Abstract
Excised roots of Pittosporum tobira Thunb. were exposed to temperatures of 25° to 60°C for 30 to 300 min before cell membrane thermostability was determined by electrolyte leakage procedures. Response to treatment temperature for each exposure duration was sigmoidal. The critical temperature causing injury to root cell membranes decreased linearily as exposure duration increased exponentially. A mathematical model to describe the interaction of treatment temperature and exposure duration on membrane thermostability is presented.
photosynthetic carbohydrate synthesis ( Huang et al., 2014 ; Wahid et al., 2007 ). Prolonged heat stress typically induces lipid peroxidation and membrane instability with subsequent effects on chlorophyll integrity and net photosynthetic rates in cool
decline, including heat stress (HT) and drought stress (DS). Because this species is often found in nature growing in wetland habitats and areas that do not have high summer temperatures ( Davy, 1980 ; Hagerup, 1939 ), tufted hairgrass may be sensitive to
; Huang et al., 1998 ; Jiang and Carrow, 2005 ; Jiang et al., 2009 ; Johnsen et al., 2009 ; Merewitz et al., 2010 ; Taghvaeian et al., 2013 ), heat stress ( Wang et al., 2013 , 2014 ), and salinity stress ( Schiavon et al., 2014 ) in both cool- and
to prevent denaturation of normal proteins ( Vierling, 1991 ). Small heat shock proteins (sHSP) with molecular weights ≈15 to 30 kD are a class of HSP that predominate in plant species during heat stress ( Waters et al., 1996 ). Some HSP are
Abstract
White and brown accessions of tepary bean (Phaseolus acutifolius Gray var. latifolius) and navy bean (Phaseolus vulgaris L. ‘Fleetwood’) were germinated at 0.0, −0.5, −1.0, −1.5, −2.0, and −2.5 MPa of NaCl at 25 or 35C for 9 days. Differences in germination percentages and rates between the two species were significant, especially at the higher salt concentrations. At 25C and salinities greater than or equal to − 2.0 MPa, tepary accessions had significantly higher percentage germination and germination rates than navy. At 35C this difference was noted at −1.5 MPa. The fresh weights of root plus hypocotyl appeared lower than controls at even the lowest concentration of salinity (− 0.5 MPa), suggesting that seeds germinated with NaCl did not produce vigorous seedlings. Of the three beans tested, the two tepary beans were more tolerant to NaCl than the navy bean, with the white tepary being most tolerant.
Rooted stem cuttings of Ilex crenata Thunb. `Rotundifolia' were grown in a controlled-environment growth chamber. Root-zone temperatures were controlled with an electric system. Shoot carbon exchange and root respiration rates were determined in response to root-zone temperatures of 28, 32, 36, and 40C for 6 hour·day–1 for 7 days. Photosynthesis was decreased by root zones ≥ 32C, while root respiration increased with increasing root-zone temperature. Decreased photosynthetic rates were not due to increased stomatal resistance.
Root growth of southern magnolia (Magnolia grandiflora Hort. `St. Mary') was studied for 16 weeks after an 8-week exposure to 30, 34, 38, or 42 ± 0.8C root-zone temperature (RZT) treatments applied for 6 hours daily. Immediately after RZT treatments, total root length of trees responded negatively to increased RZT in a quadratic pattern and the shoot and root dry weight of trees was similar. However, 8 and 16 weeks after RZT treatments, total root length responded linearly in a negative pattern to increased RZT, and shoot and root dry weight responded negatively to increased RZT in a linear and quadratic pattern, respectively. Root dry weight of trees exposed to 42C RZT treatment was 29% and 48% less than 38 and 34C RZT treatments, respectively, at week 8. By week 16, root dry weight as a function of RZT had changed such that the 42C RZT was 43% and 47% less than 38 and 34C RZT, respectively. Differences in root growth patterns between weeks 8 and 16 suggest that trees were able to overcome the detrimental effects of the 38C treatment, whereas growth suppression by the 42C treatment was still evident after 16 weeks.
Nonplanted Caladium × hortukmum Birdsey `Candidum' tubers were exposed to 26 (control), 38,43, or 48C for 1,2, or 3 days. Then tubers were planted and forced in a glasshouse for 4 weeks at 18 to 33C (air). Leaf emergence from tubers exposed to 48C for 1 or 2 days required 3-12 days longer than leaf emergence from control tubers. No leaves emerged from tubers treated at 48C for 3 days. Exposing tubers to 38C for 3 days or 43C for 1 day did not affect subsequent plant growth. Exposing tubers to 43C for 2 or 3 days or 48C for 1 or 2 days resulted in plants with reduced shoot fresh weights and fewer leaves ≥ 15 cm. In a second experiment, planted tubers were forced for 10 days at 26C so that roots had developed to the edge of the pot and shoots had emerged to the soil surface. These planted (sprouting) tubers were exposed to 43C for 0,4,8,12,16,20, or 24 hours/day for 1,3, or 5 days and then forced for 7 weeks in a glasshouse. With 3- or 5-day treatments, days to leaf emergence increased as the hours of exposure to 43C increased. Only 33% of planted tubers exposed to 43C for 24 hours/day for 5 days sprouted. Tubers exposed to 43C for≤ 12 hours/day for 3 days produced plants of similar or greater height, numbers of leaves □≥15 cm wide, and shoot fresh weights, but additional hours of daily exposure decreased these plant characteristics. At 5 days, plant height, number of ≥ 15-cm-wide leaves, and shoot fresh weight decreased linearly with increased hours of exposure of tubers to high temperature.
Abstract
Heat resistance of aspen (Populus tremuloides) leaves was assessed by stressing leaf discs in vitro and measuring electrolyte leakage. Leaves were obtained from trees growing at elevations of 1960, 2195, and 2454 m. Heat tolerance was greatest in leaf samples from trees growing at the lowest site. Trees propagated from these sites and grown at 1520 m for 2 years showed some increase in heat tolerance, but apparent ecotypic differences persisted.