Differences in stomatal and photosynthetic characteristics of five diploidy wheat species

Physiological and biochemical changes in Moroccan barley (Hordeum vulgare L.) cultivars submitted to drought stress

Barley (Hordeum vulgare L.) is the second most consumed and cultivated cereal by the Moroccan population. However, it is predicted that frequent drought periods, caused by climate change, can cause problems in plant growth. Thus, the selection of drought-tolerant barley cultivars is essential to ensure the security of barley's needs. We aimed to screen drought stress tolerance in Moroccan barley cultivars. We tested the drought tolerance of nine Moroccan barley cultivars ('Adrar', 'Amalou', 'Amira', 'Firdaws', 'Laanaceur', 'Massine', 'Oussama', 'Taffa', and 'Tamellalt') based on physiological and biochemical parameters. Drought stress was applied by maintaining field capacity at 40% (90% for the control), and plants were randomly arranged in a greenhouse at 25 °C under natural light conditions. Drought stress decreased relative water content (RWC), shoot dry weight (SDW), and chlorophyll content (SPAD index), but significantly increased electrolyte leakage, hydrogen peroxide, malondialdehyde (MDA), water-soluble carbohydrates, and soluble protein contents, as well as catalase (CAT) and ascorbate peroxidase (APX) activities. High levels of SDW, RWC, CAT, and APX activities were recorded in 'Firdaws', 'Laanaceur', 'Massine', 'Taffa', and 'Oussama', which can be interpreted by high drought tolerance. On the other hand, 'Adrar', 'Amalou', 'Amira', and 'Tamellalt' showed higher values of MDA and H₂O₂ content, which can be linked with drought sensitivity. Physiological and biochemical parameter changes are discussed in terms of barley's tolerance to drought. Tolerant cultivars could be a good background for barley breeding in areas known for the alternative of long dry spells.

Photosystems and antioxidative system of rye, wheat and triticale under Pb stress

Lead (Pb²⁺) pollution in the soil sub-ecosystem has been a continuously growing problem due to economic development and ever-increasing anthropogenic activities across the world. In this study, the photosynthetic performance and antioxidant capacity of Triticeae cereals (rye, wheat and triticale) were compared to assess the activities of antioxidants, the degree of oxidative damage, photochemical efficiency and the levels of photosynthetic proteins under Pb stress (0.5 mM, 1 mM and 2 mM Pb (NO₃)₂). Compared with triticale, Pb treatments imposed severe oxidative damage in rye and wheat. In addition, the highest activity of major antioxidant enzymes (SOD, POD, CAT, and GPX) was also found to be elevated. Triticale accumulated the highest Pb contents in roots. The concentration of mineral ions (Mg, Ca, and K) was also high in its leaves, compared with rye and wheat. Consistently, triticale showed higher photosynthetic activity under Pb stress. Immunoblotting of proteins revealed that rye and wheat have significantly lower levels of D1 (photosystem II subunit A, PsbA) and D2 (photosystem II subunit D, PsbD) proteins, while no obvious decrease was noticed in triticale. The amount of light-harvesting complex II b6 (Lhcb6; CP24) and light-harvesting complex II b5 (Lhcb5; CP26) was significantly increased in rye and wheat. However, the increase in PsbS (photosystem II subunit S) protein only occurred in wheat and triticale exposed to Pb treatment. Taken together, these findings demonstrate that triticale shows higher antioxidant capacity and photosynthetic efficiency than wheat and rye under Pb stress, suggesting that triticale has high tolerance to Pb and could be used as a heavy metal-tolerant plant.

