Search

The structural diversity and multifunctionality of carotenoids remains an important problem for many areas of biology and medicine. Interactions between carotenoids in cyclic reactions provided an understanding of their role in redox processes and their participation in the basic physicochemical, physiological, and biochemical functions of plants. This review analyzes the contribution of carotenoids to the formation of the photosynthetic apparatus (PSA) structure in plants, as well as their participation in the light-energy absorption and the protection of chlorophyll molecules from reactive oxygen species. The mechanisms of zeaxanthin involvement in the energy-dissipation process and the protective role of carotenoids as antioxidants in the lipid phase of membranes are reviewed. The function of violaxanthin-cycle (VC) pigments in water-photolysis reactions is discussed in relation to their participation in the utilization of released oxygen. A hypothesis about the involvement of balance transformations of VC pigments under subthreshold illumination in the maintenance of “plant memory” mechanisms upon a switch to high illumination is proposed. Environmental studies show that the mechanism of PSA photoprotection, which is associated with the activation of non-photochemical quenching as a part of nonspecific plant responses, is activated in response to a wide range of stress factors.

During the tidal cycle, Fucus vesiculosus L. lost moisture (up to 30% of wet weight) and was characterized by a sinusoidal pattern in photosynthetic activity. Three peaks in the photosynthesis capacity were observed at the beginning and middle of low tide and at the beginning of high tide. There were no structural changes in the photosynthetic apparatus. When analyzing the curves of CO2 gas exchange, the processes of photosynthesis in the algae exposed to the air was limited by the activity of the light and dark phases of photosynthesis. The increase in the content of lipid peroxidation products, catalase activity, and accumulation of proline in F. vesiculosus thalli indicated the presence of reversible oxidative stress during low tide.

The presented study supplements the knowledge on ion-exchange capacity, swelling capacity (elasticity) of the plant cell wall, and the accumulation of heavy metals in halophytic species Plantago maritima and Triglochin maritima in the tidal zone of the White Sea western coast. The littoral soils of the coastal territories are sandy or rocky-sandy, medium and slightly saline with poor content of organic substances, Mn, Zn, Ni, and Pb. Studied soils are considered as uncontaminated by heavy metals because they contain background amounts of Fe and Cu. Sea water is significantly polluted by Fe (3.8 MPC) and Ni (55 MPC), has poor content of Zn and Cu and background level of Pb and Mn. The coastal dominant plant species P. maritima and T. maritima were characterized by intensive metals accumulation which was reflected in the coefficient of biological absorption (CBA) of metal by a whole plant. For P. maritima the following metal accumulation series was obtained: Cu (3.29)> Zn (2.81)> Ni (1.57)> Pb (1.30)> Mn (1.21)> Fe (0.97), and for T. maritima: Ni (3.80)> Fe (2.08)> Cu (1.91)> Zn (1.84)> Pb (1.51)> Mn (1.31). Roots accumulated 50–70% of Ni, Cu, Zn, Pb and Mn of the total metal content in the plant while leaves and stems contained 30–50%. Fe was allocated mainly in the roots (80%). The ion-exchange capacity of the plant cell wall for P. maritima and T. maritima was established as follows correspondingly: 3570–3700 and 2710–3070 μmol g-1 dry cell weight per leaf; 2310–2350 and 1160–1250 μmol g-1 dry cell weight per root.

The paper describes the ontogenesis of the epiphytic lichen Lobaria pulmonaria. The studies were carried out in the Karelian forest communities with the period since the last disturbance ranging from 80 to 450 years. Based on the concept of a discrete description of plants and lichens, four periods and 14 age-related states have been distinguished in L. pulmonaria’s ontogenesis. Each ontogenetic state of L. pulmonaria is characterized by a certain thallus size as well as by the presence and the level of development of vegetative diaspores and apothecia on the thallus surface. The possible variants of the species ontogenesis are described.

