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1.
Mol Neurobiol ; 53(5): 3389-3399, 2016 07.
Article in English | MEDLINE | ID: mdl-26081155

ABSTRACT

Septic encephalopathy represents the most frequently observed form of encephalopathy in intensive care units. Interactions between the immune and nervous systems have been observed in experimental sepsis. Therefore, the aim of the current study was to characterize the effect of different severities of sepsis on encephalopathy and the inflammatory profile of the spleen. We hypothesized that different grades of sepsis severity would lead to variations in encephalopathy and activation of spleen cells. We induced sepsis of different severities in Balb/c mice by cecal ligature and puncture (CLP). Six and 12 h after CLP induction, behavioral impairment was assessed by the SmithKline/Harwell/Imperial College/Royal Hospital/Phenotype Assessment (SHIRPA) test. The animals were then killed, and the plasma, spleen, and hippocampus were removed. Levels of the encephalopathy marker S100ß were measured in plasma. Spleens were weighed and then a characterization of splenic lymphocytes was performed by flow cytometry (cytotoxic T lymphocyte, T helper lymphocytes, B lymphocytes, T regulatory cells, and Th17 cells). Cytokine levels in the spleen and hippocampus were determined by enzyme-linked immunosorbent assay (ELISA), and cytokine levels in plasma were performed with MilliPlex® technology. Our results showed that behavioral impairment as measured by the SHIRPA test and elevation in plasma S100ß levels were significant in moderate and severe CLP groups compared to those in the sham control group. Regarding immunological alterations, we were unable to observe changes in the weights of the spleen and the profile of lymphocytes 6 h after CLP. However, several cytokines, including IL-6, IL-10, and IL-1ß, were increased in spleen and plasma. In conclusion, we observed variations in encephalopathy as measured by plasma S100ß, which were mediated by the severity of sepsis; however, we did not observe a different activation of spleen cells 6 h post-CLP, despite evidence of inflammation. Taken together, our data indicate that the severity of sepsis impacts the brain in absence of a change in the spleen lymphocyte profile.


Subject(s)
Brain Diseases/pathology , Cecum/pathology , Lymphocytes/pathology , Punctures , Sepsis/etiology , Spleen/pathology , Animals , Behavior, Animal , Brain Diseases/blood , Cytokines/metabolism , Hippocampus/pathology , Ligation , Male , Mice, Inbred BALB C , Organ Size , S100 Calcium Binding Protein beta Subunit/blood , Sepsis/blood , Severity of Illness Index , Survival Analysis
2.
An Pediatr (Barc) ; 79(4): 241-7, 2013 Oct.
Article in Spanish | MEDLINE | ID: mdl-23485828

ABSTRACT

INTRODUCTION: Owing to the significant increase of mild motor delays and the strong intolerance of infants to be placed on prone position observed in the Physiotherapy Unit of the Maternal and Children's University Hospital of the Canaries (HUMIC), a study was conducted to determine whether positioning infants in the prone position while awake affected the achievement and quality of head control at three months. PATIENTS AND METHODS: A prospective comparative practice-based study of a representative sample of 67 healthy infants born in the HUMIC, and divided into an experimental group (n = 35) and control group (n = 32). The Alberta Infant Motor Scale (AIMS) and a parent questionnaire were used as measurement tools. The intervention consisted of regular home visits to the experimental group (from the first to the third month). The two groups were evaluated in their homes at the end of 3 months. RESULTS: The differences in mean raw score of the AIMS at 3 months were, 16.26 in the experimental group and 10.38 in control group (P<.001). The percentile mean was 94 in the experimental group, and less than 50 (42) in the control group. All of the experimental group babies achieved the head control, with only 8 in the control group (25%). CONCLUSIONS: The significant findings suggest a direct relationship between the time spent in the prone position when the baby is awake and the achievement of head control at three months.


