Drought-stressed Seedlings Research Articles

Drought differentially affects expression of a PR-10 protein, in needles of maritime pine (Pinus pinaster Ait.) seedlings.

A full length cDNA encoding a PR-10 protein was isolated from maritime pine drought-stressed seedlings. The predicted protein contained 150 amino acids, has a molecular mass of 16.7 kDa and an isoelectric point of 5.28. The transcript level of PR-10 displayed a transient accumulation in needles of drought-stressed plants, and was not detectable in root and stem tissues.

Acclimation of photosynthetic properties to long-term drought stress in seedlings of Japanese mountain birch

Acclimation of photosynthetic properties to long-term drought stress in seedlings of Japanese mountain birch

Turgor regulation via cell wall adjustment in white spruce

Turgor regulation at reduced water contents was closely associated with changes in the elastic quality of the cell walls of individual needles and shoots of naturally drought-resistant seedlings of white spruce (Picea glauca [Moench] Voss.) and of seedlings of intermediate resistance that had been pretreated with paclobutrazol, a stress-protecting, synthetic plant-growth regulator. Paclobutrazol-treated seedlings showed marked increases in drought resistance, and pressure-volume analysis combined with Chardakov measurements confirmed observations that water stress was ameliorated during prolonged drought. Turgor was maintained in the paclobutrazol-treated and in the naturally resistant drought-stressed seedlings despite water contents near or below the turgor-loss volumes of well-watered controls. The maintenance of turgor in these seedlings was in large part a function of the dynamic process of cell wall adjustment, as reflected by marked reductions in both the saturated and turgor-loss volumes and by large increases in the elastic coefficients of the tissues. Shear and Young's moduli, calculated from pressure-volume curves and the radii and wall thicknesses of mesophyll cells, also confirmed observed changes in the elastic qualities of the cell walls. Elastic coefficients of well-watered, paclobutrazol-treated seedlings were consistently larger than those in well-watered controls and several times larger than the values in untreated plants, which succumbed rapidly to drought. In contrast, untreated seedlings that withstood prolonged drought without wilting displayed elastic coefficients similar to those in seedlings that had been treated with paclobutrazol but that had not been exposed to drought.

Effects of ozone and mild drought stress on gas exchange, antioxidants and chloroplast pigments in current-year needles of young Norway spruce [Picea abies (L.) Karst.

To investigate the effects of ozone exposure and soil drought, singly and in combination, on gas exchange, antioxidant contents and pigments in current-year needles of Norway spruce [Picea abies (L.) Karst.] 4-year-old seedlings were fumigated in growth chambers with either charcoal-filtered air or with 100 nl l–1 ozone for 106 days. After 3 weeks a 20% reduction in gas exchange was observed in ozone-treated seedlings. However, no further decrease occurred in spite of continued ozone exposure. Whole needle ascorbate and apoplastic ascorbate increased until the end of the experiment and contents were 62% and 82%, respectively, higher than in ozone-free controls. This increase in ascorbate might have protected net photosynthesis from further decline. Ozone pre-treated plants and ozone-free controls were subjected to soil drought for 38 days which caused stomatal narrowing. Thereby ozone uptake was reduced when compared to well watered seedlings. At the end of the experiment drought alone, and even more in combination with ozone, had also caused an increase in ascorbate. Glutathione increased only in drought-stressed seedlings. The redox states of the ascorbate and the glutathione pools were not affected by any treatment. Superoxide dismutase activity declined under both stresses but was most reduced by ozone alone. While chlorophyll and neoxanthin contents remained unchanged, carotenes were significantly decreased upon drought. The combination of O3 and drought induced increased lutein contents, an increased pool size of the xanthophyll cycle as well as an increased epoxidation status of the xanthophyll cycle. These results suggest that spruce needles seem to be able to acclimate to ozone stress but also to drought stress by increasing their ascorbate pools and protecting pigments.

Geographical variation in water relations, hydraulic architecture and terpene composition of Aleppo pine seedlings from Italian provinces.

