Phototropin 1 and 2 influence photosynthesis, UV-C induced photooxidative stress responses, and cell death

Phototropins are plasma membrane-associated photoreceptors of blue light and UV-A/B radiation. The Arabidopsis thaliana genome encodes two phototropins, PHOT1 and PHOT2, that mediate phototropism, chloroplast positioning, and stomatal opening. They are well characterized in terms of photomorphogenetic processes, but so far, little was known about their involvement in photosynthesis, oxidative stress responses, and cell death. By analyzing phot1, phot2 single, and phot1phot2 double mutants, we demonstrated that both phototropins influence the photochemical and non-photochemical reactions, photosynthetic pigments composition, stomata conductance, and water-use efficiency. After oxidative stress caused by UV-C treatment, phot1 and phot2 single and double mutants showed a significantly reduced accumulation of H2O2 and more efficient photosynthetic electron transport compared to the wild type. However, all phot mutants exhibited higher levels of cell death four days after UV-C treatment, as well as deregulated gene expression. Taken together, our results reveal that on the one hand, both phot1 and phot2 contribute to the inhibition of UV-C-induced foliar cell death, but on the other hand, they also contribute to the maintenance of foliar H2O2 levels and optimal intensity of photochemical reactions and non-photochemical quenching after an exposure to UV-C stress. Our data indicate a novel role for phototropins in the condition-dependent optimization of photosynthesis, growth, and water-use efficiency as well as oxidative stress and cell death response after UV-C exposure

Novel role of JAC1 in influencing photosynthesis, stomatal conductance, and photooxidative stress signalling pathway in Arabidopsis thaliana

Regulation of light absorption under variable light conditions is essential to optimize photosynthetic and acclimatory processes in plants. Light energy absorbed in excess has a damaging effect on chloroplasts and can lead to cell death. Therefore, plants have evolved protective mechanisms against excess excitation energy that include chloroplast accumulation and avoidance responses. One of the proteins involved in facilitating chloroplast movements inArabidopsis thalianais the J domain-containing protein required for chloroplast accumulation response 1 (JAC1). The function of JAC1 relates to the chloroplast actin filaments appearance and disappearance. So far, the role of JAC1 was studied mainly in terms of chloroplasts photorelocation. Here, we demonstrate that the function of JAC1 is more complex, since it influences the composition of photosynthetic pigments, the efficiency of photosynthesis, and the CO(2)uptake rate. JAC1 has positive effect on water use efficiency (WUE) by reducing stomatal aperture and water vapor conductance. Importantly, we show that the stomatal aperture regulation is genetically coupled with JAC1 activity. In addition, our data demonstrate that JAC1 is involved in the fine-tuning of H(2)O(2)foliar levels, antioxidant enzymes activities and cell death after UV-C photooxidative stress. This work uncovers a novel function for JAC1 in affecting photosynthesis, CO(2)uptake, and photooxidative stress responses

Structural Adaptation and Physiological Mechanisms in the Leaves of Anthyllis vulneraria L. from Metallicolous and Non-Metallicolous Populations

Calamine wastes highly contaminated with trace metals (TMs) are spontaneously inhabited by a legume plant Anthyllis vulneraria L. This study determined an adaptation strategy of metallicolous (M) A. vulneraria and compared it with that of the non-metallicolous (NM) ecotype. We hypothesized that TMs may lead to (i) leaf apoplast modifications and (ii) changes in the antioxidant machinery efficiency that facilitate plant growth under severe contamination. To verify our hypothesis, we implemented immunolabelling, transmission electron microscopy and biochemical measurements. NM leaves were larger and thicker compared to the M ecotype. Microscopic analysis of M leaves showed a lack of dysfunctions in mesophyll cells exposed to TMs. However, changes in apoplast composition and thickening of the mesophyll and epidermal cell walls in these plants were observed. Thick walls were abundant in xyloglucan, pectins, arabinan, arabinogalactan protein and extensin. The tested ecotypes differed also in their physiological responses. The metallicolous ecotype featured greater accumulation of photosynthetic pigments, enhanced activity of superoxide dismutase and increased content of specific phenol groups in comparison with the NM one. Despite this, radical scavenging activity at the level of 20% was similar in M and NM ecotypes, which may implicate effective reduction of oxidative stress in M plants. In summary, our results confirmed hypotheses and suggest that TMs induced cell wall modifications of leaves, which may play a role in metal stress avoidance in Anthyllis species. However, when TMs reach the protoplast, activation of antioxidant machinery may significantly strengthen the status of plants naturally growing in TM-polluted environment

At the Edges of Photosynthetic Metabolic Plasticity—On the Rapidity and Extent of Changes Accompanying Salinity Stress-Induced CAM Photosynthesis Withdrawal

