ScienceAsia 29 (2003): 255-264 |doi: 10.2306/scienceasia1513-1874.2003.29.255

Ionic Currents Associated with Primary Root Growth of Sunflower Seedlings and the Effect of External pH

Panote Thavarungkul^1,*, Chulaphorn Muangdit¹ and Karnnika Sunbhanich²

ABSTRACT: The current-patterns along horizontally growing intact sunflower (Helianthus annuus L.) seedling roots were investigated using a two-dimensional vibrating probe system. Currents entered the root cap and the meristem and left along the remaining part for most of the shorter roots (10-15 mm). For longer roots (15-20 mm) currents entered the root tip, left the main elongation zone and entered the root again in the post elongation and the root hair zones. These currents entered the meristem with a density of about 1 to 9 A cm^-2 and left with a density of about 0.3 to 5 A cm^-2 in the elongation zone. The inward currents in the post elongation and the root hair zones were smaller, i.e., about 0.1 to 2 A cm^-2. The results suggest an association between current pattern and root growth. Ion-substitution and pH experiments showed that H⁺ ions were the major contributors to the root currents. Increased root elongation rate at low pH was associated with increased current density and the reversal of the current direction from outward to inward in the main elongation zone. The findings support the acid growth hypothesis.

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1 Biophysics Research Unit: Biosensors and Biocurrents, Department of Physics,
2 Department of Biology, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand.

* Corresponding author, Email: tpanote@ratree.psu.ac.th

Received 31 Oct 2002, Accepted 24 Mar 2003