Light absorption by anthocyanins in juvenile, stressed, and senescing leaves

The optical properties of leaves from five species, Norway maple (Acer platanoides L.), cotoneaster (Cotoneaster alaunica Golite), hazel (Corylus avellana L.), Siberian dogwood (Cornus alba L.), and Virginia creeper (Parthenocissus quinquefolia (L.) Planch.), differing in pigment composition and at different stages of ontogenesis, were studied. Anthocyanin absorption maxima in vivo, as estimated with spectrophotometry of intact anthocyanic versus acyanic leaves and microspectrophotometry of vacuoles in the leaf cross-sections, were found between 537 nm and 542 nm, showing a red shift of 5–20 nm compared with the corresponding maxima in acidic water–methanol extracts. In non-senescent leaves, strong anthocyanin absorption was found between 500 nm and 600 nm (with a 70–80 nm apparent bandwidth). By and large, absorption by anthocyanin in leaves followed a modified form of the Lambert–Beer law, showing a linear trend up to a content of nearly 50 nmol cm−2, and permitting thereby a non-invasive determination of anthocyanin content. The apparent specific absorption coefficients of anthocyanins at 550 nm showed no substantial dependence on the species. Anthocyanin contribution to total light absorption at 550 nm was followed in maple leaves in the course of autumn senescence. Photoprotection by vacuolar anthocyanins is discussed with special regard to their distribution within a leaf; radiation screening by anthocyanins predominantly localized in the epidermal cells in A. platanoides and C. avellana leaves was also evaluated

Photoprotection in Plants: Optical Screening-based Mechanisms /

Optical screening of excessive and potentially harmful solar radiation is an important photoprotective mechanism, though it has received much less attention in comparison with other systems preventing photooxidative damage to photoautotrophic organisms. This photoprotection in the form of screening appears to be especially important for juvenile and senescing plants as well as under environmental stresses—i.e. in situations where the efficiency of enzymatic ROS elimination, DNA repair and other ‘classical’ photoprotective systems could be impaired. This book represents an attempt to develop an integral view of optical screening-based photoprotection in microalgae and higher plants. Towards this end, the key groups of pigments involved in the screening of ultraviolet and visible components of solar radiation in microalgae and higher plants, and the patterns of their accumulation and distribution within plant cells and tissues, are described. Special attention is paid to the manifestations of screening pigment accumulation in the optical spectra of plants. It is also demonstrated that understanding these effects and their relationships to screening pigments’ makeup and spectroscopy in plants provides valuable insights into the state of plants’ long-term photoacclimation, as well as ample opportunities for the non-destructive quantification of screening pigments and the assessment of the efficiency of photoprotection providing by these pigments in situ

Essential Role of Potassium in Apple and Its Implications for Management of Orchard Fertilization

K (K) is of paramount importance for apple (Malus × domestica Borkh.), not only for tree growth and development but also for the size and quality of fruit yield. The apple plant’s demand for K varies, along with the progression of phenological phases, during the growing season. The K demand peaks during ripening of fruits featuring relatively high concentration of K comparable to that of the leaves. The mainstream method of apple tree K fertilization is through application of the fertilizer to the soils to improve K uptake by the roots. The bioavailability of K depends on assorted various factors, including pH, interaction with other nutrients in soil solution, temperature, and humidity. An important role in making the K from soil available for uptake by plants is played by plant growth-promoting microorganisms (PGPM), and the specific role of the PGPM is discussed. Advantages of fertigation (the combination of irrigation and fertilization) as an approach include allowing to balance application rate of K fertilizer against its variable demand by plants during the growing season. Excess K in the soil leads to competitive inhibition of calcium uptake by plants. The K-dependent deficiency of Ca leads to its predominant channeling to the leaves and hence to its decline in fruits. Consequently, the apple fruits affected by the K/Ca imbalance frequently develop physiological disorders in storage. This emphasizes the importance of the balanced K application, especially during the last months of the growing season, depending on the crop load and the actual K demand. The potential use of modern approaches to automated crop load estimation through machine vision for adjustment of K fertilization is underlined

Multiple drivers of seasonal change in PRI: Implications for photosynthesis 2. Stand level

