Calcium and pH patterning at the apical meristem are specifically altered by photoperiodic flower induction in Chenopodium spp.

Abstract

The apical meristem of the short-day plant Chenopodium rubrum responds to photoperiodic flower induction with specific changes of pH and Ca2+ patterning immediately after the inductive dark span. The red-far-red reversibility of the pH and Ca2+ patterning in response to night break treatments was measured in order to distinguish between the effect of the prolonged dark span per se and the specific effect of photoperiodic flower induction. In addition, the pH and Ca2+ patterning in C. rubrum was compared with the long-day plant Chenopodium murale. The pH was visualized using the fluorescent probe carboxy SNARF-1. Calcium ion concentrations were studied using a combination of Ca2+-probes Fluo-3 and Fura Red. It was observed that the specific changes in pH and Ca2+ patterning at the apical meristem of C. rubrum were abolished by the red-light break. This effect was fully reversed with a subsequent single far-red treatment. These observations infer the influence of phytochrome on both pH and Ca2+ patterning. Changes in pH and Ca2+ patterning upon flower induction were observed in both long-day and short-day plants. These results support the hypothesis that changes of pH and [Ca2+] in cells of the apical meristem are part of the pathway in signal transduction triggering flower initiation.