Changes in Levels of Solutes During Osmotic Adjustment to Water Stress in Leaves of Four Tropical Pasture Species

1981 ◽  
Vol 8 (1) ◽  
pp. 77 ◽  
Author(s):  
CW Ford ◽  
JR Wilson
Keyword(s):  
Water Stress ◽  
Organic Acids ◽  
Osmotic Adjustment ◽  
Inorganic Ions ◽  
Arid Environment ◽  
Low Molecular Weight ◽  
Panicum Maximum ◽  
Buffel Grass ◽  
Heteropogon Contortus ◽  
Macroptilium Atropurpureum

Three tropical grasses, green panic (Panicum maximum var. trichoglume), buffel grass (Cenchrus ciliaris), and spear grass (Heteropogon contortus), and a tropical legume, siratro (Macroptilium atropurpureum), were field-grown in a semi-arid environment. One set of plants was well watered, while another set was subjected to a continuous 35-day drying cycle. Samples of specific leaves were taken at the beginning, middle and end of the drying cycle, and 1, 5 and 14 days after rewatering. The major low-molecular-weight solutes which accumulated in the grasses during water stress were the inorganic ions sodium (green panic), potassium (buffel and spear grass) and chloride (all grasses). Accumulation of these ions largely accounted for the osmotic adjustments determined from a previous study of water relations of the leaves. Concentrations of the minor constituents glucose and fructose increased only slightly in the stressed grasses, whereas levels of sucrose, the major carbohydrate component, increased substantially, particularly in spear grass. Inositol accumulated to a small extent in spear grass. Differences between the grasses were evident in the organic acid spectrum and also in changes in concentration of organic acids due to water stress. In water-stressed tissue, malate levels increased in green panic and spear grass but were reasonably constant in buffel grass. Aconitate concentrations (not detected in buffel grass) decreased in stressed green panic, but increased in spear grass. Oxalate (only trace quantities in spear grass) was a major component in green panic and buffel grass, but did not appear to vary with increase in water stress. Succinate accumulated only in stressed spear grass. The contribution of carbohydrates and organic acids to the osmotic adjustment was relatively small. Proline accumulated to varying degrees in all stressed grasses. Betaine occurred only in trace amounts in spear grass, but accumulated substantially in green panic and buffel grass. Water-stressed leaves of siratro did not accumulate inorganic ions, sugars, organic acids, proline or betaine, but pinitol levels increased. Implications of the results relating osmotic adjustment to changes in chemical composition are discussed.

Adaptation to Water Stress of the Leaf Water Relations of Four Tropical Forage Species

1980 ◽  
Vol 7 (2) ◽  
pp. 207 ◽  
Author(s):  
JR Wilson ◽  
MM Ludlow ◽  
MJ Fisher ◽  
E Schulze
Keyword(s):  
Water Stress ◽  
Water Content ◽  
Water Relations ◽  
Bound Water ◽  
Leaf Tissue ◽  
Dry Weight ◽  
Panicum Maximum ◽  
Soil Drying ◽  
Buffel Grass ◽  
Heteropogon Contortus

Three tropical grasses, green panic (Panicum maximum var, trichoglume), spear grass (Heteropogon contortus) and buffel grass (Cenchrus ciliaris) and the tropical legume siratro (Macroptilium atropurpureum), were grown in plots in a semi-arid field environment. The water relations characteristics of leaves from plants subjected to a soil drying cycle were compared with those of unstressed leaves from plants in irrigated plots. Minimum water potentials attained in the stressed leaves were c. -44, - 38, - 33 and - 13 bar for the four species, respectively. The grass leaves adjusted osmotically to water stress, apparently through accumulation of solutes, so that there was a decrease in osmotic potential at full turgor (Ψπ100) of 5.5, 3.9 and 7.1 bar, and in water potential at zero turgor (Ψ0) of 8.6, 6.5 and 8.6 bar for green panic, spear grass and buffel respectively. Water stress appeared to increase slightly the proportion of bound water (B) and the bulk modulus of elasticity (ε) of the grass leaves, but it did not alter the relative water content at zero turgor (RWC0) or the ratio of turgid water content to dry weight of the tissue. The Ψπ100 and Ψ0 of stressed siratro leaves decreased by 2.5-4 bar and 3-5 bar respectively when subjected to soil drying cycles. These changes could be explained by the marked decrease in the ratio of turgid water content to dry weight of the leaf tissue rather than by accumulation of solutes. The values of RWC0 and ε for siratro leaves were not altered by stress but, in contrast to the grasses, B was apparently decreased although the data exhibited high variability. Adjustments in Ψπ100 and Ψ0 of stressed leaves of buffel grass and siratro were largely lost within 10 days of rewatering.

