variations of agmatine and putrescine endogenous contents in roots of P. antiscorbutica. This may be the first demonstration that, even under conditions of accumulation induced by environmental stress, polyamine levels can still be correlated with developmental processes. Com parison of mineral supply and temperature effects strongly indicated a trade-off of polyamine involvement between development and response to stress.