Effect of putrescine on the conversion of protocorm-like bodies of <Emphasis Type="Italic">Dendrobium officinale</Emphasis> to shoots

The addition of 1.5 mM putrescine to the culture medium facilitated the conversion of protocorm-like bodies (PLBs) of Dendrobium officinale to shoots. The administration of 1.0 mM of the polyamine inhibitor, α-DL-difluoromethylarginine, decreased the conversion of PLBs to shoots. Compared to the control, the PLBs treated with 1.5 mM putrescine had higher levels of total intracellular free polyamines. The enhanced conversion of PLBs to shoots following the addition of putrescine was accompanied by an increase in the ratio of total cytokinins (CTKs) to indole-3-acetic acid (IAA). Analysis of enzyme activities indicated that the increased endogenous level of total CTKs driven by putrescine was associated with the inhibition of CTK decomposition by CTK oxidase, while the decreased endogenous level of IAA was associated with the promotion of IAA decomposition by IAA oxidase. In addition, putrescine increased the ratio of reduced glutathione to oxidized glutathione in the conversion process of PLBs to shoots.     

Involvement of K+ channel-dependant pathways in lipoxin A4-induced protective effects on hypoxia/reoxygenation injury of cardiomyocytes

Studies have shown that lipoxin A₄ (LXA₄) and activation of LXA₄ receptor provided protection against myocardial ischemia/reperfusion injury in animal models. However, the mechanisms by which LXA₄ induced protective role on myocardial ischemia/reperfusion injury remains unclear. In the present studies, we investigated the protective effects of LXA₄ on H9c2 cardiomyocytes exposed to hypoxia/reoxygenation (H/R) injury and involvement of heme oxygenase-1 (HO-1)- and K⁺ channel-dependant pathways in the LXA₄ action. H9c2 cardiomyocytes were pretreated with or without LXA₄ or HO-1 specific interfering RNA (siRNA) or various blockers and openers of K⁺ channels before exposing to H/R injury. The levels of lactate dehydrogenase (LDH) and creatine kinase (CK) in cellular supernatants and necrosis factor-α (TNF-α) in cellular lysates were measured by using ELISA. Expressions of HO-1 mRNA and protein were analyzed by using RT-PCR and Western blot respectively. Pretreatment of the cells undergoing H/R injury with LXA₄ significantly reduced the LDH and CK levels induced by H/R injury, and increased the expressions and activity of HO-1. However, the protective effects of LXA₄ were completely blocked by transfection of the cells with HO-1 siRNA, and were partially but significantly blocked by pretreatment of the cells with various blockers of K⁺ channels. The LXA₄-induced expressions of HO-1 in the cells were also inhibited by HO-1 siRNA and various blockers of K⁺ channels. The inhibitory effects of LXA₄ on enhanced TNF-α levels induced by H/R injury were abolished by transfection of the cells with HO-1 siRNA. In conclusion, the protective role of LXA₄ on cardiomyocytes against H/R injury is related to upregulation of HO-1 via reduced production of TNF-α and activation of ATP-sensitive K⁺ channels and calcium-sensitive K⁺ channel.     

Additive roles of two TPS genes in trehalose synthesis,conidiation, multiple stress responses and host infection of a fungal insect pathogen

Intracellular trehalose accumulation is relevant to fungal life and pathogenicity. Trehalose-6-phosphate synthase (TPS) is known to control the first step of trehalose synthesis, but functions of multiple TPS genes in some filamentous fungi are variable. Here, we examined the functions of two TPS genes (tpsA and tpsB) in Beauveria bassiana, a fungal insect pathogen widely applied in arthropod pest control. Intracellular TPS activity and trehalose content decreased by 71–75 and 72–80% in ΔtpsA, and 21–30 and 15–45% in ΔtpsB, respectively, and to undetectable levels in ΔtpsAΔtpsB, under normal and stressful conditions. The three mutants lost 33, 50, and 98% of conidiation capacity in standard cultures. Conidial quality indicated by viability, density, intracellular trehalose content, cell wall integrity, and hydrophobicity was more impaired in ΔtpsA than in ΔtpsB and mostly in ΔtpsAΔtpsB, which was also most sensitive to nutritional, chemical, and environmental stresses and least virulent to Galleria mellonella larvae. Almost all of phenotypic defects in ΔtpsAΔtpsB approached to the sums of those observed in ΔtpsA and ΔtpsB and were restored by targeted gene complementation. Altogether, TpsA and TpsB play complementary roles in sustaining trehalose synthesis, conidiation capacity, conidial quality, multiple stress tolerance, and virulence, highlighting a significance of both for the fungal adaptation to environment and host.