A 50-year-old solitary, sun-exposed ginkgo tree had strongly been pruned in the fall of 2021. Very few buds for the formation of new leaves, twigs, and branches were left over. In spring 2022, these few remaining buds responded with the formation of a different leaf type. These leaves were 2.7 times larger and also thicker than in the years before. In addition, the mean content of total chlorophylls [Chl (a+b)] per leaf area unit of dark-green leaves was 1.45, those of green leaves two times higher as compared to the years before pruning and the two other ginkgo trees which had been investigated in parallel. A comparable increase was also found for the level of total carotenoids (x+c). The mean content for Chl (a+b) were 1,118 mg m(-2) for dark-green and 898 mg m(-2) for green leaves as compared to 435 to 770 mg m(-2) in leaves of other trees. The higher values for Chl (a+b) and total carotenoid content showed up also on a fresh and dry mass basis. Thus, with the formation of a new, larger leaf type by changes in morphology (leaf size and thickness) and the increase of photosynthetic pigments, the pruned ginkgo tree was able to compensate for the much lower number of leaves and photosynthetic units.

The content of chlorophylls (Chl) (a+b), total carotenoids (x+c), and the pigment ratios of Chl a/b and Chls to carotenoids (a+b)/(x+c) of green leaves of five C4 plants were determined and compared to those of C3 plants. The C4 plants were: Pacific and Chinese silvergrass (Miscanthus floridulus and Miscanthus sinensis), sugar cane (Saccharum officinarum) as well as feed and sugar maize (Zea mays). The three C3 plants were beech, ginkgo, and oak. C4 plants possess higher values for the ratio Chl a/b (3.4-4.5) as compared to the C3 plants (2.6-3.3). Sugar maize had the highest values for Chl a/b (4.04-4.70) and exceptionally high contents of total carotenoids and consequently lower values for the ratio of (a+b)/(x+c) (mean: 3.75 ± 0.6). During autumnal senescence also C4 plants showed a faster decline of Chl b as compared to Chl a yielding high values for Chl a/b of 6 to 8. Chlorophylls declined faster than carotenoids yielding low (a+b)/(x+c) values below 1.0.

Govindjee is a prolific and influential writer in the arena of oxygenic photosynthesis. He is internationally revered as one of the most prominent plant scientists of the 21st century, who enhanced ‘Emerson Enhancement’. He is widely regarded for extensive collaborations with hundreds of scientists from around the World and moreover, his solely authored publications are impressive in quality and quantity—a virtue not known to many—thus, we list them here. In 2022, he was recognised for his work with a Lifetime Achievement Award from the International Society of Photosynthesis Research .

Imaging the four fluorescence bands of leaves, the red (F690) and far-red (F740) chlorophyll (Chl) fluorescence as well as the blue (F440) and green (F520) fluorescence of leaves and the corresponding fluorescence ratios is a fast and excellent nondestructive technique to detect the photosynthetic activity and capacity of leaves, of gradients over the leaf area as well as the effect of various strain and stress parameters on plants. This review primarily deals with the first and pioneering multi-colour fluorescence imaging results obtained since the mid-1990s in a cooperation with French colleagues in Strasbourg and in my laboratory in Karlsruhe. Together we introduced not only the joint imaging of the red and far-red Chl fluorescence but also of the blue and green fluorescence of leaves. The two instrumental setups composed for this purpose were (1) the Karlsruhe-Strasbourg UV-Laser Fluorescence Imaging System (Laser-FIS) and (2) the Karlsruhe Flash-Light Fluorescence Imaging System (FL-FIS). Essential results obtained with these instruments are summarized as well as the basic principles and characteristics of multi-colour fluorescence imaging. The great advantage of fluorescence imaging is that the fluorescence yield in the four fluorescence bands is sensed of several thousand up to 200,000 pixels per leaf area in one image. The multi-colour FIS technique allows to sense many physiological parameters and stress effects in plants at an early stage before a damage of leaves is visually detectable. Various examples of plant stress detection by the multi-colour FIS technique are given. Via imaging the Chl fluorescence ratio F690/F740 it is even possible to determine the Chl content of leaves. The FIS technique also allows to follow the successive uptake of diuron and loss of photosynthetic function and to screen the ripening of apples during storage. Particularly meaningful and of high statistical relevance are the fluorescence ratio images red/far-red (F690/F740), blue/red (F440/F690), and blue/green (F440/F520) as well as images of the fluorescence decrease ratio RFd, which is an indicator of the net CO2 assimilation rates of leaves.

Melvin Calvin (1911–1997) was the recipient of the 1961 Nobel Prize in Chemistry for the discovery of the canonical photosynthetic carbon reduction cycle. We present here a very brief glimpse of this extraordinary American scientist, who in his time was a preeminent force in physical and organic chemistry. Besides natural photosynthesis, Calvin’s prolific career included artificial photosynthesis, colors of organic substances, the origin of life, cancer, moon rocks, molecular basis of learning, and plant lipids & algal hydrocarbons as potential renewable sources of transport fuels.

