Edited by Ulf-Ingo FlüggeKeywords: Affinity Cyclic voltammetry Guanylate cyclase H-NOX domain Nitric oxide Oxygen Square wave voltammetry Arabidopsis thaliana a b s t r a c t While there is evidence of nitric oxide (NO)-dependent signalling via the second messenger cyclic guanosine 3 0 ,5 0 -monophosphate (cGMP) in plants, guanylate cyclases (GCs), enzymes that catalyse the formation of cGMP from guanosine 5 0 -triphosphate (GTP) have until recently remained elusive and none of the candidates identified to-date are NO-dependent. Using both a GC and heme-binding domain specific (H-NOX) search motif, we have identified an Arabidopsis flavin monooxygenase (At1g62580) and shown electrochemically that it binds NO, has a higher affinity for NO than for O 2 and that this molecule can generate cGMP from GTP in vitro in an NO-dependent manner.

Salinity is a major constraint limiting plant growth and productivity worldwide. Thus, understanding the mechanism underlying plant stress response is of importance to developing new approaches that will increase salt tolerance in crops. This study reports the effects of salt stress on Sorghum bicolor during germination and the role of calcium (Ca2+) to ameliorate some of the effects of salt. To this end, sorghum seeds were germinated in the presence and absence of different NaCl (200 and 300 mM) and Ca2+ (5, 15, or 35 mM) concentrations. Salt stress delayed germination, reduced growth, increased proline, and hydrogen peroxide (H2O2) contents. Salt also induced the expression of key antioxidant (ascorbate peroxidase and catalase) and the Salt Overlay Sensitive1 genes, whereas in the presence of Ca2+ their expression was reduced except for the vacuolar Na+/H+ exchanger antiporter2 gene, which increased by 65-fold compared to the control. Ca2+ reversed the salt-induced delayed germination and promoted seedling growth, which was concomitant with reduced H2O2 and Na+/K+ ratio, indicating a protective effect. Ca2+ also effectively protected the sorghum epidermis and xylem layers from severe damage caused by salt stress. Taken together, our findings suggest that sorghum on its own responds to high salt stress through modulation of osmoprotectants and regulation of stress-responsive genes. Finally, 5 mM exogenously applied Ca2+ was most effective in enhancing salt stress tolerance by counteracting oxidative stress and improving Na+/K+ ratio, which in turn improved germination efficiency and root growth in seedlings stressed by high NaCl.

Background: U-box-containing proteins cooperate with chaperones in ubiquitinating irreversibly unfolded proteins. Results: Retinoblastoma binding protein-6 (RBBP6) contains a zinc-binding U-box-like domain and interacts directly with chaperones. Conclusion: RBBP6 may play a role in protein quality control. Significance: U-boxes should be classified in terms of their interaction with chaperones and not their zinc binding properties.

This study describes the first detailed molecular characterization of the heat shock protein 70 (Hsp70) gene from Sorghum bicolor, MN1618 designated as SbHsp70-1. The full-length cDNA of SbHsp70-1 consists of 2524 bp with a 1950 bp open reading frame, which encodes a protein of 649 amino acids. SbHsp70-1 is a cytoplasmic protein with high homology to other plant Hsp70s, especially grain crops. Recombinant SbHsp70-1 was able to bind and hydrolyse ATP in a dose-dependent manner, suggesting that SbHsp70-1 functions as an ATPase. Immunoblot assays showed that the expression of SbHsp70-1 is induced at temperatures of 37, 45, and 4 °C but reduced at 42 °C. In addition, the SbHsp70-1 mRNA transcript is constitutively expressed in both leaves and stem but is significantly increased upon heat shock at 42 °C. Upon cold shock at 4 °C, SbHsp70-1 mRNA transcript level increased in the leaf, but no significant change was observed in the stem. In addition, expression of the pET28a-SbHsp70-1 construct in Escherichia coli cells under heat stress resulted in their survival even at higher temperature (65 °C). Our results suggest that SbHsp70-1 is a heat-inducible protein that confer thermal tolerance to bacterial cells and can be claimed as a promising target to study stress tolerance in crops.Electronic supplementary materialThe online version of this article (doi:10.1007/s12192-015-0591-2) contains supplementary material, which is available to authorized users.

