Seed Selection for Potential Viability

A simple method is presented for selecting individual seedsfor growth and vigour prior to germination. The selection isbased on the measurement of an electric current originatingduring the initial stage of seed imbibition. After selecting,seeds may be returned to the quiescent state without affectingviability. Results of both laboratory germination and fieldexperiments demonstrate that high germination rates, more extensivegrowth, higher yields, and fewer defective plants are associatedwith small currents. Seeds of low viability and high currentsmay be removed to upgrade the germination and vigour. Resultsare presented from several varieties of Phaseolus vulgaris andfrom three other plant species. Experiments are discussed whichindicate that seeds graded by current levels possess markedlydifferent respiration rates.     

Ion Transport in the Testa of Germinating Seeds

Levengood, W. C. 1985, Ion transport in the testa of germinatingseeds.—J. exp. Bot. 36: 1053–1063. The current flow produced when an electrical potential is appliedto a partially hydrated seed is drastically altered by the applicationof a thermal pulse. Specific responses to thermally inducedchanges in electrical activity are related to the cell wallstructure of the seed coat and its state of hydration. It issuggested that expansion and contraction of the micropores inthe cell wall matrix provide a model based on a diffusion anddehydration during a thermal pulse and an ion-gating effectimmediately following the pulse. Mechanical flexing producedoscillatory behaviour in the electrical current flow throughseed coat tissues in a manner predicted by the thermal responses. Key words: Ion transport, testa, germinating seeds     

Bioelectric Currents and Oxidant Levels in Plant Systems

A bioelectric current measured with a polarized electrode systemin the bole of a tree or the stem of an herbaceous plant mayindicate altered intertissue redox levels. Circumference-heightratio along the stem is shown to be exponentially related tothe current level. This empirical relationship was used to evaluatequantitatively the internal perturbations. Defoliation, foliagedensity, water stress, girdling, and neoplastic growth changethe current gradient in the plant. Changes following defoliationand girdling strongly suggest altered levels of oxidation products.Under water stress both the current level and gradient are reducedand the implications of these changes are discussed. Transverse stem sections from a tree bole disclosed dark-colouredproteinaceous compounds at the site of an iron cathode. Thesecomplexes are translocated from the reaction site by ray parenchymaand stored in the secondary xylem and pith regions. Newly formedxylem and phloem are free of these complexes, indicating thatmetabolically active tissue rapidly translocates reaction products,preventing them from accumulating and interfering with electrodeoxidation reactions.