Subject(s)
Head/physiology , Prone Position , Guidelines as Topic , Humans , Infant , Prospective Studies
3.
Transplant Proc ; 40(2): 518-23, 2008 Mar.
Article in English | MEDLINE | ID: mdl-18374119

ABSTRACT

PURPOSE: The impact of pancreas transplantation (PT) on the progression of eye disease is still controversial. This study evaluated the course of retinopathy in transplanted rats in two different diabetic stages. METHODS: Sixty inbred male Lewis rats were assigned to four experimental groups: NC-15 nondiabetic control rats; DC-15 untreated diabetic control rats; PT1-15 diabetic rats that received syngeneic pancreas transplants 2 weeks after alloxan diabetes induction; PT2-15 diabetic rats that received pancreas transplants 12 weeks after diabetes onset. Clinical and laboratory parameters and lens opacity were examined in all rats prior to treatment and at 1-, 6-, and 12-months follow-up. Nucleated eyes from five rats in each group processed for ultrastructural study of the retinal at 6 and 12 months after PT or at follow-up. RESULTS: Cataracts were observed in 20%, 60%, and 100% of DC rats at 1-, 6-, and 12-months follow-up, respectively. Early PT (2 weeks) significantly reduced the prevalence of this complication but not late (12 weeks) PT. PT1 rats also showed improved ultrastructure of the superficial and deep capillary plexuses of the retina, and of Müller cells, compared with DC and PT2. In the last group, retinopathy continued to evolve despite successful PT. CONCLUSION: Our results suggested that prevention of diabetic ocular lesions by PT was closely dependent on earlier performance of the procedure.


Subject(s)
Cataract/prevention & control , Diabetes Mellitus, Experimental/surgery , Diabetic Retinopathy/prevention & control , Pancreas Transplantation/methods , Animals , Disease Models, Animal , Eye/pathology , Eye/ultrastructure , Male , Postoperative Complications/prevention & control , Rats , Rats, Inbred Lew , Transplantation, Isogeneic
4.
Transplant Proc ; 40(2): 524-8, 2008 Mar.
Article in English | MEDLINE | ID: mdl-18374120

ABSTRACT

PURPOSE: Oxidative stress is one of the most important mechanisms to explain genesis of the complications in the chronic progression of diabetes. In this investigation we studied the effects of pancreas transplantation (PT) on the imbalance caused by excessive production of free oxygen radicals by antioxidant defenses of rats with serious chronic hyperglycemia induced by alloxan. METHODS: Ninety inbred male Lewis rats were randomly distributed into three groups: NC-30 nondiabetic controls; DC-30 diabetic controls without any treatment; PT-30 diabetic rats undergoing syngeneic PT from normal donor Lewis rats. Each experimental group was then split into three subgroups of 10 animals for sacrifice after 1, 3, or 6 months. Clinical and laboratory parameters from all rats as well as lipid hydroperoxide (LPO) concentrations and renal tissue enzyme activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) were recorded for all rats. RESULTS: Successful PT corrected clinical and laboratory alterations in diabetic rats with sustained normoglycemia throughout the study. A significant increase in LPO concentration and a marked reduction in SOD and CAT enzyme activity were observed in DC rats; there was no significant variation in renal tissue GSH-Px in this group. However, alterations in DC rats were completely restored from 1st month after PT; all evaluated enzyme levels did not significantly differ (P < .01) from those in NC controls. CONCLUSION: Successful PT controlled cellular oxidative stress in diabetic kidneys, which may prevent chronic lesions.


