Effect of salt stress on photosynthesis and physiological parameters of three contrasting barley genotypes

In order to understand the physiological traits important in conferring salt tolerance in three barley genotypes, this study was performed under field conditions with three water salinity levels (2, 10, and 18 dS m–1). High salinity decreased net photosynthetic rate, transpiration rate, and stomatal conductance, K⁺ concentration, K⁺:Na⁺ ratio, and grain yield, but increased electrolyte leakage and Na⁺ content. Under 10 and 18 dS m–1 salinity, Khatam (salt-tolerant) had the maximum stomatal conductance, K⁺, K⁺:Na⁺ ratio, and the grain yield, and a minimum Na⁺ content and electrolyte leakage, whereas Morocco (salt-sensitive) had the lowest net photosynthetic rate, stomatal conductance, K⁺ content, K⁺:Na⁺ ratio, and grain yield, and the highest Na⁺ content and electrolyte leakage. This study showed that tolerant genotypes of barley may avoid Na⁺ accumulation in aboveground parts, facilitating a higher photosynthetic rate and higher grain yield.     

Contrasting responses to boron deficiency in barley and wheat

Plant and Soil - To determine if boron (B) deficiency, commonly reported to depress grain set in wheat, has the same effect in barley, a set of experiments compared five wheat and seven barley...     

Physiological responses of Tunisian grapevine varieties to bicarbonate-induced iron deficiency

Plants are frequently submitted to iron deficiency when growing on calcareous soils, which contain high concentrations of bicarbonate. The purpose of this study was to investigate the variability of physiological responses of Tunisian grapevine varieties to bicarbonate-induced iron chlorosis. Vine woodcuttings of seven autochthonous Tunisian varieties (Khamri, Mahdaoui, Blan3, Saouadi, Arich Dressé, Beldi and Balta4), two rootstocks (140Ru and S.O.4), and an introduced table variety (Cardinal) were cultivated on inert sand for 2 months using a complete nutrient solution (20 microM Fe) that was either well supplied or not supplied with 10 mM HCO3-. Young leaves of plants cultivated on bicarbonate-enriched medium showed characteristic symptoms of iron chlorosis, although the intensity of the symptoms depended on the variety and the rootstock. Chlorosis score confirmed these observations since the most sensitive varieties showed the highest values. This variability in tolerance to iron deficiency was also displayed when analysing the physiological parameters (shoot length, plant dry weight, and chlorophyll concentration) and the iron contents in the 4th leaf. Analysis of morphological and physiological parameters showed three behaviour groups. The first one corresponded to tolerant varieties (Khamri, Mahdaoui, and the root-stock: 140Ru), the second included moderately tolerant vines (Saouadi, Arich Dressé, Blanc3, and the rootstock: S.O.4) and the third represented the sensitive ones (Balta4, Beldi, and Cardinal).     

Effect of iron deficiency and iron restoration on ultrastructure of Anacystis nidulans.

The effects of iron deficiency and iron reconstitution on the ultrastructure of the unicellular cyanobacterium Anacystis nidulans R2 were studied by electron microscopy. Low-iron cells, grown with different amounts of aeration, were analyzed at 6, 12, and 24 h after the addition of iron. Low-iron cells had a decrease in the quantities of membranes, phycobilisomes, and carboxysomes and a large increase in glycogen storage granules. In cells aerated with gentle shaking, the addition of iron caused the number of carboxysomes to increase rapidly within 6 h. This was paralleled by a decrease in the quantity of glycogen storage granules. Carboxysomes were associated with the nucleoplasmic face of the inner photosynthetic membrane in normal, but not low-iron, cells; they once more contacted the membrane by 6 h after iron addition. Phycobilisome assembly was apparent by 6 h, and the number of phycobilisomes increased throughout reconstitution. Membrane restoration was accomplished in two stages: (i) components were added to preexisting membranes until about 12 h, and (ii) new membranes were synthesized beginning at 12 to 18 h. Low-iron cells grown by bubbling with air had only one to two concentric layers of membrane per cell. The addition of iron led to a pattern of reconstitution that was similar to that described above with two important exceptions. Under these conditions, the number of carboxysomes remained low and the carboxysomes rarely contacted the photosynthetic membranes. New membranes were not synthesized until the culture had reached the late-logarithmic growth phase and after all other morphological features had returned to normal.     

