Regulation of Leaf Angle Protects Photosystem I under Fluctuating Light in Tobacco Young Leaves

Fluctuating light is a typical light condition in nature and can cause selective photodamage to photosystem I (PSI). The sensitivity of PSI to fluctuating light is influenced by the amplitude of low/high light intensity. Tobacco mature leaves are tended to be horizontal to maximize the light absorption and photosynthesis, but young leaves are usually vertical to diminish the light absorption. Therefore, we tested the hypothesis that such regulation of the leaf angle in young leaves might protect PSI against photoinhibition under fluctuating light. We found that, upon a sudden increase in illumination, PSI was over-reduced in extreme young leaves but was oxidized in mature leaves. After fluctuating light treatment, such PSI over-reduction aggravated PSI photoinhibition in young leaves. Furthermore, the leaf angle was tightly correlated to the extent of PSI photoinhibition induced by fluctuating light. Therefore, vertical young leaves are more susceptible to PSI photoinhibition than horizontal mature leaves when exposed to the same fluctuating light. In young leaves, the vertical leaf angle decreased the light absorption and thus lowered the amplitude of low/high light intensity. Therefore, the regulation of the leaf angle was found for the first time as an important strategy used by young leaves to protect PSI against photoinhibition under fluctuating light. To our knowledge, we show here new insight into the photoprotection for PSI under fluctuating light in nature.

A Review of Aquilaria malaccensis Propagation and Production of the Secondary Metabolite from Callus

Aquilaria is an evergreen non-timber agarwood obtained from the 15 species of Aquilaria belonging to the family Thymelecea. There are two species endemic to Northeast India, A. malaccensis and A. khasiana. A. malaccensis generate a high-grade degree of resin as compared to the other Aquilaria species, and it contributes to the economy of the Northeast states of India and the country as a whole. Due to its profoundly valuable sources, it is overexploited, which impacted its availability in genetic environments. The cultivation of the tree is challenging due to some environmental factors like the sensitivity of the seeds to desiccation, high light intensity, low shelf life, slow growth rate, and the effect of insects and microorganisms. Therefore, conservation and proliferation are urgently required for environmental sustainability and prevention from the stage of extinction. The objective of this paper is to compile the major research works on the conservation, production of the secondary metabolite from callus of A. malaccensis and updated information on its developments and approaches that are rapidly taking place in recent years so that further novel research can be envisaged.

Comparative Anatomical Characteristics of the Subgenus Cyanus (Mill.) Hayek (Asteraceae) In Turkey

The identification of species based on anatomical characters is valuable to investigate their taxonomic status, phylogeny and understand their autoecology. The current study analysed the stem and leaf properties of 20 species of the subgenus Cyanus (Mill.) Hayek in Turkey. The Cyanus species exhibited xeromorphic anatomical features, such as tight palisade parenchyma and induced spongy parenchyma, which indicated adaptations to the arid soil and a forest ecosystem in which they occurred, as well as to high light intensity and precipitation. Anatomical features such as the midrib shape and number of vascularization patterns differed among the species. Similar anatomical characters were analysed for the investigated species. These properties can provide an important database for future studies including the phylogeny within the subgenus Cyanus. Bangladesh J. Plant Taxon. 28(2): 295-309, 2021 (December)

The Active Phytohormone in Microalgae: The Characteristics, Efficient Detection, and Their Adversity Resistance Applications

Phytohormones are a class of small organic molecules that are widely used in higher plants and microalgae as chemical messengers. Phytohormones play a regulatory role in the physiological metabolism of cells, including promoting cell division, increasing stress tolerance, and improving photosynthetic efficiency, and thereby increasing biomass, oil, chlorophyll, and protein content. However, traditional abiotic stress methods for inducing the accumulation of energy storage substances in microalgae, such as high light intensity, high salinity, and heavy metals, will affect the growth of microalgae and will ultimately limit the efficient accumulation of energy storage substances. Therefore, the addition of phytohormones not only helps to reduce production costs but also improves the efficiency of biofuel utilization. However, accurate and sensitive phytohormones determination and analytical methods are the basis for plant hormone research. In this study, the characteristics of phytohormones in microalgae and research progress for regulating the accumulation of energy storage substances in microalgae by exogenous phytohormones, combined with abiotic stress conditions at home and abroad, are summarized. The possible metabolic mechanism of phytohormones in microalgae is discussed, and possible future research directions are put forward, which provide a theoretical basis for the application of phytohormones in microalgae.

Expression of some salt tolerance genes isolated from Egyptian gray mangrove (Avicennia marina)

Mangroves are well-adapted halophytes that thrive in coastal saline environments. They live under difficult environmental conditions, such as high light intensity and external salt concentrations, as well as low-oxygen environments, such as water-logged muck, that are typically inappropriate for the survival of other plants. Salinity is a major abiotic factor that affects plant growth, productivity, and dispersal in tropical and semitropical intertidal areas. Furthermore, it affects approximately 20% of all cultivable land and 50% of all irrigated land on the planet. Mangroves have developed a sophisticated salt filtration mechanism and a complicated root structure to withstand salty water exposure and tidal movement. The expression patterns of five salt tolerance genes (amFer1, amDhna, amSod1, amCat1, and amUbc2) in the Egyptian gray mangrove (Avicennia marina Forssk.) grown under different environmental conditions in South Sinai protectorates (Nabq, Ras Mohamed, Safaga, and Wadi El-Gemal), Egypt, were investigated in this study. This study aimed to assess and examine the genetic behavior of mangroves in response to salinity by using quantitative real-time PCR. Findings revealed differences in the expression patterns of the investigated genes under various conditions, showing that salinity influences plant genetic response. Ferritin gene expression was high in all locations, indicating that ferritin represents an essential component of the mangrove response mechanisms.