Govindjee and Hartmut Lichtenthaler have a very similar curriculum vitae. Both chose photosynthesis as research field and actively applied chlorophyll fluorescence. Their research was overlapping and complementary. On the occasion of Govindjee's 88th anniversary in 2020, Hartmut Lichtenthaler gives a short retrospective on interactions and joint activities with Govindjee over the past five decades.

On August 30, 2018, Professor Emeritus Martin Bopp, an internationally highly regarded botanist and former director of the Botanical Institute at the University of Heidelberg, died in Wuppertal, Germany, at the age of 95 years. His scientific career, his valuable contributions to the progress of plant science and his manifold activities as editor and co-editor are described in this tribute. A photograph of him is shown in Fig. 1.

On the occasion of the 50th anniversary of the international journal Photosynthetica in 2017 we briefly report on the establishment of this journal and on Dr. Zdeněk Šesták, the renowned researcher of photosynthesis processes who, in cooperation with the Czechoslovak Academy of Sciences, founded this essential science journal in Prague in 1967.

Sterols and carotenoids are typical representatives of the group of isoprenoid lipids in plants. All isoprenoids are synthesized by condensation of the two active C5-units: dimethylallyl diphosphate, DMAPP, and isopentenyl diphosphate, IPP. Like animals, higher plants form their sterols via the classical cytosolic acetate/mevalonate (MVA) pathway of IPP biosynthesis. Plants as photosynthetic organisms, however possess a second, nonmevalonate pathway for IPP biosynthesis, the DOXP/MEP pathway. The latter operates in the chloroplasts and is responsible for the formation of carotenoids and all other plastidic isoprenoid lipids (phytol, prenylquinones). Although there exists some cooperation between both IPP producing pathways, one can never fully compensate for the other. Thus, in higher plants sterols are primarily made via the MVA pathway and carotenoids via the DOXP pathway. This also applies to several algae groups, such as red algae and Heterokontophyta. In the large and diverging group of 'Green Algae' the situation is more complex. The more advanced evolutionary groups (Charales, Zygnematales) possess, like higher plants, both IPP forming pathways and represent an evolutionary link to these. In contrast, the proper Chlorophyta, often single cell organisms (Chlorella, Scenedesmus, Trebouxia), represent a separate phylum and synthesize sterols and carotenoids via the DOXP pathway whereas the MVA pathway is lost. The common ancestor of both groups, Mesostigma viride, again exhibits both IPP pathways. In the photosynthetic Euglenophyta the situation is inverse, both the sterols and the carotenoids are formed exclusively via the MVA pathway, the DOXP pathway is lost during the secondary endosymbiosis. Also Fungi synthesize sterols and carotenoids via the MVA pathway. Animals possess only the MVA pathway for sterol biosynthesis. In contrast, the malaria parasite Plasmodium and other Apicomplexa have lost the MVA pathway and synthesize their isoprenoids only via the DOXP pathway of their plastid-type apicoplast. In evolutionary terms the DOXP/MEP pathway shows up first in photosynthetic and heterotrophic bacteria , whereas Archaea possess the MVA pathway. The early anoxigenic photosynthetic bacteria (one photosynthetic light reaction) and the later Cyanobacteria (two light reactions and oxigenic photosynthesis) that form a link to the endosymbiontic chloroplasts contain the DOXP/MEP pathway. The latter is also present in many heterotrophic pathogenic bacteria. Some bacteria possess, in addition to the DOXP/MEP pathway, some genes of the MVA pathway that they obtained apparently by lateral gene transfer. A few others have evidently lost the DOXP/MEP pathway and acquired the MVA pathway. Some members of the Streptomycetes, in turn, have both IPP producing routes, one for 'housekeeping' (DOXP/MEP pathway) and the other (MVA pathway) for synthesis of secondary isoprenoid products. When viewing the evolutionary trends it is clear that 1) the two pathways of IPP biosynthesis evolved independently, 2) lateral gene transfer has occurred especially on the bacteria level, 3) primary endosymbiosis has taken place and secondary endosymbiosis partially with differing results, and 4) a loss of the genes of the DOXP pathway took place in some organisms and in others a loss of the genes for the MVA pathway. On the basis of the available evidence an evolutionary view of IPP formation is presented.