Subject(s)
Diabetes Mellitus, Experimental/surgery , Diabetic Nephropathies/prevention & control , Oxidative Stress , Pancreas Transplantation/physiology , Animals , Catalase/metabolism , Diabetic Nephropathies/physiopathology , Glutathione Peroxidase/metabolism , Lipid Peroxides/metabolism , Male , Rats , Rats, Inbred Lew , Superoxide Dismutase/metabolism , Transplantation, Isogeneic
5.
Exp Clin Endocrinol Diabetes ; 116(4): 198-202, 2008 Apr.
Article in English | MEDLINE | ID: mdl-18072010

ABSTRACT

The purpose of this study was to investigate if experimental alloxanic diabetes could cause qualitative changes in intestinal anastomoses of the terminal ileum and distal colon in rats, as compared to controls. 192 male Wistar rats, weighing +/-300 g were split into four experimental groups of 48 animals each, after 3 months of follow-up: a control group with ileum anastomoses (G1), a control group with colon anastomoses (G2), a diabetic group with ileum anastomoses (G3) and a diabetic group with colon anastomoses (G4). Animals were evaluated and sacrificed on days 4, 14, 21 and 30 after surgery, and fragments of the small and large intestine where the anastomoses were performed were removed. Samples from 6 animals from each sacrifice moment were submitted to ultrastructural analysis of the collagen fibers using a scanning electron microscope and samples from another 6 animals were submitted to histopathology and optical microscopy studies using picrosirius red-staining. Histopathological analysis of picrosirius red-stained anastomosis slides using an optical microscope at 40x magnification showed that the distribution of collagen fibers was disarranged and also revealed a delay in scar tissue retraction. The morphometric study revealed differences in the collagen filled area for the ileum anastomoses 14 days post surgery whereas, in the case of colon anastomoses, differences were observed at days 4 and 30 post surgery, with higher values in the diabetic animals. Ultrastructure analysis of the ileum and colon anastomoses using a scanning electron microscope revealed fewer wide collagen fibers, the presence of narrower fibers and a disarranged distribution of the collagen fibers. We conclude that diabetes caused qualitative changes in scar tissue as well as in the structural arrangement of collagen fibers, what could explain the reduced wound strength in the anastomosis of diabetic animals.


Subject(s)
Anastomosis, Surgical/adverse effects , Diabetes Mellitus, Experimental/physiopathology , Wound Healing , Animals , Intestines/pathology , Intestines/surgery , Intestines/ultrastructure , Male , Microscopy, Electron , Rats , Rats, Wistar , Reference Values
6.
Transplant Proc ; 37(8): 3468-71, 2005 Oct.
Article in English | MEDLINE | ID: mdl-16298631

ABSTRACT

Groups of inbred alloxan-induced diabetic rats were treated with insulin (I), islets (IT), or pancreas transplantation (PT). Nondiabetic (N) and untreated diabetic (D) control groups were concurrently included. Each group was divided into five subgroups of 10 rats and killed after follow-up of 1, 3, 6, 9, and 12 months. Clinical and laboratory parameters were recorded, and kidney ultrastructural and morphometric analyses performed in each 12-month subgroup, namely glomerular basement membrane (GM) thickening, podocyte number, and number/extension of slit diaphragms (S). Rats from the I group showed poor metabolic control of diabetes compared with N group control rats. However, successfully transplanted rats (IT and PT) had complete restoration to normal levels for all metabolic parameters. GM thickening was significantly higher in diabetic compared with control rats. In contrast, the numbers of podocytes and slits as well as slit extensions were significantly decreased. Insulin therapy did not prevent any alterations upon comparison of diabetic vs control rats. Despite good metabolic control in IT rats, the degree of kidney lesion control never compared with that achieved in PT rats. In this group all glomerular changes were similar to the age-dependent lesions observed in control rats. We conclude that either IT or PT may be a good option for diabetes treatment, although pancreas transplantation seems to be the most effective treatment to control chronic complications.