The goal of this study was to explore the relationships between stand-level photochemical reflectance index (PRI) and canopy structure/ pigment pools, as well as light use efficiency (LUE) of photosynthetically active vegetation focusing on seasonal or ontogenetic time frames. PRI was originally designed as a means of assessing the xanthophyll cycle and LUE over short (e.g. diurnal) time frames, and few studies have explored the drivers of PRI over longer, seasonal time frames, particularly in crops having different photosynthetic pathways or canopy structures. Consequently, our purpose was to understand and quantify the drivers of PRI responses over seasonal time scales for two crops, maize (C4) and soybean (C3), contrasting in photosynthetic pathway, leaf structure and canopy architecture. In both crops, PRI was very closely related to green LAI (R2 \u3e 0.90) and stand chlorophyll (Chl) content (R2 \u3e 0.93). The slopes of the relationships in different phenological stages, vegetative and reproductive, were substantially different (3-fold smaller in the vegetative stage). The main cause of this disparity was the high PRI value of soil/residue background. While PRI was a sensitive indicator of the changes in stand green LAI and stand Chl content over the full growing season, it was not sensitive to LUE; LUE explained below 12% of PRI variation in maize and 19% in soybean. Unlike leaf-level PRI, stand-level PRI was not clearly related to the Car/Chl ratio, presumably because the large changes in canopy structure (affecting stand Chl and green LAI) had a dominant influence on PRI over this time frame. The strong relationship between PRI and stand Chl content as well as between PRI and Chl-related vegetation index over a growing cycle allowed us to subtract the stand Chl content effect from measured PRI to reveal the component of PRI most likely related to periods of stress. However, for accurate subtraction of the Chl effect from long-term PRI records, thoughtful study of uncertainties related to “natural” variation of PRI-stand Chl relationships, and stand Chl content estimation for different varieties of the same species and for different species is required. The findings of a strong link between stand-level PRI and stand green LAI and Chl content and the lack of a clear relationship between PRI and LUE over seasonal and ontogenetic time spans suggest the need for a more careful evaluation of the relationship between PRI and either LUE or photosynthetic activity. In particular, studies that contrast short-term (e.g. diurnal) vs. long-term (e.g. seasonal) pigment, PRI, and photosynthetic responses in contrasting vegetation types are needed to clarify the different mechanisms involved at different temporal and spatial scales. These findings have important implications for attempts to monitor photosynthetic phenology from remote sensing, many of which have relied on PRI as an indicator of photosynthetic activity

Signi®cance of skin ¯avonoids for UV-B-protection in apple fruits

An attempt has been made to assess the UV-B-protective capacity of phenolic compounds accumulated in super®cial structures of plants using apple fruit as a model. Two apple (Malus domestica Borkh.) cultivars (Braeburn and Granny Smith) differing in response to high ¯uxes of solar radiation were selected and exposed to increasing doses of UV-B radiation. The extent of UV-B-induced damage to photosystem II of apple skin correlated with its quercetin glycoside (but not anthocyanin) content. Granny Smith apples did not demonstrate a pronounced response to high sunlight in terms of the accumulation of phenolic substances in the skin and exhibited similar patterns of F o, F m, and F v/F m changes in the course of UV-B irradiation both on sun-exposed and shaded surfaces of a fruit. Unlike Granny Smith, Braeburn fruits were characterized by a signi®cant accumulation of quercetin glycosides in sun-exposed skin, however, shaded skin contained these compounds in similar amounts to those in Granny Smith. Accordingly, photosystem II in sunexposed skin of Braeburn apples was resistant to high doses of UV-B radiation (up to 97 kJ m ±2), whereas the susceptibility of the photosynthetic apparatus in shaded skin of Braeburn to UV-Binduced damage was much higher and similar to that of both sun-exposed and shaded skin of Granny Smith fruits. Anthocyanins, at least in the amounts found in Braeburn, did not show an additional effect in UV-B protection. Key words: Apple, phenolic compounds, photosystem II, protection, UV-B radiation

Multiple drivers of seasonal change in PRI: Implications for photosynthesis 1. Leaf level

