Medium Light Conditions Research Articles

Color Vision in the Gas Station Workers of Isfahan City: A Quantitative Analysis With the Farnsworth D15 Color Test

Background and Objectives: The color vision evaluation of gas station workers in Isfahan City. Methods: This cross-sectional comparative study was performed on workers at gas stations in Isfahan; all the workers were men. The participants were divided into two 40-people groups of exposure and non-exposure (the members of the fuel sales department). The participants had better vision than 8/10 and no underlying problems or eye disease. Besides, examination, including color vision was performed for all subjects. Color vision was assessed using the D15 test under high to medium light conditions. Also, the color vision test was performed monocularly. Then, the obtained data were analyzed using SPSS V. 22. Results: The two study groups significantly differed in terms of color vision impairment index (P <0.001). Also, more color vision defects were seen in the group exposed to gasoline. The color confusion index (as the indicator of color vision defects) were 1.485 and 1.129 in exposure and non-exposure to gasoline groups, respectively. Thus, color vision defects were significantly higher in the exposure to gasoline group, compared with the control group. Conclusion: The results of this study showed a difference in color vision index between the two groups. Therefore, long-term exposure to organic solvents, such as gasoline in fuel stations may cause color vision loss.

Deletion of Proton Gradient Regulation 5 (PGR5) and PGR5-Like 1 (PGRL1) proteins promote sustainable light-driven hydrogen production in Chlamydomonas reinhardtii due to increased PSII activity under sulfur deprivation.

Continuous hydrogen photo-production under sulfur deprivation was studied in the Chlamydomonas reinhardtii pgr5 pgrl1 double mutant and respective single mutants. Under medium light conditions, the pgr5 exhibited the highest performance and produced about eight times more hydrogen than the wild type, making pgr5 one of the most efficient hydrogen producer reported so far. The pgr5 pgrl1 double mutant showed an increased hydrogen burst at the beginning of sulfur deprivation under high light conditions, but in this case the overall amount of hydrogen produced by pgr5 pgrl1 as well as pgr5 was diminished due to photo-inhibition and increased degradation of PSI. In contrast, the pgrl1 was effective in hydrogen production in both high and low light. Blocking photosynthetic electron transfer by DCMU stopped hydrogen production almost completely in the mutant strains, indicating that the main pathway of electrons toward enhanced hydrogen production is via linear electron transport. Indeed, PSII remained more active and stable in the pgr mutant strains as compared to the wild type. Since transition to anaerobiosis was faster and could be maintained due to an increased oxygen consumption capacity, this likely preserves PSII from photo-oxidative damage in the pgr mutants. Hence, we conclude that increased hydrogen production under sulfur deprivation in the pgr5 and pgrl1 mutants is caused by an increased stability of PSII permitting sustainable light-driven hydrogen production in Chlamydomonas reinhardtii.

Programmed cell death activated by Rose Bengal in Arabidopsis thaliana cell suspension cultures requires functional chloroplasts.

Light-grown Arabidopsis thaliana cell suspension culture (ACSC) were subjected to mild photooxidative damage with Rose Bengal (RB) with the aim of gaining a better understanding of singlet oxygen-mediated defence responses in plants. Additionally, ACSC were treated with H2O2 at concentrations that induced comparable levels of protein oxidation damage. Under low to medium light conditions, both RB and H2O2 treatments activated transcriptional defence responses and inhibited photosynthetic activity, but they differed in that programmed cell death (PCD) was only observed in cells treated with RB. When dark-grown ACSC were subjected to RB in the light, PCD was suppressed, indicating that the singlet oxygen-mediated signalling pathway in ACSC requires functional chloroplasts. Analysis of up-regulated transcripts in light-grown ACSC, treated with RB in the light, showed that both singlet oxygen-responsive transcripts and transcripts with a key role in hormone-activated PCD (i.e. ethylene and jasmonic acid) were present. A co-regulation analysis proved that ACSC treated with RB exhibited higher correlation with the conditional fluorescence (flu) mutant than with other singlet oxygen-producing mutants or wild-type plants subjected to high light. However, there was no evidence for the up-regulation of EDS1, suggesting that activation of PCD was not associated with the EXECUTER- and EDS1-dependent signalling pathway described in the flu mutant. Indigo Carmine and Methylene Violet, two photosensitizers unable to enter chloroplasts, did not activate transcriptional defence responses in ACSC; however, whether this was due to their location or to their inherently low singlet oxygen quantum efficiencies was not determined.

