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Interdependence between oscillations and transients of delayed fluorescence induction processes in the thylakoid membrane of the intact maize leaf: Responses to effects of increased temperatures and drought

Radenović Čedomir N. (Institut za kukuruz 'Zemun Polje', Beograd + Fakultet za fizičku hemiju, Beograd)
Marković Ksenija P. (Institut za kukuruz Zemun Polje, Beograd)
Radojčić Aleksandar R. (Institut za kukuruz 'Zemun Polje', Beograd)
Anđelković Violeta B. (Institut za kukuruz 'Zemun Polje', Beograd)
Kalauzi Aleksandar J. (Centar za multidisciplinarne studije, Beograd)

Standard induction processes of delayed fluorescence (DF) of chlorophyll (induction signals) occur when an intact leaf segment of maize inbreds and hybrids is kept in the phosphoroscope darkroom for more than 15 minutes (t > 15 min), and at the same time the leaf is illuminated with the intermittent white light. 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 (500 s > t > 30 s), with the time rate t of 30 s, prior to its illumination with the intermittent white light. Induction transients: A, B, C, D and E are characterized with the time of their generation: tA = 31±6 ms (A), tB = 5 ± 0,5 s (B), tC = 15±5 s (C), tD = 360±20 s (D) and tE = 670±35 s (E), dynamics of changes in transients intensities (IA, IB, IC, ID and IE) 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 (Ea, kJ mol-1) that correspond to critical temperatures ranging from 28 to 33°C. The generation mechanisms of induction transients A, B, C, D and E classify them 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.

Keywords: Zea mays, intact leaf, thylakoid membrane, induction processes, transients, oscillations, critical temperature, activation energy, delayed chlorophyll fluorescence