Copper toxicity in Withania somnifera: Growth and antioxidant enzymes responses of in vitro grown plants

Indian ginseng (Withania somnifera L. Dunal), a medicinally important plant exposed to different concentrations of CuSO₄ (0, 10, 25, 50, 100 and 200 μM) for 30 d in vitro accumulated high amount of Cu in a concentration manner. Toxic effects of Cu on plants were reflected by the reductions in fresh weight (FW), shoot and root length, chlorophyll and carotenoids contents. Malondialdehyde (MDA), a decomposition product of polyunsaturated fatty acids hydroperoxides, often considered as a suitable biomarker for lipid peroxidation was induced in metal-treated plants compared to the control. This hypothesis is also confirmed by the higher lipoxygenase (LOX) activity, coupled with higher hydrogen peroxide (H₂O₂) and superoxide anions (O₂⁻) content in treated plants. Ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione-S-transferase (GST) and guaiacol-peroxidase (G-POD) activities of leaves were increased in the presence of Cu when compared to control plants indicated that antioxidant enzymes played an important role in protecting the plant from Cu toxicity. After native polyacrylamide gel electrophoresis (PAGE) analysis, six APX and four G-POD isoforms were detected and significantly induced in metal-treated plants as compared to control plants. The marked decrease in superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and glutathione peroxidase (GPx) activities seems to reflect its inability for eliminating the reactive oxygen species (ROS) resulting from Cu-induced oxidative stress. On the other hand, total phenolic contents increased with increasing concentration of Cu compared to the control. This study reveals that plants have the ability to grow in Cu polluted areas by altering various physiological changes. Since the level of total phenolic content in metal-treated plants increases, therefore, it is advisable to assess the biological activity of the plants before using for medicinal purposes.     

Genetic analysis of biomass and photosynthetic parameters in wheat grown in different light intensities

Growth light intensities largely determine photosynthesis, biomass, and grain yield of cereal crops. To explore the genetic basis of light responses of biomass and Researchphotosynthetic parameters in wheat(Triticum aestivum L.),a quantitative trait locus(QTL) analysis was carried out in a doubled haploid(DH) population grown in low light(LL),medium light(ML), and high light(HL), respectively. The results showed that the wheat seedlings grown in HL produced more biomass with lower total chlorophyll content(Chl), carotenoid content, and maximum photochemical efficiency of photosystem II(Fv/Fm) while the wheat seedlings grown in LL produced less biomass with higher Chl compared with those grown in ML. In total, 48 QTLs were identified to be associated with the investigated parameters in relation to growth light intensities. These QTLs were mapped to 15 chromosomes which individually explained6.3%–36.0% of the phenotypic variance, of which chromo-somes 3A, 1D, and 6B were specifically involved in LL response, 5D and 7A specifically involved in ML response,and 4B specifically involved in HL response. Several light-responsive QTLs were co-located with QTLs for photosynthetic parameters, biomass, and grain weight under various conditions which may provide new hints to uncover the genetic control of photosynthesis, biomass, and grain weight.     

Effect of copper deficiency on photosynthetic electron transport in wheat plants

Copper deficiency in wheat ( Triticum aestivum L. cv. Nazareno Stramppeli) markedly affects photosynthetic activity. Flag leaves of copper-deficient plants showed a 50% reduction of the photosynthetic rate expressed as mg CO₂ dm⁻²h⁻¹. The activities of PSI and PSII, determined for isolated chloroplasts, as well as fluorescence measurements on intact leaves of copper-deficient plants, indicated a low activity of photosynthetic electron transport. Ribulose bisphosphate carboxylase/oxygenase (Rubisco) activity was not affected by copper deficiency but copper deficiency affected the chloroplast ultrastructure, especially at the level of grana, where a disorganization of thylakoids is evident.     

Antioxidant responses of wheat plants under stress

Currently, food security depends on the increased production of cereals such as wheat (Triticum aestivum L.), which is an important source of calories and protein for humans. However, cells of the crop have suffered from the accumulation of reactive oxygen species (ROS), which can cause severe oxidative damage to the plants, due to environmental stresses. ROS are toxic molecules found in various subcellular compartments. The equilibrium between the production and detoxification of ROS is sustained by enzymatic and nonenzymatic antioxidants. In the present review, we offer a brief summary of antioxidant defense and hydrogen peroxide (H₂O₂) signaling in wheat plants. Wheat plants increase antioxidant defense mechanisms under abiotic stresses, such as drought, cold, heat, salinity and UV-B radiation, to alleviate oxidative damage. Moreover, H₂O₂ signaling is an important factor contributing to stress tolerance in cereals.     