Structural and functional traits in leaves of sea plantain (Plantago maritima L.) inhabiting intertidal and supratidal zones of the White Sea coast were studied. At the intertidal, the plants were found to have smaller and thicker leaves with more frequent stomata and thinner cover tissues in comparison with the plants collected from the supratidal. Leaf fluorescence and stomatal conductance obeyed the circadian rhythm in plants residing in the supratidal. The tested parameters considerably changed according to tidal dynamics in the intertidal plants. Two stable states (high and low tides) and two transition states (while water level ascends or descends) were defined. In both stable states, the plants demonstrated high functional parameters of fluorescence (Fv/Fm, Y(II), and ETR) and open stomata. In the transitional states, the stomata were partly closed, and the functional activity was inhibited. Leaf structural peculiarities, leaf gas films, the inducible CO2-concentrating mechanism, and the determining role of the stomata are considered in terms of the hypotheses explaining the responses of sea plantain to tidal dynamics on the White Sea coast.

Nowadays, it is relevant to study the mechanisms of rhythmic processes that are the basis of the vital activity of all organisms. From this point of view, it is necessary to study the functioning of organisms living in tidal conditions on the coastal zone of the northern seas. Twice a day, plants are flooded with water on the intertidal zone, and then they go out for drying—there is a change in the water and air environment, which is accompanied by changes in light, temperature, oxygen and CO2 concentrations, pressure, and other parameters. These conditions have led to the formation of a unique halophyte complex of higher terrestrial plants, which have formed various adaptive mechanisms that provide the possibilities for normal existence. Three zones are distinguished on the coastal zone of the White Sea: supratidal, intertidal, and subtidal zones. For each zone, the following species was investigated: for supratidal—Alopecurus arundinaceus, Atriplex glabriuscula, Carex subspathacea; for intertidal—Tripolium vulgare, Triglochin maritima, Salicornia europaea, and three species of Plantago genus; for subtidal—Zostera marina. Species growing on intertidal and subtidal zones are resistant to flooding and have various structural and functional adaptations. The photosynthetic characteristics (CO2 rate of gas exchange, transpiration, stomatal conductivity, and CO2 concentration in the intercellular spaces of the leaves) were studied using the LCPro + portable gas analyzer at natural light intensity and air temperature. Analysis of CO2 exchange curves by the model of Farquhar et al. showed a difference in the values of the maximum carboxylation rate (Vcmax), the electron transport rate at light saturation (Jmax), the utilization rate of triose phosphate, and a number of other parameters in plants of different zones. A comparative study of physiological parameters showed the highest functional activity in plants in the intertidal zone, which undergo daily tidal dynamics. The influence of environmental factors on the content of chlorophylls a and b and the amount of carotenoids was estimated. Evaluation of the implementation of photosynthetic activity in natural habitats in relation to the maximum values at saturating concentration of CO2 showed that the species of higher vascular plants realize their potential in the range of 6–20% on the supratidal zone, from 10 to 70% on the intertidal zone, and from 30 to 60% on the subtidal zone. In the case of a global increase of CO2 concentration, we can expect a significant increase in CO2 absorption by the following halophytes: T. vulgare, Plantago maritima, Z. marina, Al. arundinaceus, and At. glabriuscula, as well as an increase in productivity of P. maritima and Z. marina among the studied halophytes of the coastal zones of the northern Holarctic seas.

Melatonin (N-acetyl‑5-methoxy tryptamine) is an indole hormone; for a long time, it was thought to occur only in animals and humans. Thirty years after its discovery, melatonin was also detected in plants. The ubiquitous presence and high concentrations of melatonin in higher plants, as opposed to animals, led to introduction of the term “phytomelatonin” in 2004. At present, phytomelatonin has been shown to induce antioxidant, antistress, and growth-promoting effects. At the same time, the contribution of melatonin to circadian rhythms and photoperiodic regulation, though well-studied in animals, is still questionable in plants. It is supposed that melatonin could be used in agricultural practice to enhance the stress-tolerance and productivity of plants. This review discusses the history of melatonin research in plants and recent advances in the understanding of its functions.

