Effects of bulk and nano-ZnO particles on functioning of photosynthetic apparatus in barley (Hordeum vulgare L.).

The functioning of the photosynthetic apparatus in barley (Hordeum vulgare L.) after 7-days of exposure to bulk (b-ZnO) and nanosized ZnO (n-ZnO) (300, 2000, and 10,000 mg/l) has been investigated. An impact on the amount of chlorophylls, photosynthetic efficiency, as well as the zinc accumulation in chloroplasts was demonstrated. Violation of the chloroplast fine structure was revealed. These changes were generally more pronounced with n-ZnO exposure, especially at high concentrations. For instance, the chlorophyll deficiency under 10,000 mg/l b-ZnO treatment was 31% and with exposure to 10,000 mg/l n-ZnO, the chlorophyll deficiency was already 52%. The expression analysis of the photosynthetic genes revealed their different sensitivity to b-ZnO and n-ZnO exposure. The genes encoding subunits of photosystem II (PSII) and, to a slightly lesser extent, photosystem I (PSI) showed the highest suppression of transcriptional levels. The mRNA levels of the subunits of cytochrome-b6f, NADH dehydrogenase, ribulose-1,5-bisphosphate carboxylase and ATP synthase, which, in addition to linear electron flow (LEF), participate in cyclic electron flow (CEF) and autotrophic CO2 fixation, were more stable or increased under b-ZnO and n-ZnO treatments. At the same time, CEF was increased. It was assumed that under the action of b-ZnO and n-ZnO, the processes of LEF are disrupted, and CEF is activated. This allows the plant to prevent photo-oxidation and compensate for the lack of ATP for the CO2 fixation process, thereby ensuring the stability of photosynthetic function in the initial stages of stress factor exposure. The study of photosynthetic structures of crops is important from the point of view of understanding the risks of reducing the production potential and the level of food security due to the growing use of nanoparticles in agriculture.

Comparative analysis of chloroplast genomes of seven perennial Helianthus species.

Sequencing and a comparative analysis of the complete chloroplast genomes of seven perennial Helianthus species were carried out. The chloroplast genomes have a typical quadripartite structure, including large and small single regions and a pair of inverted repeats. Genome sizes were between 151,152 bp and 151,289 bp. The genome of H. grosseserratus was the smallest, while that of H. microcephalus was the largest. The size variation of the chloroplast genomes is substantially due to the change in the length of simple sequence repeats (SSRs) in non-coding regions. An analysis of these SSRs revealed 35 polymorphic loci (average PIC value > 0.5) that can be used to examine ecological and evolutionary processes in wild Helianthus species. Eight divergence hotspots, including five intergenic regions (petN-psbM, clpP intron, rps3-rpl16, ndhD-ccsA, and ndhF-rpl32) and three gene regions (rbcL, ycf1, and ndhF) were also identified in Helianthus chloroplast genomes. The evolutionary selection pressure analysis revealed a strong purifying selection. Only the rbcL gene experienced efficiency of positive selection at the annual/perennial transitions. The inverted repeat (IR)/single copy (SC) boundaries were identical in all of these (Helianthus) species. In general, the comparison of the genomes revealed low levels of sequence variability (Pi = 0.00051). This indicates that the chloroplast genomes of the studied perennial species of Helianthus, in addition to purifying selection, are closely related and have a recent divergence time.

Data on the polymorphic sites in the chloroplast genomes of seven perennial Helianthus species.

Data present the chloroplast genome sequences of seven wild perennial Helianthus species obtained by using the Illumina HiSeq and NextSeq platforms. Datasets not included in the primary publication [1] are a source for further evolutionary studies. In particular, the annotated chloroplast genomes and datasets of single nucleotide polymorphisms (SNP), simple sequence repeats (SSR), insertion and deletion polymorphisms (INDEL) for H. tuberosus, H. salicifolius, H. pauciflorus, H. microcephalis, H. hirsutus, H. strumosus, and H. grosseserratus are presented. The raw reads are available in Figshare (https://doi.org/10.6084/m9.figshare.12600155). The complete chloroplast genome sequences for the seven perennial Helianthus species are available on GenBank NCBI under the accessions MT302562.1 - MT302568.1; the remaining data are provided in this article.