Involvement of G6PD5 in ABA response during seed germination and root growth in Arabidopsis.

BACKGROUND: Glucose-6-phosphate dehydrogenase (G6PDH or G6PD) functions in supply of NADPH, which is required for plant defense responses to stresses. However, whether G6PD functions in the abscisic acid (ABA) signaling pathway remains to be elucidated. In this study, we investigated the involvement of the cytosolic G6PD5 in the ABA signaling pathway in Arabidopsis. RESULTS: We characterized the Arabidopsis single null mutant g6pd5. Phenotypic analysis showed that the mutant is more sensitive to ABA during seed germination and root growth, whereas G6PD5-overexpressing plants are less sensitive to ABA compared to wild type (WT). Furthermore, ABA induces excessive accumulation of reactive oxygen species (ROS) in mutant seeds and seedlings. G6PD5 participates in the reduction of H2O2 to H2O in the ascorbate-glutathione cycle. In addition, we found that G6PD5 suppressed the expression of Abscisic Acid Insensitive 5 (ABI5), the major ABA signaling component in dormancy control. When G6PD5 was overexpressed, the ABA signaling pathway was inactivated. Consistently, G6PD5 negatively modulates ABA-blocked primary root growth in the meristem and elongation zones. Of note, the suppression of root elongation by ABA is triggered by the cell cycle B-type cyclin CYCB1. CONCLUSIONS: This study showed that G6PD5 is involved in the ABA-mediated seed germination and root growth by suppressing ABI5.

The monokaryotic filamentous fungus Ustilago sp. HFJ311 promotes plant growth and reduces Cd accumulation by enhancing Fe transportation and auxin biosynthesis.

Infection with smut fungus like Ustilago maydis decreases crop yield via inducing gall formation. However, the in vitro impact of Ustilago spp. on plant growth and stress tolerance remains elusive. This study investigated the plant growth promotion and cadmium stress mitigation mechanisms of a filamentous fungus discovered on a cultural medium containing 25 µM CdCl2. ITS sequence alignment revealed 98.7 % similarity with Ustilago bromivora, naming the strain Ustilago sp. HFJ311 (HFJ311). Co-cultivation with HFJ311 significantly enhanced the growth of various plants, including Arabidopsis, tobacco, cabbage, carrot, rice, and maize, and improved Arabidopsis tolerance to abiotic stresses like salt and metal ions. HFJ311 increased chlorophyll and Fe contents in Arabidopsis shoots and enhanced root-to-shoot Fe translocation while decreasing root Fe concentration by approximately 70 %. Concurrently, HFJ311 reduced Cd accumulation in Arabidopsis by about 60 %, indicating its potential for bioremediation in Cd-contaminated soils. Additionally, HFJ311 stimulated IAA concentration by upregulating auxin biosynthesis genes. Overexpression of the Fe transporter IRT1 negated HFJ311's growth-promotion effects under Cd stress. These results suggest that HFJ311 stimulates plant growth and inhibits Cd uptake by enhancing Fe translocation and auxin biosynthesis while disrupting Fe absorption. Our findings offer a promising bioremediation strategy for sustainable agriculture and food security.

Alternative Pathway Is Involved in Hydrogen Peroxide-Enhanced Cadmium Tolerance in Hulless Barley Roots.