Early responses to cadmium exposure in barley plants: effects on biometric and physiological parameters

Cadmium represents one of the most toxic pollutants in plant ecosystems: at high concentrations it can cause severe effects, such as plant growth inhibition, decrease in photosynthesis and changes in plant basal metabolism. Changes in pigments’ content, RubisCO large subunit, and D1 protein indicated a severe reduction in photosynthetic efficiency. Furthermore, the decrease of nitrate reductase activity and changes in free amino acids levels show a general stress condition of nitrogen assimilation. Cadmium increased the activities of ROS scavenging enzymes; among these, ascorbate peroxidase rate was the most noticeably increased. It is worth noting that glucose-6-phosphate dehydrogenase (G6PDH; EC 1.1.1.64), showed changes in both activities and occurrence during cadmium stress. Interestingly, our data suggest that G6PDH would modulate redox homeostasis under metal exposure, and possibly satisfy the increased request of reductants to counteract the oxidative burst induced by cadmium. Therefore, the results suggest that APX and G6PDH may play a pivotal role to counteract the oxidative stress induced by cadmium in young barley plants.     

Effect of prolonged running on physiological responses to subsequent exercise

The purpose of this study was to compare metabolic and cardiopulmonary responses for submaximal and maximal exercise performed several days preceding (pre-test) and 45 min after (post-test) 21 miles of high intensity (70% VO2 max) treadmill running. Seven aerobically trained subjects' oxygen uptake, oxygen pulse, respiratory exchange ratio, heart rate, pulmonary ventilation, ventilatory equivalent of oxygen, and blood lactate concentration were determined for exercise during the pre- and post-test sessions. No differences were found for submaximal oxygen uptake, oxygen pulse, pulmonary ventilation and ventilatory equivalent of oxygen between the pre- and post-test values. Generally, submaximal heart rate responses were higher, and respiratory exchange ratio values were lower during the post-test. Reductions of maximal work time (12%), maximal oxygen uptake (6%) and maximal blood lactate concentration (47%) were found during the post-test. Thermal stress and glycogen depletion are possible mechanisms which may be responsible for these observed differences.     

Iron nutrition and physiological responses to iron stress in Nitrosomonas europaea

Nitrosomonas europaea, as an ammonia-oxidizing bacterium, has a high Fe requirement and has 90 genes dedicated to Fe acquisition. Under Fe-limiting conditions (0.2 μM Fe), N. europaea was able to assimilate up to 70% of the available Fe in the medium even though it is unable to produce siderophores. Addition of exogenous siderophores to Fe-limited medium increased growth (final cell mass). Fe-limited cells had lower heme and cellular Fe contents, reduced membrane layers, and lower NH₃- and NH₂OH-dependent O₂ consumption activities than Fe-replete cells. Fe acquisition-related proteins, such as a number of TonB-dependent Fe-siderophore receptors for ferrichrome and enterobactin and diffusion protein OmpC, were expressed to higher levels under Fe limitation, providing biochemical evidence for adaptation of N. europaea to Fe-limited conditions.     

