Annals of Botany

RAMs and roots in fields

Generation of electrical activity is a feature of  all plant cells and is involved in several aspects of plant growth and  physiology. The ability of plants to maintain an electromagnetic field  (EMF) has evolved against a background of the Earth’s own EMFs and  thus it is interesting to observe the effect on plant growth of changes  in the ‘electrical environment’. Wawrecki and Zagórska-Marek, Wroclaw, Poland (pp. 791–796) have applied  DC electric fields of 0·5–1·5 V cm^–1 to roots of Zea mays grown in liquid medium. Exposure  was for 3 h and roots were then observed immediately and over the  next 5 d. At 0·5 V cm^–1 there  was no observable effect on root growth or architecture but at 1·0  and 1·5 V cm^–1 roots bent strongly  towards the cathode. This was continued for about 24 h after switching off the electricity before the roots resumed normal gravitropic growth  (although some of the roots exposed to 1·5 V cm^–1 died after the electrical treatment). In addition to these  obvious morphological effects, there were also effects on the architecture  of the root apical meristem (RAM). Zea mays has a RAM of the  closed type in which there is a clear junction between the root proper  and the root cap. In treated roots, this junction became much less distinct  over a period of 24–48 h from the end of the treatment. The  process started with the occurrence of new periclinal divisions in first  tier of the root body, giving a new layer of cells between the procambial  cylinder and the root cap junction; these grew into the root cap, converting  the organisation from closed to open. However, cells in the epidermis–c ortex complex gradually became organized as a new junction, now deeper  in the root, eventually restoring the closed type of architecture. Exposure  to a low-level electric field, even for just 3 h, clearly disrupts  normal patterns of cell lineage and differentiation and raises again the  question of the significance of change in electromagnetic field as an  environmental factor influencing plant development.