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ABSTRACT

Spinescence (including spines, thorns, and prickles) plays an important role in defense from herbivores. To examine whether spinescence evolved at random or differently in various life forms, plant organs, and aquatic taxa at the level of families, we analyzed the characteristics of wild spinescent aquatic plant species in the Yangtze Delta, East China. There were 92 such species, belonging to 33 genera and 21 families out of 203 wild aquatic vascular macrophyte species. Reproductive structures (including flowers, seeds, fruits and appendages) were well defended in the majority of aquatic plants compared with vegetative organs, especially for emerged macrophytes, probably resulting from the selective pressure from herbivores. Overall, most of the aquatic plants (67 species, 62.0% of the total number of species) had spiny reproductive structures while the others (41 species, 38.0% of the total number of species) had spiny vegetative organs, mostly in leaves, and only a few had thorny or prickly stems. In terms of spinescent aquatic species, there were significant differences among various life forms. Emerged macrophytes had 63 species, accounting for 58.3% of the whole; furthermore, the majority of such species (i.e. 42) were spinescent in reproductive organs. In contrast, the number of spiny floating and submerged plant species was eight and 37, respectively. It is noted that some families had more spiny species than others, especially the Cyperaceae and Najadaceae, which mainly defended their reproductive organs. Therefore, like terrestrial flora, aquatic plants also evolved spinescence as a defense against herbivores.

In: Israel Journal of Plant Sciences

ABSTRACT

Being sessile organisms, plants are continuously challenged by phytopathogenic fungi, contributing the largest share in loss due to plant disease. Plants naturally possess a well-developed and programmed protein-based defense system, capable of producing antimicrobial cationic peptides to ward off pathogen attack. Numerous genes encoding antifungal proteins have been isolated, cloned, sequenced and transgenically expressed against multiple phytopathogenic fungi successfully. Genetic engineering technology has been widely utilized to produce transgenic plants with enhanced resistance against pathogens. Pathogenesis-related proteins (PR-proteins) is a group of the most important inducible defense-related antifungal proteins, including defensins, thionins, osomtin-like proteins, thaumatin-like proteins, chitinases, glucanases, oxalate oxidase or oxalate oxidase-like proteins and lipid transfer proteins. Transgenic plants have been developed by imparting the artificial expression of genes encoding antifungal PR-proteins. The expression of transgenes belonging to a single group of PR-proteins or synergistic action of transgenes from different groups has greatly uplifted the level of defense response in plants against fungi. Transgenic expression of antifungal PR-proteins has led to remarkably enhanced resistance in transgenic plants. In this review, we have summarized the role of PR-proteins in plant defense against fungi and 15 years of success achieved so far to generate a variety of transgenic plants resistant against fungi through overexpression of transgenes from different groups of PR-proteins.

In: Israel Journal of Plant Sciences
Collecting, Recording and Preserving the Natural World from the Fifteenth to the Twenty-First Century
Interposed between the natural world in all its diversity and the edited form in which we encounter it in literature, imagery and the museum, lie the multiple practices of the naturalists in selecting, recording and preserving the specimens from which our world view is to be reconstituted. The factors that weigh at every stage are here dissected, analysed and set within a historical narrative that spans more than five centuries. During that era, every aspect evolved and changed, as engagement with nature moved from a speculative pursuit heavily influenced by classical scholarship to a systematic science, drawing on advanced theory and technology. Far from being neutrally objective, the process of representing nature is shown as fraught with constraint and compromise.

With a Foreword by Sir David Attenborough

Contributors are: Marie Addyman, Peter Barnard, Paul D. Brinkman, Ian Convery, Peter Davis, Felix Driver, Florike Egmond, Annemarie Jordan Gschwend, Geoff Hancock, Stephen Harris, Hanna Hodacs, Stuart Houston, Dominik Huenniger, Rob Huxley, Charlie Jarvis, Malgosia Nowak-Kemp, Shepard Krech III, Mark Lawley, Arthur Lucas, Marco Masseti, Geoff Moore, Pat Morris, Charles Nelson, Robert Peck, Helen Scales, Han F. Vermeulen, and Glyn Williams.

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.

In: Israel Journal of Plant Sciences

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.

In: Israel Journal of Plant Sciences

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.

In: Israel Journal of Plant Sciences
In: Israel Journal of Plant Sciences

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.

In: Israel Journal of Plant Sciences

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.

In: Israel Journal of Plant Sciences

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.

In: Israel Journal of Plant Sciences