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Cuttings of Populus kangdingensis C. Wang et Tung and Populus cathayana Rehder, originating from high and low altitudes in the eastern Himalaya, respectively, were examined during one growing season in a greenhouse to determine the effects of progressive drought stress. The results manifested that the adaptive responses to progressive drought stress were different in these two species from different altitudes. Significant changes in stem height, leaf development, relative water content (RWC), malondialdehyde (MDA) and hydrogen peroxide (HO) appeared earlier in P. cathayana than in P. kangdingensis, whereas changes in soluble protein, soluble sugar, free proline and antioxidant enzymes appeared earlier in P. kangdingensis. In addition, changes in these parameters became more and more significant when the drought stress progressed, especially under severe drought stress in P. cathayana. Plant growth showed significant positive correlations with soluble proteins and sugars, free proline and antioxidants and a significant negative correlation with RWC under water stressed treatment in two poplar species. Compared with P. cathayana, P. kangdingensis was able to maintain a superior height growth and leaf development under drought stress. Also, P. kangdingensis possessed greater increments in soluble protein, soluble sugar, free proline and antioxidant enzymes, but lower increments in MDA and HO than did P. cathayana when the cuttings were exposed to progressive drought stress. Our results suggest that P. kangdingensis originating from the high altitude has a better drought tolerance than does P. cathayana originating from the low altitude. Furthermore, this study manifested that acclimation to drought stress are related the rapidity, severity, duration of the drought event and the altitude of two poplar species.2222

Plant growth and development are regulated by phytohormones, such as abscisic acid, auxins, or gibberellins. Under drought stress, melatonin and the signaling calcium (Ca2+) are involved in plant defense and stress responses by controlling phytohormone and antioxidant machineries. Exogenous melatonin (MT) promotes drought stress tolerance in plants. As an essential second messenger, the signaling molecule Ca2+ is necessary in the stress tolerance of plants and might increase stress tolerance induced by exogenous melatonin. The present study elucidated the effects of Ca2+-MT on Dalbergia odorifera seedlings under drought stress. Results showed increases in growth traits and photosynthesis indexes (pigments, net photosynthetic rate, water use efficiency, stomatal conductance, and transpiration) by MT and Ca2+ under non stress and stress conditions. Under drought stress, the water status in leaves was slightly ameliorated by MT and Ca2+ treatments, whereas the Ca2+-MT combination strongly improved water status. Comparison between combined Ca2+-MT and single Ca2+/MT treatments showed that superoxide anion was significantly lower in Ca2+-MT-treated seedlings. Lipid peroxidation was lower in Ca2+-MT-treated seedlings under drought stress. Further, relative conductivity was significantly decreased by Ca2+ and MT treatments under stress compared with seedlings untreated with Ca2+ or MT under drought. The accumulation of proline decreased by Ca2+ and MT under stress, but the carbohydrates and protein contents were increased by exogenous MT and Ca2+. Under drought, antioxidant systems (peroxidase, superoxide dismutase, and catalase activities, and glutathione [GSH] and ascorbic acid [ASA] levels) were significantly increased by the Ca2+ and MT treatments. The combined treatment showed better performance in increasing GSH and ASA levels than single MT or Ca2+ treatment. The gibberellin GA3 and cytokine ZR increased significantly under non stress and stress conditions, but exogenous Ca2+ or MT did not increase their activities compared with those in the control groups. Exogenous Ca2+ and Ca2+-MT enhanced indole-3-acetic acid (IAA) content in D. odorifera leaves under stress compared with the control. Moreover, abscisic acid (ABA) level is downregulated by MT and Ca2+-MT treatments compared with the control. The seedlings treated with Ca2+ only showed increase in ABA concentration under drought stress. This study provides an insight into a possible coordination between Ca2+ and melatonin and into drought tolerance in woody plants. [ABSTRACT FROM AUTHOR]