Ecotypic variations in leaf conductance, soil-to-leaf hydraulic conductance, components of tissue water potential, hydraulic architecture parameters and xylem embolism were examined in greenhouse-grown two-year-old Aleppo pine (Pinus halepensis Mill.) seedlings from six origins representing the geographic range of the species in Italy. Cortical resin composition of the seedlings was also determined. Measurements were made on well-watered seedlings and on seedlings subjected to recurring severe drought. Drought-stressed seedlings had lower mean leaf conductances, transpiration rates and soil-to-leaf hydraulic conductances than well-watered seedlings. They also exhibited more negative osmotic potentials, higher relative water deficit at incipient plasmolysis, but a similar maximum modulus of elasticity. Drought-stressed seedlings showed a higher degree of xylem embolism, a lower Huber value, lower leaf specific conductivity and lower specific conductivity than well-watered seedlings. Drought-stressed seedlings of provenances from more xeric habitats (Tremiti, Porto Pino and Mottola) had greater leaf conductances, transpiration rates and soil-to-leaf hydraulic conductances than drought-stressed seedlings of provenances from more mesic habitats (Imperia, Otricoli and Vico del Gargano). They also showed higher osmotic adjustment and a lower degree of xylem embolism. Among provenances, there were no significant differences in hydraulic architecture parameters in response to the drought treatment; however, Tremiti and Porto Pino seedlings displayed smaller drought-induced reductions in specific conductivity and leaf specific conductivity, respectively, than seedlings from other provenances. These differences suggest that seedlings from xeric provenances, especially Tremiti, have greater resistance to desiccation than seedlings from mesic provenances. No clear association was found between terpene variability and the other traits investigated, although terpene composition was related to the geographical distribution of the provenances. We conclude that the drought-tolerance responses of Tremiti make it a more suitable provenance than the others for establishment on sites prone to severe soil water deficits.

Changes of the photosystem 2 activity and thylakoid proteins in spruce seedlings during water stress

We subjected spruce [Picea glauca (Moench) Voss × P. engelmanni Parry hybrid complex] seedlings to a severe water stress (shoot water potential ≤-3.5 MPa) to permit assessment of stress effects on photosystem 2 (PS2) in isolated photosynthetic membranes. The thylakoids and Triton-treated membranes isolated from stressed seedlings showed declines in O2-evolving capacity (H2O → 2,6-dichloro-p-benzoquinone, DCBQ) and electron transport activity (H2O → 2,6-dichlorophenol indophenol, DCIP). A partial restoration of O2-evolution by adding CaCl2 suggested an effect of water stress on the oxygen-enhancing extrinsic (OEE) polypeptides. Water stress had an additional impact on the reaction centre, shown by the inability of 1,5-diphenylcarbazide (DPC) to restore the electron transport (DPC → DCIP) to the levels seen in control membranes. Quantification of specific photosynthetic membrane proteins by immunoblots strengthened the above suggestions: after drought stress, concentrations of OEE1 and OEE2 declined by 40 %, and amount of the reaction centre protein D1, ATP synthetase, and cytochrome f also declined. The specific effect of stress on these proteins was confirmed by the fact that the amount of chlorophyll-protein complex CP2 was unchanged in membranes isolated from drought-stressed seedlings.

Drought stress in seedlings: Lipid metabolism and lipid peroxidation during recovery from drought in Lotus corniculatus and Cerastium fontanum

Drought stress in seedlings: Lipid metabolism and lipid peroxidation during recovery from drought in Lotus corniculatus and Cerastium fontanum

Drought stress in seedlings: Lipid metabolism and Lipid peroxidation during recovery from drought in Lotus comiculatrus and Cerastium fontanum