In the past 55 years, enormous scientific progress was made in many fields of plant physiology and plant biochemistry. Throughout these years, our knowledge on the photosynthetic light processes, the chemical composition and biosynthesis of the photosynthetic apparatus, the ultrastructure of chloroplasts, and their large adaptation capacity to high-light and low-light was extremely enhanced. The author of this article reviews the substantial scientific evolution in these and other fields in which he was actively involved together with his group. The topics that are reviewed also include forest decline research, the mode of action of herbicides in photosynthesis, and in blocking biosynthetic pathways of chloroplasts, such as de novo fatty acid and isoprenoid biosynthesis, as well as the application of chlorophyll fluorescence imaging in the fast noninvasive determination of photosynthetic activity and early detection of plant stress. Moreover, the detection, elucidation, and metabolic significance of the non-mevalonate chloroplast pathway for isopentenyl diphosphate and isoprenoid biosynthesis, the DOXP/MEP pathway, is reviewed. The author further documents that this extreme progress in plant science was largely due to the continuous development and application of new scientific methods and instruments.

SummaryThe overview provides basic information on the appearance and biosynthesis of thylakoids and osmiophilic plastoglobuli and their association with chloroplast development and senescence. The light-induced formation of sun chloroplasts at high irradiation with a different thylakoid arrangement, grana stacking and plastoglobuli content as compared to shade chloroplasts at low irradiation is reviewed. During the light-induced biosynthesis of thylakoids from etioplasts of dark-grown seedlings the osmiophilic plastoglobuli disappear. Young chloroplasts are actually free of osmiophilic plastoglobuli. With increasing age of chloroplasts osmiophilic plastoglobuli appear again and are either fairly frequent at a small diameter or show up in a lower number with rather large size. In senescing chloroplasts and in their final form, gerontoplasts, thylakoids and chlorophylls are successively broken down with formation of large plastoglobuli. In addition to the plastoglobuli of chloroplasts, the occurrence and role of plastoglobuli during the development of chlorophyll-free plastid forms, such as proplastids, leucoplasts, and chromoplasts are presented. The main function of plastoglobuli as stores for plastidic lipids, such as plastoquinone-9, plastoquinol-9 and α-tocopherol and in certain plastid stages also other lipids is discussed. Recent observations suggest that plastoglobuli contain on their outer surface certain functional chloroplast proteins participating in biosynthesis and the channeling of lipid molecules.

The chlorophyll (Chl) fluorescence induction kinetics, net photosynthetic CO2 fixation rates P N, and composition of photosynthetic pigments of differently light exposed leaves of several trees were comparatively measured to determine the differences in photosynthetic activity and pigment adaptation of leaves. The functional measurements were carried out with sun, half-shade and shade leaves of seven different trees species. These were: Acer platanoides L., Ginkgo biloba L., Fagus sylvatica L., Platanus x acerifolia Willd., Populus nigra L., Quercus robur L., Tilia cordata Mill. In three cases (beech, ginkgo, and oak), we compared the Chl fluorescence kinetics and photosynthetic rates of blue-shade leaves of the north tree crown receiving only blue sky light but no direct sunlight with that of sun leaves. In these cases, we also determined in detail the pigment composition of all four leaf types. In addition, we determined the quantum irradiance and spectral irradiance of direct sunlight, blue skylight as well as the irradiance in half shade and full shade. The results indicate that sun leaves possess significantly higher mean values for the net CO2 fixation rates P N (7.8–10.7 μmol CO2 m−2 s−1 leaf area) and the Chl fluorescence ratio R Fd (3.85–4.46) as compared to shade leaves (mean P N of 2.6–3.8 μmol CO2 m−2 s−1 leaf area.; mean R Fd of 1.94–2.56). Sun leaves also exhibit higher mean values for the pigment ratio Chl a/b (3.14–3.31) and considerably lower values for the weight ratio total chlorophylls to total carotenoids, (a + b)/(x + c), (4.07–4.25) as compared to shade leaves (Chl a/b 2.62–2.72) and (a + b)/(x + c) of 5.18–5.54. Blue-shade and half-shade leaves have an intermediate position between sun and shade leaves in all investigated parameters including the ratio F v/F o (maximum quantum yield of PS2 photochemistry) and are significantly different from sun and shade leaves but could not be differentiated from each other. The mean values of the Chl fluorescence decrease ratio R Fd of blue-shade and half-shade leaves fit well into the strong linear correlation with the net photosynthetic rates P N of sun and shade leaves, thus unequivocally indicating that the determination of the Chl fluorescence decrease ratio R Fd is a fast and indirect measurement of the photosynthetic activity of leaves. The investigations clearly demonstrate that the photosynthetic capacity and pigment composition of leaves and chloroplasts strongly depend on the amounts and quality of light received by the leaves.

