A response of the imbibed dormant red rice caryopsis to biotic challenges involves extracellular pH increase to elicit superoxide production

Seeds often survive in the soil in a dormant state, but their persistence is endangered by micro-organisms that could feed on them. Seed–microbe interactions in the soil are, however, poorly understood. We used dormant caryopses of red rice to study the defence response induced by pronase, a mixture of proteases secreted by Streptomyces griseus, a non-pathogenic bacterium. Pronase was shown to activate the plant immune reaction, indicating that its activity was recognized as a potential microbial attack. The defence reaction included extracellular alkalinization and superoxide production, and the former was necessary to activate the latter, since buffering at pH 6 inhibited the oxidative burst. Alkalinization was sufficient to trigger the oxidative burst, as superoxide production increased when caryopses were incubated in buffered solutions of increasing pH without pronase. Release of proanthocyanidins was observed, with or without pronase. These diverse mechanisms are hypothesized to cooperate in reinforcing seed protection. Finally, time profiles of superoxide production by dormant and non-dormant red rice caryopses during imbibition did not support a relationship between extracellular superoxide and dormancy breaking or germination. Thus, the role of this reactive oxygen species in red rice imbibed caryopses appears to be essentially aimed at defence against attacks by challenging micro-organisms.

Physiological factors determine the accumulation of D-glycero-D-ido-octulose (D-g-D-i-oct) in the desiccation tolerant resurrection plant Craterostigma plantagineum

The relationship between the accumulation of D-glycero-D-ido-octulose (D-g-D-i-oct) and sucrose and desiccation tolerance was analysed in leaves of Craterostigma plantagineum Hochst. in various conditions. The D-g-D-i-oct level is strictly controlled in C. plantagienum. Light is an important factor enhancing D-g-D-i-oct synthesis when exogenous sucrose is supplied. Desiccation tolerance is lost during natural senescence and during sugar starvation that leads to senescence. The differences in expression patterns of senescence-related genes and the carbohydrate status between vigorous and senescent plants indicate that desiccation tolerance and accumulation of octulose in C. plantagineum is dependent on the developmental stage. Sucrose synthesis is affected more by dehydration than by senescence. D-g-D-i-oct has superior hydroxyl scavenging ability to other common sugars accumulating in C. plantagineum. In the presence of reactive oxygen species (ROS) D-g-D-i-oct levels decreased, probably as a defence reaction.

Effects of water soluble oncostatic fraction from Rheum officinale Baill. rhizomes on Allium cepa root meristem. III. Morphological changes in cytoplasm

Spiral concentric and linear configurations of membraneous structures were observed in the cytoplasm of fixed meristematic cells from the root apex of <i>Allium cepa</i> under the light microscope. They appeared after incubation in sublethal and lethal conditions in <i>Rheum ofiicinale</i> rhizome extracts. During postincubation these structures disappeared. They were interpreted as ER membranes. On the basis of literature data the physiological significance of these structures is discussed. It would seem that they are an indication of enhanced metabolic activity evoked either exogenously by various injuries as a form of defence reaction of the protoplast or endogenously during cytodifferentiation. Prolonged treatment in ,noxious conditions causes the ER membranes to transform into inactive myelin structures

Seasonal changes of pigments concentration in the leaves of Vaccinium myrtillus and Vaccinium vitis-idaea and the influence of industrial emissions

The current-year leaves of both<i> Vaccinium</i> species show a similar chlorophyll o level iii summer, ca. 3.0 mg/g d.w., however, they differ in the earliest period of possible analysis. The <i>Vaccinium myrtillus</i> leaves showed at that time a level of ca. 6 mg/g d.w., decreasing by one half in mid June, i.e. in the period in which the fastest increase in leaf dry matter was noted. Autumn depression reaches about 20°/o. The pigment level in biennial leaves of <i>Vaccinium vitis-idaea</i> is rather constant and typical of the current year ones, in the triennial leaves it is lower by ca. 20%. Zinc-plant emissions influence differently the two species, both showing some defence reaction. Chlorophyll b level, in summer in the range of 1.6-1.9 mg/g d.w., shows seasonal changes rather similar to those of chlorophyll a.

Effect of water activity and temperature on growth of Aspergillus carbonarius and Aspergillus tubingensis and their interactions on ochratoxin A production

Aspergillus section Nigri are described as the main source of ochratoxin A (OTA) contamination in grapes and wine worldwide. The grape-growing area in Argentina has a wide latitudinal extension with ecological variations that allow the classification of well-demarcated regions. The aims of this study were: to determine the effect of eco-physiological parameters on growth of Aspergillus tubingensis and Aspergillus carbonarius and to evaluate the interaction between these species on OTA production in synthetic grape juice medium under different water activity (aw) and temperature conditions. The results showed that optimal growth conditions for A. tubingensis and A. carbonarius were 0.980 aw and 28 °C, however A. tubingensis grew faster than A. carbonarius at all temperatures and aw tested. OTA production by A. carbonarius was favoured at 20 °C and 0.950-0.965 aw, during 14 days of incubation. The effect of A. tubingensis on OTA production by A. carbonarius was mainly dependent on temperature. At 35 °C, A. tubingensis reduced the OTA production while this effect was not observed at 20 °C. More OTA could be produced as a defence reaction against fungal competitors to maintain niche colonisation, but in this study no effects by a related species were observed.

Requirements for a successful defence reaction by the CRISPR–Cas subtype I-B system

Uptake of foreign mobile genetic elements is often detrimental and can result in cell death. For protection against invasion, prokaryotes have developed several defence mechanisms, which take effect at all stages of infection; an example is the recently discovered CRISPR (clustered regularly interspaced short palindromic repeats)–Cas (CRISPR-associated) immune system. This defence system directly degrades invading genetic material and is present in almost all archaea and many bacteria. Current data indicate a large variety of mechanistic molecular approaches. Although almost all archaea carry this defence weapon, only a few archaeal systems have been fully characterized. In the present paper, we summarize the prerequisites for the detection and degradation of invaders in the halophilic archaeon Haloferax volcanii. H. volcanii encodes a subtype I-B CRISPR–Cas system and the defence can be triggered by a plasmid-based invader. Six different target-interference motifs are recognized by the Haloferax defence and a 9-nt non-contiguous seed sequence is essential. The repeat sequence has the potential to fold into a minimal stem–loop structure, which is conserved in haloarchaea and might be recognized by the Cas6 endoribonuclease during the processing of CRISPR loci into mature crRNA (CRISPR RNA). Individual crRNA species were present in very different concentrations according to an RNA-Seq analysis and many were unable to trigger a successful defence reaction. Recognition of the plasmid invader does not depend on its copy number, but instead results indicate a dependency on the type of origin present on the plasmid.