S. I. Pogosyan

Application of Reflectance Spectroscopy for Analysis of Higher Plant Pigments

Nondestructive techniques developed by the authors for assessment of chlorophylls, carotenoids, and anthocyanins in higher plant leaves and fruits are presented. The spectral features of leaf reflectance in the visible and near infrared regions are briefly considered. For pigment analysis only reflectance values at several specific wavelengths are required. The chlorophyll (Chl) content over a wide range of its changes can be assessed during leaf ontogeny using reflectance near 700 nm and, in the absence of anthocyanins, at 550 nm. The approaches used for elimination of Chl interference in the analysis of carotenoids (reflectance at 520 nm) and anthocyanins (at 550 nm) are described. The suitability of reflectance spectroscopy for estimates of carotenoid/chlorophyll ratios during leaf senescence and fruit ripening is demonstrated. The algorithms developed for pigment analysis are presented, and the conditions of their applicability are considered. Further perspectives for the application of reflectance spectroscopy including remote sensing for estimation of plant pigment content and physiological states are discussed.

Optical properties of rhodoxanthin accumulated in Aloe arborescens Mill. leaves under high-light stress with special reference to its photoprotective function

In Aloe arborescens Mill. leaves, strong sunlight or its combination with drought induces the accumulation of the red keto-carotenoid, rhodoxanthin. Simultaneously, the transformation of chloroplasts into chromoplasts accompanied by degradation of thylakoid membranes and formation of plastoglobuli, large in size and number, takes place. Depending on stress conditions the build up of rhodoxantin occurred along with the loss of chlorophyll or on the background of relatively high content of the pigment in the leaves. Microspectrophotometrical measurements showed the presence of chlorophyll-free plastids and retention of carotenoids during leaf adaptation to strong sunlight. The plastid spectra contained absorption bands of common for higher plants carotenoids together with those of rhodoxantin, with absorption maxima situated in the blue (440-480 nm) and the green ranges of the spectrum, respectively. The studies of whole-leaf optical properties revealed a broad band of rhodoxanthin absorption in the blue-green range peaking near 540-550 nm. Within this spectral band the accumulation of rhodoxanthin occurring, probably, in plastoglobuli considerably increased light absorption by stressed Aloe leaves. A possible photoprotective function of rhodoxanthin and other carotenoids as an internal light trap analogous to that accomplished by anthocyanins in other plant species is discussed.

Growth and photosynthesis of Chinese cabbage plants grown under light-emitting diode-based light source

We compared growth and the content of sugar, protein, and photosynthetic pigments, as well as chlorophyll fluorescence parameters in 15- and 27-day-old Chinese cabbage (Brassica chinensis L.) plants grown under a high-pressure sodium (HPS) lamps or a light source built on the basis of red (650 nm) and blue (470 nm) light-emitting diodes (LEDs) with a red to blue photon ratio of 7: 1. One group of plants was grown at a photosynthetic photon flux (PPF) level of 391 ± 24 μ mol/(m2 s) (normal level); the other, at a PPF level of 107 ± 9 μ mol/(m2 s) (low light). Plants of the third group were firstly grown at the low light and then (on the 12th day) transferred to the normal level. When grown at the normal PPF level, the plants grown under LEDs didn’t differ from plants grown under HPS lamps in shoot fresh weight, but they showed a lower root fresh and dry weights and the lower content of total sugar and sugar reserves in the leaves. No differences in the pigment content and photosystem II quantum yield were found; however, a higher Chl a/b ratio in plants grown under LEDs indicates a different proportion of functional complexes in thylakoid membranes. The response to low light conditions was mostly the same in plants grown under HPS lamps and LEDs; however, LED plants showed a lower growth rate and a higher nonphotochemical fluorescence quenching. In the case of the altered PPF level during growth, the plant photosynthetic apparatus adapted to new conditions of illumination within three days. Plants grown under HPS lamps at a constant normal PPF level and those transferred to the normal PPF level on the 12th day, on the 27th day didn’t differ in shoot fresh weight, but in plants grown under LEDs, the differences were considerable. Our results show that LED-based light sources can be used for plant growing. At the same time, some specific properties of plant photosynthesis and growth under these conditions of illumination were found.

Stimulation of nadph-dependent lipid peroxidation by 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid and diquat in microsomes isolated from Pisum sativum

Abstract 2,4-Dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and diquat (DQ) stimulate NADPH-dependent lipid peroxidation (in the presence of ADP-Fe 2+ complex) in microsomes from green leaves and etiolated seedlings. The activity was not shown with 2,6-D and 2,4,6-T which are non-active as herbicides. The stimulation was not observed when NADPH was replaced with NADH or ascorbate. It is suggested that the increasing of dark lipid peroxidation in microsomes plays some role in the toxicity of the herbicides to plants.

Intrapopulation heterogeneity of the fluorescence parameters of the marine plankton alga Thalassiosira weissflogii at various nitrogen levels

Fluorescence of the marine alga Thalassiosira weissflogii (Grunow) Fryxell et Hasle with open (Fo) and closed (Fm) reaction centers of photosystem 2 (PS 2) and its relative variable fluorescence (Fv/Fm) were measured at various levels of inorganic nitrogen. A significant heterogeneity of the population in terms of these parameters was revealed. Some cells within the population were more sensitive to nitrogen deficiency, and their photosynthetic apparatus was disrupted to a greater extent. The cells within a population also differed in terms of their ability to recover after incubation at low nitrogen levels. Enhancement of nitrogen deficiency resulted in an increase in the variability of the Fo and Fv/Fm values of the cells. Fluorescence variability decreased at a less pronounced deficiency. Fluorescence variability should be taken into consideration in the studies concerning responses of algae to changes in nutrient contents.