An overview of research seeking and studying the potential low temperature sensors in plants is provided. It was shown that the number of potential candidates for low temperature sensors is quite wide and includes both individual intracellular structures and substances: membranes, cytoskeletal elements, chromatin, phytochromes, DNA, RNA, specific proteins, and sugars. It was noted that, depending on the mode of thermal exposure (intensity, cooling rate, duration, etc.), the leading role of temperature sensors may be played by different structures or substances. Apparently, this variety allows plants to respond to cold more flexibly and appropriately.

At present, chlorophyll meters are widely used for a quick and nondestructive estimate of chlorophyll (Chl) contents in plant leaves. Chl meters allow to estimate the Chl content in relative units - the Chl index (CI). However, using such meters, one can face a problem of converting CI into absolute values of the pigment content and comparing data acquired with different devices and for different plant species. Many Chl meters (SPAD-502, CL-01, CCM-200) demonstrated a high degree of correlation between the CI and the absolute pigment content. A number of formulas have been deduced for different plant species to convert the CI into the absolute value of the photosynthetic pigment content. However, such data have not been yet acquired for the atLEAF+ Chl meter. The purpose of the present study was to assess the applicability of the atLEAF+ Chl meter for estimating the Chl content. A significant species-specific exponential relationships between the atLEAF value (corresponding to CI) and extractable Chl a, Chl b, Chl (a+b) for Calamus dioicus and Cleistanthus sp. were shown. The correlations between the atLEAF values and the content of Chl a, Chl b, and Chl (a+b) per unit of leaf area was stronger than that per unit of dry leaf mass. The atLEAF value- Chl b correlation was weaker than that of atLEAF value-Chl a and atLEAF value-Chl (a+b) correlations. The influence of light conditions (Chl a/b ratio) on the atLEAF value has been also shown. The obtained results indicated that the atLEAF+ Chl meter is a cheap and convenient tool for a quick nondestructive estimate of the Chl content, if properly calibrated, and can be used for this purpose along with other Chl meters.

Effects of daily short-term low temperature treatment (DROP) applied during different prereproductive developmental stages on growth and development of tomato plants grown under continuous light (CL) has been studied. It was shown that DROP treatment (daily decrease of temperature from 26 to 10 C for 2 h) applied to plants of different age is not equally effective in preventing or moderating CL injury in tomatoes grown under CL. DROP treatment of seedlings and juvenile plants proved to be ineffective in preventing leaf chlorosis in the aftereffect. DROP treatment of immature and virginile plants of different age had moderate protective effect, reducing the degree of leaf chlorosis. The maximum effect was obtained when plants were treated by DROP throughout the entire prereproductive period.

Anatomic–morphological and functional features of sea aster (Aster tripolium L.) leaves were investigated in the field study on the northern limit of A. tripolium’s range of distribution, using plants growing in the intertidal zone on the Pomorsky coast of the White Sea. The largest leaf area was found in plants grown close to the shore, near the high tide mark. In plants grown near the low tide mark, the leaf area decreased fourfold, while the leaf thickness increased by 30%. The plants sampled near the low and high tide marks showed different rates of photosynthesis and transpiration; they also differed in stomatal conductance and the number of stomata on the upper and lower leaf sides. Analysis of carbon dioxide plots of photosynthesis revealed the habitat-related differences in photosynthetic characteristics. Under saturating concentrations of carbon dioxide, the plants grown near the shore exhibited larger rates of photosynthetic electron transport and carboxylation. Characteristics of plants in the examined transect were found related to the local environmental conditions. A hypothesis is put forward that A. tripolium possesses an inducible CO2 concentrating mechanism during the growing season under northern summer conditions.

