Germination and pH of intracellular compartments in seeds of Phacelia tanacetifolia

Abstract

S. M. 1995, Germination and pH of intracellular compartments in seeds of Phaceha uinaccttfoiia. -Physiol, Plant, 93: 577-58.1.•'P nuclear magnetic resonance spectroscopy (NMR) was used to study the response of PhaceUa tmwcenfiiliii seeds to dark and light conditions during the first 72 h of incubation. Changes in the chemical shifts id] of the pH-dependent ''P-NMR signals from the vacuolar and the cytoplasmic orthopbosphate pools were correlated with the different incubation conditions. In the dark (favorable to germination), the cytoplasmic pH remained nearly constant over the whole penod considered, while the vacuolar pH shifted to more acidic values after the 24th h of incubation. In the light (inhibiting termination), the values of cytopiasmic pH tended to become more acidic than in the dark after the 24th h of incubation, while the \acuolar pH remained practically conslanl. When seed germination was inhibited in the dark by butync acid (BA), a permeanl weak acid, the values of cytoplasmic and \ acuolar pH were similar tn those of the ungerminated seeds incubated in the light. When, vice versa, seed germination was promoted in the light by fusicoccin (FC), the \alues of cytoplasmic and vacuolar pH were similar to those of the dark-germinated seeds, A progressive augmentation of Pi metabolism occurred both in the dark and in the lighi up to the 24th h of incubation. Subsequently, light hlocked any further evolution of this parameter. Treatment v\ith hutyric acid in the dark again mimicked the effect of light, while FC reversed the negative effect of light. Tbe data show that in Phaielia lanacetifoiia seeds germination is linked to a more alkaline cytoplasmic pH, The finding that the light-dependent metabolic inhibition occurs after an early acti\ ation ot metabolism, i.e. after the first 24 h. su^izesls that the effects of light on the cytoplasmic and vacuolar pH depend on the early metabolic processes involved in the control of the homeostasis of cell pH and/or on the inhihition of tbe reactivation of the transport mecbanisms.Ke\ words -Germination, intracellular pH, metabolism. Phuveliu uinaceiijhliu. pholoblastic seed. "P-NMR.L. Espen. S. Mm-t:uui. C. Alisi. L Piwvimo and S. M. Ciicmri Uorrc.ipomlini> aushor'i.