Key message: Supplying Ca2+ and MT can be a key approach to elucidating the diverse physiological and biochemical mechanisms of plant growth, development, and resistance under environmental stresses. Although many studies have demonstrated the positive effects of exogenous melatonin (MT) under diverse stresses, most are related to crops and few have focused on woody trees. Moreover, the best outcomes related to the positive influence of MT on plants under chilling stress were obtained by applying MT alone. Thus, this work aimed to boost the strength of MT in the woody plant Dalbergia odorifera under cold stress through combination with the signaling molecule Ca2+, which has a major role in plant defense against abiotic stresses. Results showed that in D. odorifera seedlings, exogenous MT and Ca2+ application improved growth traits and relieved injuries, whereas chilling stress caused injuries and reduced growth. Exogenous MT and Ca2+increased photosynthetic activity and compatible solute (proline, glucose, fructose, and sucrose) accumulation. Starch degradation induced by chilling stress was significantly reduced in seedlings under treatment with MT combined with Ca2+. Furthermore, in D. odorifera seedlings, relative conductivity, lipid peroxidation, and reactive oxygen species were elevated under cold stress, whereas these indexes were strongly decreased by exogenous MT and Ca2+. Exogenous MT and Ca2+ enhanced the antioxidant activities against chilling stress. In addition, in D. odorifera seedlings under cold stress, exogenous MT and Ca2+ strongly elevated the levels of the phytohormones gibberellin (GA3) and auxin (IAA) but decreased those of abscisic acid (ABA) was decreased. The IAA and GA3 contents were increased respectively by 17.34% and 22.47% in seedlings treated with MT-Ca2+ compared to MT treatment. Meanwhile, the ABA content was decreased by 44.80% in MT-Ca2+-treated seedlings compared to MT treatment. In conclusion, exogenous MT and Ca2+ improved chilling stress tolerance in D. odorifera seedlings by regulating phytohormones, osmolytes, and antioxidant activities. [ABSTRACT FROM AUTHOR]

Aim: Glucose fluctuations may be responsible for, or further the onset of arterial hypertension, but the exact mechanisms remain unclear. The purpose of this study was to investigate the mechanisms behind and related to aortic fibrosis and aortic stiffening induced by glucose fluctuations. Methods: Sprague-Dawley rats were injected with streptozotocin (STZ) and randomly divided into three treatment groups: controlled STZ-induced diabetes (C-STZ); uncontrolled STZ-induced diabetes (U-STZ); and STZ-induced diabetes with glucose fluctuations (STZ-GF). After 3 weeks, rat blood pressure (BP) was tested, and aortic fibrosis was detected by using the Masson trichrome staining technique. Levels of p38 mitogen-activated protein kinase (p38 MAPK), runt-related transcription factor 2 (Runx2), collagen type 1 (collagen I), and NADPH oxidases were determined by Western blot.Rat vascular smooth muscle cells in vitro were used to explore underlying mechanisms. Results: The systolic BP of diabetic rats in the C-STZ, U-STZ, and STZ-GF groups was 127.67 ± 6.53, 150.03 ± 5.24, and 171.63 ± 3.53 mm Hg, respectively (p< 0.05). The mean BP of diabetic rats in the three groups was 91.20 ± 10.07, 117.29 ± 4.28, and 140.58 ± 2.14 mm Hg, respectively (p< 0.05). The diastolic BP of diabetic rats in the three groups was 73.20 ± 12.63, 101.93 ± 5.79, and 125.37 ± 4.62 mm Hg, respectively (p< 0.05). The ratios of fibrosis areas in the aortas of the three groups were 11.85 ± 1.23, 29.00 ± 0.87, and 48.36 ± 0.55, respectively (p< 0.05). The expressions of p38 MAPK, Runx2, and collagen I were significantly increased in the STZ-GF group. In vitro, applications of inhibitors of reactive oxygen species (ROS) and p38 MAPK successfully reversed glucose fluctuations that would have possibly induced aortic fibrosis. Conclusions: Blood glucose fluctuations aggravate aortic fibrosis via affecting the ROS/p38 MAPK /Runx2 signaling pathway. [ABSTRACT FROM AUTHOR]