MODULATION, BY PHENOLIC COMPOUNDS, OF ENDOGENOUS MANGANESE DURING IAA‐INDUCED GROWTH IN AVENA COLEOPTILE SEGMENTS: AN ELECTRON SPIN RESONANCE STUDY

Abstract

SummaryThe behaviour of endogenous manganese (Mn2+) was studied by electron spin resonance spectroscopy during growth induced by indol‐3‐ylacetic acid (IAA) and modulated by phenolic acids in Avena coleoptile segments. Oat coleoptile segments show a characteristic sextet hyperfine spectrum which is similar in appearance to the sextet of Mn2+ In aqueous solution. Endogenous Mn2+ shows a concentration response to IAA, Coleoptile segments treated with p‐hydroxy benzoic acid and 2,4‐dicblorophenol, which inhibit IAA‐induced growth, show a decline in the concentration of endogenous Mn2+. Chlorogenic acid and caffeic acid, which synergize IAA‐induced growth, keep endogenous manganese in the reduced state (i.e. Mn2+) probably by donating electrons in the reaction. It appears that conditions inhibitory to IAA‐induced growth are associated with a decreased level of tissue Mn2+ while those stimulatory to growth seem to be associated with a higher level of endogenous Mn2+. The changes in endogenous Mn2+ may be mediated either by complex formation or by a change in the redox state.