Showing papers in "Australian Journal of Plant Physiology in 1978"

Salt stress and comparative physiology in the Gramineae. II. Glycinebetaine and proline accumulation in two salt and water-stressed barley cultivars

Abstract: Under low-salt conditions, the glycinebetaine levels in the shoot exceeded the proline levels in two barley cultivars, California Mariout and Arimar. Stress induced by both polytheylene glycol (PEG) and NaCl caused an accumulation of both compounds. However, a gradual incremental increase in stress led to higher glycinebetaine than proline levels, whereas salt and osmotic shock led to proline levels far in excess of the glycinebetaine levels. Both stress regimes caused a greater proportional increase in proline than in glycinebetaine. Preliminary data suggest that proline may be used as an internal assay for water stress in barley leaves. Comparison of the physiological responses of the barley cultivars to NaCl and PEG stress suggested that the suppression of growth by salt treatment was not due directly to the low external water potential but arose either from the ions, Na+ and Cl-, interfering with metabolic processes or from a number of possible but unsubstantiated interactions leading to a reduction in turgor potential and thus in the rate of cell expansion.

Salt Stress and Comparative Physiology in the Gramineae. I. Ion Relations of Two Salt- and Water-Stressed Barley Cultivars, California Mariout and Arimar

Abstract: Two barley cultivars, California Mariout and the somewhat more salt-sensitive Arimar, were grown under different salinity regimes and in isosmotic polyethylene glycol (PEG) solutions. Shoot growth of both cultivars was inhibited more by NaCl than by PEG. The effects of various salt and osmotic stress regimes on the K+, Na+ and Cl- status, the fresh weight : dry weight ratio and osmotic potential of the tissue were determined. The changes in these parameters were dependent on the rate at which the stress was applied. A gradual increase in stress led to K+/Na+ exchange in the shoot so as to maintain an almost constant (K+ + Na+) content on a dry weight basis. Tissue dehydration largely accounted for the increase in osmotic pressure. In contrast, salt shock resulted in a rapid nonselective accumulation of salt. Both osmotic stress and shock similarly brought about a dehydration of shoot tissue. A gradual osmotic stress slightly enhanced K+ accumulation in the roots. The greater salt sensitivity of the Arimar cultivar appeared to be related to a poorer ability to regulate Na+ plus Cl- accumulation in shoots.

Agronomic and physiological responses of soybean and sorghum crops to water deficits IV. Photosynthesis, transpiration and water use efficiency of leaves

Abstract: Detailed diurnal measurements of photosynthesis, transpiration and water use efficiency of leaves of sorghum and soybean were made during the reproductive growth of field plants. Photosynthesis was measured mainly by infrared gas techniques. The indication in well watered plants was that diurnal net carbon fixation per unit area of sorghum leaves was some 2.3 times greater than that of comparably illuminated soybean leaves while concurrent transpiration losses were less. Simple carbon budgets for the two crops over 24 h suggested that the assimilation by a leaf area equivalent to that of the flag leaf was required solely to sustain respiration by the sorghum head during mid- grain filling, while approximately 5 cm² of leaf was required to sustain respiration of each soybean pod. The comparisons made on a diurnal basis between plants of soybean exposed to different water deficits during grain filling demonstrated the increasing importance of early morning and late afternoon photosynthesis as water became less available. They also showed the rapidity with which plants can recover from stress once water is supplied. It is calculated that, for continuously clear conditions, as daily minimum leaf water potential fell from - 1 .5 to - 2.5 MPa, the integrated daily assimilation by leaves was reduced by about 9 % for every 0.1 MPa change; soybean leaves were not measured at leaf water potentials much below - 2.6 MPa. A ratio between gas phase and residual resistances remained relatively stable over the range of leaf water potential measured. However, the water use efficiency of single leaves was reduced with increasing soil water deficits because of changes in leaf temperature and leaf-to-air vapour pressure differences.

Assimilate Source-Sink Relationships in Capsicum annuum L. III. The Effects of Fruit Excision on Photosynthesis and Leaf and Stem Carbohydrates.