Ecological plasticity in the tidal zone, specifically the effects of daily and seasonal dy-namics of environmental factors on the dominant species of vascular plants and epilithic lichens has been studied. The investigations were conducted on the Pomorian coast of the White Sea (Republic of Karelia) during two growing seasons (2012-2013). The studies of the morphological and anatomical characteristics of dominant individuals in the plant and lichen cover types have been made along the model transect through different substrate types. Determination of plasticity of plants and lichens was made by the method of Cornelissen exploiting coefficient of variation (CV). The obtained data showed that the investigated groups of vascular plants and lichens on the tidal zone on all measured morphological and anatomical parameters have a high level of plasticity.

Cold tolerance of cucumber (Cucumis sativus L.) seedlings was investigated using wild-type plants and the phytochrome B-deficient mutant (lh-mutant). Plants were subjected for 6 days to intermittent short-term cooling (12°C for 2 h per day) and to continuous chilling under conditions of 16-h photoperiod (day/night = 16/8 h) and permanent illumination. “Dehardening” process was initiated by the transfer of plants to either light or dark conditions at 23°C. It was concluded that phytochrome B participates in the development of cold tolerance in cucumber plants under stress conditions, i.e., under short-term intermittent chilling at nights and during dehardening in continuous darkness.

When plants are grown in a greenhouse or in controlled environment growth rooms, prolonging the photoperiod, including towards continuous light, is one of the ways to increase plant productivity and energy savings. However, exposing some plant species to long photoperiods causes leaf injuries and growth reductions. We studied the effect of the photoperiod (8, 12, 16, 20, and 24 h) and photosynthetic photon flux density (60, 120, and 160 μmol/m2 s PAR) on cucumber plants Cucumis sativus L. in a prereproductive period. It was shown that the response of the cucumber plants to a photoperiod over 20 h, including continuous light, depending on the plant age and light intensity, may include leaf movement or paraheliotropism, non-photochemical energy dissipation, and/or reversible photoinhibition of a reaction center of photosystem II, development of reversible chlorosis, reduction of a light-harvesting complex, and increase in the content of carotenoids. Reaction of immature and virginile plants to long photoperiods was different, which high-lights the need for experimental separation of the prereproductive period in terms of age states and consideration of this when developing crop production plan.

CO2 gas exchange, transpiration, stomatal conductance, water use efficiency and chlorophyll content were investigated at the leaves of three species of the family Plantaginaceae: Plantago maritima L., Plantago subpolaris Andrejev and Plantago schrenkii C.Koch under natural conditions of the habitat on high and low tide areas of the White Sea’ coasts. The high rate of photosynthesis at saturating CO2 (PNmax) at P. maritima (85.0±4.8 μmol m-2 s-1), as compared to P. subpolaris and P. schrenkii (45.2± 7.5 and 36.9±3.2 μmol m-2 s-1) was caused by high activity of ribulose-1,5-bisphoshate carboxylase/oxygenase (RuBPCO), the rate of electron transport, the rate of triose phosphate utilization, TPU), as well as high efficiency of carboxylation. The rates of photosynthesis at ambient concentration of CO2 (PN) at P. maritima were 1.4 and 1.7 times higher compared to P. subpolaris and P. schrenkii. Plants of P. schrenkii are characterized by lower values of stomatal conductance and water use efficiency compared to P. maritima and P. subpolaris. In natural habitat, the limiting factor of CO2 assimilation P. subpolaris is the rate of photosynthetic electron transport, the activity of RuBPCO in P. schrenkii.

David Iosifovich Sapozhnikov (17.06.1911–23.11.1983), a well-known plant physiologist and evolutionist would have been 100 this year. Sapozhnikov investigated the role of carotenoids in plant life and acquired worldwide recognition for his discovery of the violaxanthin cycle. This review considers the most important Sapozhnikov’s results and hypotheses elaborated by subsequent research, as well as the modern concepts in this area of investigation.