The common ice plant (Mesembryanthemum crystallinum L.) is a facultative crassulacean acid metabolism (CAM) plant, and its ability to recover from stress-induced CAM has been confirmed. We analysed the photosynthetic metabolism of this plant during the 72-h response period following salinity stress removal from three perspectives. In plants under salinity stress (CAM) we found a decline of the quantum efficiencies of PSII (Y(II)) and PSI (Y(I)) by 17% and 15%, respectively, and an increase in nonphotochemical quenching (NPQ) by almost 25% in comparison to untreated control. However, 48 h after salinity stress removal, the PSII and PSI efficiencies, specifically Y(II) and Y(I), elevated nonphotochemical quenching (NPQ) and donor side limitation of PSI (YND), were restored to the level observed in control (C3 plants). Swelling of the thylakoid membranes, as well as changes in starch grain quantity and size, have been found to be components of the salinity stress response in CAM plants. Salinity stress induced an over 3-fold increase in average starch area and over 50% decline of average seed number in comparison to untreated control. However, in plants withdrawn from salinity stress, during the first 24 h of recovery, we observed chloroplast ultrastructures closely resembling those found in intact (control) ice plants. Rapid changes in photosystem functionality and chloroplast ultrastructure were accompanied by the induction of the expression (within 24 h) of structural genes related to the PSI and PSII reaction centres, including PSAA, PSAB, PSBA (D1), PSBD (D2) and cp43. Our findings describe one of the most flexible photosynthetic metabolic pathways among facultative CAM plants and reveal the extent of the plasticity of the photosynthetic metabolism and related structures in the common ice plant

The Effect of LED and HPS Assimilation Lighting on Leaf Anatomy, Chlorophyll and Carotenoid Autofluorescence Signals, and Some Physiological and Chemical Leaf Traits Related to the Productivity of Cucumber (Cucumis sativus L.) in High-Wire Cultivation

Supplemental lighting with light-emitting diode (LED) lamps and/or high-pressure sodium (HPS) lamps was applied to increase the activity of the photosynthetic apparatus and thus productivity of greenhouse cucumber (Cucumis sativus L.) in a high-wire growing system. The colocalisation of the chlorophyll of PSII (located mainly in grana) and carotenoid fluorescence signals in chloroplasts of cucumber leaves was studied under confocal microscopy. Leaf anatomy and some chemical quality traits (dry matter, chlorophyll, carotenoids, total soluble solids, total sugars and nitrate reductase activity) as well as selected chlorophyll fluorescence parameters were also investigated and subjected to the multidimensional principal component analysis together with the data on fruit yield. Under LED lighting, a lower correlation between the occurrence of chlorophyll and carotenoid fluorescence signals was observed, especially in older (lower-located) leaves, which may have resulted from changes in the distribution of carotenoids within chloroplasts and/or relative concentrations of chlorophyll and carotenoids. Compared to toplighting with HPS lamps, most commonly used in commercial greenhouse cucumber production, the application of LED interlighting, especially in combination with LED toplighting, led to the increase in chlorophyll and carotenoid content and photosynthetic performance index in older leaves, which was related to the increased cucumber productivity

The Effect of LED and HPS Assimilation Lighting on Leaf Anatomy, Chlorophyll and Carotenoid Autofluorescence Signals, and Some Physiological and Chemical Leaf Traits Related to the Productivity of Cucumber (<i>Cucumis sativus</i> L.) in High-Wire Cultivation

Supplemental lighting with light-emitting diode (LED) lamps and/or high-pressure sodium (HPS) lamps was applied to increase the activity of the photosynthetic apparatus and thus productivity of greenhouse cucumber (Cucumis sativus L.) in a high-wire growing system. The colocalisation of the chlorophyll of PSII (located mainly in grana) and carotenoid fluorescence signals in chloroplasts of cucumber leaves was studied under confocal microscopy. Leaf anatomy and some chemical quality traits (dry matter, chlorophyll, carotenoids, total soluble solids, total sugars and nitrate reductase activity) as well as selected chlorophyll fluorescence parameters were also investigated and subjected to the multidimensional principal component analysis together with the data on fruit yield. Under LED lighting, a lower correlation between the occurrence of chlorophyll and carotenoid fluorescence signals was observed, especially in older (lower-located) leaves, which may have resulted from changes in the distribution of carotenoids within chloroplasts and/or relative concentrations of chlorophyll and carotenoids. Compared to toplighting with HPS lamps, most commonly used in commercial greenhouse cucumber production, the application of LED interlighting, especially in combination with LED toplighting, led to the increase in chlorophyll and carotenoid content and photosynthetic performance index in older leaves, which was related to the increased cucumber productivity