E. Navakoudis

Influence of polyamine inhibitors on light-independent and light- dependent chlorophyll biosynthesis and on the photosynthetic rate

Abstract The mutant C-2A′ of the unicellular green alga Scenedesmus obliquus behaves at 32°C like higher plants in that it accumulates protochlorophyllide in darkness and converts it to chlorophyll when exposed to light. By lowering the growth temperature from 32 to 22°C, protochlorophyllide can be reduced in darkness. Thus this organism allowed us to study the effects of the inhibition of several enzymes of polyamine biosynthesis on light-dependent and light-independent chlorophyll biosynthesis. Reduction of the intracellular level of putrescine by the use of 1,4-diamino-2-butanone inhibitor blocked the light-independent chlorophyll biosynthesis (dramatically increasing the photochlorophyllide levels with parallel reduction of chlorophyll). The influence of the inhibitor in question is even more dramatic in light-dependent chlorophyll biosynthesis, where small concentrations of 1,4-diamino-2-butanone resulted in considerable reduction of chlorophyll during illumination. The above reduction of chlorophyll was accompanied by an increase in photosynthetic activity and respiration rate, which suggests the formation of a photosynthetic apparatus that behaves similarly to one adapted to high light intensities. Decreases in the intracellular levels of spermidine and spermine by the inhibitors cyclohexylamine and 1,3-diaminopropane respectively, although not showing changes in light-independent chlorophyll biosynthesis, do exhibit a regular reduction of light-dependent chlorophyll biosynthesis and a decrease in the photosynthetic activity as well as in the respiration rate. These characteristics are typical for a photosynthetic apparatus adapted to low light intensities with a higher antenna composition per reaction centre. The possible effects of the reduction of putrescine, spermidine and spermine levels on the stabilization-destabilization of photosynthetic subcomplexes are discussed.

The regulatory role of polyamines in structure and functioning of the photosynthetic apparatus during photoadaptation

In this contribution we describe the changes in structure and functioning of the photosynthetic apparatus of the unicellular green alga Scenedesmus obliquus induced by inhibition or induction of polyamine biosynthesis. The synthesis or inhibition is controlled by white light of low and high intensities, as well as by blue and red irradiation. We observe that a decrease of the intracellular putrescine level and, vice versa, an increase of spermine, indicated by a raised ratio of spermine to putrescine, simulate a low-light photoadapted photosynthetic apparatus. Action spectra of the spermine/putrescine ratio compared with action spectra on characteristics of photoadaptation, e.g., chlorophyll biosynthesis, or the rate of primary photochemistry and electron transport, show that the photoreceptors for both the adaptation of the photosynthetic apparatus to low-light conditions and for the regulation of the spermine/putrescine ratio are, at least, very similar. We show that the photoreceptor is primarily a blue-light receptor with a superimposed red-light receptor that absorbs around 680 nm.

Effects of ammonia from livestock farming on lichen photosynthesis

This study investigated if atmospheric ammonia (NH3) pollution around a sheep farm influences the photosynthetic performance of the lichens Evernia prunastri and Pseudevernia furfuracea. Thalli of both species were transplanted for up to 30 days in a semi-arid region (Crete, Greece), at sites with concentrations of atmospheric ammonia of ca. 60 microg/m3 (at a sheep farm), ca. 15 microg/m3 (60 m from the sheep farm) and ca. 2 microg/m3 (a remote area 5 km away). Lichen photosynthesis was analysed by the chlorophyll a fluorescence emission to identify targets of ammonia pollution. The results indicated that the photosystem II of the two lichens exposed to NH(3) is susceptible to this pollutant in the gas-phase. The parameter PI(ABS), a global index of photosynthetic performance that combines in a single expression the three functional steps of the photosynthetic activity (light absorption, excitation energy trapping, and conversion of excitation energy to electron transport) was much more sensitive to NH3 than the FV/FM ratio, one of the most commonly used stress indicators.