The content of photosynthetic pigments and the ratios between them were studied in 71 species of vascular plants, 17 species of Bryophyta, and 10 species of lichens inhabiting West Spitsbergen. With an increase in the level of organization from lichens to vascular plants, the content of photosynthetic pigments (chlorophylls (Chl) and carotenoids (Car)) increased; the Chl a/b ratios and light-harvesting complex values varied independently of organism taxonomy; the Chl/Car ratio tended to increase. The content of pigments is related to taxon advancement at the level of both divisions and higher plant families. In plants inhabiting Arctic region, the pigment content in primitive species was lower than in more advanced ones. In angiosperms inhabiting Spitsbergen, the amount of Chl was lower than in plants inhabiting other botanicgeographical regions.

The content of particular components of water-soluble carbohydrates and cold tolerance of cucumber (Cucumis sativus L.) cotyledonary leaves were studied at early developmental stages in dynamics during 6-day-long treatment with a temperature reduced to 12°C at two regimes: short-term cooling (2 h in the end of the night period, DROP) or permanent low-temperature treatment (PLT). PLT cucumber plants were characterized by the accumulation of oligosaccharides, whereas DROP plants contained increased amounts of glucose, fructose, and raffinose, indicating their higher metabolic status. When changes in carbohydrate fractions were compared with the dynamics of cold tolerance, it was found that these changes were synchronous in PLT plants but asynchronous for glucose and oligosaccharides in DROP plants. We suppose that, in cotyledonary leaves of DROP plants, two pools of sugars are produced; one of them used for tolerance development and another one — in active metabolism. This provides for the combination of activated metabolism and high cold tolerance of these plants. In PLT plants, all components of water-soluble carbohydrates are involved in cold tolerance development.

Phenomenological responses of plants to daily short-term exposure to low hardening temperature was studied under chamber and field conditions. Experiments were carried out on cucumber (Cucumis sativus L.), barley (Hordeum vulgare L.), marigolds (Tagetes L.), and petunia (Petunia x hybrida) plants. The obtained data demonstrated a similar pattern of response in all studied plant species to different variants of exposure to low hardening temperature. The main features of plant response to daily short-term exposure to low hardening temperature include: a higher rate of increase in cold tolerance (cf. two- or threefold increase relative to constant low hardening temperature) that peaked on day 5 (cf. day 2 at constant low hardening temperature) and was maintained for 2 weeks (cf. 3-4 days at constant low hardening temperature); a simultaneous increase in heat tolerance (cf. twofold relative to constant low hardening temperature) maintained over a long period (cf. only in the beginning of the exposure to constant low hardening temperature); a sharp drop in the subsequent cold tolerance after plant incubation in the dark (cf. a very low decrease in cold tolerance following the exposure to constant low hardening temperature); a combination of high cold tolerance and high photochemical activity of the photosynthetic apparatus (cf. a low non-photochemical quenching at constant low hardening temperature); and the capacity to rapidly increase cold tolerance in response to repeated short-term exposures to low hardening temperature in plants grown outdoors (cf. a gradual increase after repeated exposure to constant low hardening temperature). Possible methods underlying the plant response to daily short-term exposure to low temperature are proposed.

The mechanisms of plant responses to short-term cold treatments applied daily in the period of active growth remain unknown. Cucumber (Cucumis sativus L.) plants were subjected to brief drops of temperature (2 h, 12°C) at the end of each night over a 6-day period (DROP treatment) and to prolonged (6 days) cooling at 12°C (permanent low-temperature treatment, PLT). The plants exposed to cold treatments and control plants grown at 20°C were compared in terms of cold resistance and changes in gene expression. Cold resistance of plants was determined on the basis of LT50 temperature. The response of cucumber genetic machinery was assessed by means of a differential display method based on polymerase chain reaction (PCR). The changes in mRNA pool in cells of cucumber plants subjected to permanent and periodic chilling were assessed after comparing the populations of PCR fragments of cDNA. In both types of chilling protocols, the cold resistance started to increase from the 2nd day of low temperature treatment. At the end of the experiment (on the 6th day), the increment in cold resistance was three times larger for DROP compared to PLT treatment. Analysis of mRNA pool showed that the numbers of amplified fragments were nearly identical in both types of low-temperature treatment. The higher level of cold resistance under DROP conditions was assumed to depend on features of metabolism.

