Growth,photosynthesis and H+-ATPase activity in two Jerusalem artichoke varieties under NaCl-induced stress

In order to evaluate differential growth, photosynthesis and H⁺-ATPase activity responses to salt-induced stress, two Jerusalem artichoke (Helianthus tuberosus L.) genotypes (Nanyu No. 1 and Qingyu No. 2) were used in sand-culture experiment with different concentrations of NaCl (0, 30, 60, 90, 120 and 150 mM). After 20 days of growth, the NaCl stress resulted in a decrease of biomass accumulation, relative leaf expansion rate and photosynthetic rate, but an increase of proline content in both genotypes. Compared with Qingyu No. 2, Nanyu No. 1 had lower biomass, photosynthetic rate, gas exchange and transpiration rate, but higher proline content, activities of plasma membrane H⁺-ATPase (PM H⁺-ATPase) and vacuolar membrane H⁺-ATPase (VM H⁺-ATPase). Hence, the NaCl adaptation strategy in Nanyu No. 1 was by lowering photosynthetic rate, stomatal conductance and transpiration rate while maintaining high H⁺-ATPase activities, whereas the adjustment of Qingyu No. 2 was by keeping much higher rate of proline accumulation and concentration of chlorophyll. The differences in salt tolerance showed that different adaptation mechanisms existed between cultivars of Jerusalem artichoke. The findings offered the possibility of selecting salt-tolerant genotypes of Jerusalem artichoke.     

Rhizosphere Properties of Poaceae Genotypes Under P-limiting Conditions

Plant genotypes differ in P efficiency, i.e. their capacity to grow in soil with low P availability. Plant properties such as root and root hair length, release of P mineralising and mobilising compounds by the roots and P requirement for optimal growth are known to influence P efficiency. In order to improve the understanding of the role of rhizosphere properties in plant P uptake, we grew three Poaceae genotypes [two wheat (Triticum aestivum L.) genotypes (the P-efficient Goldmark and the P-inefficient Janz), and the Australian native grass Austrostipa densiflora L.] to maturity in an acidic loamy sand with low P availability. Addition of 120 mg P as FePO₄ kg⁻¹ (P120) improved the growth of all three genotypes. In both P0 and P120, growth and P uptake were smaller in Janz than in Goldmark. During the vegetative phase, growth and P uptake of Austrostipa were smaller than in Goldmark in P0 but greater in P120. These differences can be explained by plant properties such as root growth, specific P uptake, mobilisation of inorganic and organic P by root exudates and P utilisation efficiency. In P120, P availability in the rhizosphere was least in Janz and greatest in Austrostipa. Microbial biomass P in the rhizosphere was least in Janz. Acid phosphatase activity was greatest in the rhizosphere of Austrostipa and least in Janz. Plant growth and P uptake were positively correlated with microbial P, acid phosphatase activity and resin P in the rhizosphere, suggesting that microorganisms contribute to uptake of P by plants in this soil. Microbial community composition in the rhizosphere [analysed by fatty acid methylester (FAME) analysis and denaturing gradient gel electrophoresis (DGGE)] differed among genotypes, changed during plant development and was affected by P addition to the soil. Genotype-specific microbial community composition in the rhizosphere may have contributed to the observed differential capacity of plants to grow at low P availability.     