Genotype-dependent effects of phosphorus supply on physiological and biochemical responses to Al-stress in cultivated and Tibetan wild barley

Aluminium (Al) toxicity and phosphorus (P) deficiency often co-exist in acidic soils and limit plant growth and crop production. To investigate the alleviating effects of different levels of phosphorus on Al stress, greenhouse hydroponic experiments were conducted using two contrasting Tibetan wild barley genotypes XZ16 and XZ61 of Al tolerant and sensitive, respectively, and Al tolerant cv. Dayton. The results showed that Al stress induced reduction in P accumulation in plants; and stem and leaf P concentrations of the three genotypes, except of XZ16 under HP + Al (100 µM Al with high level of 360 µM P) which was close to the control level. XZ16 recorded significantly higher P accumulation in plants, compared with XZ61 and Dayton, and P concentrations in leaves under Al stress, and in stems under NP + Al (100 µM Al with normal level of 180 µM P) and HP + Al. Meanwhile, H⁺-, Ca²⁺Mg²⁺-, and Total- ATPase activities in XZ16 and Dayton under Al stress were markedly higher than in XZ61. Normal or high level of P under Al stress could relieve Al stress as enhanced plant biomass, with increased photosystem II photochemistry (Fv/Fm) and P content, relative to the low level of 90 µM P. Compared with XZ61, addition of high P concentration for XZ16 significantly increased the values of Gs and Tr, with higher root GPX and H⁺-ATPase activities, and such nutrient elements as P, Mg and Ca in stems and leaves, and induced more malate secretion, but less MDA accumulation.     

The physiological and nutritional responses of seven different citrus rootstock seedlings to boron deficiency

Key message

Carrizo citrange was the most tolerant citrus rootstock to B-deficiency and some physiological performance could be attributed to the decreased mineral nutrient concentrations caused by B-deficiency.

Abstract

Boron (B) is an essential microelement for normal growth and development in vascular plants, and adequate B nutrition is crucial for agricultural production. Although citrus plants are not classified as the most sensitive species to B-deficiency, the occurrence of B-deficiency has been reported in the major citrus producing countries of the world, including the east and south of China. In this study, in order to evaluate the effects of B-deficiency on plant growth, root-morphological traits, B and other nutritional responses of citrus rootstock and to investigate the relationship between this physiological performance and mineral nutrients seven common rootstock seedlings, including Trifoliate orange (TO), Carrizo citrange (CC), Chongyi tangerine (CT), Red tangerine (RT), Cleopatra mandarin (CM), Fragrant citrus (FC), and Sour orange (SO), were treated by B-deficiency (0 mg L^?1) or moderate B (0.25 mg L^?1). All the seedlings were grown in hydroponics situation with modified 1/2-strength Hoagland’s solution under greenhouse conditions for 10 weeks. The results showed that B-deficiency inhibited the growth and development of all tested citrus rootstocks, but substantial differences were observed among these rootstocks. Different visible symptoms were observed both in the leaf and root. Corking of the leaf veins and leaf yellowing symptoms were observed on all rootstock genotypes except on CC, which exhibited a little discoloration at the end of the experiment. In addition, root growth of the citrus seedlings were also decreased by B-deficiency, but the decreases were more obvious in TO and FC. It was worth noting that B-deficiency inhibited lateral root growth and development more significantly than tap root, but not in lateral root initiation. The different performance of these rootstock genotypes indicated that CC was the most tolerant while TO was the most sensitive to B-deficiency. In addition, under B-deficiency conditions, not only the B concentration, but also the other mineral nutrient concentrations were influenced, especially in Mg, Fe and Mn. This change in nutrient concentrations might partly contribute to the seedlings’ physiological performances under B-deficiency.     