Hulless barley, grown in the Qinghai Tibet Plateau, has a wide range of environmental stress tolerance. Alternative pathway (AP) and hydrogen peroxide (H2O2) are involved in enhancing plant tolerance to environmental stresses. However, the relationship between H2O2 and AP in hulless barley tolerance to cadmium (Cd) stress remains unclear. In the study, the role and relationship of AP and H2O2 under Cd stress were investigated in hulless barley (Kunlun14) and common barley (Ganpi6). Results showed that the expression level of alternative oxidase (AOX) genes (mainly AOX1a), AP capacity (Valt), and AOX protein were clearly induced more in Kunlun14 than in Ganpi 6 under Cd stress; moreover, these parameters were further enhanced by applying H2O2. Malondialdehyde (MDA) content, electrolyte leakage (EL) and NAD(P)H to NAD(P) ratio also increased in Cd-treated roots, especially in Kunlun 14, which can be markedly alleviated by exogenous H2O2. However, this mitigating effect was aggravated by salicylhydroxamic acid (SHAM, an AOX inhibitor), suggesting AP contributes to the H2O2-enhanced Cd tolerance. Further study demonstrated that the effect of SHAM on the antioxidant enzymes and antioxidants was minimal. Taken together, hulless barley has higher tolerance to Cd than common barley; and in the process, AP exerts an indispensable function in the H2O2-enhanced Cd tolerance. AP is mainly responsible for the decrease of ROS levels by dissipating excess reducing equivalents.

Ictal cerebral haemodynamic characteristics during typical absence seizures, compared to focal seizures with brief alteration of awareness.

To investigate ictal cerebral haemodynamic characteristics during spontaneous typical absence seizures (TAS) and hyperventilation-evoked absence seizures in paediatric patients, relative to brief complex partial seizures (BCPS). All children diagnosed with seizures using real-time transcranial doppler ultrasonography (TCD) and sleep-deprived video-EEG (vEEG) from 2015 to 2017 in our hospital were included. The seizures were diagnosed based on the video and EEG findings. Mean cerebral blood flow velocity (CBFVm) of the unilateral middle cerebral artery was measured using TCD. TCD and vEEG data were integrated for a synchronous assessment of CBFVm changes and epileptic status. Baseline and peak CBFVm for TAS and BCPS were compared by T-test. Six children (two boys and four girls) with TAS and two girls with BCPS were enrolled. A total of 15 spontaneous TAS, 14 hyperventilation-evoked absence seizures, and six BCPS were recorded using real-time TCD-vEEG monitoring. During spontaneous TAS, whether awake or asleep, the CBFVm decreased by 20-40% compared to baseline. During hyperventilation-evoked absence seizures and BCPS, the CBFVm increased by 50-150% and 20-30% over baseline levels, respectively. The haemodynamic characteristics during TAS and BCPS are distinct, and thus our results may provide a new method to diagnose typical absence seizures using dynamic CBFVm curves. Ictal cerebral haemodynamic characteristics during spontaneous typical absence seizures and hyperventilation-evoked absence seizures may reflect different pathophysiological mechanisms and networks compared with BCPS.

Alternative Pathway is Involved in Nitric Oxide-Enhanced Tolerance to Cadmium Stress in Barley Roots.

Alternative pathway (AP) has been widely accepted to be involved in enhancing tolerance to various environmental stresses. In this study, the role of AP in response to cadmium (Cd) stress in two barley varieties, highland barley (Kunlun14) and barley (Ganpi6), was investigated. Results showed that the malondialdehyde (MDA) content and electrolyte leakage (EL) level under Cd stress increased in two barley varieties. The expressions of alternative oxidase (AOX) genes (mainly AOX1a), AP capacity (Valt), and AOX protein amount were clearly induced more in Kunlun14 under Cd stress, and these parameters were further enhanced by applying sodium nitroprussid (SNP, a NO donor). Moreover, H2O2 and O2- contents were raised in the Cd-treated roots of two barley varieties, but they were markedly relieved by exogenous SNP. However, this mitigating effect was aggravated by salicylhydroxamic acid (SHAM, an AOX inhibitor), suggesting that AP contributes to NO-enhanced Cd stress tolerance. Further study demonstrated that the effect of SHAM application on reactive oxygen species (ROS)-related scavenging enzymes and antioxidants was minimal. These observations showed that AP exerts an indispensable function in NO-enhanced Cd stress tolerance in two barley varieties. AP was mainly responsible for regulating the ROS accumulation to maintain the homeostasis of redox state.