Based on the data obtained in the experiments with constant and alternating diurnal temperatures, the temperature dependence of developmental rate was calculated for different photoperiodic groups of plants using the square regression equations. These equations made it possible to calculate the temperature regions of maximum developmental rates of plants under different photoperiods.

We studied the influence of gradient temperature regimes on various parameters of the formation of shoots and roots of cucumber plants, such as rate of leaf appearance, rate of growth, duration of growth and length of leaves, and the rate of growth shoots organs and roots. The plants were grown under the controlled conditions: at different combinations of day and night temperature, illumination 100 W/m2, and 12 h photoperiod. The comparison of constant and fluctuating diurnal temperature regimes has shown that in the optimal area for all studied indices, the highest values were recorded at the constant daily temperature (25°C for all growth indices of shoots and 20°C for growth of roots), while all gradient regimes either did not affect, or exerted inhibitory effects on the plant. Outside the optimum area, the effects of gradient temperatures differed. The main acting fluctuating temperatures, that exerted stimulating effects, combined low hardening (15°C) and optimal temperatures (25°C), which was earlier described for animals. The 15/35 and 35/15°C combinations were unambiguously inhibitory, since both temperatures are hardening for the cucumber. A lesser stimulating effect of gradient temperatures on the developmental rate in a plant, as compared to poikilothermic animals, could be due to a greater autonomy of plant ontogenesis because of autotrophy and, correspondingly, a greater degree of homeostasis. The mechanisms accounting for the responses to temperature gradients are similar in different groups of ectotherms.

The composition and amount of pigments were studied in temperature-dependent chlorophyll-deficient seedlings of wild type (control) and several mutant lines of Festuca pratensis Huds. at room (25°C) and high (35°C) temperatures. In seedlings of all mutant lines grown at 25°C, chlorophyll b content was lower and the concentration of carotenoids was higher than in control seedlings. At 35°C, the concentration of all pigments decreased in a row from dark-green to xantha phenotypes, and this trend was retained when the temperature was lowered to 25°C. The phenotype xantha completely lacked violaxanthin and neoxanthin. The observed effects are related to the protective dissipative function of the xanthophyll cycle.

The object of the study is Stellaria humifusa (Caryophyllaceae) – a polycarpic herb with a long taproot; an almost Arctic hygrophyte with circumpolar distribution. Plants form mats and grow on rock outcrops near coastal areas. The plant community consists of only one species, and is covered with a layer of dead leaves from the previous year. The study of lipids showed that during active growth S. humifusa has lipid fractions in the functionally active state. The fraction of neutral lipids (a structural component of the cell and its emergency stores) dominates in terms of the percentage of saturated fatty acids (FA). The fraction of phospholipids (the main membrane system of the cell) has the greatest content of FA with high quantities of diene, triene and saturated FA. This fraction contains the maximum amount of linoleic acid. The fraction of glycolipids (lipids of chloroplast membranes) accounts for around 32 % of the plant’s total FA. It indicates a tense lipid metabolism associated with photosynthetic activity. This fraction contains less of diene and saturated FA, but significantly more of triene FA, including linolenic acid, comparing to the other groups The study of AOS activity in S. humifusa leaves revealed relatively lowperoxidase activity (2.2 and 1 μmol TG/mg protein at pH 5 and 7.8, respectively) simultaneously with high catalase activity (366 μmol H2O2/mg protein) as compared to other herbaceous plants. This fact possibly indicates the species is adapted to the environment. The high level of unsaturation of the lipid structure of the photosynthetic apparatus membrane system contributes a lot to the maintenance of its high functional activity in S. humifusa.

