Photosynthetica covers wide range of photosynthesis research or research including photosynthetic parameters of both experimental and theoretical nature.

Subject of study. The rate of electron transfer between plant photosystems based on fluorescence measurements and calculated density graphs of photon processes is studied. Aim of study. The purpose of this paper is to determine how the structural and optical parameters of plants are affected by their growth conditions. Method. The morphology of chloroplasts was examined by electron microscopy of tissue samples of barley flag leaves grown under the same intensity of illumination in a growing chamber and in the field. The samples underwent full preparation for electron microscopy, including staining with heavy metals to increase the contrast, and were analyzed using a Hitachi HT 7700 transmission electron microscope. Chlorophyll fluorescence parameters of the flag leaves were measured in vivo using the LI-6800 photosynthesis system in a closed leaf chamber that included a built-in fluorimeter. Main results. The role of structural coloration caused by interference and diffraction of light on structural elements of a green leaf having a period comparable with the wavelength of light has only been described in recent years. The study also identified a significantly denser and better-ordered grana structure in the chloroplasts of barley leaf cells grown under artificial conditions. Despite this difference, the maximum quantum yield of Photosystem II in both samples lay in the range of values typical for plants in their normal physiological state. Since electron transport is highly dependent on the spatial organization of the photosynthetic apparatus in the chloroplast thylakoid membranes, the denser “packing” of grana will clearly support more efficient electron transport because the molecular complexes involved in the process are closely arranged. We found that the electron transport rate was different for the plants grown in the field and those grown in the chamber. The electron transport rate for the plants grown in the growth chamber was 1.7 times faster than that for plants grown in the field. Thus, numerical calculations and the spectroscopy/electron microscopy results showed a connection between the photon state density, electron transport rate, and the occurrence of chemical reactions during photosynthesis. Practical significance. Comparing the photosynthetic parameters of the same plants grown in different environments provides useful information on the mechanism behind the photosynthesis process. Identification of the main factors (quantity and quality of water, external environment, amount of nutrients, etc.) affecting the structure and optical properties of plants will increase agricultural yields and reduce costs by optimizing resources and technological processes.

Possible use of integral characteristics of slow stage of chlorophyll fluorescence induction (CFI) for monitoring of physiological state of plants in phytocenoses was studied in the leaves of wheat Triticum aestivum L. and radish Raphanus sativus var. radicula Pers., cv. Virovskii belyi, grown in artificial-light culture. Investigation concerned the behavior of Т_0.5 (half-time of fluorescence intensity decrease from its peak to a steady-state level), R_fd (fluorescence decrease ratio also known as vitality index), parameter \({{{{\overline V }}_{{{\text{max}}}}}}\) (maximum possible average rate of induction transient), and \(\bar {\alpha }\) (average efficiency of PSA in the induction period) during leaf ontogenesis. Plant material was the discs cut from uniformly illuminated wheat leaves of different age from the top (sixth) storey of plants and the disks from the second (in the order of emergence) true leaves of radish at the age from 3 to 24 days. The plants were grown in controlled-climate chambers in hydroponic culture on claydite at irradiance of 100 W/m² of photosynthetically active radiation (PAR). CFI curves were recorded using a single-beam unit. Values of parameter Т_0.5 slightly changed during leaves’ ontogenesis up to the time of senescence (the age of 26 days). Relative changes in the values of CFI parameters (Δ rel., %) at the age from 2 to 24 days were 28% for \(\bar {\alpha }\) and 30% for Т_0.5. For \({{{{\overline V }}_{{{\text{max}}}}}}\) and R_fd, the values were 67 and 70%, respectively. Upon more advanced ageing and comparison of parameters for 24- and 26-day-old leaves, more pronounced changes were observed for Т_0.5 (by 37.6%) and \({{{{\overline V }}_{{{\text{max}}}}}}\) (by 36.0%) and less pronounced for \(\bar {\alpha }\) (by 23.0%) and R_fd (by 13.0%). Thus, the pattern of parameter Т_0.5 behavior observed in the course of wheat leaves’ ontogenesis distinguished it from other fluorescence parameters of CFI slow stage (R_fd, \(\bar {\alpha }\), and \({{{{\overline V }}_{{{\text{max}}}}}}\)); this gives grounds for a potential use of Т_0.5 as one of the simplest integral indicators of physiological state and pathophysiological (irreversible) changes occurring in plant leaves within a wide age interval and upon senescence. Unambiguous interpretation of the data obtained by means of parameter Т_0.5 under stress conditions for estimation of irreversibility of the observed changes in PSA requires more detailed investigations.

Two barley samples were taken for the study – one grown in the field and the other in a special chamber under intensive light. Chloroplasts structure was obtain