Salt Pretreatment-Mediated Alleviation of Boron Toxicity in Safflower Cultivars: Growth, Boron Accumulation, Photochemical Activities, Antioxidant Defense Response.

The study aims to elucidate alleviant effects of boron (B) toxicity by salt pretreatment (SP) on growth response, phytoremediation capacity, photosynthesis, and defense mechanisms in two safflower cultivars (Carthamus tinctorius L.; Dinçer and Remzibey-05). Eighteen-day-old plants were divided into two groups: SP (75 mM NaCl for 5 days) and/or B treatment (C, 2, 4, 6, and 8 mM B for 10 days). Depending on the applied B toxicity, B concentrations in roots and leaves of both cultivars, necrotic areas of leaves, ion leakage (RLR), and H2O2 synthesis increased, while shoot and root length as well as biomass, water, chlorophyll a+b, and carotenoid content decreased. In addition, chlorophyll a fluorescence results revealed that every stage of the light reactions of photosynthesis was adversely affected under B toxicity, resulting in decreases in performance indexes (PIABS and PITOT). However, the cultivars tended to induce the synthesis of anthocyanins and flavonoids and increase the activity of antioxidant enzymes (SOD, POD, APX, and GR) to detoxify reactive oxygen species (ROS) under B toxicity. SP mitigated the negative effects of toxic B on biomass, water and pigment content, membrane integrity, photosynthetic activity, and defense systems. Considering all results, Remzibey-05 was able to better overcome the biochemical and physiological changes that may be caused by B toxicity by more effectively rendering B harmless, although it accumulated more B than Dinçer.

Physiological, photochemical, and antioxidant responses of wild and cultivated Carthamus species exposed to nickel toxicity and evaluation of their usage potential in phytoremediation.

The impacts of Ni toxicity on growth behaviors, photochemical, and antioxidant enzymes activities of wild (Carthamus oxyacantha M. Bieb.) and cultivated (Carthamus tinctorius L.) safflower species were investigated in this study. Fourteen-day-old seedlings were treated with excessive Ni levels [control, 0.5, 0.75, and 1.0 mM NiCl2·6H2O] for 7 days. The results of chlorophyll a fluorescence indicated that toxic nickel exposure led to changes in specific, phenomenological energy fluxes and quantum yields in thylakoid membranes, and activities of donor and acceptor sides of photosystems. These changes resulted in a significant decrease in the photosynthetic activities by about 50% in both species, but these negative effects of Ni were not in a level to destroy the functionality of the photosystems. At the same time, toxic Ni affected membrane integrity and the amount of photosynthetic pigments in the antenna and active reaction centers. Additionally, the accumulation of Ni was higher in roots than in stem and leaves for both species. Depending on Ni accumulation, a significant reduction in dry biomass of root by approx. 64.8 and 45.7% and shoot by 41 and 24.7% were observed in wild and cultivated species, respectively. Two species could probably withstand deleterious Ni toxicity with better upregulating own protective defense systems such as antioxidant enzymes and phenolic compounds. Among of them, SOD and POD activities were increased with increasing Ni concentrations. The POD activities of both species were most prominent and consistently increased (approx. 2 folds in roots and 6 folds in leaves) in highly toxic Ni levels and may be protected them from damaging effect of H2O2. When all results are evaluated as a whole, Carthamus species produced similar responses to toxicity and also both species have bioconcentration (BCF) and bioaccumulation factor (BF) > 1 and translocation factor < 1 under Ni toxicity may be regarded a good indication of Ni tolerance. Furthermore, it is possible to use the Carthamus species as phytostabilizers of soils contaminated with nickel, because of their roots accumulating more nickel.

Comparative physiological and proteomic analysis of cultivated and wild safflower response to drought stress and re-watering.

Drought is one of the major environmental stress that adversely affect the growth and development of oil seed plant, safflower. There is a limited knowledge on proteomic responses to support physiological, biochemical changes in how safflowers can regulate growth and metabolism under drought conditions and followed by re-watering. The changes in morphological, physiological, biochemical and proteomics of safflower genotypes (Carthamus tinctorius L.; Remzibey-05 and Linas, tolerant and sensitive cultivars, respectively, and C. oxyacantha M. Bieb., wild type) after exposure to drought and followed by re-watering have been examined. Drought negatively affected the shoot weight, water content, chlorophyll fluorescence, and biochemical parameters, including photosynthetic pigment, proline, MDA, and H2O2 contents and antioxidant enzyme activities in all genotypes, while the re-watering period allowed Remzibey-05 to recover, and it even provided the wild type completely recovered (approximately 100%). A total of 72 protein spots were observed as differently accumulated under treatments. The identified proteins were mainly involved in photosynthesis and carbohydrate, protein, defense, and energy metabolisms. Protein accumulation related to these metabolisms in Remzibey-05 were decreased under drought, while increased following re-watering. However, sensitive cultivar, Linas, could not exhibit an effective performance under drought and recovery when compared with other safflower genotypes. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at (10.1007/s12298-021-00934-2).

PSII photochemistry and antioxidant responses of a chickpea variety exposed to drought.