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Reflectance images of various intact leaves were taken in four selected bands at 440, 550, 690, and 800 nm and compared with their reflectance spectra in the visible to near infra-red (range: 400 to 800 nm). The images showed high local resolution over the leaf surface (0.025 mm(2) per pixel) with a low spectral resolution, whereas the reflectance spectra were acquired with a high spectral resolution (1 nm). In addition, the individual leaf samples were further characterized by their specific colorimetric values for visual impression (CIE 1931). The results demonstrate that leaf reflectance is determined by the following basic parameters: (a) the leaf pigment content (absorption of chlorophylls and carotenoids in the pigment protein complexes of chloroplasts and, in red leaves, also of epidermal anthocyanins), (b) the leaf tissue structure (size of aerial interspaces between cells, which influence leaf optical properties), and (c) the structure of the leaf surface (e. g., waxes and hairs). These in-vivo measurements of leaves have the advantage of being fast and non-destructive, with the possibility for high-throughput evaluation and repetition measurements. The data are discussed in view of their importance for basic research (e. g., stress detection) and quality assessment of plant material ranging from contact measurements to remote sensing.

With a multicolor fluorescence imaging system the fluorescence images of freshly harvested light-green apples were measured in the four major fluorescence bands of green plant tissue, i.e., the fluorescence bands F440 (blue), F520 (green), F690 (red), and F740 (far-red). By a pixel-to-pixel division of the fluorescence images we also determined the fluorescence ratio images blue/green (F440/F520), blue/red (F440/F690), and blue/far-red (F440/F740), as well as the chlorophyll fluorescence ratio red/far-red (F690/F740). In addition, the changes of fluorescence yield in the four fluorescence bands and of the fluorescence ratios were studied during the storage and ripening of Braeburn apples during 2,3, and 6 months at standard conditions of 4 °C and 90% relative humidity. The blue and green fluorescence bands increased during storage and ripening, whereas the far-red band continuously declined with decreasing chlorophyll content. In contrast, the intensity of the red chlorophyll fluorescence band F690 slight...

Some vascular angiosperm plants, which are sometimes addressed as "resurrection plants," can survive severe drought periods and regain full physiological function in the subsequent rainy season. These desiccation-tolerant (DT) plants are poikilohydric and capable of surviving the loss of at least 80–95% of their cell water content for shorter or longer periods. DT plants are important constituents of many ecosystems from the arctic (lichen and moss vegetations) to the tropics (lichen, moss, and mainly vascular/flower vegetations). The inselbergs in the tropics, as habitats ecologically isolated from their surrounding areas, are evolutionary centers of the flowering DT plants and vegetations. DT plants may be subdivided into homoiochlorophyllous (HDT) plants and poikilochlorophyllous (PDT) plants, which are using contrasting strategies to solve the same ecological problem of longer severe dryness. The HDT plants keep their chlorophyll and thylakoids during desiccation, whereas the PDT strategy is bound to desiccoplasts, a unique type of chloroplast, that break down and reconstitute their chlorophylls and thylakoids. The HDT pteridophytes and angiosperms are generally adapted to more rapid alternations of wet and dry periods than the PDT species. The PDT strategy, in turn, has evolved in habitats where the plants remain in the desiccated state for 6–10 months. Under these conditions, it is evidently more advantageous to dismantle the whole photosynthetic apparatus and to reconstitute it after rehydration. This chapter summarizes the recent developments in our understanding of physiology and ecophysiology of HDT and PDT plants and vegetations.

The plastidic pathway for isopentenyl diphosphate (IPP) and isoprenoid biosynthesis, the DOXP/MEP pathway, possesses an essential function in the biosynthesis of thylakoidal prenylllipids chlorophylls (phytyl side-chain), carotenoids, plastoquinone-9, phylloquinone KI and alpha-tocopherol, as well as for monoterpenes and diterpenes Here we review its detection, its enzymes, intermediates, genes, cofactor requirements and inhibitors. This plastidic isoprenoid pathway is also contrasted against the acetate/mevalonate(MVA) pathway of isoprenoid biosynthesis operating in the cytosol for the biosynthesis of sterols, sesquiterpenes and polyterpenes. The DOXP/MEP pathway can specifically be inhibited by fosmidomycin and the acetate/MVA pathway by statins (e.g. mevinolin). By applying specifically marked substrates (H-2-deoxyxylulose, C-14-DOXP, H-3-MVA or C-14-MVA) and specific inhibitors a cross-talk between both IPP yielding cell pathways was detected that operates preferentially in the chloroplast-to-cytosol direction. The DOXP/MEP pathway is also involved in the biosynthesis of the volatile hemiterpenes isoprene and methylbutenol. The distribution of the DOXP/MEP pathway in photosynthetic organisms (bacteria, algae, higher plants) and its putative origin in anoxigenic photosynthetic bacteria is reviewed. The DOXP/MEP pathway does not occur in Archaea, fungi or animals. The use of etiolated seedlings with their light-induced pigment accumulation as a test system for inhibitors of the DOXP/MEP pathway in the search of active ingredients against pathogenic bacteria and the malaria parasite Plasmodium is discussed.