Plasticity in Pinus pinaster populations of diverse origins: Comparative seedling responses to light and Nitrogen availability

The effects of light and N availability, and population on seedling morphology and biomass allocation were assessed in eleven months seedlings from ten Pinus pinaster populations. We conducted a garden experiment using a light gradient (full sunlight, HL= 337.1 μmol m2 s-1; medium light, ML= 120.6 μmol m2 s-1 and low light, LL= 30 μmol m2 s-1) and two contrasting soil fertility regimes: low-N and high-N availability. Light availability was an important factor controlling phenotypic plasticity. However, differences between productivity environments were observed, especially in full sunlight and medium light conditions, which suggest that soil fertility may be very important at early successional stages at open and medium shaded microsites, but would exert low influence in deep shade conditions. Population-specific responses were observed for many traits, which suggest a genetic control of morphological plasticity. All populations produced more total dry weight with HL and high-N. When light and/or N richness varied, growth depended upon which resource was more limiting. Results indicated ontogenetic drift but when seedlings were compared at the same size, results fitted with optimal partitioning theory. Allocation to needles was higher in HL and ML/high-N conditions, while allocation to root was higher in low-N seedlings in HL and ML conditions. With shade (ML and LL) all populations allocated more dry weight to stem, regardless N availability. A significant increment in stem height was observed with shade increase.

Evolution of a divinyl chlorophyll-based photosystem in Prochlorococcus

Acquisition of new photosynthetic pigments has been a crucial process for the evolution of photosynthesis and photosynthetic organisms. In this process, pigment-binding proteins must evolve to fit new pigments. Prochlorococcus is a unique photosynthetic organism that uses divinyl chlorophyll (DVChl) instead of monovinyl chlorophyll. However, cyanobacterial mutants that accumulate DVChl immediately die even under medium-light conditions, suggesting that chlorophyll (Chl)-binding proteins had to evolve to fit to DVChl concurrently with Prochlorococcus evolution. To elucidate the coevolutionary process of Chl and Chl-binding proteins during the establishment of DVChl-based photosystems, we first compared the amino acid sequences of Chl-binding proteins in Prochlorococcus with those in other photosynthetic organisms. Two amino acid residues of the D1 protein, V205 and G282, are conserved in monovinyl chlorophyll-based photosystems; however, in Prochlorococcus, they are substituted with M205 and C282, respectively. According to the solved photosystem II structure, these amino acids are not involved in Chl binding. To mimic Prochlorococcus, V205 was mutated to M205 in the D1 protein from Synechocystis sp. PCC6803 and Synechocystis dvr mutant was transformed with this construct. Although these transgenic cells could not grow under high-light conditions, they acquired light tolerance and grew under medium-light conditions, whereas untransformed dvr mutants could not survive. Substitution of G282 for C282 contributed additional light tolerance, suggesting that the amino acid substitutions in the D1 protein played an essential role in the development of DVChl-based photosystems. Here, we discuss the coevolution of a photosynthetic pigment and its binding protein.

Can Chlorophyll-a in-vivo fluorescence be used for quantification of carbon-based primary production in absolute terms?

We tested the Chlorophyll-a in-vivo fluorescence technique as a method to measure absolute values of primary production by the application of a bio-optical model. In this model, absolute values of gross photosynthetic oxygen evolution were calculated on the basis of Chlorophyll-a in-vivo fluorescence, such as photosystem II quantum yield and the amount of absorbed light quanta per time (Q Phar ). Simultaneous measurements of photosynthesis rates, as measured by a Clark-type electrode and estimated via the fluorescence based model, yield similar results. The P-I-curves measured by these two independent methods are nearly identical under light limitation, whereas maximal photosynthetic activities under saturating light are found to be higher using the bio-optical model. Furthermore, we determined the relationship between carbon-based biomass formation and the photosynthesis rate under low and high light. The quantity of electrons consumed for C and N assimilation is the same as the quantity of electrons produced by the photosystems under low light. Under high light, the electron production exceeds the electron consumption for N and C assimilation. We found that an oxygen production of 55-60 μmol O 2 is equivalent to the production of 1 mg dry matter. We conclude that the photosynthetic electron transport rate represents a fairly good estimated measure of newly synthesised organic matter under the applied conditions. Therefore, the use of fluorescence data in an appropriate bio-optical model is a powerful tool for measuring biomass formation in absolute terms but is restricted to replete nutrient and medium light conditions. The validity of this experimental approach for measuring primary production under stress conditions still needs to be elaborated.

