Biosystems analysis of plant development concerning photoperiodic flower induction by hydro-electrochemical signal transduction

Abstract

In contrast to the classical hypothesis of photoperiodic flower induction involving a flower-inducing hormone 'florigen', it is the goal of this contribution to present the higher plant as a hydraulic-electrochemical signal transducer integrating the plant organs via action potentials in communication with intrinsic and environmental constraints and to replace 'florigen' by a frequency-coded hydro-electrochemical signal pattern. Observation of whole plant behaviour by time lapse photography clearly shows rhythmic integration of the main shoot axis and side branches in rhythmic growth as well as in leaf movements. This was observed with short-day ecotypes of Chenopodium rubrum L. and a long-day ecotype of Chenopodium murale L. Upon flower induction the phase relationship between rhythmic SER and leaf movements is altered in a very specific way both in the short-day and long-day plant (Wagner et al., Flowering Newslett, 26:62-74, 1998). The experimental set-up for running these investigations is shown in Fig. 11.1. The recording of surface sum action potentials from the surface of Chenopodium plants is achieved with bipolar electrodes and differential amplifiers similar to the equipment used for recording EEGs and ECGs in medicine. Finally, electrophysiograms (EPGs) can be obtained from various phases of plant development (i.e. juvenility, maturity) to be used for applied purposes like plant characterisation and manipulation in nurseries or glasshouse crops. Rhythmic integration of the whole plant possibly involves modulation of turgor pressure via stretch-activated ion channels and concomitant changes in membrane potential. The perception of a flower inducing dark period might lead to a change in electrochemical signalling between leaves and the shoot apical meristem (SAM) and thus represent 'florigen'. The switch from the vegetative to the flowering state is a threshold response, systemic in nature and involving not only the apical meristem but also the axillary buds. Thus we believe that the flower inducing signal may be electrical in nature, requiring a holistic biosystem analysis for quantitative ilucidation.