Subject(s)
Diabetes Mellitus, Experimental/drug therapy , Diabetes Mellitus, Experimental/surgery , Insulin/therapeutic use , Islets of Langerhans Transplantation/physiology , Kidney Glomerulus/pathology , Pancreas Transplantation/physiology , Animals , Basement Membrane/pathology , Basement Membrane/ultrastructure , Blood Glucose/metabolism , Diabetes Mellitus, Experimental/pathology , Kidney Glomerulus/drug effects , Kidney Glomerulus/ultrastructure , Male , Pancreas Transplantation/methods , Pancreas Transplantation/pathology , Rats , Rats, Inbred Lew
10.
New Phytol ; 157(3): 617-631, 2003 Mar.
Article in English | MEDLINE | ID: mdl-33873411

ABSTRACT

• We tested the hypothesis that biological trait-based plant functional groups provide sufficient differentiation of species to enable generalization about a variety of plant ecophysiological traits or responses to nitrogen (N). • Seedlings of 34 North American grassland and savanna species, representing 5 functional groups, were grown in a glasshouse in an infertile soil with or without N fertilization. • Forbs, C3 and C4 grasses, on average, had similar relative growth rates (RGR), followed in declining order by legumes and oaks, but RGR varied greatly among species within functional groups. All measured attributes differed significantly among functional groups, of these, only RGR and photosynthesis differed among functional groups in response to N. All groups, except the legumes, had significantly greater photosynthetic and respiration rates at elevated N supply. Principal components analyses and cluster analyses yielded groupings that corresponded only moderately well to the biologically based a priori functional groupings. • Variation in RGR among species and treatments was positively related to net CO2 exchange (photosynthesis and respiration) and net assimilation rate, but unrelated to leaf area ratio. Photosynthetic and respiration rates were related to tissue %N among treatments and species. Our data indicate that RGR and related traits differ among the functional groups in significant ways, but in a complex pattern that does not yield simple generalizations about relative performance, controls on RGR, or response to resource supply rate.

12.
Rev Esp Anestesiol Reanim ; 44(8): 330-2, 1997 Oct.
Article in Spanish | MEDLINE | ID: mdl-9424689

ABSTRACT

Quality of analgesia provided by continuous infusion of tramadol through an elastomeric infuser (Baxter PC1071) was studied in a group of 40 women undergoing laparotomy to treat non tumoral disease. After a loading dose of 100 mg of tramadol in the recovery room, the elastomeric infuser was connected, loaded with 300 mg of tramadol in 48 ml of saline. The patient was then transferred to the ward. Analgesic quality was assessed on a visual analog scale (VAS) of 1 to 10 and on a semantic scale. Side effects, the need for supplemental analgesia and the opinion of the nurse were all recorded. The highest VAS score in the 24 h period was 2.69. Pain was described as slight by 52.5% of the women, moderate by 12.5% and absent by 35%. The main side effects were nausea and vomiting (12.5%). Three patients needed supplementary analgesia. The technique was described by 85% of the nurses as good (62.5%) or very good (22.5%). Elastomeric infusers are an effective way to deliver analgesics, and tramadol proved to be a valid analgesic for continuous infusion.


Subject(s)
Analgesia, Obstetrical , Analgesics, Opioid/administration & dosage , Pain, Postoperative/prevention & control , Tramadol/administration & dosage , Adult , Female , Humans , Infusion Pumps , Infusions, Intravenous/instrumentation , Middle Aged , Rubber
13.
Braz J Med Biol Res ; 29(8): 1019-24, 1996 Aug.
Article in English | MEDLINE | ID: mdl-9181084

