Physiological responses to lead and PEG-simulated drought stress in metallicolous and non-metallicolous Matthiola (Brassicaceae) species from Iran

Aims Plants growing on quarry tailings at the Irankouh Pb/Zn mine encounter both drought stress and high levels of Pb. To better understand role of drought and Pb in plant adaptation to Pb/Zn quarry tailings, we compared effects of drought stress (simulated by polyethylene glycol - PEG) and Pb, individually and in concert, to determine how these stressors affected two plant species: the metallicolous species Matthiola flavida and the non-metallicolous M. incana. Methods Plants were exposed to Pb (Pb(NO3)2) and three levels of PEG (0, -0.5, and − 0.75 MPa) in a complete factorial design. Results Lead had non-significant effects on growth and oxidative stress but enhanced levels of osmoprotectants and phenol compounds in the metallicolous M. flavida, whereas in the non-metallicolous M. incana Pb had non-significant or toxic effects on the same variables (except for the osmoprotectants proline and glycine betaine, and anthocyanins). In contrast to M. incana, the metallicolous species was hypertolerant of Pb, showing strongly reduced root-to-shoot translocation and enhanced Pb accumulation in the root, especially when under drought stress. Conclusion We conclude that enhanced Pb accumulation in the root and reduced translocation to the shoot, particularly when under high PEG exposure in the metallicolous species, reduced toxic effects of Pb in the shoot. This was aided by the accumulation of reducing sugars and phenolic compounds as well as greater catalase activity.

CO2 Responses of Winter Wheat, Barley and Oat Cultivars under Optimum and Limited Irrigation

Field crop production must adapt to the challenges generated by the negative consequences of climate change. Yield loss caused by abiotic stresses could be counterbalanced by increasing atmospheric CO2 concentration, but C3 plant species and varieties have significantly different reactions to CO2. To examine the responses of wheat, barley and oat varieties to CO2 enrichment in combination with simulated drought, a model experiment was conducted under controlled environmental conditions. The plants were grown in climate-controlled greenhouse chambers under ambient and enriched (700 ppm and 1000 ppm) CO2 concentrations. Water shortage was induced by discontinuing the irrigation at BBCH stages 21 and 55. Positive CO2 responses were determined in barley, but the CO2-sink ability was low in oats. Reactions of winter wheat to enriched CO2 concentration varied greatly in terms of the yield parameters (spike number and grain yield). The water uptake of all wheat cultivars decreased significantly; however at the same time, water-use efficiency improved under 1000 ppm CO2. Mv Ikva was not susceptible to CO2 fertilization, while no consequent CO2 reactions were observed for Mv Nádor and Mv Nemere. Positive CO2 responses were determined in Mv Kolompos.

The influence of growing medium composition on pine and birch seedling response during the period of simulated spring drought

Climate change increases the earliness and effect of spring dry spells. The efforts to reduce their negative effects on tree regeneration include improvement in physical properties of soil aimed at an increase in water retention and availability. Clinoptilolite from the group of zeolites belongs among such water-absorbent natural materials. The article aims to assess the effect of clinoptilolite admixture in a growing medium, along with different fertilizer concentration, on the growth of pine and birch seedlings and their development during simulated drought. A common (reference) growing medium was tested along with 4 treatments of the growing medium with clinoptilolite. The birch responded to the fertilizer concentration more intensively than to the clinoptilolite admixture and was more vulnerable to drought damage due to a closer dependence of physiological responses on a decrease in the growing medium moisture. The onset of pine withering was slowest in the reference growing medium. A positive effect of clinoptilolite addition on the growth of pine seedlings was confirmed but its unambiguously positive effect on overcoming of spring dry spells was not demonstrated. Clinoptilolite addition with higher fertilizer rate was found as fully unsuitable.

Extensive Variation in Drought-Induced Gene Expression Changes Between Loblolly Pine Genotypes

Drought response is coordinated through expression changes in a large suite of genes. Interspecific variation in this response is common and associated with drought-tolerant and -sensitive genotypes. The extent to which different genetic networks orchestrate the adjustments to water deficit in tolerant and sensitive genotypes has not been fully elucidated, particularly in non-model or woody plants. Differential expression analysis via RNA-seq was evaluated in root tissue exposed to simulated drought conditions in two loblolly pine (Pinus taeda L.) clones with contrasting tolerance to drought. Loblolly pine is the prevalent conifer in southeastern U.S. and a major commercial forestry species worldwide. Significant changes in gene expression levels were found in more than 4,000 transcripts [drought-related transcripts (DRTs)]. Genotype by environment (GxE) interactions were prevalent, suggesting that different cohorts of genes are influenced by drought conditions in the tolerant vs. sensitive genotypes. Functional annotation categories and metabolic pathways associated with DRTs showed higher levels of overlap between clones, with the notable exception of GO categories in upregulated DRTs. Conversely, both differentially expressed transcription factors (TFs) and TF families were largely different between clones. Our results indicate that the response of a drought-tolerant loblolly pine genotype vs. a sensitive genotype to water limitation is remarkably different on a gene-by-gene level, although it involves similar genetic networks. Upregulated transcripts under drought conditions represent the most diverging component between genotypes, which might depend on the activation and repression of substantially different groups of TFs.