Nitrogen Utilization Efficiency in Canola Cultivars at Grain Harvest

Canola (Brassica napus L.) cultivars with improved nitrogen utilization efficiency (NUE) at grain harvest are of interest to growers to reduce fertilizer inputs. Our objective was to determine whether cultivar-specific responses in NUE (seed yield per N accumulated in the whole plant) could be related to the differences in dry matter and N partitioning among various plant parts. Four spring canola cultivars were grown in a glasshouse under the conditions of low and high N supply. When compared to high-N treatment, deficient N conditions resulted in a similar decrease in dry weight for all cultivars, averaging 46% for shoot, 47% for root, and 45% for dropped leaves. The reductions in N concentrations at low-N compared to high-N treatment were much smaller and averaged 15% for shoot, 16% for root and 10% for dropped leaves. Although significant variations occurred for dry weight, N concentration and N uptake in various plant sections, all cultivars accumulated a similar amount of N in total plant biomass at harvest. However, significant differences in plant biomass, seed yield and consequently, NUE existed because more N-efficient cultivars Eyre and Charlton produced larger seed yields than less N-efficient cultivars Pinnacle and Rainbow. No consistent variations in N concentration in various plant parts could be established among tested cultivars. Thus, cultivar-specific responses in NUE were mainly attributed to the differences in the root-to-shoot ratio and harvest index. N-efficient Eyre produced seed yield similar to the highest yielding Charlton, though it had the smallest plant dry weight of all cultivars. In contrast, N-inefficient Rainbow had the largest plant biomass, but produced the smallest seed yield because of its lowest harvest index and the highest root-to-shoot ratio. The absence of cultivar×N treatment interactions indicated that cultivars performed similarly for plant biomass, N uptake and seed yield across two contrasting N supplies. Canola cultivars significantly differed in NUE despite a similar amount of absorbed N in plant biomass; more N-efficient cultivars outyielded less N-efficient ones primarily because of cultivar-specific variations in the root-to-shoot ratio and harvest index.     

Genetic control of root exudation

The literature on genetics of root exudation and on genotypic differences in qualitative and quantitative composition of root exudates in crop and native plant species was critically assessed. Differences in exudation have been reported for genotypes that differ in tolerance to nutrient deficiencies, ion toxicities, and pathogen attack. The exudation profile of a limited number of genotypes (frequently only two genotypes with the contrasting response to the environmental stress) have been reported to date. Little is known about the variability in larger samples of the germplasm or about actual genetics behind differential qualitative and quantitative composition of root exudates. Changing the exudation profile of a given genotype may be achieved by manipulating the biosynthetic capacity and by increasing the capacity of the plasma membrane to transport the specific compound out into the rhizosphere. Overexpression of the bacterial citrate synthase gene in the cytoplasm of tobacco plants resulted in exudation of large quantities of citrate into the rhizosphere and partial alleviation of the aluminium (Al) toxicity stress. A similar strategy of transforming plants with citrate synthase gene is being tried as a way of improving plant capacity to extract phosphorus (P) from soils with notoriously low P availability.More research into the genetic basis of qualitative and quantitative differences in root exudation is warranted. Understanding the genetic control of root exudation, followed by manipulation of qualitative and quantitative composition of root exudates, will result in better adaptation of plants to environmental conditions and a greater yield of crops.     

The effect of manganese supply on exudation of carboxylates by roots of lucerne (Medicago sativa)

Some low-molecular-weight carboxylates commonly found in plant root exudates have the potential to increase the availability of Mn in the rhizosphere. Release of various compounds into the rhizosphere by plant roots may also be a mechanism by which certain species and genotypes are able to tolerate conditions of low Mn availability better than others. Lucerne (Medicago sativa L.) plants of Salado, a genotype tolerant to Mn deficiency, and Sirosal, an intolerant genotype, were grown in solution culture with 0, 5 or 500 nM Mn (Mn-0, Mn-5 and Mn-500). Exudates of whole root systems were collected at 14, 24 and 36 d and analysed by HPLC. Oxalate, tartarate, L-malate, lactate, malonate, maleate, citrate and succinate were detected and quantified in exudates under all Mn treatments. Malonate, citrate and succinate accounted for the majority of carboxylates in the exudates. Exudation increased with plant age, but amounts of individual carboxylates remained constant in proportion to the total amount exuded. A significant increase in exudation of all carboxylates other than malonate and maleate resulted from omission of Mn from nutrient solutions. Salado exuded more oxalate, tartarate, L-malate, lactate, citrate and succinate than Sirosal at Mn-0, and more citrate and succinate than Sirosal at Mn-5. Genotypic differences in carboxylate exudation under Mn-0 were associated with production of roots with diameter <100 μm. Plant Mn concentrations and growth rates suggested carboxylate exudation differences were not the sole factor responsible for differential tolerance to Mn deficiency in the lucerne genotypes.     