ABSTRACT

We studied the effects of pancreas transplantation on kidney lesions of rats with alloxan-induced diabetes. Ninety inbred male Lewis rats were randomly assigned to 3 experimental groups: group NC included 30 non-diabetic control rats, group DC included 30 alloxan-induced diabetic control rats, and group PT included 30 alloxan-induced diabetic rats that received pancreas transplants from normal donor Lewis rats. Each group was further divided into 3 subgroups of 10 rats which were sacrificed at 1, 3, and 6 months of follow-up, respectively. Clinical and laboratory parameters during these periods were documented. The kidneys of 5 rats in each subgroup were studied and 50 glomeruli and tubules from each kidney were analyzed by light microscopy by two different investigators in a double-blind study. There was progressive glomerular basement membrane thickening (GBMT), mesangial enlargement (ME), and Bowman's capsule thickening (BCT) in kidneys of rats in the 3 experimental groups during follow-up. These alterations were significantly higher in DC rats (GBMT: 1.99 +/- 0.31; ME: 2.00 +/- 0.33; BCT: 1.88 +/- 0.27) when compared to NC (GBMT: 1.54 +/- 0.30; ME: 1.56 +/- 0.47; BCT: 1.36 +/- 0.35) and PT rats (GBMT: 1.49 +/- 0.29; ME: 1.57 +/- 0.36; BCT: 1.35 +/- 0.28) at 6 months (P < 0.01). The extent of GBMT, ME, and BCT observed in DC rats at 1 and 3 months was not significantly different from NC and PT rats. The amount of kidney lesions in PT rats was similar to that of NC rats and lower than those of DC rats at 6 months (P < 0.01). In addition, Armanni-Ebstein lesions of the tubules (AE) and tubular lumen protein (PRO) observed in DC rats were not present in NC or PT rats. We conclude that pancreas transplantation in alloxan-induced diabetic rats prevents the development of kidney lesions beginning at 6 months after transplantation.


Subject(s)
Diabetic Nephropathies/prevention & control , Pancreas Transplantation , Animals , Diabetes Mellitus, Experimental/therapy , Male , Rats , Rats, Inbred Lew
14.
Braz. j. med. biol. res ; 29(8): 1019-24, Aug. 1996. ilus, tab
Article in English | LILACS | ID: lil-187372

ABSTRACT

We studied the effects of pancreas transplantation on kidney lesions of rats with alloxan-induced diabetes. Ninety inbred male Lewis rats were randomly assigned to 3 experimental groups: group NC included 30 non-diabetic control rats, group DC included 30 alloxan-induced diabetic control rats, and group PT include 30 alloxan-induced diabetic rats that received pancreas transplants from normal donor Lewis rats. Each group was further divided into 3 subgroups of 10 rats which were sacrificed at 1,3, and 6 months of follow-up, respectively. Clinical and laboratory parameters during these periods were documented. The kidneys of 5 rats in each subgroup were studied and 50 glomeruli and tubules from each kidney were analyzed by light microscopy by two different investigators in a double-blind study. There was progressive glomerular basement membrane thickening (GBMT), mesangial enlargement (ME), and Bowman's capsule thickening (BCT) in kidneys of rats in the 3 experimental groups during follow-up. These alterations were significantly higher in DC rats (GBMT: 1.99 ñ 0.31; ME: 2.00 ñ 0.33; BCT: 1.88 ñ 0.27) when compared to NC (GBMT: 1.54 ñ 0.30; ME: 1.56 ñ 0.47; BCT: 1.36 ñ 0.35) and PT rats (GBMT: 1.49 ñ 0.29; ME: 1.57 ñ 0.36; BCT: 1.35 ñ 0.28) at 6 months (P<0,01). The extent of GBMT, ME, and BCT observed in DC rats at 1 and 3 months was not significantly different from NC and PT rats. The amount of kidney lesions in PT rats was similar to that of NC rats and lower than those of DC rats at 6 months (P<0.01). In addition, Armanni-Ebstein lesions of the tubules (AE) and tubular lumen protein (PRO) observed in DC rats were not present in NC or PT rats. We conclude that pancreas transplantation in alloxan-induced diabetic rats prevents the development of kidney lesions beginning at 6 months after transplantation.