Time Trends for Change in Osmotic Adjustment and Water Relations of Leaves of Cenchrus ciliaris During and After Water Stress

1983 ◽  
Vol 10 (1) ◽  
pp. 15 ◽  
Author(s):  
JR Wilson ◽  
MM Ludlow
Keyword(s):  
Water Stress ◽  
Water Potential ◽  
Water Relations ◽  
Osmotic Adjustment ◽  
Leaf Growth ◽  
Weight Ratio ◽  
Bound Water ◽  
Arid Environment ◽  
Leaf Water ◽  
Buffel Grass

Buffel grass was subjected to a soil drying cycle for 5 weeks in a semi-arid environment. As water stress developed, the leaf water relations characteristics of these plants (Dry treatment) were compared with those of irrigated plants (Wet treatment). Leaf water potential (Ψ) of the Dry treatment measured at 1400 h decreased to a minimum of -6.9 MPa. The stressed leaves adjusted osmotically, with the osmotic potential at full turgor (Ψπ100) decreasing (becoming more negative) linearly with time (0.017 MPa day-1) and with decreasing water potential measured at 1400 h (0.11 MPa per 1 MPa decrease in Ψ). Maximum osmotic adjustment (Ψπ100 Wet -Ψπ100 Dry) was 0.66 MPa, and this change together with lower cell wall elasticity decreased by 1.03 MPa the water potential (Ψ0) at which the stressed leaves lost turgor. Differences between the stress- acclimated Dry leaves and the Wet leaves in bound water, turgid weight:dry weight ratio and the relative water content at which they reached zero turgor were small and inconsistent. At 18 days after rewatering, the Ψπ100 value of acclimated leaves was still 0.18 MPa lower than that of the control leaves. The substantial shift in Ψ0 gained the stress-acclimated leaves only one extra day before they lost turgor at 1400 h, and only 2.5 extra days before being permanently wilted. This small gain in time and the rapid cessation of leaf growth even before positive turgor was completely lost suggests that osmotic adjustment may not contribute greatly to continued leaf growth in water-stressed plants of buffel grass.

Leaf water potentials of pasture plants in a semi-arid subtropical environment

1975 ◽  
Vol 15 (76) ◽  
pp. 645 ◽  
Author(s):  
DCI Peake ◽  
GD Stirk ◽  
EF Henzell
Keyword(s):  
Water Stress ◽  
Leaf Water ◽  
Panicum Maximum ◽  
Research Station ◽  
Buffel Grass ◽  
Heteropogon Contortus ◽  
Drought Avoidance ◽  
Water Potentials ◽  
Severe Water Stress ◽  
Pasture Plants

Leaf water potentials (�1) were measured on pasture plants at the Narayen Research Station in southern Queensland. The main findings were: 1. There were marked differences between species in the value of �1, measured during drought. Lucerne (Medicago sativa cv. Hunter River) and buffel grass (Cenchrus ciliaris cv. Biloela) usually showed a lower (i.e. more negative) �1 than Siratro (Macroptilium atropurpureum cv. Siratro), when they were grown together in a mixed pasture. Siratro seemed to possess a useful degree of drought avoidance. High drought resistance was observed in buffel grass; this was attributed to its tolerance of water stress. Green panic (Panicum maximum var. trichoglume cv. Petrie) was found to have as low a �1 as lucerne during drought when the two species were grown with Siratro in a mixed pasture. 2. The plants were under severe water stress before all the available water was removed from the deeper soil horizons. 3. �1 was lower in nitrogen-fertilized buffel grass or spear grass (Heteropogon contortus), than in the corresponding unfertilized controls. 4. The vapour-exchange and dye-marker densiometric methods gave different values for �1 in buffel grass, green panic and Siratro; the vapour exchange technique recorded lower, i.e, more negative figures than the other method when the plants were under severe water stress. The two methods gave similar values for lucerne. The relation between the values obtained for buffel grass by the two methods was affected by nitrogen fertilization. The reaction of sown pasture plants to drought at Narayen is discussed.