INFLUENCE OF THE HABITAT ALTITUDE ON THE (PROTO) HYPERICIN AND (PROTO)PSEUDOHYPERICIN LEVELS OF HYPERICUM PLANTS FROM CRETE

Environmental factors are known to influence strongly the accumulation of secondary metabolites in plant tissues. In a previous paper, we studied the contents of (pseudo)hypericin and its immediate precursors in wild populations of various HYPERICUM species on the island of Crete, Greece, in dependence on their developmental stage. In this study, we investigated the effect of the habitat altitude on the total hypericins content of the plants, which is defined as the sum of protohypericin, hypericin, protopseudohypericin and pseudohypericin. Taking into account our previous finding that the highest accumulation is found during the flowering period in June, we collected the aerial parts of spontaneously growing H. PERFORATUM L. , H. TRIQUENTRIFOLIUM Turra , H. EMPETRIFOLIUM Willd. and H. PERFOLIATUM L. during that time frame at elevations between 100 and 600 m above sea level, however, bearing in mind the time lag in development with increasing altitude. HPLC analysis of the plant material, separated again into a flowers and a leaves/petioles fraction, revealed great differences in the total hypericin content in dependence on the altitude of the habitat. Specifically, a clear trend was revealed, showing an increase of the total hypericin content with increasing altitude. However, no changes could be observed in the ratio of hypericin to protohypericin and in that of pseudohypericin to protopseudohypericin. The habitats of the employed plants were again randomly distributed all over Crete. It is proposed that higher light intensities accompanied by enhanced UV-B radiation and lower air temperature might be responsible for the increasing levels of total hypericins with increasing altitude

The Genetic Reprogramming of Polyamine Homeostasis During the Functional Assembly, Maturation, and Senescence-Specific Decline of the Photosynthetic Apparatus in Hordeum vulgare

Polyamines (PAs) are ubiquitous aliphatic amines important and, in many cases, essential for plant growth, abiotic stress response, and tolerance. Here we provide evidence for genetic reprogramming of PA homeostasis that occurs during the de-etiolation, maturation, and senescence of the primary leaf in Hordeum vulgare (barley). We analyzed expression levels of key genes in the anabolic and catabolic branches of PA metabolism throughout the life cycle of etioplasts, at all steps of the functional assembly of the photosynthetic apparatus, and during leaf senescence. The changes in the total PAs titer of the leaf were followed throughout the different developmental stages. Furthermore, we align all three stages of the photosynthetic performance (rapid light-dependent de-etiolation, phase of optimal efficiency, and senescence-induced deterioration) with the changes in PA homeostasis. Finally, we focus on two phases during aging (early and late senescence) and we present their bioenergetic (for example, PSII maximal efficiency, ATPase conductivity) and genetic profiles, with emphasis on sensitive parameters that describe this process for the photosynthetic apparatus and PA metabolism, respectively. In conclusion, the fine tuning of PA homeostasis is regulated by the simultaneous genetic reprogramming of the anabolic and catabolic branches of PA metabolism and adjusts all the developmental changes from de-etiolation to maturation and senescence.

Characterization of the photoreceptor(s) responsible for the regulation of the intracellular polyamine level and the putative participation of heterotrimeric G-proteins in the signal transduction chain

Abstract In previous publications we have demonstrated a photoregulation of the intracellular polyamine content during chloroplast development. In the present paper action spectra of the changes in the intracellular polyamine levels of putrescine (Put), spermidine (Spd) and spermine (Spm) are presented, giving first evidence for the existence of three photoreceptor systems: a protochlorophyllide photoreceptor is possibly responsible for the inhibition of Put and Spd formation during chloroplast development; a blue-light photoreceptor that probably mediates in general the formation of polyamines, possibly in the semiquinone form in the case of Spm; and, finally, a red-light (possibly the PSII reaction centre) photoreceptor that could be responsible for the induction of the polyamine increase. The function and the physiological role of these three photoreceptor systems are discussed. Although chloroplast photodevelopment and the inhibition of polyamine biosynthesis have the same photoreceptor, it seems that this inhibition is not directly linked to the signal transduction chain of chlorophyll biosynthesis. However, there are hints that a separate transduction chain, in which heterotrimeric G-proteins are involved, leads to the inhibition of polyamine biosynthesis. Dark-grown cultures, supplemented with a non-hydrolysable GTP analogue, GTP-γ-S, as well as cells treated with cholera (CTX) and pertussis (PTX) toxins, simulate polyamine changes similar to those of cells grown under light qualities that do not significantly influence chlorophyll biosynthesis. A possible hypothesis for the mode of interaction of polyamine regulation and chloroplast development is presented.

