Mycorrhizal fungi enhance plant nutrient acquisition and modulate nitrogen loss with variable water regimes

Climate change will alter both the amount and pattern of precipitation and soil water availability, which will directly affect plant growth and nutrient acquisition, and potentially, ecosystem functions like nutrient cycling and losses as well. Given their role in facilitating plant nutrient acquisition and water stress resistance, arbuscular mycorrhizal (AM) fungi may modulate the effects of changing water availability on plants and ecosystem functions. The well‐characterized mycorrhizal tomato (Solanum lycopersicum L.) genotype 76R (referred to as MYC+) and the mutant mycorrhiza‐defective tomato genotype rmc were grown in microcosms in a glasshouse experiment manipulating both the pattern and amount of water supply in unsterilized field soil. Following 4 weeks of differing water regimes, we tested how AM fungi affected plant productivity and nutrient acquisition, short‐term interception of a ${}^{15}{\text{NH}}_4^{+}$ pulse, and inorganic nitrogen (N) leaching from microcosms. AM fungi enhanced plant nutrient acquisition with both lower and more variable water availability, for instance increasing plant P uptake more with a pulsed water supply compared to a regular supply and increasing shoot N concentration more when lower water amounts were applied. Although uptake of the short‐term ${}^{15}{\text{NH}}_4^{+}$ pulse was higher in rmc plants, possibly due to higher N demand, AM fungi subtly modulated ${\text{NO}}_3^{?}$ leaching, decreasing losses by 54% at low and high water levels in the regular water regime, with small absolute amounts of ${\text{NO}}_3^{?}$ leached (<1 kg N/ha). Since this study shows that AM fungi will likely be an important moderator of plant and ecosystem responses to adverse effects of more variable precipitation, management strategies that bolster AM fungal communities may in turn create systems that are more resilient to these changes.     

Isolation and Structure of Sclerothionine,a Metabolite of Sclerotinia Fungus

A new sulfur-containing imidazole compound, m.p. 218~223°C (decomp.), ${[\alpha ]}_{\text{D}}^{24}+{7.4}^{°}$ in water), C₁₁H₁₉N₃O₃S was isolated from sclerotia of Sclerotinia libertiana and named sclerothionine. The chemical structure of sclerothionine was identified with 2-hydroxyethyl-ergothioneine which was synthesized from ethylene chlorhydrine and ergothioneine.     

Controlling Electron Transfer between the Two Cofactor Chains of Photosystem I by the Redox State of One of Their Components

Two functional electron transfer (ET) chains, related by a pseudo-C₂ symmetry, are present in the reaction center of photosystem I (PSI). Due to slight differences in the environment around the cofactors of the two branches, there are differences in both the kinetics of ET and the proportion of ET that occurs on the two branches. The strongest evidence that this is indeed the case relied on the observation that the oxidation rates of the reduced phylloquinone (PhQ) cofactor differ by an order of magnitude. Site-directed mutagenesis of residues involved in the respective PhQ-binding sites resulted in a specific alteration of the rates of semiquinone oxidation. Here, we show that the PsaA-F689N mutation results in an ∼100-fold decrease in the observed rate of PhQA− oxidation. This is the largest change of PhQA− oxidation kinetics observed so far for a single-point mutation, resulting in a lifetime that exceeds that of the terminal electron donor, P700+. This situation allows a second photochemical charge separation event to be initiated before PhQA− has decayed, thereby mimicking in PSI a situation that occurs in type II reaction centers. The results indicate that the presence of PhQA− does not impact the overall quantum yield and leads to an almost complete redistribution of the fractional utilization of the two functional ET chains, in favor of the one that does not bear the charged species. The evolutionary implications of these results are also briefly discussed.     

Physicochemical Properties and Amino Acid Composition of Alkaline Proteinase from Aspergillus sojae

Some physicochemical properties and amino acid composition of alkaline proteinase from Aspergillus sojae were found to be as follows: The isoelectric point was at pH 5.1. The molecular weight was 25,500 using the Sheraga-Mandelkern’s formula, based upon the values of the sedimentation coefficient $(s_{20,w}^{°}=\text{?}2.82\text{?}\text{S})$, the intrinsic viscosity ([η] = 0.027 dl/g), and the partial specific volume $({\displaystyle \overline{V}}\text{?}=\text{?}0.726\text{?}\text{ml}/\text{g})$. The enzyme contains 16.8% of nitrogen and is composed of 250 residues of amino acid; Asp₃₁ Glu₁₉, Gly₂₇, Ala₃₂, Val₁₈, Leu₁₄, Ile₁₄, Ser₂₈, Thr₁₈, ${\text{(}{\displaystyle \stackrel{}{{\displaystyle \stackrel{?}{\text{Cys C}}}}}\text{ys})}_1$, Met₂, Pro₆, Phe₇, Tyr₈, Trp₂, His₅, Lys₁₄, Arg₃, (amide-NH₃)₂₀.     

Radiation Chemistry of Foods

In food irradiation, water-soluble food constituents undergo the attack of ${\text{e}}_{\text{aq}}^{?}$ and OH at the neutral region.

Reaction rate constants of some food constituents with ${\text{e}}_{\text{aq}}^{?}$ and OH were measured by competition methods using nitrous oxide and ³H-formate as competitors, respectively. High selectivity was observed among the reactions with ${\text{e}}_{\text{aq}}^{?}$ and the ${\text{e}}_{\text{aq}}^{?}$-reaction rate constants are 10¹⁰ M^?1 sec^?1 (cysteine), 10⁹ M^?1 sec^?1 (methionine, ascorbic acid, and histidine), and much smaller (sugars, and the other types of amino acids). The OH-reaction rate constants range from 10⁹ M^?1 sec^?1 (cysteine, histidine, methionine, aromatic amino acids, and ascorbic acid) to 10⁸ M^?1 sec^?1 (sugars and the other amino acids), indicating that the reactions with OH are less selective. Selective destructions of cysteine and ascorbic acid in food irradiation may be partly ascribed to their selective reactivities with some less reactive species which are produced by reactions of ${\text{e}}_{\text{aq}}^{?}$ or OH with oxygen or the other constituents as well as their higher reactivity with ${\text{e}}_{\text{aq}}^{?}$.