Seedling survival of drought during the first days following germination can be one of the most critical factors in successful establishment of the species. Seventy‐two hour old seedlings of Cerastium fontanum Baumg. and Lotus corniculatus L. were exposed to severe desiccation for 36 h and the recovery of the whole plants monitored over the subsequent 17 days. The analysis exposed the very different responses to water stress in the two species. The effects of water stress on the less drought tolerant L. corniculatus within the first 5 to 10 days after drought treatment included a 2‐fold larger loss in dry weight than in C. fontanum and a 2‐fold rise in lipid peroxidation (thiobarbituric acid‐reactive substances), in triacylglycerols and in free fatty acids. The ratio of mo‐nogalactosyl diacylglycerols/digalactosyl diacylglycerols (MGDG/DGDG) declined 3‐fold, while the proportion of MGDG was some 12‐fold lower. In contrast, in the relatively drought‐tolerant seedlings of C. fontanum no changes of this order were recorded in the days immediately following rehydration. The relationship between these changes in lipid metabolism, lipid peroxidation and drought‐induced damage in terms of growth is discussed in the context of seedling recovery and survival in the two species.

Differences in Plant and Soil Water Relations in and Around a Forest Gap in West Africa during the Dry Season may Influence Seedling Establishment and Survival

Summary 1 Soil and plant-water relations were studied in a canopy opening and surrounding forest shade in a moist tropical forest in Ghana using seedlings of two tree species with different regeneration strategies, the pioneer Terminalia superba and the nonpioneer light demander Entandrophragma utile. 2 During two consecutive dry seasons, soil matric potential varied from -30 kPa at the end of the rainy season, to below -2.5 MPa in the middle of the dry season. During part of the first dry season soil matric potential was higher in the gap than in the surrounding forest. In the second dry season no differences were observed. 3 Leaf water potential varied from about -750 kPa at dawn for unstressed seedlings of both species to <-2.5 MPa when seedlings were permanently wilted. For both species, the maximum stomatal conductance of unstressed seedlings varied from 300 to 450 mmol m-2 s-' for those in the gap centre to 150 mmol m-2 s-' for those under forest shade. Maximum conductance decreased to between 10 and 30 mmol m-2 s-1 in drought-stressed seedlings during the middle of the dry season. The two species responded similarly to a drying soil profile but the decrease in leaf water potential and stomatal conductance was more rapid under forest canopy than in the centre of the gap. 4 Only 7% of the seedlings of Terminalia superba and 4% of Entandrophragma utile survived the dry season under forest shade. In contrast, 85% and 78%, respectively, survived of those growing in the centre of the forest gap. At all positions, seedlings of T. superba had larger relative height growth rates during the wet season than E. utile (29.6, 21.4 and 8.4% month-' compared with 5.2, 20.0 and 1.6% month-', for gap centre, margin and forest shade, respectively). 5 The observed changes in leaf water potential and stomatal conductance indicated that despite the reduced irradiance, shaded seedlings experienced more drought stress during the dry season than seedlings growing in the forest gap. The reasons for this and possible consequences for trees which differ in leaf phenology and regeneration strategy are discussed.

Stomatal and mesophyll limitations of photosynthesis in black spruce seedlings during multiple cycles of drought.

Container-grown black spruce (Picea mariana (Mill.) B.S.P.) seedlings were planted in trays containing a sand and peat mixture, and placed in a climate-controlled greenhouse. One group of seedlings was kept well-watered, and another group was subjected to three cycles of drought. Gas exchange analysis showed that mesophyll photosynthetic function was largely unimpaired by drought. In contrast, stomatal conductance was sensitive to drought, although it became less sensitive with each drought cycle. Both stomatal and mesophyll conductances increased with time in control and drought-stressed seedlings, but mesophyll conductance increased with time more rapidly than did stomatal conductance. Limitation of photosynthetic rate was dominated by the mesophyll. In control seedlings, relative stomatal limitation increased from 6 to 16% by the end of the experiment. In drought-stressed seedlings, relative stomatal limitation of photosynthesis reached 40% during the first drought, but decreased to near control values immediately after rewatering. Because the third, most severe drought had only a minor effect on stomatal conductance, relative stomatal limitation of photosynthesis was similar to that in control seedlings by the end of the experiment. Inhibition of ontogenetic change during drought stress may be responsible for the apparent acclimation of mesophyll photosynthetic processes. We conclude that it would be more effective to select for high photosynthetic capacity than for reduced stomatal sensitivity when breeding for increased drought resistance in black spruce seedlings.

