Mechanisms and parameters of transients and oscillations of delayed chlorophyll fluorescence in the thylakoid membrane of the intact maize leaf

Abstract

Standard induction processes of delayed fluorescence (DF) of chlorophyll (induction signals) occur when an intact leaf segment of maize inbreds and hybrids is initially kept in the phosphoroscope darkroom for more than 15 min (τ > 15 min), and then the leaf is illuminated with the intermittent white light and measured. Resolved induction processes of DF chlorophyll into transients: A, B, C, D, and E occur when the intact leaf segment of maize inbreds and hybrids is kept in the phosphoroscope darkroom for a significantly shorter period (30 s ≤ τ ≤ 240 s), with the time rate τ of 30 s, prior to its illumination with the intermittent white light. Induction transients: A, B, C, D, and E are characterised with their temporal parameters: t _A, t _B, t _C, t _D, and t _E, dynamics of changes in transients intensities and mechanisms of their generation. The induction processes of chlorophyll DF of the intact leaf of maize inbreds and hybrids resolved into transients: A, B, C, D, and E are accompanied by the occurrence and different levels of activation energy (E _a, kJ mol⁻¹) that correspond to different critical temperatures. The generation mechanisms of induction transients: A, B, C, D, and E are classified into two groups. Transients A and B are of a physical character, while the transients: C, D, and E are of a chemical character. It is shown that the generation of the induction transients: B, C, D, and E simultaneously follows establishing of the oscillations of induction processes of the DF chlorophyll. Oscillating of induction processes of DF chlorophyll is explained by the ion (K⁺, Na⁺, H⁺, Cl⁻) transport mechanism across the thylakoid membrane of the intact leaf of maize inbreds and hybrids grown under conditions of air drought, increased temperatures and water deficiency in the medium.