Role of salicylic acid pre-treatment on the photosynthetic performance of tomato plants (Lycopersicon esculentum Mill. L. cvar. Rio Fuego) under salt stress

Imposition of salt stress reduced the net CO2 assimilation rate, chlorophyll (Chl), anthocyanin and carotenoid contents, stomatal conductance and soluble sugar contents of tomato (Lycopersicon esculentum Mill. L. cv. Rio Fuego). Pre-treatments of plant with 10-4 M salicylic acid (SA) could partially restore the CO2 fixation rate and photosynthetic pigment levels under 100 mM NaCl exposure. Accumulation of soluble sugars, a biochemical marker of salinity tolerance in tomato, could be detected in pre-treated plants exposed to high salinity. The improved photosynthetic performance, the accumulation of soluble sugars as compatible osmolytes contributed to the successful acclimation of 10-4 M SA pre-treated tomato plants to salt stress

Light to moderate alcohol consumption and acute myocardial infarction, heart failure and atrial fibrillation

Background and aim: A large number of studies found an inverse association between light to moderate alcohol consumption and the risk of acute myocardial infarction (AMI) and heart failure (HF). Whether this consumption is associated with the risk of atrial fibrillation (AF) is less clear. Methodological shortcomings may limit causal inference in these studies, most importantly the “sick-quitter” bias and the confounding by social factors. Furthermore, how drinking frequency, binge- and problem drinking or beverage types may influence these associations is not well understood. The overall aim of this thesis is to contribute to a better understanding of the prospective associations between light-to-moderate alcohol intake and the risk of AMI, HF and AF by addressing the above described unresolved issues. Methods and results: The Nord-Trøndelag Health Study (HUNT) is a large Norwegian population-based study conducted in three waves. For study I and II, we used data from HUNT2 conducted in 1995 -1997. In HUNT2, 65 215 individuals (70% of the eligible) participated and were followed for AMI and HF. For study III and IV, HUNT3 conducted in 2006-2008, was used: 50 807 individuals (54% of the eligible) participated and were followed for AF. In study III, 1 266 healthy individuals were selected randomly from HUNT3 and had an echocardiography examination. The quantity, type and frequency of alcohol consumption were ascertained by questionnaires. Binge drinking, i.e. drinking ≥ five glasses in one sitting and problem drinking were assessed. To identify abstainers who were former drinkers, information from the preceding waves of HUNT, i.e. HUNT1 or HUNT2 were used. They were categorized as long-term abstainers, abstainers who were former drinkers, rare drinkers, and drinkers, who were further categorized based on average alcohol consumption in a two-week period. Information on socioeconomic position, demographics, smoking, physical activity, common chronic conditions, and anxiety and depression symptoms were assessed, and anthropometrics, blood pressure and blood lipids were measured. The average alcohol consumption in the HUNT was 3-4 grams per day. The quantity of alcohol consumption was inversely associated with the risk of AMI and HF (study I, II). There was no clinically meaningful association between light to moderate alcohol intake and LV function (study III). Compared to abstainers, drinkers who consumed over seven drinks per week had an increased risk of AF. However, when we excluded those who consumed alcohol over the recommended limits, i.e., > seven drinks per week for women and >14 drinks per week for men and reported binge and/or problem drinking the attributable risk of alcohol consumption was negligible in this low-drinking population (study IV). Frequent, more evenly distributed alcohol consumption was more protective for AMI and HF than less frequent intake of the same quantity (study I, II). Among binge and/or problem drinkers, alcohol consumption was associated with a slightly increased risk of HF and worse LV structural characteristics (study II, III). Conclusions: Light to moderate alcohol consumption, within the recommended limits was associated with a reduced risk of AMI and HF, but not with the risk of AF. While frequent low-level consumption is associated with the lowest risk of AMI and HF, binge drinking seems to be harmful even if the average alcohol intake is moderate. Alcohol consumption within the recommended limits may provide some cardiovascular benefits without increasing the risk of AF

Polyamine Oxidase-Generated Reactive Oxygen Species in Plant Development and Adaptation: The Polyamine Oxidase—NADPH Oxidase Nexus

Metabolism and regulation of cellular polyamine levels are crucial for living cells to maintain their homeostasis and function. Polyamine oxidases (PAOs) terminally catabolize polyamines or catalyse the back-conversion reactions when spermine is converted to spermidine and Spd to putrescine. Hydrogen peroxide (H2O2) is a by-product of both the catabolic and back-conversion processes. Pharmacological and genetic approaches have started to uncover the roles of PAO-generated H2O2 in various plant developmental and adaptation processes such as cell differentiation, senes- cence, programmed cell death, and abiotic and biotic stress responses. Many of these studies have revealed that the superoxide-generating Respiratory Burst Oxidase Homolog (RBOH) NADPH oxidases control the same processes either upstream or downstream of PAO action. Therefore, it is reasonable to suppose that the two enzymes co-ordinately control the cellular homeostasis of reactive oxygen species. The intricate relationship between PAOs and RBOHs is also discussed, posing the hypothesis that these enzymes indirectly control each other’s abundance/function via H2O2

