The high-affinity nitrate transporter of green plants is composed of two polypeptides, NRT2.1 and NAR2.1, while in fungi it appears that nitrate influx is mediated by NRT2 alone. Another difference between plants and fungi is that the central (cytoplasmic) loop of the 12 membrane spanning regions of NRT is quite large in fungi, consisting of 91 amino acid residues, compared with the relatively short (21 amino acid residues) plant NRT2.1. Here we examine potential amino acid residues involved in the plant NRT2.1:NAR2.1 association by mutation of conserved amino acids in Arabidopsis thaliana AtNRT2.1. Only the replacement of leucine 85 by glutamine disrupted the association between AtNRT2.1 and AtNAR2.1, as examined using the yeast two-hybrid system. Further, to investigate the nitrate-transporting function of AtNRT2.1 in a context free of other members of the NRT2 family, we expressed AtNRT2.1 in Aspergillus nidulans. In the fungal context the plant NRT alone was capable of restoring nitrate transport to a nitrate transport defective mutant, but only when the AtNRT2.1 central loop was replaced by its fungal counterpart.
Long-term application of fertilizer and manure may change soil fertility, crop yield, N uptake efficiency, and nitrate and chloride leaching to underground water. The objectives were to quantify those aspects in a long-term (35-year) permanent plots field experiment in a typical arid zone (~250 mm rain) soil, and suggest fertilization and manuring regimes leading to reduced aquifer pollution by nitrate and chloride without compromising crop yield and soil sustainability. Results proved that mineral-N application exceeding plant demand leached, subject to recommended irrigation plus rainfall, below 4 m, thus becoming a potential underground water pollution hazard. Leaching was significantly reduced by partially replacing fertilizer-N by manure-N, with negligible adverse effect on crop yield. Under ample manure (M2) and mineral N (N3) supply (treatment M2N3), the estimated cumulative (35-year) NO3– leaching was 557 g N/m2 and the corresponding Cl– leaching 4097 g Cl–/m2. In treatment M2N0 the corresponding leaching was 0 and 4135 g/m2. The cumulative solute leaching depth was estimated to be 66 m in treatment M2N3 (that gave maximum fruit and dry matter yield) and 125 m in treatment M0N0 (minimum fruit and dry matter yield). Soil cultivation and cropping for 35 years had negligible effect on the plants’ response to fertilizer level and on the soil mineralogical composition.
The irrigation and fertilization regime of different varieties of Grevillea in Israel are based on existing knowledge for growing various varieties of the Proteaceae family for production of cut flowering branches. However, growers face problems in cultivating Grevillea “Spiderman,” such as leaf chlorosis, prolonged growth until flowering, and reduced quality of cut flowering branches. The present study aimed to examine whether these problems stem from deficiency or excess of Fe, Mn, Zn, P, and Mg, focusing on the effect of these nutrients on growth, flowering, and appearance of visual leaf symptoms and on yield, quality, and vase life longevity of cut flowering branches. The nutrient treatments significantly affected plant development and flowering. Increasing the Fe concentration from 1 to 2 or 3 mg l–1 resulted in improved leaf color, from slightly yellow to dark green. The combination of 2 mg l–1 Fe + 1.8 mg l–1 Mn resulted in early flowering, highest yield, and development of long lateral branches. Low levels of P caused in the first year of treatment leaf chlorosis, which was intensified during the third year, resulting in severe yellowing of the flowering branches. Leaf necrosis and tip burn appeared in treatments with high concentrations of Zn, Mn, and Mg. Deficiency of Fe and Mn and high concentration of P and Mg led to the development of a large number of branches without flowers. The optimal fertilization treatment that yielded the highest quality of flowering branches after harvest was 2 mg l–1 Fe. Branches of this treatment had green foliage at harvest and the longest vase life (10 days) following the recommended postharvest treatment and air transport simulation. Based on the findings of the present research, it can be concluded that the problems in the cultivation of G. “Spiderman,” such as leaf chlorosis, delayed flowering, and reduced quality of flowering branches, result from improper fertilization.