Canopy development and solar conversion efficiency in Acacia auriculiformis under drought stress

A glasshouse experiment was performed with Acacia auriculiformis seedlings to investigate the effects of decreased soil water potential on phyllode extension, abscission and solar conversion efficiency, e. Six-month-old seedlings were subjected for 39 days to one of four treatments: well watered (soil water potential maintained above -0.5 MPa), moderately drought stressed (soil water potential maintained above -1.5 MPa), severely drought stressed (soil water potential maintained above -2.5 MPa) and well watered but pruned to maintain a leaf area approximating that of the severely drought-stressed treatment. Aboveground biomass accumulation decreased by 21% below that of the well-watered controls in the moderately drought-stressed seedlings and by 47% in the severely drought-stressed seedlings as a result of both decreased interception of solar radiation and lower e. Differences in phyllode extension rate, rather than in phyllode abscission, were primarily responsible for the differences in interception of solar radiation among treatments. Decreases in phyllode extension rate and water use occurred simultaneously in response to decreasing soil water potential. Specific leaf area decreased and water use efficiency increased in response to drought stress.

Growth responses of ponderosa pine to long-term exposure to ozone, wet and dry acidic deposition, and drought

A 3-year field study of the cumulative effects of ozone (O3), wet and dry acidic deposition, and soil water availability was conducted on ponderosa pine (Pinusponderosa Laws.) in the Sierra Nevada of California from 1988 to 1990. Thirty-six 2-year-old potted seedlings were placed in each of 30 chambers and exposed from May through October to three levels of O3 (charcoal-filtered (CF), nonfiltered (NF), and NF plus 1.5 times ambient O3 (NF150)); three levels of acidity in simulated rain (pH 3.5, 4.4, 5.3); two levels of dry deposition (60 or 90% filtration), and two levels of soil water availability (well watered (WW) or drought stressed (DS)). An additional six plots served as ambient air (AA) controls. One-third (432) of the trees were harvested at the end of each exposure season. Low soil water availability was the only stress factor to significantly affect growth following the first exposure season. After the second season, O3 significantly reduced foliar biomass in WW–NF150 trees, but DS seedlings did not respond to O3. After 3 years of exposure, WW–NF150 trees averaged 70% loss of 1988 needles and 48% loss of 1989 foliage. Ozone-injured seedlings compensated for these losses by increased growth of current-year needles and stems and also increased growth of fine feeder roots. Radial stem growth and coarse-root growth were significantly reduced in O3-injured trees. DS trees in NF150 chambers averaged half the needle loss of WW trees and showed no reduction in radial growth in response to O3. Rain pH and dry deposition had no direct effects on growth of ponderosa pine. These cumulative responses to interacting stresses indicate the importance of multifactorial, long-term studies to evaluate forest tree responses to atmospheric deposition.

Variation in seedling hydraulic architecture as a function of species and environment.

Northern red oak (Quercus rubra L.) and yellow-poplar (Liriodendron tulipifera L.) were grown for two years in full sunlight (unshaded) or 20% of full sunlight (shaded) under either well-watered or drought conditions. There was a close association between evaporative flux (in situ) and leaf-specific conductivity (LSC) in stem segments of both species. Shaded, drought-stressed seedlings of both species had significantly reduced leaf area, evaporative flux, volume flow rate in xylem, flow velocity, potentially functional xylem area, and LSC than unshaded, well-watered seedlings. Reductions in LSC associated with drought or shade were similar for both species; and within a treatment, both species had similar LSC. Species differed in the manner of LSC adjustment to drought and shade. Reductions in leaf area associated with drought or shade were accompanied primarily by reductions in potentially functional xylem area for L. tulipifera, and by reductions in flow velocity for Q. rubra. These results suggest (1) the existence of a homeostatic balance between evaporative flux and LSC, (2) that species with widely different growth patterns and xylem anatomies may develop similar LSC within the same environment, and (3) a possible hydraulic basis for differences in habitat between ring- and diffuse-porous species.

Effects of long-term ozone exposure and drought on the photosynthetic capacity of ponderosa pine (Pinus ponderosa Laws.).