Characterization of photosynthetic pigment composition, photosystem II photochemistry and thermal energy dissipation during leaf senescence of wheat plants grown in the field

Photosynthetic pigment composition and photosystem II (PSII) photochemistry were characterized during the flag leaf senescence of wheat plants grown in the field. During leaf senescence, neoxanthin and beta-carotene decreased concomitantly with chlorophyll, whereas lutein and xanthophyll cycle pigments were less affected, leading to increases in lutein/chlorophyll and xanthophyll cycle pigments/chlorophyll ratios. The chlorophyll a/b ratio also increased. With the progression of senescence, the maximal efficiency of PSII photochemistry decreased only slightly in the early morning (low light conditions), but substantially at midday (high light conditions). Actual PSII efficiency, photochemical quenching and the efficiency of excitation capture by open PSII centres decreased significantly both early in the morning and at midday and such decreases were much greater at midday than in the early morning. At the same time, non-photochemical quenching, zeaxanthin and antheraxanthin contents at the expense of violaxanthin increased both early in the morning and at midday, with a greater increase at midday. The results in the present study suggest that a down-regulation of PSII occurred in senescent leaves and that the xanthophyll cycle plays a role in the protection of PSII from photoinhibitory damage in senescent leaves by dissipating excess excitation energy, particularly when exposed to high light.     

Nutrient accumulation and translocation in maturing wheat plants grown on waterlogged soil

Wheat plants (Triticum aestivum L., cv. Arina) growing in large pots (perforated at the bottom for controls, intact for flooding) were embedded in the field in spring. Waterlogging was initiated at anthesis and was maintained throughout the maturation period. Grain yield as well as potassium, phosphorus and magnesium contents in the shoot were decreased on flooded soil, while manganese and iron contents increased considerably. Total calcium and zinc contents per shoot remained comparable to those in controls. The reduction of potassium, phosphorus and magnesium contents by waterlogging was greatest in the grains, while manganese and iron accumulated mostly in the vegetative parts and the glumes. Zinc contents were also lowered in the grains during waterlogging due to an inhibited redistribution from the vegetative parts to the grains. Our results indicate that flooding caused not only an accumulation of manganese and iron in the shoot, but also affected the redistribution of macro- and micronutrients to the maturing gains.     

Effects of growth temperature on photosynthetic carbon metabolism in green plants III. Differences in structure, photosynthetic activities and activities of ribulose diphosphate carboxylase and glycolate oxidase in leaves of wheat grown under varied temperatures

The rate of ferricyanide photoreduction in broken chloroplastsisolated from leaves of wheat acclimatized to a low temperature(mean temperature, 5–7?C) was similar to that in chloroplastsfrom wheat acclimatized to a high temperature (20–25?C). There was no practical difference in glycolate oxidase activityin leaf extracts of wheat plants grown at low and high temperatures.In contrast, the ribulose diphosphate carboxylase activity ofchloroplasts from low temperature sample was less than halfthat for the high temperature sample. Chloroplasts having a high rate of photosynthetic CO₂-fixationwere obtained from wheat acclimatized to a low temperature,whereas the CO₂-fixation activity in chloroplasts isolated fromhigh temperature-acclimatized wheat was very low. Electron microscopy revealed that chloroplasts in high temperature-acclimatizedwheat were ellipsoidal, electron dense and contained starchgranules. Those in low temperature-acclimatized leaves wereround and did not contain starch granule. ²Present address: Department of Botany, Faculty of Science,University of Tokyo, Tokyo, Japan (Received August 7, 1973; )     

Different photosynthetic responses of wild and cultivated plants to high irradiance

In addition to other factors, high altitude (HA) environment is characterized by high photosynthetic photon flux density (PPFD). Photosynthetic characteristics of wild and cultivated plants were studied at different irradiances at Losar, India (altitude 4 200 m). Wild plants were tolerant to high PPFDs. Slopes of curve between net photosynthetic rate (P _N) and intercellular CO₂ concentration (C _i) or stomatal conductance (g _s) increased with increase in irradiance suggesting insensitivity or tolerance of these plants to higher PPFD. Cultivated plants, however, were sensitive to higher PPFD, their slopes of curves between P _N and C _i or g _s decreased with increased PPFD. Tolerance or insensitivity to higher PPFD was an important parameter affecting plant performance at HA.     

