Differences in the reactivation process in thermosensitive seeds of Phacelia tanacetifolia with germination inhibited by high temperature (30oC)

Abstract

The changes in several metabolic parameters induced in thermosensitive seeds of Phacelia tanacetifolia Benth. (cv. Bleu Clair) by an inhibitory temperature of 30°C were evaluated and compared to those occurring at the optimum temperature for germination (16°C). The severe inhibition of germination (70%) at 30°C was accompanied by an inhibition of the increase in total RNA and glucose-6-phosphate followed by an inhibition of the increase in DNA, reducing sugars and ATP. Both transcriptional and translational activities occurred at the two temperatures, but with substantial differences. They were higher at 30 than at 16°C after 9 h of imbibition. With time, translational activity became much lower at 30°C, as indicated by the inhibition of the increases in the polysome/monosome ratio and of the levels of activities, evaluated in vitro, of glucose-6-phosphate dehydrogenase, pyruvate kinase, glucokinase and malate dehydrogenase. Transport also occurred at 30°C, as indicated by the positive net flux of K + into the cells and by the electrochemical equilibrium of mobile K + between the outside and inside of the cells. There was much less mobile K + inside the cells at 30 than at 16°C (50 and 13%, respectively, after 24 and 72 h of imbibition). The values of cytoplasmic pH were the same at 16 and 30°C. At 30°C, the vacuolar pH did not change, whereas at 16°C it became more acidic at 72 h. The possible roles of cytoplasmic K+ concentration and pH in the control of the reactivation of metabolism during germination of Phacelia tanacetifolia seeds are discussed.