Seedlings of ponderosa pine (Pinus ponderosa Laws.) were grown for three years under three atmospheric ozone concentrations - clean air (CF), ambient ozone (NF), and 15 times ambient ozone (NF150)-at a moderately-polluted site in the Sierra Nevada, under either well-watered or drought-stressed conditions. When the trees were 5 years old, photosynthetic capacities of 2-year-old, 1-year-old, and current-year needles were measured during August and September of the 3rd season of exposure. Current-year needles of NF150 trees had higher photosynthetic capacity than NF and CF trees during late summer, an effect due to greatly enhanced photosynthesis in well-watered plants that had lost older needles as a result of ozone damage. This photosynthetic compensation in well-watered NF150 seedlings was related to higher tissue nitrogen concentration in the current-year foliage and possibly to increased inorganic phosphate cycling, both responses to the loss of older needles. Drought-stressed NF150 seedlings were partially protected from ozone damage by decreased stomatal conductance and did not exhibit the same degree of photosynthetic compensation. No differences in photosynthetic rate were found between CF and NF seedlings or between well-watered and drought-stressed seedlings (across ozone treatments) in any needle age class.

Foliar injury responses of ponderosa pine seedlings to ozone, wet and dry acidic deposition, and drought

A 3-year field study of the potential interactions of ozone (O 3), wet and dry acidic deposition, and soil water availability on foliar injury responses of 18 ponderosa pine ( Pinus ponderosa Laws.) families was conducted in the Sierra Nevadas of California. Thirty-six 2-year-old seedlings in each of 30 open-top chambers (plus six ambient air plots) were exposed to combinations of three levels of O 3 [charcoal-filtered (CF), non-charcoal filtered (NF), and NF plus 1.5 times ambient O 3 (NF150)]; three simulated rain pH treatments (pH 3.5, 4.4, 5.3); two levels of dry deposition (60% filtration of ambient dry deposition and 90% filtration), and two irrigation regimes (approximately weekly watering vs irrigation every other week) for three growing seasons. One-third of the trees were harvested at the end of each year. O 3, irrigation level, amount of dry deposition, and family (genotype) significantly affected degree of foliar injury responses to O 3. The interactions of O 3 with irrigation amount and O 3 with dry deposition were also statistically significant. Drought-stressed seedlings had significantly less O 3 injury than well-watered trees, but seedlings exposed to 60% filtration of dry deposition had significantly greater O 3 injury than those in the 90% filtered treatments. Ponderosa pine families differed greatly in susceptibility to O 3, ranging from two with an average of > 20% O 3 injury to several with nearly no O 3 injury. These results reflect the complex patterns ofponderosa pine responses to natural and pollutant stresses and emphasize the importance of long-term, multifactorial experiments to elucidate those patterns.

Growth and water relationships of red spruce seedlings exposed to atmospheric deposition and drought

Two-year-old containerized seedlings of red spruce (Picearubens Sarg.) were subjected to ozone (O3) fumigation (0.25 ppm), simulated acid rain (pH 4.2 or 3.0), and drought prior to measurement of changes in growth and plant water status. Drought caused a significant decline in terminal height growth and new-shoot dry weight, but old-shoot dry weight, root dry weight, and root/shoot ratio were not appreciably affected. Deposition treatment (O3 and (or) acid rain) influenced both shoot and root dry weight but did not significantly affect height or root/shoot ratio. Treatment with either 0.25 ppm O3 alone or pH 3.0 rainfall alone caused the greatest reduction in growth, while treatment with 0.25 ppm O3 + pH 4.2 rain had the least effect. The influence of deposition treatment generally was more pronounced in seedlings subjected to drought than in well-watered plants. Seedlings subjected to drought had lower (more negative) water potentials than well-watered plants regardless of deposition treatment. While there were no significant differences in the water status of well-watered seedlings exposed to various deposition treatments, xylem water potential and osmotic potential of drought-stressed seedlings treated with O3 alone were consistently lower than these characteristics in seedlings treated with O3 + acid rain together. Except for one deposition treatment (0.25 ppm O3 + pH 3.0 rain) there was no evidence for osmotic adjustment of red spruce seedlings in response to stress factors imposed in this study.

