The present study performed experiments to identify the superior pH for Arabidopsis root growth base on its development (radical root length and lateral root density); and then approached the mechanism by which optimized pH primes root development. The results showed that neutral to slightly alkaline pH (7.0−8.0) in medium was the optimum range in which the plant had longer primary roots and denser lateral roots. Auxin reporter DII:VENUS transgenic line cultured in standard (5.8) and slightly alkaline (7.5) pH indicated that in pH 7.5 conditions, there was less fluorescence in the root cap compared to in acidic conditions. Furthermore, the DR5:Luciferase transgenic plant showed pH 7.5 accelerated the auxin oscillation frequency, was 17.83% shorter than that in pH 5.8. Later, a series of mutant germplasms showed slightly alkaline conditions promoting root development were independent from PLT transcript factors, but mainly mediated by auxin transportation. Transcriptomic dynamic analysis showed pH 7.5 conditions could trigger the changes in the pathways of plant hormones signal transduction and ABC transporter. The mutants of the ABC transporter coding genes were thus tested and the results showed that mutant abcb20 could block the slightly alkaline (7.5) pH promoting root development completely, as well as several other mutants blocking it partially.
Abstract Although aerobic methane (CH 4 ) release from plants leads to an intense scientific and public controversy in the recent years, the potential functions of endogenous CH 4 production in plants are still largely unknown. Here, we reported that polyethylene glycol (PEG)-induced osmotic stress significantly increased CH 4 production and soluble sugar contents in maize ( Zea mays L.) root tissues. These enhancements were more pronounced in the drought stress-tolerant cultivar Zhengdan 958 (ZD958) than in the drought stress-sensitive cultivar Zhongjiangyu No.1 (ZJY1). Exogenously applied 0.65 mM CH 4 not only increased endogenous CH 4 production, but also decreased the contents of thiobarbituric acid reactive substances. PEG-induced water deficit symptoms, such as decreased biomass and relative water contents in both root and shoot tissues, were also alleviated. These beneficial responses paralleled the increases in the contents of soluble sugar and the reduced ascorbic acid (AsA), and the ratio of AsA/dehydroascorbate (DHA). Further comparison of transcript profiles of some key enzymes in sugar and AsA metabolism suggested that CH 4 might participate in sugar signaling, which in turn increased AsA production and recycling. Together, these results suggested that CH 4 might function as a gaseous molecule that enhances osmotic stress tolerance in maize by modulating sugar and AsA metabolism.
Abstract Recent studies have demonstrated that hydrogen sulfide (H 2 S) produced through the activity of l ‐cysteine desulfhydrase (DES1) is an important gaseous signaling molecule in plants that could participate in abscisic acid (ABA)‐induced stomatal closure. However, the coupling of the DES1/H 2 S signaling pathways to guard cell movement has not been thoroughly elucidated. The results presented here provide genetic evidence for a physiologically relevant signaling pathway that governs guard cell in situ DES1/H 2 S function in stomatal closure. We discovered that ABA‐activated DES1 produces H 2 S in guard cells. The impaired guard cell ABA phenotype of the des1 mutant can be fully complemented when DES1/H 2 S function has been specifically rescued in guard cells and epidermal cells, but not mesophyll cells. This research further characterized DES1/H 2 S function in the regulation of LONG HYPOCOTYL1 (HY1, a member of the heme oxygenase family) signaling. ABA‐induced DES1 expression and H 2 S production are hyper‐activated in the hy1 mutant, both of which can be fully abolished by the addition of H 2 S scavenger. Impaired guard cell ABA phenotype of des1/hy1 can be restored by H 2 S donors. Taken together, this research indicated that guard cell in situ DES1 function is involved in ABA‐induced stomatal closure, which also acts as a pivotal hub in regulating HY1 signaling.
Metabolism of molecular hydrogen (H2) in bacteria and algae has been widely studied, and it has attracted increasing attention in the context of animals and plants. However, the role of endogenous H2 in lateral root (LR) formation is still unclear. Here, our results showed that H2-induced lateral root formation is a universal event. Naphthalene-1-acetic acid (NAA; the auxin analog) was able to trigger endogenous H2 production in tomato seedlings, and a contrasting response was observed in the presence of N-1-naphthyphthalamic acid (NPA), an auxin transport inhibitor. NPA-triggered the inhibition of H2 production and thereafter lateral root development was rescued by exogenously applied H2. Detection of endogenous nitric oxide (NO) by the specific probe 4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate (DAF-FM DA) and electron paramagnetic resonance (EPR) analyses revealed that the NO level was increased in both NAA- and H2-treated tomato seedlings. Furthermore, NO production and thereafter LR formation induced by auxin and H2 were prevented by 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO; a specific scavenger of NO) and the inhibitor of nitrate reductase (NR; an important NO synthetic enzyme). Molecular evidence confirmed that some representative NO-targeted cell cycle regulatory genes were also induced by H2, but was impaired by the removal of endogenous NO. Genetic evidence suggested that in the presence of H2, Arabidopsis mutants nia2 (in particular) and nia1 (two nitrate reductases (NR)-defective mutants) exhibited defects in lateral root length. Together, these results demonstrated that auxin-induced H2 production was associated with lateral root formation, at least partially via a NR-dependent NO synthesis.
Background and aims Boron is essential for plant growth but hazardous when present in excess. As the antioxidant properties of hydrogen gas (H2) were recently described in plants, oxidative stress induced by excess boron was investigated along with other biological responses during rice (Oryza sativa) seed germination to study the beneficial role of H2. Methods Rice seeds were pretreated with exogenous H2. Using physiological, pharmacological and molecular approaches, the production of endogenous H2, growth status, reactive oxygen species (ROS) balance and relative gene expression in rice were measured under boron stress to investigate mechanisms of H2-mediated boron toxicity tolerance. Key Results In our test, boron-inhibited seed germination and seedling growth, and endogenous H2 production, were obviously blocked by exogenously applying H2. The re-establishment of ROS balance was confirmed by reduced lipid peroxidation and ROS accumulation. Meanwhile, activities of catalase (CAT) and peroxidase (POX) were increased. Suppression of pectin methylesterase (PME) activity and downregulation of PME transcripts by H2 were consistent with the alleviation of root growth inhibition caused by boron. Water status was improved as well. This result was confirmed by the upregulation of genes encoding specific aquaporins (AQPs), the maintenance of low osmotic potential and high content of soluble sugar. Increased transcription of representative AQP genes (PIP2;7 in particular) and BOR2 along with decreased BOR1 mRNA may contribute to lowering boron accumulation. Conclusions Hydrogen provides boron toxicity tolerance mainly by improving root elongation, water status and ROS balance.
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