开顶式气室内外冬小麦光合特性差异比较

为探明开顶式气室(OTC)内外冬小麦光合特性的差异,测定了OTC内(T1处理组,冬小麦整个生育期生长在OTC内)和OTC外(T2处理组,大田自然环境组)冬小麦(扬麦16)不同生育期的气体交换参数、光合色素含量和叶绿素荧光参数。结果表明,T1处理的净光合速率Pn、气孔导度Gs、胞间CO2浓度Ci、最大光合速率Pm和半饱和光强Ik大部分生育期均大于T2;灌浆之前T1的表观量子效率AQY较高,蒸腾速率Tr和暗呼吸速率Rd较低,灌浆之后则出现逆转。大部分生育期T1处理叶绿素和类胡萝卜素含量均显著大于T2。T1处理的初始荧光Fo和最大荧光Fm均大于T2,而两者最大光量子产量Fv/Fm大部分生育期无显著差异,孕穗期和扬花期T1处理光化学淬灭系数q P显著低于T2。T1和T2处理PSⅡ的实际光化学量子效率Y(II)大部分生育期无显著差异,但灌浆期以后T1的非光化学淬灭系数NPQ和PSⅡ处调节性能量耗散的量子产量Y(NPQ)显著大于T2,而PSⅡ处非调节性能量耗散的量子产量Y(NO)显著低于T2。由此可见,OTC内冬小麦的气体交换能力和光响应能力均优于OTC外,光合色素含量也更高;OTC内外冬小麦内禀光能转换效率和实际光化学量子效率相当,但OTC内冬小麦过剩光能向调节性热耗散分配的比例较高而向非调节性热耗散分配的比例较低,其光保护能力更强,光能分配也更加合理。     

Age-dependent changes of photosynthetic responses induced by electrical signals in wheat seedlings

Electrical signals in plants, namely, the action potential (AP) and variation potential (VP) alter the activity of many processes, including photosynthesis. The functional responses induced by electrical signals vary in direction and amplitude, which might be determined by variable conditions of plants prior to stimulation, by the development stage in particular. In this work, the parameters of VP-induced photosynthetic responses were analyzed at various stages of wheat seedling development. Local wounding of the second leaf in wheat plants induced the propagation of VP and altered the activity of photosynthesis at a distance from the wound location. The amplitude of VP was enlarged when the seedling age increased from 11 to 18 days. The VP-induced photosynthetic response changed with age both qualitatively and quantitatively. The amplitude of VP-induced changes in CO₂ assimilation and nonphotochemical quenching (NPQ) increased with age, which might be due to the increase in VP amplitude and associated changes in Ca²⁺ and H⁺ concentrations. The quantum yield of photosystem II photoreaction was subject to age-dependent changes: the photochemical quantum yield (γ(PSII)) was found to increase after VP in young leaves, whereas the decline in γ(PSII) was observed after the VP propagation in mature leaves. The results may explain the diversity of photosynthetic responses caused by the electrical signals.     

Senescence and protein remobilisation in leaves of maturing wheat plants grown on waterlogged soil

Nicotianamine (NA), the key precursor of the mugineic acid family phytosiderophores (MAs), is synthesized from S-adenosylmethionine (SAM). The NA synthase was strongly induced by Fe-deficiency treatment, and the activity increased to the maximum level faster than the time of maximum level of MAs secretion and also before the appearance of severest chlorosis. The enzyme was mainly localized in the roots of barley. NA synthase had the optimum pH at 9.0, a molecular weight of about 40,00050,000 estimated by gel filtration or about 30,000 by SDS-PAGE. Using hydrophobic chromatography, hydroxylapatite chromatography, and preparative SDS-PAGE, NA synthase was purified as one band on SDS-PAGE.     

Structural and functional reorganization of the photosynthetic apparatus in adaptation to cold of wheat plants

In seedlings of a cold-resistant wheat variety, the dynamics was studied of the main structural-functional parameters of the photosynthetic apparatus (PSA) and of cold resistance of leaf cells in low-temperature plant adaptation. It has been established that a complex of structural-functional PSA changes takes place in seedling leaves under the influence of cold. As a result, as early as in the first hours of hardening, the formation of chloroplasts begins to occur in mesophyll cells of larger sizes and with a thylakoid system of the “sun type.” Owing to structural and functional readjustment (a change of content of pigments, stabilization of pigment-protein complexes, and enhancement of nonphotochemical quenching of excess energy) in the process of cold adaptation, the rate of photosynthesis stabilizes. It is suggested that the observed structural-functional PSA rearrangement is a necessary condition for formation of increased cold resistance of leaf cells; this, alongside with other physiological-biochemical changes occurring in parallel in cells and tissues of the plants, provides their survival under conditions of low temperatures.     