Effects of drought stress on hydraulic architecture of seedlings from five populations of green ash

Two-year-old seedlings of green ash, Fraxinus pennsylvanica Marsh., representing five native populations from an east to west precipitation gradient, were grown under contrasting moisture regimes in the greenhouse. At midsummer and the end of the growing season, leaf areas, earlywood and latewood transverse areas, and several structural attributes of the xylem hydraulic system were compared between well-watered and drought-stressed seedlings. Xylem hydraulic capacity was essentially fixed by midsummer. Drought significantly reduced both earlywood and latewood production but had no significant effect on potentially functional xylem area (Apf) or flow velocity (v). The principal effect of drought on hydraulic architecture was a significant reduction in leaf area and therefore the ratios of potentially functional xylem area to unit leaf area (Apf to A1) and leaf specific conductivity (LSC). In contrast, populations differed significantly in all measured parameters, especially under drought conditions. Path analysis of LSC and its component variables revealed that treatment differences in LSC arose primarily through differences in A1; contributions from variation in Apf and especially flow velocity were relatively minor. In contrast, population variation in LSC could be attributed in roughly equal measure to variation in Apf and A1, and to a lesser degree to variation in flow velocity. The covariance between A1 and Apf was important for both treatment and population variation in LSC, suggesting a fundamental physiological linkage between these two aspects of plant hydraulic architecture. Among populations, high flow velocity tended to be associated with low Apf to A1 values, thereby minimizing population differences in the composite character LSC. Populations differed significantly in all attributes studied, in one environment or another, but those at either end of the precipitation gradient did not differ in several presumably important structural attributes. Although plant hydraulic architecture is genetically controlled and variable in green ash seedlings, its adaptive significance cannot be considered in isolation from other factors that control plant response to water stress. Key words: leaf specific conductivity, ecotypic variation, xylem structure.

Analysis by high-performance liquid chromatography of free amino acids extracted from needles of drought-stressed and shaded Pinus ponderosa seedlings

Analysis by high-performance liquid chromatography of free amino acids extracted from needles of drought-stressed and shaded Pinus ponderosa seedlings

Some physiological considerations on sulfur dioxide sensitivity in drought-stressed seedlings of sweetgum ( Liquidambar styraciflua L.)

Two-year-old containerized seedlings of sweetgum ( Liquidambar styraciflua L.) were subjected to sulfur dioxide (SO 2) fumigation (0.25 ml l −1, 6 h daily for 5 consecutive days) and drought stress (2, 4, 7 or 13 days without water) prior to measuring net photosynthesis ( P n), stomatal conductance ( G s), xylem pressure potential ( ψ x) and foliar abscisic acid (ABA) content. Seedlings exposed to drought alone exhibited significant reductions in P n (30%), G s (43%) and ψ x (25%), but ABA content remained unchanged. For seedlings fumigated with SO 2 only, ABA content was reduced 46%, but P n, G s and ψ x were not significantly affected. P n, G s and ψ x decreased over time (2–13 days) regardless of the stress treatment. Interactions involving drought × time and SO 2 fumigation × time were found to affect both P n and G s, but the combination of drought and SO 2 had no appreciable influence on any of the physiological parameters measured.

Pressure–volume analysis of leaves of Robiniapseudoacacia L. with the sap expression and free transpiration methods

Leaf tissue water relations parameters of well-watered and drought-stressed black locust (Robiniapseudoacacia L.) seedlings were compared using the sap expression and free transpiration pressure–volume analysis techniques. Osmotic potentials at full tissue hydration and at the turgor loss point were higher using the sap expression method for well-watered but not for drought-stressed seedlings. These differences appeared to be related to the percentage of water left uncollected during the sap expression procedure. Osmotic adjustment in response to drought was detected by both methods. Leaf relative water content at the turgor loss point and the symplastic water fraction did not differ between methods. The relationship between bulk tissue elastic modulus (E) and turgor potential estimated by both techniques was not significantly different, although E values derived from sap expression curves for well-watered seedlings were generally higher at a given turgor potential.