Suitability of hydroxyapatite and iron phosphate as P sources for Lupinus albus grown in nutrient solution

In the framework of efforts to introduce Tuber melanosporum as a cultivated crop to Israel, spores of the truffle, obtained from fruit-bodies procured in Italy and France, were used to inoculate oak seedlings and hazel suckers. Typical T. melanosporum mycorrhizas were observed 3 months after inoculation on roots of both plant species. One- to two-year-old mycorrhizal seedlings were outplanted at a number of experimental sites and irrigated regularly. Two sites characterized by alkaline soil but differing in soil composition and climatic conditions were chosen for the present study. DNA of ascocarps used for inoculation, DNA of re-isolated cultures and fungal DNA taken from tree mycorrhizas 4 years after outplanting were compared with T. melanosporum reference cultures by molecular methods. All T. melanosporum profiles proved to be identical except for one belonging to a reference culture, which exhibited an unusual HinfI ITS-RFLP pattern. A single base substitution, responsible for the different HinfI restriction site, distinguished the ITS region of this culture from a published T. melanosporum ITS sequence. ITS restriction polymorphism analyses determined that roots of all potted plants tested and many 4-year-old trees from the two experimental plots (irrespective of soil and climatic differences) were colonized by T. melanosporum.     

Uptake of zinc from chelate-buffered nutrient solutions by wheat genotypes differing in zinc efficiency

Zinc-efficient Triticum aestivum (cv. Warigal) and Zn-inefficientTriticum turgidum conv. durum (cv. Durati) were grown in chelate-buffered,complete nutrient solutions providing either deficient or sufficientZn supply. When transferred to fresh chelatebuffered nutrientsolutions containing a wide range of Zn supplies (0–1.28µmol m^–3 Zn²⁺ activity) for 24–48 h, bothgenotypes increased net Zn uptake linearly with an increasein solution Zn²⁺ activities. Zincefficient Warigal accumulatedZn at a greater rate than Zn-inefficient Durati. The greaterrate of net Zn uptake was observed by plants of both genotypeswhen pretreated at deficient Zn supply. Net loss of Zn to thesolution was higher in plants pretreated with sufficient Znand was inversely related to Zn²⁺ activity in the external solution.When continuously supplied with 40 nmol m^–3 Zn²⁺, netZn uptake by Zn-efficient Warigal was significantly greaterthan that of Zn-inefficient Durati, but the difference diminishedwith plant age. Shoot concentrations of Fe, Mn and Cu were higherwhen plants were grown at deficient than at sufficient Zn supply.The Zn-efficient genotype transported less Zn and Fe to shootsand had higher Fe concentrations in roots than the Zn-inefficientgenotype, supporting the hypothesis that Zn efficiency may beconnected with inefficient transport of Fe from roots to shootsand thus initiation of the Fe-deficiency response resultingin increased release of Zn- and Fe-binding phytosiderophores.It is concluded that differential Zn efficiency of wheat genotypesis at least partly due to a greater ability of efficient genotypesto accumulate Zn. Key words: Chelate-buffering, genotypes, micronutrients, Triticum spp., uptake, zinc efficiency     

Determination of cation exchange capacity of ryegrass roots by summing exchangeable cations

Cations were desorbed from root exchange sites of ryegrass (Lolium multiflorum Lam. cvs. Gulf, Marshall, Urbana, and Wilo) using BaCl₂, BaCl₂-triethanolamine, NH₄OAc, and KCl. Results were analysed using multivariate analysis of variance. Ba²⁺-containing desorbents displaced more Ca²⁺ while monovalent desorbents displaced more exchangeable monovalent cations. The sum of adsorbed cations was significantly correlated with root exchange capacity (CEC) as determined by the H⁺ titration procedure, although slightly larger values were obtained with all desorbents. Lower CEC values were obtained for ryegrass cultivars less sensitive to Al.     

The early effects of valproic acid in low doses in liver metabolism

The effect of low doses of valproic acid (VPA), 0.6 mM in arterial blood, in liver metabolism was studied. Twenty four hour fasted rats were infused into the jugular vein with VPA at a dose of 4 mg/kg/min during 50 min. The right carotid artery was also catheterized in order to draw arterial blood samples for determining VPA concentrations and acid-base parameters. After VPA infusion, a tissue sample of liver was obtained and freeze-clamped. VPA did not change the arterial blood acid-base parameters. The liver tissue concentration of pyruvate and alanine increased in VPA group while lactate concentrations did not change. Concentration of glutamine, glutamate, malate, citrate and aspartate in the liver fell significantly. These results suggest that VPA in low doses may modify the hepatic metabolism of the rat in vivo.