The goal of this study was to explore the relationships between the photochemical reflectance index (PRI) at the leaf level and pigment pools, focusing on the constitutive role of pigments in influencing PRI over seasonal or ontogenetic time frames. The purpose was to re-evaluate the role of PRI as an indicator of seasonally shifting pigment (chlorophyll, carotenoid and anthocyanin) contents, and hence photosynthetic activity, across a range of tree and crop species. We studied natural vegetation — three tree species (maple, chestnut and beech) and two managed irrigated and rain-fed crop species (maize and soybean), contrasting in photosynthetic pathway and leaf structure, and having wide variation of pigment content and composition. In anthocyanin-free leaves, PRI related to both total chlorophyll (Chl) and carotenoid (Car) contents, however, much closer relationships were found between PRI and Car to Chl ratio (Car/Chl). The sensitivity of PRI to Car/Chl varied widely in tree species with the degree of secondary carotenoids. In crop leaves where the Car vs. Chl relationship was very close, the slopes of PRI vs. Car/Chl relationships for maize and soybean were almost identical. PRI vs. Car/Chl relationships for leaves of different tree species formed a significant, uniform relationship with PRI. Two crops also formed a significant, uniform PRI vs. Car/Chl relationship with a slope half the value found for trees. In anthocyanin-containing leaves, PRI did not clearly relate to any pigment content because reflectance values at both PR wavebands are affected by anthocyanin content. The findings of a strong link between leaf level PRI and Car/Chl over seasonal and ontogenetic time spans supports recent findings calling for a more careful evaluation of the relationship between PRI and either LUE or photosynthetic activity. In particular, studies that contrast short-term (e.g. diurnal) vs. long-term (e.g. seasonal) pigment, PRI, and photosynthetic responses in contrasting vegetation types are needed

Differential Responses to UV-A Stress Recorded in Carotenogenic Microalgae <i>Haematococcus rubicundus</i>, <i>Bracteacoccus aggregatus</i>, and <i>Deasonia</i> sp.

UV-A is the main ultraviolet component of natural (solar) radiation. Despite it, its effect on phototrophs is studied less than UV-B. Effects of UV-A on photosynthetic apparatus of three carotenoid-producing microalgae were elucidated. Photosynthetic activity was studied using chlorophyll fluorescence analysis. Cell extracts were evaluated by absorbance spectroscopy. On the one hand, there were some common features of three strains. In all cases the changes involved PSII primary photochemistry and antennae size. All strains accumulated UV-absorbing polar compounds. On the other hand, some responses were different. Upregulation of non-photochemical quenching was observed only in B. aggregatus BM5/15, whereas in other cases its level was low. H. rubicundus BM7/13 and Deasonia sp. NAMSU 934/2 accumulated secondary carotenoids, whereas B. aggregatus BM5/15 accumulated primary ones. Microscopic features of the cultures were also different. H. rubicundus BM7/13 and Deasonia sp. NAMSU 934/2 were represented mostly by solitaire cells or small cell clusters, lacking their green color; the cells of B. aggregatus BM5/15 formed aggregates from green cells. Cell aggregation could be considered as an additional UV-protecting mechanism. Finally, the strains differed by their viability. B. aggregatus BM5/15 was most resistant to UV-A, whereas massive cell death was observed in two other cultures

Soil fertility management in apple orchard with microbial biofertilizers

Intensification of horticulture in Russia involves planting of new high-density orchards with drip irrigation and fertigation as well as intensification of the exploitation of traditional orchards. This approach involves an increase in mineral fertilizer application imposing the risk of soil fertility loss. For several reasons, the use of traditional organic fertilizers like manure in orchards is currently marginal. Although bacteria-based biofertilizers cannot substitute mineral fertilizers completely, they can significantly reduce the need for mineral fertilizer application. The effect of microbial biofertilizers of the brands “Azotovit” (Azotobacter chroococcum), “Phosphatovit” (Bacillus mucilaginosus), as well as a mixture of bacteria and the fungus, “Organic” (Azotobacter chroococcum, Bacillus subtilis, Bacillus megaterium, Trichoderma harzian) was studied in two field experiments. In the experiment #1, the preparations “Azotovit” and “Phosphatovit” were delivered through a drip irrigation system in various combinations with mineral fertilizers. In experiment #2, the preparation “Organic” was also applied to the soil with irrigation water, also in combination with the mineral fertilizer. When solely applied, none of the studied preparations changed significantly the soil nutrient content and yield as compared with the variant fertilized by the mineral fertilizer at the maximum studied application rate. The combination of the microbial biofertilizer and mineral fertilizers applied at a low rate ensured the yield commensurate to that obtained under high-rate application of the mineral fertilizer