Distinct physiological responses of two rice cultivars subjected to iron toxicity under field conditions

Iron toxicity is recognised as the most widely distributed nutritional disorder in lowland and irrigated rice, derived from the excessive amounts of ferrous ions generated by the reduction of iron oxides in flooded soils. Rice cultivars with variable degrees of tolerance to iron toxicity have been developed, and cultural practices such as water management and fertilisation can be used to reduce its negative impact. However, because of the complex nature of iron toxicity, few physiological data concerning tolerance mechanisms to excess iron in field conditions are available. To analyse the physiological responses of rice to iron excess in field conditions, two rice cultivars with distinct tolerance to iron toxicity [BR‐IRGA 409 (susceptible) and IRGA 420 (tolerant)] were grown in two areas, with a well‐established history of iron toxicity (in Camaquã, RS, Brazil) and without iron toxicity (in Cachoeirinha, RS, Brazil). Plants from the susceptible cultivar grown in the iron‐toxic site showed lower levels of chlorophylls and soluble proteins (together with higher carbonyl levels) indicating photooxidative and oxidative damage. The toxic effects observed were because of the accumulation of high levels of iron and not because of any indirectly induced shoot deficiency of other nutrients. Higher activities of antioxidative enzymes were also observed in leaves of plants from the susceptible cultivar only in the iron‐toxic site, probably as a result of oxidative stress rather than because of specific involvement in a tolerance mechanism. There was no difference between cultivars in iron accumulation in the symplastic and apoplastic space of leaves, with both cultivars accumulating 85–90% of total leaf iron in the symplast. However, susceptible plants accumulated higher levels of iron in low‐molecular‐mass fractions than tolerant plants. The accumulation of iron in the low‐molecular‐mass fraction probably has a direct influence on iron toxicity, and the adaptive strategy of tolerant plants may rely on their capacity to buffer the iron amounts present in the low mass fraction, a new parameter to be considered when evaluating tolerance to iron excess in field‐cultivated rice plants.     

Comparative physiological responses to stressors in animals.

1. The species-specific experimental response to stressors (SSERTS) analysis has been applied to a number of species under varied short and long term conditions. 2. The measure provides quantitative data relating to the physiological responses of animals when exposed to stressors and results are presented comparing these for different methods of immobilization, euthanasia, etc. at intra- and inter-species level. 3. It is suggested that the SSERTS measure is of greater value for measuring the responses of animals to stressors than is the measurement of the concentration of single blood variables.     

Light-mediated release of phytosiderophores in wheat and barley under iron or zinc deficiency

The effect of varied light intensity (50 – 600 mol m-2 s-1) on the rate of phytosiderophore release was studied under zinc (Zn) deficiency using a bread (Triticum aestivum L. cv. Aroona) and a durum wheat cultivar (Triticum durum Desf. cv. Durati) differing in zinc (Zn) efficiency and under iron (Fe) deficiency using a barley cultivar (Hordeum vulgare L. Europe). Plants were grown under controlled environmental conditions in nutrient solution for 15 days (wheat plants) or 11 days (barley plants). Phytosiderophore release was determined by measuring capacity of root exudates to mobilize copper (Cu) from a Cu-loaded resin.With increasing light intensity visual Zn deficiency symptoms such as whitish-brown lesions on leaf blade developed rapidly and severely in wheat, particularly in the durum cultivar Durati. In wheat plants supplied well with Zn, increases in light intensity from 100 to 600 mol m-2 s-1 did not clearly affect the rate of phytosiderophore release. However, under Zn deficiency increases in light intensity markedly enhanced release of phytosiderophores in Zn-deficient Aroona, but not in Zn-inefficient Durati. When Fe-deficient barley cultivar Europe was grown first at 220 mol m-2 s-1 and then exposed to 600 mol m-2 s-1 for 24 and 48 h, the rate of release of phytosiderophores was enhanced about 4-fold and 7-fold, respectively. Transfer of Fe-deficient plants from 600 to 50 mol m-2 s-1 for 48 h reduced the rate of release of phytosiderophores by a factor of 7. The effect of light on phytosiderophore release was similar regardless of whether the rate of phytosiderophore release was expressed per plant or per unit dry weight of roots.The results demonstrate a particular role of light intensity in phytosiderophore release from roots under both Zn and Fe deficiency. It is suggested that in the studies concerning the role of phytosiderophore release in expression of Zn or Fe efficiency among and within cereals, a special attention should be given to the light conditions.