Assessment of factual measurement times for chlorophyll-a fluorescence in rubber (Hevea brasiliensis) clones

Cahyo AN, Murti RH, Putra ETS, Nuringtyas TR, Fabre D, Montoro P. 2021. Assessment of factual measurement times for chlorophyll-a fluorescence in rubber (Hevea brasiliensis) clones. Biodiversitas 22: 3470-3477. Chlorophyll-a fluorescence is widely used to determine the stress tolerance levels of some plant species. Measurement of chlorophyll-a fluorescence is accurate if the duration of dark adaptation is well defined and optimal Fv/Fm (maximum quantum yield of primary photochemistry/photosynthesis) is achieved. Leaf clips are usually used to darken the leaf prior to measurement. This procedure takes time and limits the use of chlorophyll-a fluorescence parameter in high-throughput screening of genetic populations. This study aimed to determine the most suitable time for the chlorophyll-a fluorescence measurement. This study was carried out on several rubbers (Hevea brasiliensis Müll. Arg.) clones and consisted of two steps. The first step was conducting the measurements at five different times at night: at 7.30, 8.00, 8.30, 9.00, and 9.30 p.m. The second step was conducting the measurements at daytime, which consisted of two factors. The first factor was the measurement time, which was divided into two categories: 7.30 a.m. and 1.30 p.m. The second factor was the duration of dark adaptation using leaf clips, which consisted of nine levels: 0, 15, 30, 45, 60, 75, 90, 105, and 120 min. Additional treatment (measurement at 9.00 p.m. without using leaf clips to darken the leaf) was used as a control. This study revealed that a dark adaptation time of two hours after the sunset was long enough for the rubber leaves chlorophyll-a fluorescence transient to be measured without using leaf clips for the dark adaptation. If the measurement is conducted by 7.30 a.m., the clone RRIM 600, GT1, and SP 217 required 15 min of dark adaptation, whereas clone PB 260 required 60 min of dark adaptation. Furthermore, measurement of chlorophyll-a fluorescence in the afternoon is not recommended due to the potentially high microclimate fluctuation.

Hyperspectral Identification of Chlorophyll Fluorescence Parameters of Suaeda salsa in Coastal Wetlands

The stomata of Suaeda salsa are closed and the photosynthetic efficiency is decreased under conditions of water–salt imbalance, with the change to photosynthesis closely related to the chlorophyll fluorescence parameters of the photosystem PSII. Accordingly, chlorophyll fluorescence parameters were selected to monitor the growth status of Suaeda salsa in coastal wetlands under conditions of water and salt. Taking Suaeda salsa in coastal wetlands as the research object, we set up five groundwater levels (0 cm, –5 cm, –10 cm, –20 cm, and –30 cm) and six NaCl salt concentrations (0%, 0.5%, 1 %, 1.5%, 2%, and 2.5%) to carry out independent tests of Suaeda salsa potted plants and measured the canopy reflectance spectrum and chlorophyll fluorescence parameters of Suaeda salsa. A polynomial regression method was used to carry out hyperspectral identification of Suaeda salsa chlorophyll fluorescence parameters under water and salt stress. The results indicated that the chlorophyll fluorescence parameters Fv/Fm, Fm', and ΦPSII of Suaeda salsa showed significant relationships with vegetation index under water and salt conditions. The sensitive canopy band ranges of Suaeda salsa under water and salt conditions were 680–750 nm, 480–560 nm, 950–1000 nm, 1800–1850 nm, and 1890–1910 nm. Based on the spectrum and the first-order differential spectrum, the spectral ratio of A/B was constructed to analyze the correlation between it and the chlorophyll fluorescence parameters of Suaeda salsa. We constructed thirteen new vegetation indices. In addition, we discovered that the hyperspectral vegetation index D690/D1320 retrieved Suaeda chlorophyll fluorescence parameter Fv/Fm with the highest accuracy, with a multiple determination coefficient R2 of 0.813 and an RMSE of 0.042, and that D725/D1284 retrieved Suaeda chlorophyll fluorescence parameter ΦPSII model with the highest accuracy, with a multiple determination coefficient R2 of 0.848 and an RMSE of 0.096. The hyperspectral vegetation index can be used to retrieve the chlorophyll fluorescence parameters of Suaeda salsa in coastal wetlands under water and salt conditions, providing theoretical and technical support for future large-scale remote sensing inversion of chlorophyll fluorescence parameters.