Establishment of four pasture grasses and Siratro from seed oversown into dense and open speargrass pastures

1984 ◽  
Vol 24 (126) ◽  
pp. 360 ◽  
Author(s):  
SJ Cook
Keyword(s):  
Seedling Emergence ◽  
Weather Conditions ◽  
Panicum Maximum ◽  
Brachiaria Decumbens ◽  
Heteropogon Contortus ◽  
Pasture Grasses ◽  
Macroptilium Atropurpureum ◽  
Signal Grass ◽  
Native Pastures ◽  
Better Than

In two experiments, seed of Gayndah and Biloela buffel grass (Cenchrus ciliaris), green panic (Panicum maximum var. trichoglume), signal grass (Brachiaria decumbens) and Siratro (Macroptilium atropurpureum) was broadcast into a range of seedbeds imposed on native speargrass (Heteropogon contortus) pastures that had either been cleared of trees 4-5 years before sowing (C) or had the trees killed at sowing (K). The seedbeds were: untreated control (NP); mown to 3 cm before and at sowing (M); M followed by regular clipping (MD); burnt (B); B followed by regular clipping (BD); and herbicide (H). Seed was also sown into a cultivated seedbed (P) in C. The number of plants established 15-16 months after sowing was highest in the cultivated seedbed and lowest in seedbeds where competition from the native grasses was greatest. Competition was greater in C than in K, the native pastures in C having about three times more dry matter than those in K. Burning reduced competition but also reduced seedling emergence. It increased establishment slightly in K but not in C. The M and MD treatments failed to increase establishment over that of the NP control. Herbicides reduced competition and increased establishment in C and K, but only for signal grass and Siratro in C when drier conditions occurred in the second experiment. Siratro established better than the grasses in the presence of competition when weather conditions were favourable, but there was little Siratro or grass establishment when water deficits occurred soon after emergence, especially in C

Effect of fertilizer, root and shoot competition on the growth of Siratro (Macroptilium atropurpureum) and green panic (Panicum maximum var. trichoglume) seedlings in a native speargrass (Heteropogon contortus) sward

1985 ◽  
Vol 36 (2) ◽  
pp. 233 ◽  
Author(s):  
SJ Cook ◽  
D Ratcliff
Keyword(s):  
Seedling Growth ◽  
Seedling Emergence ◽  
Root Competition ◽  
Panicum Maximum ◽  
Leaf Production ◽  
Heteropogon Contortus ◽  
Shoot Competition ◽  
Native Grassland ◽  
Supplementary Irrigation ◽  
Macroptilium Atropurpureum

The effect of root and shoot competition and the application of fertilizer on the growth of Siratro (Macroptilium atropurpureum) and green panic (Panicum maxinzum var. trichoglume) seedlings under supplementary irrigation in an existing native grassland dominated by Heteropogon contortus was studied. The seedlings were grown in both the presence and absence of root competition and varying levels of shoot competition. Root competition was prevented by the use of steel tubes while shoot competition was varied by: clipping the native pasture to a height of either 3-5 cm or 10-15 cm every 7-10 days, leaving the native sward unclipped, and unclipped sward with wire-netting guards fitted around each seedling to prevent overtopping and facilitate light penetration. Seedling growth was assessed by determining dry weights after 29 days and also by measuring plant heights, leaf and tiller numbers and the leaf widths at 7-day intervals during this period. Application of superphosphate and nitrogen fertilizer increased the growth of both species, the initial effects being evident within 1-2 days of seedling emergence. However, at both fertilizer levels the growth of both species was primarily affected by root competition for nutrients. Where fertilizer was applied and no root competition was present heavy shading in the lower 5-10 cm of the sward canopy restricted seedling growth by reducing tiller and leaf production. The removal of shoot competition increased seedling yields fivefold whereas the removal of root competition and the removal of both root and shoot competition increased yields by 25- and 45-fold, respectively. Siratro and green panic yields were the same in the absence of root competition but Siratro yields were 11 times those of green panic where root competition was present.