Reactive oxygen intermediates produced by photosynthetic electron transport are enhanced in short-day grown plants

Leaves of tobacco plants grown in short days (8h light) generate more reactive oxygen species in the light than leaves of plants grown in long days (16h light). A two fold higher level of superoxide production was observed even in isolated thylakoids from short day plants. By using specific inhibitors of photosystem II and of the cytochrome b(6)f complex, the site of O(2) reduction could be assigned to photosystem I. The higher rate of O(2) reduction led to the formation of a higher proton gradient in thylakoids from short day plants. In the presence of an uncoupler, the differences in O(2) reduction between thylakoids from short day and long day plants were abolished. The pigment content and the protein content of the major protein complexes of the photosynthetic electron transport chain were unaffected by the growth condition. Addition of NADPH, but not of NADH, to coupled thylakoids from long day plants raised the level of superoxide production to the same level as observed in thylakoids from short day plants. The hypothesis is put forward that the binding of an unknown protein permits the higher rate of pseudocyclic electron flow in thylakoids from short-day grown plants and that this putative protein plays an important role in changing the proportions of linear, cyclic and pseudocyclic electron transport in favour of pseudocyclic electron transport. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Articifical.     

From fresh vegetables to the harvest of wheat plants grown in the "SVET" space greenhouse onboard the MIR orbital station

Researchers report the results of experiments conducted onboard MIR in 1990, 1995, and 1996 in raising edible crops. In the 1990 experiment, radishes and Chinese cabbage were grown successfully, though the experimental plants were up to four times smaller than controls at harvest. The 1995 experiment in growing wheat through a complete life cycle was not completed. The 1996 experiment was successful in growing wheat through a complete life cycle to the seed stage. No seeds developed on any of the 279 ears harvested in that experiment. Reasons for the seedless development are explored.     

Growth and photosynthetic responses in Jatropha curcas L. seedlings of different provenances to watering regimes

Seedlings from four provenances of Jatropha curcas were subjected to 80, 50, and 30% of soil field capacity in potted experiments in order to study their responses to water availability. Our results showed that with the decline of soil water availability, plant growth, biomass accumulation, net photosynthetic rate, stomatal conductance (g_s), and transpiration rate (E) decreased, whereas leaf carbon isotope composition (δ¹³C), leaf pigment contents, and stomatal limitation value increased, while maximal quantum yield of PSII photochemistry was not affected. Our findings proved that stomatal limitation to photosynthesis dominated in J. curcas under low water availability. The increase of δ¹³C should be attributed to the decrease in g_s and E under the lowest water supply. J. curcas could adapt to low water availability by adjusting its plant size, stomata closure, reduction of E, increasing δ¹³C, and leaf pigment contents. Moreover, effects of provenance and the interaction with the watering regime were detected in growth and many physiological parameters. The provenance from xeric habitats showed stronger plasticity in the plant size than that from other provenances under drought. The variations may be used as criteria for variety/provenance selection and improvement of J. curcas performance.     

Dependence of photosynthetic rates on leaf density thickness in deciduous woody plants grown in sun and shade

Comparisons of photosynthetic rates were made on leaves of ten species of woody dicotyledons grown in the field under full sun or under a canopy which transmitted approximately 18% of full light. Photosynthesis and dark respiration were measured and compared on various bases: area, chlorophyll, fresh weight of lamina, density thickness (fresh weight per unit area), and protein.

Light-saturated photosynthesis per unit area or unit chlorophyll was about 1.5 times greater in the sun leaves than in the shade leaves and essentially equal per unit fresh weight or unit protein. Sun leaves were thicker but the enzymes per unit fresh weight remained constant as thickness varied. Chlorophyll per unit area remained about constant; chlorophyll per unit fresh weight varied inversely with changes in leaf thickness. Thus, density thickness variation is important in photosynthetic adaptation to sun and shade. This is also shown by the relationship between light-saturated photosynthesis per unit area and density thickness.