Treated wastewater (TWW) is a major source of water for agriculture in Israel; however, recent reports indicate a marked yield loss in TWW-irrigated avocado and citrus orchards planted in clayey soils. The association of the yield loss with clayey soils rather than sandy soils suggests that it is associated with conditions in the root zone, and specifically poor aeration. A three-year study (2012–2015) was conducted in an avocado orchard planted in clayey soil, comparing the oxygen and redox conditions in the root zone of TWW-irrigated plots with fresh water (FW)-irrigated plots, together with the physiological status of the trees. Soil parameters included: continuous in-situ measurement of soil-water tension (SWT), soil oxygen, and soil redox potential, and periodic measurements of soil solution composition. Physiological parameters included: mineral composition of plant tissue from the leaves, trunk xylem and roots, root growth, yield, fruit setting, plant volume, and yield. TWW-irrigated plots were found to endure longer periods of low SWT indicating higher water content, accompanied by lower oxygen levels and more reduced conditions in comparison to FW-irrigated plots. The differences in these soil parameters between treatments were greater during the irrigation season than during the rainy period. The more reduced conditions in the TWW plots did not lead to significant differences in Fe or Mn concentrations in the soil solution or in plant leaves. TWW soil solution had significantly higher Na levels compared with FW. This did not affect the leaf Na content, but was expressed in substantially higher Na content in the root and trunk xylem, with up to seven times more trunk xylem Na in TWW-irrigated plants compared with FW-irrigated plants. Root growth was significantly hindered in TWW-irrigated plots compared with FW-irrigated plots. A negative correlation was found between root growth and the duration of hypoxic conditions, and similarly between root growth and the Na levels in the roots. TWW-irrigated plants had greater fruitlet numbers at the initial fruit-setting stage, but had a smaller number of fruit and a lower yield at harvest. The yield (kg/tree) negatively correlated with the duration of hypoxic conditions in the root zone but not with the Na levels in the roots or xylem. Our findings point towards a substantial role of oxygen deprivation as a major factor leading to the damage to TWW-irrigated orchards in clayey soils. Based on the assimilation of data, we suggest that a downward cascade is instigated in the TWW-irrigated orchards by increased input of Na into the soil, leading to degradation of soil hydraulic properties and reduced aeration. Impaired physiological functioning of the roots due to limited oxygen supply results in less roots growth, lower water uptake and impaired selectivity against Na uptake, thus imposing a negative feedback to increase soil water content, reduce aeration and root-zone oxygen availability for the roots, and further impair plant resistance to the high Na levels.
Rhizopus arrhizus was grown in an iron-free nutrient solution growth medium. Mass production of the siderophores was achieved in a short time by continuous growth of the fungi: after the secretion of the siderophores into the growth medium the spent medium was collected and replaced by a fresh medium while the fungus mat was kept in the flask. The medium exchange was repeated several times and the optimal time for the collection of the siderophore was found to be when the fungus was fully developed, usually about 3 days after the exchange. It was found that it is feasible to grow the fungi continuously for five growth periods, after which the fungus culture becomes too old and collapses.
The siderophore was isolated and cleaned from the spent medium using a series of columns on an FPLC at room temperature. Additional tests were used to verify the existence of the siderophore in the solution. The concentrations of rhizoferrin in the various fractions was measured using an exchange reaction between the siderophore and that of an added chelate solution (CAS) while employing a series of dilutions of the CAS.
For a precise analytical determination of the siderophore rhizoferrin, Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTICR-MS) was used to validated that the siderophore is indeed rhizoferrin which has been structurally identified earlier.
Nitrate fertilizers are the most commonly used nitrogen sources for growing vegetables. The use of nitrate fertilizers in vegetable production may result in its accumulation in the plants if uptake exceeds assimilation. High nitrate concentrations in leafy vegetables represent a possible threat to human health. Leafy vegetables are the highest contributor to total food nitrate intake as a result of their high specific concentration and the large amount consumed. Consequently, European Union regulations were established for nitrate concentrations in leafy vegetables such as lettuce, spinach and rucola (Diplotaxis tenuifolia). Therefore, the need for a reliable, easy, fast and universal method to meet these demands is essential. We reassessed nitrate determination by comparing fresh and dry leaf material extracts of rucola. Our results indicate that the leaf nitrate concentration with both measurement methods is similar. Consequently, the use of the dry leaf extracts method is feasible and worth recommending to the European Union as an official method for determining nitrate concentrations in leafy vegetables.