Deregulation of apoplastic polyamine oxidase affects development and salt response of tobacco plants

Polyamine (PA) homeostasis is associated with plant development, growth and responses to biotic/abiotic stresses. Apoplastic PA oxidase (PAO) catalyzes the oxidation of PAs contributing to cellular homeostasis of reactive oxygen species (ROS) and PAs. In tobacco, PAs decrease with plant age, while apoplastic PAO activity increases. Our previous results with young transgenic tobacco plants with enhanced/reduced apoplastic PAO activity (S-ZmPAO/AS-ZmPAO, respectively) established the importance of apoplastic PAO in controlling tolerance to short-term salt stress. However, it remains unclear if the apoplastic PAO pathway is important for salt tolerance at later stages of plant development. In this work, we examined whether apoplastic PAO controls also plant development and tolerance of adult plants during long-term salt stress. The AS-ZmPAO plants contained higher Ca2+ during salt stress, showing also reduced chlorophyll content index (CCI), leaf area and biomass but taller phenotype compared to the wild-type plants during salt. On the contrary, the S-ZmPAO had more leaves with slightly greater size compared to the AS-ZmPAO and higher antioxidant genes/enzyme activities. Accumulation of proline in the roots was evident at prolonged stress and correlated negatively with PAO deregulation as did the transcripts of genes mediating ethylene biosynthesis. In contrast to the strong effect of apoplastic PAO to salt tolerance in young plants described previously, the effect it exerts at later stages of development is rather moderate. However, the different phenotypes observed in plants deregulating PAO reinforce the view that apoplastic PAO exerts multifaceted roles on plant growth and stress responses. Our data suggest that deregulation of the apoplastic PAO can be further examined as a potential approach to breed plants with enhanced/reduced tolerance to abiotic stress with minimal associated trade-offs. © 2017 Elsevier Gmb

Absence of Arabidopsis Polyamine Oxidase 5 Influences the Cytokinin-Induced Shoot Meristem Formation from Lateral Root Primordia

Lateral root primordia (LRPs) of Arabidopsis can be directly converted to shoot meristems (SMs) by the application of exogenous cytokinin. Here, we report that Arabidopsis POLYAMINE OXIDASE 5 (AtPAO5) contributes to this process, since the rate of SM formation from LRPs was significantly lower in the pao5-2 knockout mutant. Furthermore, the presented experiments showed that AtPAO5 influences SM formation via controlling the thermospermine (T-Spm) level. Gene expression analyses supported the view that the pao5-2 mutation as well as exogenous T-Spm downregulate the expression of the class 3 haemoglobin coding genes AtGLB1 and AtGLB2. AtGLB1 and 2 have been reported to augment cytokinin sensitivity, indirectly inhibiting the expression of type-A ARABIDOPSIS RESPONSE REGULATORs (ARRs). In agreement, the same ARR-coding genes were found to be upregulated in the pao5-2 mutant. Although GLB proteins might also control cytokinin-induced nitric oxide (NO) accumulation, we could not find experimental evidence for it. Rather, the negative effect of NO-donor treatment on AtPAO5 gene expression and SM formation was seen. Nevertheless, a hypothetical pathway is set up explaining how AtPAO5 may affect direct shoot meristem formation, controlling cytokinin sensitivity through T-Spm and GLBs. © 2023 by the authors

Timely removal of exogenous cytokinin and the prevention of auxin transport from the shoot to the root affect the regeneration potential of Arabidopsis roots

In vitro regeneration of Arabidopsis from roots is generally achieved via indirect organogenesis. First, transdifferentiation of lateral root primordia to calli is achieved by a balanced auxin-to-cytokinin ratio that is followed by the induction of shoot meristem formation using a high cytokinin level. Here we demonstrate that if the root explants were transferred onto a hormone-free medium after a transient (4-days) cytokinin treatment, embryogenic marker genes (LEC1, LEC2, FUS3) started to be expressed. App. 50% of the regeneration foci developed into plantlets with trichome-less cotyledon-like leaves. Moreover, the somatic embryogenesis defective lec1 mutant could regenerate only shoots with trichome-bearing leaves under this condition. Based on these observations, the mixed accomplishment of shoot organogenesis and somatic embryogenesis is hypothesized in the Arabidopsis root explants cultured under hormone-free conditions following cytokinin induction. Using whole seedlings instead of root explants in the same experimental set up, no regenerates were formed on the roots. Applying the auxin transport inhibitor TIBA to the root-to-shoot junction of the seedlings, the regeneration ability of the root could be restored. The observations indicate that shoot-derived endogenous auxin blocks the cytokinin-induced regeneration process in the roots of whole seedlings. The expression of the wound-induced transcription factor WIND1 could be detected in the roots of unwounded seedlings if the shoot-to-root auxin transport was inhibited. Manipulating the exogenous cytokinin level together with the endogenous shoot-to-root auxin transport therefore could mimic the effect of wounding (removal of shoot) on plant regeneration from roots. Key message Transferring root explants from high cytokinin to hormone-free conditions resulted in the expression of embryogenic markers. Inhibiting the shoot-to-root auxin transport had similar effect on regeneration as wounding