Water-stress tolerance of black and eastern cottonwood clones and four hybrid progeny. II. Metabolites and inorganic ions that constitute osmotic adjustment

1994 ◽  
Vol 24 (4) ◽  
pp. 681-687 ◽  
Author(s):  
T.J. Tschaplinski ◽  
G.A. Tuskan
Keyword(s):  
Water Stress ◽  
Water Potential ◽  
Osmotic Adjustment ◽  
Soil Water Potential ◽  
Inorganic Ions ◽  
Male Parent ◽  
Hybrid Progeny ◽  
Eastern Cottonwood ◽  
Water Stress Tolerance ◽  
Male Hybrid

The biochemical bases of water-stress tolerance in a pedigree consisting of black cottonwood (Populustrichocarpa Torr. & Gray female) and eastern cottonwood (Populusdeltoides Bartr. male) parental clones and four hybrid progeny were investigated. Trees were grown outdoors in pots; well-watered trees (soil water potential greater than −0.03 MPa) were kept moist in trays, and stressed trees (soil water potential less than −2.0 MPa) were subjected to repeated cyclical stress of 1 or 2 days duration over the 14-week study. Analysis of the major metabolites and ions in fully expanded leaves demonstrated that the greatest degree of osmotic adjustment was displayed by male hybrid 242, the P. deltoides male parent, and male hybrid 239 to a lesser extent. Osmotic adjustment in leaves of both hybrid 242 and the P. deltoides male parent was primarily constituted by malic acid, K, sucrose, and glucose, with the same metabolites also increasing in fine roots of hybrid 242, the only clone to display osmotic adjustment in roots. Female clone 240 and P. deltoides displayed organic solute-based adjustments to water stress that were offset by declines in inorganic ions, particularly Na and Mg. Given that the P. trichocarpa female parent did not display osmotic adjustment in either tissue, the hybrids' capacity for adjustment was likely conferred by the P. deltoides male parent.

Stomatal Adjustment to Water Deficits in Three Tropical Grasses and a Tropical Legume Grown in Controlled Conditions and in the Field

1985 ◽  
Vol 12 (2) ◽  
pp. 131 ◽  
Author(s):  
MM Ludlow ◽  
MJ Fisher ◽  
JR Wilson
Keyword(s):  
Soil Water ◽  
Field Experiments ◽  
Panicum Maximum ◽  
Water Deficits ◽  
Buffel Grass ◽  
Heteropogon Contortus ◽  
Tropical Legume ◽  
Controlled Conditions ◽  
Leaf Photosynthetic Rate ◽  
Response To Water

Stomatal conductance (g) and leaf photosynthetic rate (P) of many species in the field are often less sensitive to water deficits than when grown in small pots under controlled conditions. This may result from stomatal adjustment in field-grown plants in response to water deficits that develop slowly, whereas adjustment does not occur under the rapid drying experienced by plants in small pots. To test this hypothesis we studied the response to water potential (Ψl) of g and P in three tropical C4 grasses, green panic (Panicum maximum var. trichoglume), buffel grass (Cenchrus ciliaris) and spear grass (Heteropogon contortus) and a tropical legume, Siratro (Macroptilium atropurpureum), grown under controlled conditions and in the field. Field experiments clearly showed that stomatal adjustment occurred so that g and P were progressively less sensitive to the decline in Ψl as water deficits increased during a long soil drying cycle. For example in one experiment, the Ψl at which P approached zero fell from - 1.9, -2.0 and -2.4 MPa to -4.0, -4.0 and -3.3 MPa for green panic, spear grass and buffel grass, respectively. This stomatal adjustment was reversed within 10 days after rewatering to the well watered condition. Little stomatal adjustment occurred in plants grown under controlled conditions in small pots in which both soil water and Ψl fell rapidly. However, if plants were grown in similar conditions but in large pots of soil so that soil water and Ψl decreased slowly, stomatal adjustment comparable with field-grown plants was observed. Siratro showed much less stomatal adjustment than the grasses and Ψl at which P approached zero only fell from - 1.2 to - 1-5 MPa.

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