SummaryThe effects of a pre-sowing seed treatment with a temperature drop (i.e., seed thermo-priming) on the growth and development of two popular bedding plant species, Tagetes patula nana L. (marigold) and Viola wittrockiana Gams. (pansy), were studied. A temperature drop from 22°C to 10°C was applied for 2 h each day during seed germination, over the 6 d before sowing. This seed priming increased plant dry mass, hastened flowering in both species, and increased flower numbers in marigold, but not in pansy. An involvement of certain phytochromes in these temperature-dependent effects on time-to-flowering is suggested.

The study aimed to provide information on the involvement of plant cold resistance in a whole cucumber (Cucumis sativus L.) plant response to temperature drop treatments. The main objective was to explain the effects of a temperature drop on dry matter production and plant morphogenesis. The experimental design included temperature drops to 12°C for 0, 1, 2, 4 and 6 hours at the beginning, in the middle and at the end of the night. The overall average temperature for all treatments was 20°C. A 2-hour temperature drop resulted in the most significant reduction in plant dry weight and leaf petiole length, but the highest degree of cold resistance. With the extension of a temperature drop duration to 4--6 hours, dry matter production was similar to that in the control plants, leaf petiole length increased, but not up to the control level and cold resistance was reduced, but was still higher compared to that of the control plants. Changes in dry matter production, leaf petiole length and cold resistance, depending on the duration of the temperature drop, were interrelated and their patterns varied little with the timing (position effect) of the temperature drop. It is concluded that plant cold resistance mechanisms play an important role in a whole plant response to temperature drop treatments. Thus, plant response to temperature drop treatments can be considered as a response to stress.

The thermomorphological responses of young cucumber plants to a temperature drop lasting 2, 4 and 6 hours applied at the beginning, in the middle and at the end of the night were examined. Plant height, leaf petiole length and plant dry weight were measured and, based on the experimental data, the regression dependences of growth variables on the temperature drop were fitted. A method to determine the optimal temperature drop (the duration and time of exposure) which results in shortened plant height and leaf petiole length without a decrease in plant dry weight is proposed.

The experiments were conducted with Cucumis sativus L., Triticum aestivum L., Brassica capitata, Solanum tuberosum, Zea mays L. and Pisum sativum L. Temperature drop increased cold resistance in all studied species. Level of cold resistance under the drop treatments was much higher than under the constant low temperature. It remained at a higher level for a longer period during de-acclimation. It is concluded that DROP technology is a good way for successful transplantation of greenhouse agricultural and bedding plants in early spring.

SUMMARYA method for investigating the thermoperiodicity of crop plants is described. On the basis of our experimental results and published data, crop plants were assessed to establish whether they were thermoperiodic or not. Tomato and maize were classified as thermoperiodic species. Cucumber, beans, peas, oats and wheat were not thermoperiodic. Strategies for climate control based on the estimation of optimum temperature are proposed. These can be used to minimize energy consumption and, together with other environmental treatments, could optimize the yield of glasshouse crops.

The article is dedicated to the 50th anniversary of the PetrSU Botanic Garden. The idea of its creation is ex- plained by its opportune location close to the northern boundaries of the nemoral species’ natural distribution, and also between the Polar-Alpine and St.-Petersburg botanical gardens, which is conducive to the creation of a link, an introduction point. The history of the Botanic Garden’s formation and development can be divided in three periods: organization (1950—60s), creation and formation of collections (1970—90s), modern stage (since 1990). The full characteristic of the Botanic Garden’s activity since its foundation time is presented. The themes of scientific-research works are detailed; the priority directions of the collections’ formation are elucidated. The contribution of the Botanic Garden’s employers, professors and students of PetrSU and other collaborators have been working for the Garden the last 50 years, is described. The nowadays development of the Botanic Garden is based on the three priority trends of its activity: formation of a new image of the Garden, attractive for visitors; study and preservation of the aboriginal flora’s biodiversity; working out and putting into practice of new infor- mation technologies in botanic gardens.