The effect of drought on the chickpea variety ILC 3279 was investigated at the vegetative stage. After 20 days from sowing, the plants subjected to drought stress for 3, 5 and 7 days imposed by withholding water were permitted to recover by rewatering for 2 days after 3, 5 and 7 days of drought. Shoot elongation, leaf production, fresh and dry biomass reduced while MDA and proline accumulation increased with extended duration of stress. The plants stressed for 3 days exhibited a rapid drop in their relative and absolute water contents. The quantum efficiency of PSII open centres in the dark-adapted and light-saturated state, excitation energy trapping of PSII and electron transport rate decreased significantly from the 5th day to the end of the drought treatments. Plants drought-stressed for 7 days brought about a marked increase in non-photochemical energy dissipation and a marked decline in photochemical quenching. After rewatering all chlorophyll a fluorescence characteristics except for F(M) completely recovered and reached the control values. Under 5 and 7 days of drought, the anthocyanin content increased gradually while the total chlorophyll content of leaves declined compared to the controls. The total carotenoid content remained unchanged during the experiments. The antioxidant enzyme response to drought treatments was quite variable. The total SOD activity upregulated with increasing duration of stress. On the other hand, the total APX activity was significantly higher only on the 7th day while the total POD activity increased from the 5th day. Differences in the total GR activity of treated groups were not statistically significant compared to their controls throughout the treatments. The present results indicate that the chickpea variety ILC 3279 withstands severe drought with its upregulated protective mechanisms at the vegetative stage.

Effects of cadmium on antioxidant enzyme and photosynthetic activities in leaves of two maize cultivars.

Effects of cadmium (Cd(2+)) on photosynthetic and antioxidant activities of maize (Zea mays L.) cultivars (3223 and 32D99) were investigated. Fourteen-day-old cultivar seedlings were exposed to different Cd concentrations [0, 0.3, 0.6 and 0.9mM Cd(NO(3))(2) x 4H(2)O] for 8 days. The results of chlorophyll fluorescence indicated that different levels of Cd affected photochemical efficiency in 3223 much more than that in 32D99. In parallel, the level of Cd at 0.9mM caused oxidative damage but did not indicate cessation of PSII activity of the cultivars; plant death was not observed at highly toxic Cd levels. Additionally, the increase in Cd concentration caused loss of chlorophylls and carotenoid and membrane damage in both cultivars, but greater membrane damage was observed in 3223 than in 32D99. Depending on Cd accumulation, a significant reduction in dry biomass was observed in both cultivars at all Cd concentrations. The accumulation of Cd was higher in roots than in leaves for both cultivars. Nevertheless, cultivar 3223 transferred more Cd from roots to leaves than did 32D99. On the other hand, our results suggest that there were similar responses in SOD, APX and GR activities with increasing Cd concentrations for both cultivars. However, POD activity significantly increased at highly toxic Cd levels in 32D99. This result may be regarded as an indication of better tolerance of the Z. mays L. cultivar 32D99 to Cd contamination.

Changes in photochemical and antioxidant enzyme activities in maize (Zea mays L.) leaves exposed to excess copper.

Changes in photosynthetic and antioxidant activities in maize (Zea mays L.) leaves of cultivars 3223 and 31G98 exposed to excess copper (Cu) were investigated. Cu treatment reduced the shoot and root length of both cultivars. No significant difference of Cu accumulation in the roots of both cultivars was observed while the cultivar 3223 accumulated significantly higher Cu in leaves than 31G98. The observed decreases in effective quantum efficiency of PSII, ETR and qP indicate an over excitation of photochemical system in 3223 compared to 31G98. The leaf chlorophyll and carotenoid contents of both cultivars decreased with increasing Cu concentration. A far higher production of anthocyanins in 31G98 has been observed than that of 3223. At 1.5 mM Cu concentration, all antioxidant enzyme activities increased in leaves of the cultivar 31G98 while there were no significant changes in SOD and GR activities in 3223 compared to the control except increased APX and POD activities. The lower Cu accumulation in leaves and higher antioxidant enzyme activities in 31G98 suggested an enhanced tolerance capacity of this cultivar to protect the plant from oxidative damage.

Photochemical and antioxidant responses in the leaves of Xerophyta viscosa Baker and Digitaria sanguinalis L. under water deficit.

In this study, photochemical and antioxidant responses of the monocotyledonous resurrection plant Xerophyta viscosa Baker and the crab grass Digitaria sanguinalis L. under water deficit were investigated as a function of time. Water deficit was imposed by withholding irrigation for 21 d. Gas exchange and chlorophyll a fluorescence analyses indicated that the dehydration treatment caused photoinhibition in both species. The reduction in the photosynthesis rate in both species during water deficit probably contributed to the decline in the photochemical efficiency of PSII and electron transport rate. However, the stomatal conductance of both species did not change during treatment whereas the intercellular CO2 pressure increased after 10 d of water deficit treatment. These observations could be related to nonstomatal limitations. The increasing net transpiration rate of both species may have contributed to leaf cooling because of water limitations. Prolonged water deficit resulted in photosynthetic pigment chlorophyll (a + b) and carotenoids content loss in only D. sanguinalis. Both species especially D. sanguinalis had increased the level of anthocyanin after 15 d of treatment, possibly to prevent the damaging effect of photooxidation. The total SOD activity of D. sanguinalis was significantly different from X. viscosa during the treatment. The total peroxidase activity in D. sanguinalis was significantly higher than in X. viscosa. X. viscosa acclimated to water deficit with no ultimate apparent oxidative damage due to endogenous protective mechanisms of resurrection. In case of D. sanguinalis, water deficit induced considerable stress and possibly caused some oxidative damage, despite the upregulation of protection mechanisms.