Salinity is an abiotic stress that is responsible for more than 50% of crop losses worldwide. Current strategies to overcome salinity in agriculture are limited to the use of genetically modified crops and chemicals including fertilizers, pesticides and herbicides; however these are costly and can be hazardous to human health and the environment. Green synthesis of nanoparticles (NPs) is an eco-friendly and cost-effective method, and they might serve as novel biostimulants. This study investigated for the first time the efficiency of ZnO NPs, synthesized from Agathosma betulina to mitigate salt stress in Sorghum bicolor. Hexagonal wurtzite ZnO NPs of about 27.5 nm, were obtained. Sorghum seeds were primed with ZnO NPs (5 and 10 mg/L), prior to planting on potting soil and treatment with high salt (400 mM NaCl). Salt significantly impaired growth by decreasing shoot lengths and fresh weights, causing severe deformation on the anatomical (epidermis and vascular bundle tissue) structure. Element distribution was also affected by salt which increased the Na+/K+ ratio (2.9). Salt also increased oxidative stress markers (reactive oxygen species, malondialdehyde), enzyme activities (SOD, CAT and APX), proline, and soluble sugars. Priming with ZnO NPs stimulated the growth of salt-stressed sorghum plants, which was exhibited by improved shoot lengths, fresh weights, and a well-arranged anatomical structure, as well as a low Na+/K+ ratio (1.53 and 0.58) indicating an improved element distribution. FTIR spectra confirmed a reduction in the degradation of biomolecules correlated with reduced oxidative stress. This study strongly suggests the use of green-synthesized ZnO NPs from A. betulina as potential biostimulants to improve plant growth under abiotic stress.

Drought is a major abiotic stress that confronts plant growth and productivity, thus compromising food security. Plants use physiological and biochemical mechanisms to cope with drought stress, but at the expense of growth. Green-synthesized nanoparticles (NPs) have gained great attention in agriculture due to their environmental friendliness and affordability while serving as potential biofertilizers. This study investigates the role of hematite (αFe2O3) NPs, synthesized from Aspalathus linearis (rooibos), to improve Sorghum bicolor growth under drought stress. About 18 nm, spherical, and highly agglomerated hematite (αFe2O3) NPs were obtained. Sorghum seeds were primed with 5, 10, and 15 mg/L αFe2O3 NPs, and, after seven days of germination, the seedlings were transferred into potting soil, cultivated for fourteen days, and were subsequently water deprived (WD) for a further seven days. A reduction in plant height (78%), fresh (FW; 35%) and dry (DW; 36%) weights, and chlorophyll (chl) content ((total chl (81%), chla (135%), and chlb (1827%)) was observed in WD plants, and this correlated with low nutrients (Mg, Si, P, and K) and alteration in the anatomic structure (epidermis and vascular bundle tissues). Oxidative damage was observed as deep blue (O2●−) and brown (H2O2) spots on the leaves of WD plants, in addition to a 25% and 40% increase in oxidative stress markers (H2O2 and MDA) and osmolytes (proline and total soluble sugars), respectively. Seed priming with 10 mg/L αFe2O3 NPs improved plant height (70%), FW (56%), DW (34%), total Chl (104%), chla (160%) and chlb (1936%), anatomic structure, and nutrient distribution. Priming with 10 mg/L αFe2O3 NPs also protected sorghum plants from drought-induced oxidative damage by reducing ROS formation and osmolytes accumulation and prevented biomolecule degradation. The study concludes that green synthesized hematite NPs positively influenced sorghum growth and prevented oxidative damage of biomolecules by improving nutrient uptake and osmoregulation under drought stress.

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The basal level of the plant defense hormone jasmonate (JA) in unstressed leaves is low, but wounding causes its near instantaneous increase. How JA biosynthesis is initiated is uncertain, but the lipolysis step that generates fatty acid precursors is generally considered to be the first step. Here, we used a series of physiological, pharmacological, genetic, and kinetic analyses of gene expression and hormone profiling to demonstrate that the early spiking of JA upon wounding does not depend on the expression of JA biosynthetic genes in Arabidopsis (Arabidopsis thaliana). Using a transgenic system, we showed how decoupling the responses to wounding and JA prevents the perpetual synthesis of JA in wounded leaves. We then used DEFECTIVE IN ANTHER DEHISCENCE1 (DAD1) as a model wound-responsive lipase to demonstrate that although its transient expression in leaves can elicit JA biosynthesis to a low level, an additional level of activation is triggered by wounding, which causes massive accumulation of JA. This wound-triggered boosting effect of DAD1-mediated JA synthesis can happen directly in damaged leaves or indirectly in undamaged remote leaves by the systemically transmitted wound signal. Finally, protein stability of DAD1 was influenced by wounding, α-linolenic acid, and mutation in its catalytic site. Together, the data support mechanisms that are independent of gene transcription and translation to initiate the rapid JA burst in wounded leaves and demonstrate how transient expression of the lipase can be used to reveal changes occurring at the level of activity and stability of the key lipolytic step.