Analysis and use of neural networks as a tool for a rapid non-invasive estimation

Water deficit is one of the most important environmental factors limiting sustainable crop yields and it requires a reliable tool for fast and precise quantification. In this work we use simultaneously recorded signals of photoinduced prompt fluorescence (PF) and delayed fluorescence (DF) as well as modulated reflection (MR) of light at 820 nm for analysis of the changes in the photosynthetic activity in detached bean leaves during drying. Depending on the severity of the water deficit we identify different changes in the primary photosynthetic processes. When the relative water content (RWC) is decreased to 60% there is a parallel decrease in the ratio between the rate of excitation trapping in the Photosystem (PS) II reaction center and the rate of reoxidation of reduced PSII acceptors. A further decrease of RWC to 20% suppresses the electron transfer from the reduced plastoquinone pool to the PSI reaction center. At RWC below values 15%, the reoxidation of the photoreduced primary quinone acceptor of PSII, QA–, is inhibited and at less than 5%, the primary photochemical reactions in PSI and II are inactivated. Using the collected sets of PF, DF and MR signals, we construct and train an artificial neural network, capable of recognizing the RWC in a series of “unknown” samples with a correlation between calculated and gravimetrically determined RWC values of about R2 ≈ 0.98. Our results demonstrate that this is a reliable method for determination of RWC in detached leaves and after further development it could be used for quantifying of drought stress of crop plants in situ. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial

Drought-induced modifications of photosynthetic electron transport in intact leaves: Analysis and use of neural networks as a tool for a rapid non-invasive estimation

AbstractWater deficit is one of the most important environmental factors limiting sustainable crop yields and it requires a reliable tool for fast and precise quantification. In this work we use simultaneously recorded signals of photoinduced prompt fluorescence (PF) and delayed fluorescence (DF) as well as modulated reflection (MR) of light at 820nm for analysis of the changes in the photosynthetic activity in detached bean leaves during drying. Depending on the severity of the water deficit we identify different changes in the primary photosynthetic processes. When the relative water content (RWC) is decreased to 60% there is a parallel decrease in the ratio between the rate of excitation trapping in the Photosystem (PS) II reaction center and the rate of reoxidation of reduced PSII acceptors. A further decrease of RWC to 20% suppresses the electron transfer from the reduced plastoquinone pool to the PSI reaction center. At RWC below values 15%, the reoxidation of the photoreduced primary quinone acceptor of PSII, QA–, is inhibited and at less than 5%, the primary photochemical reactions in PSI and II are inactivated. Using the collected sets of PF, DF and MR signals, we construct and train an artificial neural network, capable of recognizing the RWC in a series of “unknown” samples with a correlation between calculated and gravimetrically determined RWC values of about R2≈0.98. Our results demonstrate that this is a reliable method for determination of RWC in detached leaves and after further development it could be used for quantifying of drought stress of crop plants in situ. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial

Delayed Fluorescence Measurements Show Increased S(2)Q(B)(-) Charge Recombination in PS2 of Tobacco Pigment-Deficient Aurea Mutant

Genetic transformation of plants often results in changed pigment content. Variation in pigment content directly induces changes in photosynthetic electron transport reactions. Fully expanded and deficient in chlorophylls tobacco leaves of aurea mutant, A1146, that expresses enhanced level of Q(B)-nonreducing PS2 centres and increased possibility for charge recombination of separated states in PS2 reaction centres were investigated. Long-term delayed fluorescence, DF, measured in second-to-minute time domains and temperature curve of delayed fluorescence, DFTC, was used to study slow PS2 charge recombination (S(2)Q(A)(-) and S(2)Q(B)(-)) in both wild type (line N1146) and a mutant A1146 tobacco plants. In conditions when S(2)Q(B)(-) recombination prevails in PS2 reaction centres, it causes increased possibility for PS2 photodamages. We found that despite of higher possibility for S(2)Q(B)(-) recombination in A1146 as evaluated by DF decay kinetics these plants do not differ from WT in their efficiency for photoprotection. The lack of B-like-band' in DFTC of leaves of both studied tobacco lines pre-illuminated for 6 min with low light intensities of 45 mu mol m(-2)s(-1) PPFD (LL) was observed. It was considered a manifestation of photoprotection at LL conditions through limiting possibility for S(2)Q(B)(-)-recombination. In leaves pre-illuminated for 6 min with high light intensities of 1200 mu mol m-(2)s(-1) PPFD (HL) A1146 half-drop of well-expressed B-band was shifted to higher temperatures. A possible photoprotection based on accumulation of Q(B)-nonreducing centres was discussed in details