Response of the photosynthetic apparatus of the diatom Thallassiosira weisflogii to high irradiance light

The response of the photosynthetic apparatus to high irradiance illumination (440–2200 W/m2) was studied in the diatom Thallassiosira weisflogii by fluorescence methods. Changes in the photosynthetic apparatus were monitored by measuring characteristics of chlorophyll fluorescence F0, Fm, Fv /Fm, and qN for several hours after illumination of the alga with high-intensity light. Incubation of the alga with 2 mM DTT, an inhibitor of de-epoxidase of carotenoids in the diadinoxanthin cycle, led to a decrease in the nonphotochemical quenching of chlorophyll fluorescence and a drop in the Fv /Fm ratio, a characteristic that reflects the quantum efficiency of the functioning of the photosynthetic apparatus. Light-induced absorption changes associated with transformations of carotenoids of diadinoxanthin cycle were recorded in vivo in algal suspensions in the absence and in the presence of DTT. Using the microfluorometric method, we measured cell distribution over the efficiency of the primary processes of photosynthesis (Fv /Fm) after illumination. We found cells with a high tolerance of their photosynthetic apparatus to photooxidative damage. The relatively high tolerance of a portion of the cell population to high-light illumination can be related to light-induced transformation of carotenoids and to the functioning of other protective systems of the photosynthetic apparatus in diatoms.

Changes in the condition of photosynthetic apparatus of a diatom alga Thallassiosira weisflogii during photoadaptation and photodamage

Two populations of a diatom alga Thallassiosira weisflogii were grown at photon flux densities (PFD) of 0.8 and 8 µmol/(m2 s). For both diatom populations, the recovery of chlorophyll fluorescence parameters (F0, Fm, Fv/Fm, and NPQ) was monitored after nondestructive irradiation by visible light at PFD of 40 µmol/(m2 s) and after high-intensity irradiation by visible light (1000–4000 µmol/(m2 s)). The exposure of diatoms to PFD of 40 µmol/(m2 s)—higher than PFD used for algal growth but still nondamaging to photosynthetic apparatus—induced nonphotochemical quenching (NPQ), which was stronger in algae grown at higher PFD (8 µmol/(m2 s)) than in algae grown at low light. After irradiation with high-intensity light, the recovery of chlorophyll fluorescence parameters was more pronounced in algae grown at elevated PFD level. During short-term irradiation of diatoms with high-intensity visible light (1000 µmol/(m2 s)), a stronger NPQ was observed in the culture adapted to high irradiance. After the treatment of algae with dithiothreitol (an inhibitor of carotenoid deepoxidase in the diadinoxanthin cycle) or NH4Cl (an agent abolishing the proton gradient at thylakoid membranes), a short exposure of algae to PFD of 40 µmol/(m2 s) induced hardly any nonphotochemical quenching. The results indicate the dominant contribution of xanthophyll cycle carotenoids to energy-dependent quenching.

Fv/Fm as a Stress Indicator for Woody Plants from Urban-Ecosystem

Plants grown under urban environmental conditions are exposed to different anthropogenic stress factors: air pollutants e.g. SO2, NO, NO2, photochemical smog, photooxidants, acid rains, mineral soil deficiency induced by acid rains, heavy metal load, enhanced UV-B radiation. Photosynthetic apparatus of plants is sensitive to stress conditions caused by anthropogenic and natural stress factors [1,2]. Chlorophyll fluorescence measurements provide a powerful non-destructive method for fast outdoor screening of trees. Some parameters of chlorophyll fluorescence can be widely used to characterize photosynthetic activity of a whole plant in vivo [3]. Phelloderm cells of bark of woody plants containing a lot of chlorophyll demonstrate photosynthetic activity. Application of chlorophyll fluorescence measured on intact shoots of trees make it possible to monitor urban woody plantations since early spring till late autumn in many east and west European parts of Russia. The goal of this work was to conduct reliable measurements of chlorophyll fluorescence parameters on one-year-old shoots of trees for stress detection on plants under urban conditions.

Assessing the physiological state of woody plants by parameters of chlorophyll fluorescence in the bark of annual shoots.

The relative yield of variable chlorophyll fluorescence in the bark of annual shoots of woody plants was measured with a portable pulse-modulated fluorometer designed for this purpose at the Department of Biophysics (Biological Faculty, Moscow State University). Experiments were performed to study the response of this parameter to external influences (treatment with an herbicide, water loss, etc.). The results demonstrated the possibility of reliably recording the parameters of fluorescence in the annual shoots of various woody plants without damaging these shoots. It is concluded that measurements of chlorophyll fluorescence in the bark of woody plants can be used for analyzing changes in the physiological state of tree stands under the effects of natural and anthropogenic factors.

Experience of continuous fluorimetric monitoring of phytoplankton at a mooring station

The natural phytoplankton was monitored by means of fluorimetric equipment in Vostok Bay of the Sea of Japan. A gradual increase in the microalgae abundance was revealed in the course of the main water current, which enters the bay and leaves it. The continuous registration of chlorophyll fluorescence at a fixed point in the bay indicates the significant microscale variation of the abundance and functional state of the phytoplankton.