Effects of sub-optimal illumination in plants. Comprehensive chlorophyll fluorescence analysis

The fluorescence signals emitted by chlorophyll molecules of plants is a promising non-destructive indicator of plant physiology due to its close link to photosynthesis. In this work, a deep photophysical study of chlorophyll fluorescence was provided, to assess the sub-optimal illumination effects on three plant species: L. sativa, A. hybridus and S. dendroideum. In all the cases, low light (LL) treatment induced an increase in pigment content. Fluorescence ratios - corrected by light reabsorption processes - remained constant, which suggested that photosystems stoichiometry was conserved. For all species and treatments, quantum yields of photophysical decay remained around 0.2, which meant that the maximum possible photosynthesis efficiency was about 0.8. L. sativa (C3) acclimated to low light illumination, displayed a strong increase in the LHC size and a net decrease in the photosynthetic efficiency. A. hybridus (C4) was not appreciably stressed by the low light availability whereas S. dendroideum (CAM), decreased its antenna and augmented the quantum yield of primary photochemistry. A novel approach to describe NPQ relaxation kinetics was also presented here and used to calculate typical deactivation times and amplitudes for NPQ components. LL acclimated L. sativa presented a much larger deactivation time for its state-transition-related quenching than the other species. Comprehensive fluorescence analysis allowed a deep study of the changes in the light-dependent reactions of photosynthesis upon low light illumination treatment.

Non-destructive methodologies applied to track the occurrence of natural micropollutants in watering: Glycine max as a biomonitor

Groundwater is habitually used for watering purposes in rural areas where the rainfall is not enough to adequately cover the crop requirements. However, groundwater sources could be naturally contaminated with trace micropollutants like As and associated elements (B, V and F) adversely affecting the plant health. In this work, non-destructive methodologies based on reflectance and chlorophyll emission processes were applied to assess the presence of micropollutants in watering by using a widespread crop (soybean plant). One of the most substantial results is that the co-occurrence of As, V, B and F in the watering solution clearly produced a synergistic effect in the plants. In fact, both reflectance and fluorescence techniques were proved in this work to be effective in detecting non-destructively stress by multielement treatment. Particularly, for reflectance measurements the most sensitive parameters were the derivative peak area between 480 and 560 nm and the chlorophyll content. Furthermore, it was demonstrated that it is possible to successfully use a portable hyperspectral spectroradiometer instead of a conventional spectrophotometer as the determinations performed with both instruments were positively correlated. Concerning fluorescence, variable emission of chlorophyll-a was more sensitive to stress than steady-state emission. The parameter Fv/F0 was a valuable indicator of stress but the quantum yields of PSII and NPQ stood out as the most sensitive indices with variations of around 60 and 100% respectively.

Meso-substituted cationic porphyrins of biological interest. Photophysical and physicochemical properties in solution and bound to liposomes

A series of cationic porphyrins with 1-4 positive charges are studied: mono(N-methyl-4-pyridyl)triphenylporphine chloride [Mono], cis(N-methyl-4-pyridyl)diphenylporphine chloride [Cis], tri(N-methyl-4-pyridyl)monophenylporphine chloride [Tri] and tetra(N-methyl-4-pyridyl)porphine chloride [Tetra]. Their photophysical properties are measured in small unilamellar vesicles and compared with those in homogeneous solution. Liposomes of L-alpha-dimyristoyl-phosphatidylcholine (100 nm diameter) and L-alpha-dipalmitoyl-phosphatidylcholine (50 nm diameter) in phosphate-buffered saline (pH = 7.4) or D2O 0.15 M NaCl were used. The effect of the medium microheterogeinity is discussed. The triplet quantum yields in liposomes for all the porphyrins are about 0.7, similar to the value obtained for Tetra in aqueous media. The singlet molecular oxygen quantum yields for the hydrophilic compounds Tri and Tetra are greater than those of the hydrophobic ones, Mono and Cis. Also, association constants (KL) of the dyes to liposomes and their localization within the membranes are determined from fluorescence and fluorescence polarization measurements, respectively. KL values are in the range of 10(4)-10(5) M-1 for all the compounds, indicating that hydrophobic and coulombic interactions between porphyrins and liposomes are responsible for the dye association. Fluorescence polarization experiments indicate that Mono and Cis can penetrate into the lipidic phase, and that Tri and Tetra are located near the polar heads of the lipidic molecules.