Subject(s)
Rats , Animals , Male , Diabetic Nephropathies/prevention & control , Pancreas Transplantation/pathology , Diabetes Mellitus, Experimental/therapy , Rats, Inbred Lew
15.
Arq Gastroenterol ; 33(3): 158-66, 1996.
Article in Portuguese | MEDLINE | ID: mdl-9201329

ABSTRACT

In this study we present the technical details, adaptations and modifications of the original procedure of pancreaticoduodenal transplantation in rats described by Lee et al. in 1972. We also present the results and technical failures observed in a follow-up of 12 years. From March, 1982 to December, 1994, we performed in the Laboratory of Surgical Technique and Experimental Surgery of Faculty of Medicine, Botucatu-UNESP, Brazil, 665 duodenopancreatectomies in donor rats and 592 surgeries for revascularization of the pancreatic graft in recipient animals. The observed percentage of technical failures in donor rats was 11% due to bleeding and/or vascular complications, irregular flushing of the graft with saline and respiratory insufficiency. In recipients of grafts, we observed a percentage of technical failures of 22.5% due to porto-caval thrombosis, vascular bleeding, pancreatitis and graft ischemia. In both surgeries, the successful results are directly related to the technical performance of the surgeon and the cares in the postoperative period.


Subject(s)
Diabetes Mellitus, Experimental/surgery , Duodenum/transplantation , Pancreas Transplantation/methods , Animals , Female , Follow-Up Studies , Humans , Microsurgery/methods , Pancreaticoduodenectomy , Postoperative Complications , Rats , Rats, Inbred Lew , Rats, Wistar , Treatment Failure
16.
Braz J Med Biol Res ; 28(9): 977-80, 1995 Sep.
Article in English | MEDLINE | ID: mdl-8580886

ABSTRACT

Müller cells provide nutrition for neural cells. We studied the structure and ultrastructure of Müller cells in the retina of thirty 3-month old Wistar rats, divided equally into 3 groups: normal rats, alloxan diabetic rats and treated alloxan diabetic rats, 1 and 12 months after induction of diabetes. We observed that the Müller cell nuclei under light microscope examination had hexagonal shape and higher density than the other nuclei. Differences between groups could be observed only by electron microscopy. In the diabetic rats, Müller cells presented dispersion of nuclear chromatin and electrondense nuclear granulations, with the presence of increased glycogen, dense bodies and lysosomes in the cytoplasm. The alterations were more frequent in the perivascular region and at 12 months. The treated diabetic rats exhibited some alterations we observed in diabetic rats, but these alterations were less intense. We conclude that, despite the treatment, the diabetic retinopathy continues to evolve.


Subject(s)
Diabetes Mellitus, Experimental/pathology , Diabetic Retinopathy/pathology , Neuroglia/ultrastructure , Animals , Rats , Rats, Wistar , Retina/ultrastructure
17.
Braz. j. med. biol. res ; 28(9): 977-80, Sept. 1995. ilus
Article in English | LILACS | ID: lil-161088

ABSTRACT

Müller cells provide nutrition for neural cells. We studied the structure and ultrastructure of Müller cells in the retina of thirty 3-month old Wistar rats, divided equally into 3 groups: normal rats, alloxan diabetic rats and treated alloxan diabetic rats, 1 and 12 months after induction of diabetes. We observed that the Müller cell nuclei under light microscope examination had hexagonal shape and higher density than the other nuclei. Differences between groups could be observed only by electron microscopy. In the diabetic rats, Müller cells presented dispersion of nuclear chromatin and electrondense nuclear granulations, with the presence of increased glycogen, dense bodies and lysosomes in the cytoplasm. The alterations were more frequent in the perivascular region and at 12 months. The treated diabetic rats exhibited some alterations we observed in diabetic rats, but these alterations were less intense. We conclude that, despite the treatment, the diabetic retinopathy continues to evolve


Subject(s)
Animals , Rats , Diabetes Mellitus, Experimental/pathology , Neuroglia/ultrastructure , Diabetic Retinopathy/pathology , Alloxan , Insulin/administration & dosage , Rats, Wistar , Retina/ultrastructure
18.
Tree Physiol ; 14(3): 219-40, 1994 Mar.
Article in English | MEDLINE | ID: mdl-14967698