REMARKS ON WEST PACIFIC NUMMULITIDAE (FORAMINIFERA)

Living Nummulitidae achieve their highest diversity in the subtropical and tropical West Pacific. Although all house symbiotic microalgae, they avoid highly illuminated areas near the water surface, since their flat tests could be easily damaged by the hydrodynamic regime. The preference for calm water conditions extends their depth distribution down to the base of the photic zone. West Pacific Nummulitidae can be differentiated into ten species belonging to six genera according to an ecological species concept. The genus Operculina d’Orbigny is represented by three species. While O. discoidalis (d’Orbigny) prefers a fine-grained bottom under medium light conditions (10% surface intensity), O. ammonoides (Gronovius) prefers a coarser substrate and sometimes can be found on hard bottoms. Light dependence ranges from 1.5% to 68% surface intensity. Less illuminated coarse sands are inhabited by Operculina cf. O. complanata (Defrance), which is the dominant symbiont-bearing foraminifer between light intensities of 0.2% to 12% surface illumination. The genus Planostegina Banner and Hodgkinson demonstrates transitions to the genus Operculina in test form and surface, while the division into chamberlets is similar to Heterostegina. Planostegina operculinoides (Hofker) is distinguished by flat tests and delicate chamberlets. It lives on sandy bottoms restricted to light intensities between 0.45% and 26% surface illumination. The more robust Planstegina aff. P. operculinoides (Hofker) prefers light intensities between 0.4% and 2.7% surface illumination. Planoperculina heterosteginoides (Hofker) shows morphological transition to Operculina cf. O. complanata in developing incomplete septula. This species lives in low illuminated areas (0.3% to 2.5% surface intensity) and prefers medium to fine-grained sands. Heterostegina depressa d’Orbigny spans a broad range in light intensities (2% to 70% surface illumination), and is protected against irradiation by thick tests and a cryptic life mode near the surface. Test construction enables life under strong hydrodynamic regimes. This species lives firmly attached to hard substrates, thus counteracting transportation by water movement. Nummulites venosus (Fichtel and Moll) differs from H. depressa in having undivided chambers. It lives exclusively on coarse sand and avoids high sediment movement, thus starting its distribution beneath the fair weather wave base. According to light intensities, the upper limit may be similar to O. ammonoides (80%), while the lower limit is 2.5% surface illumination. Operculinella cumingii (Carpenter) inhabits coarse to medium sand in deeper regions between 1.2% and 25% surface illumination. Tests of the cyclic, large-sized species Cycloclypeus carpenteri Brady are easily transported due to the thin, plate-like form. The upper distribution limit correlates with the storm wave base, restricting C. carpenteri to depths below 50 m. The lower distribution limit depends on light intensity and is located near the base of the photic zone (0.4% surface illumination).

Intercellular communication in plants: electrical stimulation of proteinase inhibitor gene expression in tomato

Tomato (Lycopersicon esculentum L.) plants accumulate proteinase inhibitor ( pin) mRNA in response to various stimuli in leaves distant from those treated. Most earlier work suggests that the intercellular wound signals are chemical; we have tried to determine whether electrical or hydraulic signals can also evoke systemic pin expression. We used a mild flame to evoke a hydraulic signal and its local electrical aftermath, the variation potential (VP), and an electric stimulus to trigger an action potential. Under medium light, wounding evoked a 3- to 5-fold systemic increase in pin mRNA within 15 min, suggesting involvement of a rapidly transmitted signal. Wounding also triggered a transient systemic increase in calmodulin (cal ) mRNA, under medium light conditions. Wounded plants exhibited electrical responses (VP) and yielded 5-to 15-fold increases in pin mRNA within 1 h. Electrically stimulated plants that transmitted an action potential to the analyzed leaf exhibited similarly large, rapid increases in pin transcript. Plants which generated no signal had unchanged levels of pin mRNA. Thus, in addition to the previously shown chemical signals, both hydraulically induced VPs and electrically induced action potentials can elicit systemic pin expression.