An Isoelectric Point for Plant Tissue and Its Significance

The study of the relation of hydrogen-ion concentration to the growth and development of plants or plant parts has, in many cases, indicated that there is between the extreme limits of acidity or of alkalinity which are • injurious to and interfere with growth and development a third region where the reaction affects the plant injuriously.This produces, when the growth of the plant or the intensity of the process is plotted against the hydrogenion concentration of the solution, a curve having a double maximum with a minimum located between the two maxima.Webb ( 25) was apparently the first to call attention to this phenomenon.He found that, when the spores of Penicillium cyclopium were germinated in buffer mixtures of H3PO4 and NaOH containing mannite, two maxima appeared with a minimum between when the percentage of spore germination was plotted against the pH of the solutions.He found similar curves for Fusarium sp., and, under certain temperature conditions, for Aspergillus niger.For Botrytis cinerea-and Lenzites saepiaria his curves.showed but one maximum.In a more recent paper (26) he has studied the germination of the spores of a large number of fungi in various media the hydrogen-ion concentration of which was adjusted by means of H3P04 and NaOH.In various forms, notably Penicillium and Fusarium, and under certain conditions, two maxima were found in the curve of spore germination plotted against the hydrogen-ion concentration of the medium.In at least one set of condi¬ tions, two maxima were found for Aspergillus niger , Penicillium cyclopium , Botrytis cinerea , Fusarium sp., Penicillium italicum , Lenzites saepiaria , and Puccinia graminis.Only one maximum was found for Colletotrichum Gossypii.Salter and Mcllvaine ( 22) found a double-maximum curve for the growth of wheat seedlings in solution cultures the reaction of which was adjusted with citric acid and NaOH.They concluded that this curve resulted from the exhaustion of nitrates due to the development of bacteria in the cultures.