pH-patterning at the shoot apical meristem as related to time of day during different light treatments

Cytoplasmic pH is an important regulatory factor in metabolism. It changes during the cell cycle and during development. The timing of changes in pH-distribution at the apical meristem during three different photoperiods was examined in the short-day plant Chenopodium rubrum in order to study the role of pH in changes of sensitivity of the shoot apex to a photoperiodic flower inducing treatment. pH-changes were visualized in vivo by means of a fluorescent cytoplasmic pH-probe, carboxy SNARF-1 and by confocal laser scanning microscopy. Typical stripy, patchy and uniform patterns could be determined on the basis of pH-patterning at the apical meristem under different photoperiodic treatments. Under continuous light no change in pH-patterning could be observed. The pattern of pH-distribution at the apical meristem specifically changed in response to light-off. During the subsequent dark span pH-pattern changed again after exceeding the critical flower inducing dark period. Responsiveness of pH-distribution at the apical meristem to conditions inductive for flowering is suggestive of the involvement of intracellular pH-changes in the pathway of photoperiodic signal transduction.