Absorption and mobility of foliar-applied boron in soybean as affected by plant boron status and application as a polyol complex

In the present study (i) the impact of plant Boron (B) status on foliar B absorption and (ii) the effect of B complexation with polyols (sorbitol or mannitol) on B absorption and translocation was investigated. Soybean (Glycine max (L.) Meer.) plants grown in nutrient solution containing 0 μM, 10 μM, 30 μM or 100 μM 11B labelled boric acid (BA) were treated with 50 mM 10B labelled BA applied to the basal parts of two leaflets of one leaf, either pure or in combination with 500 mM sorbitol or mannitol. After one week, 10B concentrations in different plant parts were determined. In B deficient leaves (0 μM 11B), 10B absorption was significantly lower than in all other treatments (9.7% of the applied dose vs. 26%–32%). The application of BA in combination with polyols increased absorption by 18–25% as compared to pure BA. The absolute amount of applied 10B moving out of the application zone was lowest in plants with 0 μM 11B supply (1.1% of the applied dose) and highest in those grown in 100 μM 11B (2.8%). The presence of sorbitol significantly decreased the share of mobile 10B in relation to the amount absorbed. The results suggest that 11B deficiency reduces the permeability of the leaf surface for BA. The addition of polyols may increase 10B absorption, but did not improve 10B distribution within the plant, which was even hindered when applied a sorbitol complex

Boron Stress Responsive MicroRNAs and Their Targets in Barley

Boron stress is an environmental factor affecting plant development and production. Recently, microRNAs (miRNAs) have been found to be involved in several plant processes such as growth regulation and stress responses. In this study, miRNAs associated with boron stress were identified and characterized in barley. miRNA profiles were also comparatively analyzed between root and leave samples. A total of 31 known and 3 new miRNAs were identified in barley; 25 of them were found to respond to boron treatment. Several miRNAs were expressed in a tissue specific manner; for example, miR156d, miR171a, miR397, and miR444a were only detected in leaves. Additionally, a total of 934 barley transcripts were found to be specifically targeted and degraded by miRNAs. In silico analysis of miRNA target genes demonstrated that many miRNA targets are conserved transcription factors such as Squamosa promoter-binding protein, Auxin response factor (ARF), and the MYB transcription factor family. A majority of these targets were responsible for plant growth and response to environmental changes. We also propose that some of the miRNAs in barley such as miRNA408 might play critical roles against boron exposure. In conclusion, barley may use several pathways and cellular processes targeted by miRNAs to cope with boron stress

Mitigation effects of mycorrhiza on boron toxicity in wheat (Triticum durum) plants

A greenhouse study was conducted to investigate the effect of mycorrhiza on wheat (Triticum durum) boron (B) uptake under excessive B concentrations. Three levels of B (0, 3, and 6 mg B litre(-1)) were added to pots with or without mycorrhiza. Plant nutrients were added as Hoagland nutrient solution. In general, additions of B with or without mycorrhiza decreased wheat relative yield and increased shoot and root B concentrations. B concentrations in shoots ranged from 30.8 to 589 mg kg(-1). The highest shoot B concentrations were with the highest B treatments (6 mg B litre(-1)). whereas the lowest concentrations were in the control (0 mg B litre(-1)). Mycorrhiza inoculation significantly improved relative yield of unstressed (control) plants, but those increases in relative yield of B-stressed plants were not significant. In general, mycorrhiza inoculation decreased shoot and root B concentrations and uptake. Wheat growing at high B concentrations (6 and 3 mg B litre(-1)) with or without mycorrhiza showed leaf edge burning and necrosis compared with control treatments. The data suggested that mycorrhiza infection can prevent plants from an excessive concentration and uptake of B although that did not improve plant yield. Further evaluation is needed for the effects of mychorriza inoculation on B toxicity

Assessment of the agronomic value of QTL on chromosomes 2H and 4H linked to tolerance to boron toxicity in barley (Hordeum vulgare L.)

Improved boron (B) tolerance has been an objective of barley breeding programs in regions where B toxicity occurs. Traits associated with B tolerance have been mapped on chromosomes 2H and 4H and it has been proposed that these be used for marker assisted selection for B tolerance. However, there has been little or no improvement in yield using this strategy. This study examined the reasons for the small yield differences among different lines of barley that differ in B tolerance. Experiments used backcross lines derived from crosses between the B-tolerant landrace Sahara 3771 and two adapted recurrent parents, Sloop and VB9104. Lines with different combinations of the Sahara 3771 alleles on chromosomes 2H and 4H were grown over three growing seasons at sites where barley is prone to B toxicity. Grain yields of the backcross lines were similar to or lower than those of the recurrent parents despite showing differences in the expression of B toxicity symptoms and in B concentration in vegetative tissue. There were few significant differences in grain yield among the backcross lines. Variation in dry matter production among the backcross lines in each of the three growing seasons was unrelated to shoot B concentrations while grain yield was correlated with shoot B concentration only among the backcross lines of VB9104 in one season. In this case the yield loss was 4% per 10 mg kg -1 increase in shoot B concentration. Variation in shoot B concentration and yield across seasons was much greater than that observed among the different barley lines. Reduced B accumulation was associated with higher shoot sodium concentration among the Sloop backcross lines. The results suggest that yield gains from selection based largely on B exclusion and symptoms expression may be small and strongly affected by site and seasonal effects. In the regions where other soil constraints, such as soil salinity and micronutrient deficiencies are also important, reducing B uptake alone may have little effect on yield if these other soil properties are also limiting yields. © Springer Science + Business Media B.V. 2009.G. K. McDonald, J. K. Eglinton & A. R. Bar