Analyzing and optimizing the carbon utilization and lipid yield at different light intensities for Scenedesmus arcuatus

Microalgae, the photosynthetic microorganism growing abundantly in marine and aquatic ecosystems, are potential source for biological sequestration of CO2. The carbon uptake differs in the presence of other nutrients, light intensity etc. The biomass yield of Scenedesmus arcuatus var capitatus was studied based on the Face Centred Central Composite design (FCCD) of Response Surface Methodology (RSM) for nitrate, phosphate and carbonate under different conditions (laboratory, room and sunlight conditions). Various pre-treatments (osmotic shock, autoclaving, microwave and ultrasonication) were employed to find the best method for maximum lipid yield. The biomass yield reached a maximum of 1 g/L under sunlight conditions of nitrate concentration 500 ppm and carbonate 2000 ppm. The laboratory conditions resulted in a biomass yield of 0.59 g/L at 500 ppm nitrate, 1000 ppm carbonate and 250 ppm phosphate. Under room conditions, the yield was very low (0.11 g/L). Osmotic shock resulted in higher lipid yield than the other pre-treatment methods. The ability of Scenedesmus arcuatus to uptake high carbon under sunlight conditions and to adapt to high light intensity and fluctuations in light intensity concludes that this species is suitable for large-scale open pond cultivation for CO2 sequestration and production of metabolites.

The quantitative contribution of different Photosystem II compartments to non-photochemical quenching in Arabidopsis

Excess excitation energy in the light-harvesting antenna of Photosystem II (PSII) can cause irreversible damage to the photosynthetic apparatus. In periods of high light intensity, a feedback mechanism known as non-photochemical quenching (NPQ), induces the formation of quenchers which can safely dissipate excess excitation energy as heat. Although quenchers have been identified in more than one compartment of the PSII supercomplex, there is currently no quantitative description of how much NPQ is occurring at each of these locations. Here, we perform time-resolved fluorescence measurements on WT and antenna mutants lacking LHCII (NoL) and all peripheral antenna (Ch1 and Ch1lhcb5). By combining the results with those of steady-state fluorescence experiments we are able to estimate the intrinsic rate of NPQ for each plant and each PSII compartment. It is concluded that 60-70% of quenching occurs in LHCII, 15-20% in the minor antenna and 15-20% in the PSII core.

The Effect of Sucrose Supplementation on the Micropropagation of Salix viminalis L. Shoots in Semisolid Medium and Temporary Immersion Bioreactors

The effect of sucrose concentration on the micropropagation of axillary shoots of willow was investigated. The following factors were examined: the culture system (semisolid medium in glass jars versus liquid medium in temporary immersion bioreactors), the type of explant (apical and basal sections), the frequency of immersion, and CO2 enrichment. Shoots and leaf growth were significantly higher in RITA® bioreactors than in the jars for all the sucrose treatments. Apical or basal sections of willow cultured in bioreactors under high light intensity (150 µmol m−2 s−1) and ventilated six times a day with CO2-enriched air were successfully proliferated without sucrose, whereas shoots cultured in jars did not proliferate well if sucrose concentration was 0.5% or lower. More roots were formed when sucrose was added to the medium. Shoots cultured in bioreactors were successfully acclimatized irrespective of the sucrose treatment and the root biomass when transferred to ex vitro conditions. This is the first report of photoautotrophic willow micropropagation, our results confirm the importance of proper gaseous exchange to attain autotrophy during in vitro propagation.

Genetic and Environmental Factors Jointly Impact Leaf Phenolic Profiles of Iris variegata L.

A plant’s main mechanism to diminish the effects caused by high free radical levels generated during high irradiance is the synthesis of various secondary metabolites. In addition to interspecies differences, their concentrations may be influenced by genetic, ontogenic, morphogenetic or environmental factors. We investigated the influence of genetic (genotypes from different natural habitats) and environmental (contrasting light regimes as well as successive parts of the vegetation period) variability on the accumulation of 10 selected phenolic compounds (phenolic acids, flavonoids, and xanthones) in Iris variegata genotypes. Genotypes originated from either sun-exposed or shaded natural habitats were transplanted to two experimental light treatments (high light intensity with a higher R/FR ratio and low light intensity with a lower R/FR ratio). Significant impacts of both genetic and environmental seasonal variability (spring, summer and fall during the vegetation period) on phenolic compound profiles were detected. Their highest amounts were detected in spring. The magnitude of difference between light treatments (high vs. low light intensity) and the direction of this change varied depending on the secondary compound class. Phenotypic correlations among the 10 analyzed secondary metabolites differed across the experimental light treatments and their number decreased from spring to fall.