Alternative electron pathways of photosynthesis drive the algal CO2 concentrating mechanism

Global photosynthesis consumes ten times more CO2 than net anthropogenic emissions, and microalgae account for nearly half of this consumption1. The great efficiency of algal photosynthesis relies on a mechanism concentrating CO2 (CCM) at the catalytic site of the carboxylating enzyme RuBisCO, thus enhancing CO2 fixation2. While many cellular components involved in the transport and sequestration of inorganic carbon (Ci) have been uncovered3,4, the way microalgae supply energy to concentrate CO2 against a thermodynamic gradient remains elusive4-6. Here, by monitoring dissolved CO2 consumption, unidirectional O2 exchange and the chlorophyll fluorescence parameter NPQ in the green alga Chlamydomonas, we show that the complementary effects of cyclic electron flow and O2 photoreduction, respectively mediated by PGRL1 and flavodiiron proteins, generate the proton motive force (pmf) required by Ci transport across thylakoid membranes. We demonstrate that the trans-thylakoid pmf is used by bestrophin-like Ci transporters and further establish that a chloroplast-to-mitochondria electron flow contributes to energize non-thylakoid Ci transporters, most likely by supplying ATP. We propose an integrated view of the CCM energy supply network, describing how algal cells distribute photosynthesis energy to power different Ci transporters, thus paving the way to the transfer of a functional algal CCM in plants towards improving crop productivity.One sentence summaryPhotosynthetic alternative electron flows and mitochondrial respiration drive the algal CO2 concentrating mechanism

Identification of Heat Tolerance in Chinese Wildgrape Germplasm Resources

Global climate warming will significantly impact grapevine growth and development, and thus grape and wine industries worldwide. Heat-tolerant germplasms are very valuable for grapevine breeding programs. In this study, we assessed the thermotolerance of 247 wild grape accessions by chlorophyll fluorescence parameter (Fv/Fm) under critical high temperature according to Xu et al. in 2016, 2017, and 2018. The results showed that 36 grape accessions showed strong heat tolerance. Therefore, these accessions can be used as parents for breeding heat-tolerant grape cultivars.

Chlorophyll Fluorescence Parameters and Antioxidant Defense System Can Display Salt Tolerance of Salt Acclimated Sweet Pepper Plants Treated with Chitosan and Plant Growth Promoting Rhizobacteria

Salinity stress deleteriously affects the growth and yield of many plants. Plant growth promoting rhizobacteria (PGPR) and chitosan both play an important role in combating salinity stress and improving plant growth under adverse environmental conditions. The present study aimed to evaluate the impacts of PGPR and chitosan on the growth of sweet pepper plant grown under different salinity regimes. For this purpose, two pot experiments were conducted in 2019 and 2020 to evaluate the role of PGPR (Bacillus thuringiensis MH161336 106–8 CFU/cm3) applied as seed treatment and foliar application of chitosan (30 mg dm−3) on sweet pepper plants (cv. Yolo Wonder) under two salinity concentrations (34 and 68 mM). Our findings revealed that, the chlorophyll fluorescence parameter (Fv/Fm ratio), chlorophyll a and b concentrations, relative water content (RWC), and fruit yield characters were negatively affected and significantly reduced under salinity conditions. The higher concentration was more harmful. Nevertheless, electrolyte leakage, lipid peroxidation, hydrogen peroxide (H2O2), and superoxide (O2−) significantly increased in stressed plants. However, the application of B. thuringiensis and chitosan led to improved plant growth and resulted in a significant increase in RWC, chlorophyll content, chlorophyll fluorescence parameter (Fv/Fm ratio), and fruit yield. Conversely, lipid peroxidation, electrolyte leakage, O2−, and H2O2 were significantly reduced in stressed plants. Also, B. thuringiensis and chitosan application regulated the proline accumulation and enzyme activity, as well as increased the number of fruit plant−1, fruit fresh weight plant−1, and total fruit yield of sweet pepper grown under saline conditions.

The effect of different shading net on the Quantum Efficiency of PS II in chilli pepper cultivar ‘Star Flame’

The study was undertaken to identify the effect of different shading net on the quantum efficiency of PS II on ‘Star Flame’ chilli pepper (Capsicum annuum) over a period of time cultivated under plastic house environment. ‘Star Flame’ pepper was grown under red shading net and samples without shading were used as control. Analysis of photosynthetic activity revealed a significant difference (p<0.05) between Fv/Fm values in control and red shading at the end of July (p = 0.031) after the first harvest. Chlorophyll fluorescence parameter Fv/Fm reflects the maximum quantum efficiency of photosystem II (PS II) used in the detection of early stress in plants.

Physiological response of Miscanthus x giganteus grown in nutritionally poor post-military soil

Background: To determine the level of plant stress of second-generation biofuel crop Miscanthus x giganteus ( Mxg ) grown in poor quality post-military soils using physiological parameters; to identify impact of plant growth regulators (PGRs) on the stress reduction and to select the fluorescence indicators most suitable for quantification of stress. Plant fitness was quantified with non-invasive measurement of leaf fluorescence using 16 different indexes. Simultaneously visible stress signs were observed on stems and leaves and differences were revealed by microscopy of leaf sections. Results: Leaf fluorescence analysis, visual observation and changes of leaf anatomy revealed significant stress in all tested subjects . Besides commonly used F v /F m and P.I. (performance index), the fluorescence parameter T fm (time to achieve maximum fluorescence) seems to be rather sensitive and applicable for revealing finer differences. However, none of investigated parameters proved significant positive effect of PGRs on stress reduction. Conclusions: Measuring F v /F m , P.I., and T fm is a suitable method for revealing stress affecting Mxg in poor post-military soils. Since PGRs application did not reduce the stress level, direct application of soil amendments should be considered for stress reduction and improving the biomass quality.