ABSTRACT

Many authors have attempted to explain the adaptive response of tropical plants to drought based on studies of water relations at the leaf level. Little attention has been given to the role of the xylem system in the control of plant water requirements. To evaluate this role, we studied the hydraulic architecture and water relations parameters of two tropical canopy trees with contrasting leaf phenologies: deciduous Pseudobombax septenatum (Jacq.) Dug and evergreen Ochroma pyramidale (Cav. ex lamb) Urban, both in the family Bombacaceae. The hydraulic architecture parameters studied include hydraulic conductivity, specific conductivity, leaf specific conductivity, and Huber value. Water relations parameters include leaf water potential, stem and leaf water storage capacitance, transpiration, stomatal conductance, and vulnerability of stems to cavitation and loss of hydraulic conductivity by embolisms. Compared to temperate trees, both species showed a pattern of highly vulnerable stems (50% loss of conductivity due to embolism at water potentials less than 1 MPa) with high leaf specific conductivities. The vulnerability of xylem to water-stress-induced embolism was remarkably similar for the two species but the leaf specific conductivity of petioles and leaf-bearing stems of the evergreen species, Ochroma (e.g., 9.08 and 11.4 x 10(-4) kg s(-1) m(-1) MPa(-1), respectively), were 3.4 and 2.3 times higher, respectively, than those of the deciduous species, Pseudobombax (e.g., 2.64 and 5.15 x 10(-4) kg s(-1) m(-1) MPa(-1), respectively). A runaway embolism model was used to test the ability of Ochroma and Pseudobombax stems to maintain elevated transpiration rates during the higher evaporative demand of the dry season. The percent loss of leaf area predicted by the runaway embolism model for stems of Pseudobombax ranged from 5 to 30%, not enough to explain the deciduous phenology of this tree species without analysis of root resistance or leaf and petiole vulnerability to embolism.

19.
Proc Natl Acad Sci U S A ; 89(19): 9084-8, 1992 Oct 01.
Article in English | MEDLINE | ID: mdl-11607329

ABSTRACT

Psychotria marginata, a shrub common to humid tropical forests in Central America, produces leaves in two seasonal flushes with contrasting morphology and physiology. Leaf production is bimodal with a major peak at the beginning of the annual wet season and a secondary peak at the end of the wet season. Together these peaks account for 75-87% of annual leaf production. Leaves produced just prior to the dry season have higher specific mass and, during drought, have lower stomatal conductances and higher water-use efficiencies. Plants irrigated during two consecutive dry seasons continued to produce leaves with these morphological and physiological differences, indicating that this feature has been strongly canalized by some factor other than water availability in this highly predictable yet seasonal habitat. The bimodal leaf production results in acclimation to changing conditions through co-occurring leaves that lack the physiological plasticity usually associated with acclimation. Heterophylly of this form suggests that the moderate drought of the dry season has been a significant selective factor for understory plants.

20.
Tree Physiol ; 10(4): 411-5, 1992 Jun.
Article in English | MEDLINE | ID: mdl-14969978

ABSTRACT

Despite many studies of the percent loss of hydraulic conductivity in excised branches, there is doubt as to whether cutting stems in air introduces unnatural embolism into the xylem at the cut surface. To address this question, hydraulic conductivity was measured in seedlings of northern red oak (Quercus rubra L.) and rooted scions of eastern cottonwood (Populus deltoides Bartr. ex Marsh.) that had been droughted in pots. Results indicate that in situ dehydration produced a very similar vulnerability curve (% loss of conductivity versus water potential) to those previously obtained by bench-top dehydration of excised branches of eastern cottonwood and red oak. In eastern cottonwood cuttings, conductivity loss increased sharply below water potentials of -1.0 MPa, with 100% loss of conductivity occurring by -2.0 MPa, whereas conductivity loss in red oak seedlings was more gradual, i.e., increasing below -1.5 MPa and sustaining 100% loss of conductivity by about -4.0 MPa.

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