Photobiological Control of Crop Production and Plant Diseases

Plants, as well as fungi, use ambient sunlight as information to regulate photomorphogenetic processes. The photobiological control of this information showed that the development of photobiological greenhouse plastic covers simulates a photonic information that leads to a physiological enhancement of plant productivity and fungal disease control, thus minimizing the need for the use of agrochemicals. The main characteristics of these photobiological greenhouse plastic covers are the high transmission of photosynthetically active radiation (PAR, 400 − 700 nm) combined with an increase of the factor ζ =RL(655 −665 nm)/FRL(725 −735 nm), which affects the cellular phytochromic equilibrium Φ = Pfr/(Pfr + Pr) and regulates the photosynthetic activity and therefore the plant productivity. Additionally, increase of the spectral ratios from the transmitted light: BL(420-500 nm)/nearUV(290-370 nm) and BL(420 −500 nm)/ FRL(725 −735 nm), cause mainly the induction of biochemical, physiological and morphological responses, regulated by cryptochromes in plants (e. g. inflorescence and infructescence) and mycochrome in fungi (e. g. inhibition of sporulation). In the present work, comparative studies with randomly selected greenhouse plastics showed that small changes in the abovementioned “photobiological” parameters raise the productivity of tomato plants and inhibit the sporulation of several isolates of the fungal pathogen Botrytis cinerea. Thus, a model for the photoregulation of these two phenomena in greenhouses is proposed.

The Regulatory Role of Polyamines on the Structural and Functional Photoadaptation of the Photosynthetic Apparatus

The adaptation of the photosynthetic apparatus to low and high light intensities is a well documented phenomenon, as well in higher plants [1], as in green algae [2]. The organisms respond to shade conditions by increased amounts of chlorophyll at a lowered photosynthetic capacity. Their photosynthetic compensation point is shifted to lower light intensities and the respiratory oxygen uptake decreased. Low light intensities can be mimiced by monochromatic red light in higher plants [3] and by blue light in algae [4]. The photoreceptors responsible for the adaptation to the different light qualities are phytochrome [5] and blue light photoreceptors [6], respectively. Changes in the molecular organization of the photosynthetic apparatus of green algae adapting to low intensities of white light result in an increase of the light harvesting complex, preferentially of photosystem II [7]. The ability of green algae to adapt unexpectedly fast (in about 8h, [8]) to new irradiation conditions demonstrates the high capability of the photosynthetic apparatus to respond to changes in the environmental conditions.

Regulatory Effects of Polyamines on Chloroplast Development

The main naturally occuring polyamines, the diamine putrescine (Put), the triamine spermidine (Spd) and the tetramine spermine (Spm) are ubiquitous in living organisms [1]. At cellular pH values, polyamines behave as polycations, and can interact with anionic macromolecules such as DNA, RNA, phospholipids and certain proteins [1]. This association of polyamines with macromolecules is generally thought to constitute the physical basis for their physiological action. The possibility that polyamines could play a role in photosynthesis was suggested by their occurrence in isolated chloroplasts [2] and isolated chlorophyll/protein complexes [3]. Besford et al. [4] identified D1, D2, Cyt f and the large Rubisco subunit as the proteins which were stabilized by the addition of exogenous polyamines. Andreadakis and Kotzabasis [2] as well as Dornemann et al. [5] showed that the level of prolamellar body/prothylakoid-bound polyamines is higher than the corresponding one in thylakoids.