Ozone Tolerance Found in Aegilops tauschii and Primary Synthetic Hexaploid Wheat

Modern wheat cultivars are increasingly sensitive to ground level ozone, with 7-10% mean yield reductions in the northern hemisphere. In this study, three of the genome donors of bread wheat, Triticum urartu (AA), T. dicoccoides (AABB), and Aegilops tauschii (DD) along with a modern wheat cultivar (T. aestivum 'Skyfall'), a 1970s cultivar (T. aestivum 'Maris Dove'), and a line of primary Synthetic Hexaploid Wheat were grown in 6 L pots of sandy loam soil in solardomes (Bangor, North Wales) and exposed to low (30 ppb), medium (55 ppb), and high (110 ppb) levels of ozone over 3 months. Measurements were made at harvest of shoot biomass and grain yield. Ae. tauschii appeared ozone tolerant with no significant effects of ozone on shoot biomass, seed head biomass, or 1000 grain + husk weight even under high ozone levels. In comparison, T. urartu had a significant reduction in 1000 grain + husk weight, especially under high ozone (-26%). The older cultivar, 'Maris Dove', had a significant reduction in seed head biomass (-9%) and 1000 grain weight (-11%) but was less sensitive than the more recent cultivar 'Skyfall', which had a highly significant reduction in its seed head biomass (-21%) and 1000 grain weight (-27%) under high ozone. Notably, the line of primary Synthetic Hexaploid Wheat was ozone tolerant, with no effect on total seed head biomass (-1%) and only a 5% reduction in 1000 grain weight under high ozone levels. The potential use of synthetic wheat in breeding ozone tolerant wheat is discussed.

Comparison on Photosynthesis and Antioxidant Defense Systems in Wheat with Different Ploidy Levels and Octoploid Triticale

To investigate the evolutionary differences of wheat with different ploidy levels and octoploid Triticale, photosynthetic capacity, and antioxidant defenses system were compared within and between diploid, tetraploid and hexaploid wheat, and octoploid Triticale seedlings. The results showed that seed germination rate, chlorophyll content, and photochemical activity of photosystems, and the activities of antioxidative enzymes in hexaploid wheat and octoploid Triticale were significantly higher than in diploid and tetraploid wheat. Compared to other two wheat species and octoploid Triticale, hexaploid wheat presented lower levels of reactive oxygen species (ROS). Furthermore, we found that the levels of photosystem II reaction center protein D1, light-harvesting complex II b4 (CP29), and D subunit of photosystem I (PsaD) in diploid wheat were significantly lower compared with hexaploid wheat and octoploid Triticale. Taken together, we concluded that hexaploid wheat and octoploid Triticale have higher photosynthetic capacities and better antioxidant systems. These findings indicate that different ploidy levels of chromosome probably play an important regulatory role in photosystems and antioxidative systems of plants.

Effects of ploidy level and haplotype on variation of photosynthetic traits: Novel evidence from two Fragaria species

To reveal the effects of ploidy level and haplotype on photosynthetic traits, we chose 175 genotypes of wild strawberries belonging to two haplotypes at two types of ploidy levels (diploidy and tetraploidy) and measured photosynthetic traits. Our results revealed that ploidy significantly affected the characteristics of light-response curves, CO2-response curves, and leaf gas exchange parameters, except intercellular CO2 concentration (Ci). Tetraploid species had a lower light saturation point (LSP) and CO2 saturation point (CSP), higher light compensation point (LCP), dark respiration (Rd), and CO2 compensation point (CCP) than diploid species. Furthermore, tetraploid species have lower photosynthetic capacity than diploid species, including net photosynthetic rate (Pn), stomatal conductivity (Gs), and transpiration rate (Tr). In addition, haplotype had a significant effect on LSP, CSP, Tr, and Ci as well as a significant interactive effect between ploidy and haplotype on the maximal photosynethic rate of the light-response curve and Rd. Most of the variance existed within haplotypes among individuals. These results suggest that polyploidization was the main driver for the evolution of photosynthesis with increasing ploidy level (i.e. from diploidy to tetraploidy in Fragaria species), while the origin of a chromosome could also affect the photosynthetic traits and the polyploidization effect on photosynthetic traits.