Plant branching shoot number is strongly influenced by nitrogen (N) supply status. However, detailed descriptions of this phenomenon and the regulatory mechanism are lacking. In this study, we show that, in rice, in comparison to sufficient supply of ammonium sulfate or ammonium nitrate (2.5 or 5 mM N), low N (0.2 mM) or nitrate as the only N source limited shoot branching, i.e., tillering number. We observed that N deficiency did not affect the initiation, but suppressed the elongation of the tiller buds. We carried out in-situ hybridization of the tiller buds and showed that the expression of histone H4, a marker of S-phase in the cell cycle, could not be detected in the tiller buds that had stopped growing, indicating that cell division was suppressed in the tissues. Consistent with this finding, we further detected that the expression of other cell cycle marker genes was decreased in the N-deficient tiller buds in comparison to N-sufficient tiller buds. In addition, expression of the genes involved in the strigolactone pathway was induced in the tiller buds by N deficiency, in accordance with other reports. These results shed light on the importance of proper N application to control tiller bud outgrowth in grain production.
Desalinated water has become a legitimate alternative water resource for the irrigation of intensive crops in semiarid regions. The concentrations of calcium (Ca) and magnesium (Mg) in water (CCa and CMg, respectively) supplied from desalinated plants are much lower than the values typically found in irrigation water resources in semiarid regions. blossom-end rot (BER), a physiological disorder at the blossom-end part of the fruit resulting in tissue disintegration and dehydration, is considered a Ca-related disorder and therefore the optimization of CCa has to consider not only total fruit production but also the occurrence of BER. There is a lack of information regarding the optimal CCa and CMg and Ca/Mg ratio in low-salinity water under Mediterranean conditions for high-quality yield of tomato fruits.
The main objective of the research was to optimize CCa and CMg for the production of high tomato fruit yield with minimal occurrence of BER. A secondary objective was to determine critical levels of Ca, Mg and Ca/Mg ratio in leaves in relation to yield and the occurrence of BER.
Tomato plants were grown in an inert media and fed with a wide range of CCa and CMg. Fruit yield was shown to decrease significantly when CCa was at or below 0.40 mmol l–1. In moderate CMg (1.4 mmol l–1) treatment, BER was negatively correlated to Ca level up to and including 1.4 mmol l–1 and was not manifested above that level under the prevailing conditions. Elevating CMg above 0.25 mmol l–1 enhanced BER occurrence. Concentrations of Ca and Mg in tomato organs increased with the respective mineral concentration in irrigation solution, whereas each element was reduced in organs as a function of the increased solution concentration of the other. The Ca concentration in diagnostic leaves (the diagnostic leaf is the fully developed youngest leaf) for optimal fruit yield with minimum BER was found to be 1.6%. The optimum CCa for high fruit yield with minimal BER occurrence was found to be in the range of 1.5–2.5 mmol l–1 combined with CMg at 0.25 mmol l–1.
High-throughput phenotyping is a rapidly evolving field, with new technologies being developed that need to be tested under different experimental conditions. In this study, the PlantEye, a high-resolution three-dimensional (3D) laser scanner was used to phenotype wheat plants grown under control and salt stress in controlled environment conditions. The PlantEye scans plants from overhead, creating a data cloud from which the system computes traits such as 3D leaf area, plant height and leaf number. Moderately high correlations were observed between automatically calculated trait; 3D leaf area, and the manually measured traits leaf area, fresh biomass and dry biomass, although correlations were lower than those reported in previous studies in different crop species. As expected, salt stress caused significant reduction in plant growth, particularly leaf area and biomass production, which resulted in significantly reduced grain number and yield. The results here suggest that PlantEye was effective in phenotyping wheat, although improvements in the system setup, data processing and customer support would make this phenotyping tool suitable to be widely adopted for a range of plant species under diverse environmental conditions.