Abstract: Removal of the rapidly growing fruit from a Capsicum plant reduced the rate of net CO2 uptake by its leaves by up to 30% during the time period explored (0.5 - 7 days). This reduction was associated with increases in both the leaf (to about 200%) and intracellular (to about 30%) resistances, these changes having about equal effects on reducing the rate of CO2 uptake. Changes in photorespiration, dark respiration and CO2 compensation point were very small. The rate of CO2 uptake and the associated resistances were also changed by modifying the light regime and other factors affecting the source-sink balance. Changes in the leaf resistance were not attributable to variations in the internal CO2 concentration or in the water economy of the leaf; its control mechanism remains unexplained. The concentration of soluble sugars in the source leaf was completely unaffected but that of polysaccharides was changed by defruiting and by 50% defoliation. However, variations in the intracellular resistance were not closely related to these changes and there is yet no evidence of the nature of its control mechanism. Changes in both soluble sugars and polysaccharides in the stem were more pronounced than in the leaves.

Alcoholic fermentation and malate metabolism in rice germinating at low oxygen concentrations

Abstract: Germinating rice was exposed, in the dark, to low or zero O2 concentrations for 4-5 days by: (1) submergence under 4-5 cm of stagnant solution (3 ppm 02); (2) exposure to a N2 atmosphere;. or (3) submergence under solutions flushed with N2. These treatments completely inhibited root growth. Elongation of coleoptiles was stimulated in the stagnant solutions, but not in the N2 treatments. In most experiments, low O2 concentrations resulted in twofold to eightfold increases of malate concentrations in the shoots. Absence of 0, during exposure to Hi4C03-, for 30-60 min, inhibited C02 dark fixation. This inhibition was considerably smaller when seedlings had been raised in N2 rather than in air. Under aerobic conditions during fixation, excised shoots from seedlings raised in N2 fixed more C02 than shoots from seedlings raised in air. Malate always contained 70% or more of the total fixed 14C, irrespective of the 0, regime during germination and during I4CO2 fixation. Ethanol in stagnant solutions was shown to be formed by the rice seedlings, rather than by bacteria. Ethanol formation during one single day was 20-30-fold greater than the highest recorded amounts of malate in the seedlings. Alcoholic fermentation also responded quickly to changes in aeration regimes, indicating it was an important adaptive factor. Another likely adaptive feature was the high K+ concentration in shoots, even of seedlings grown in the complete absence of 0,. It is suggested that these high K+ concentrations have a function in maintaining turgor required for the rapid extension growth of the coleoptiles under low 0, concentrations.

Water Uptake by Mycorrhizal Roots of Radiata Pine Seedlings.

Abstract: Seedlings of radiata pine (Pinus radiata D. Don) grown in a sandy soil inoculated with Rhizopogon luteolus had 72% of their short roots mycorrhizal at age 5 months whereas the uninoculated controls had only 6.0 %. When water was withheld from the soil and soil water matric potential became more negative, the leaf water potential of both inoculated and uninoculated plants became more negative, transpiration rate was reduced, and the derived resistance of the plant plus soil to the flow of water increased. There was no significant difference between inoculated and uninoculated plants in transpiration rate, but leaf water potential was more negative and consequently the derived resistance of plant plus soil was greater in the inoculated plants. The resistance of plant plus soil was partitioned using a simple whole-plant model. Resistance within the soil was considered more significant than that in the plant, and the greater soil resistance associated with the inoculated plants was considered to be due to differences in root geometry.

Stomatal and Mesophyll Resistances in Two Clones of Pinus radiata D.don Known to Differ in Transpiration and Survival Rate

Abstract: The gaseous exchange characteristics of two clones of P. radiata were compared. Clone 457, which had a low survival rate in the field, showed a transpiration rate up to twice that of clone 456, which had a high survival rate. Transpiration in both clones was not markedly affected by leaf-air vapour pressure differences varying between 0.4 and 1.4 kPa. The stomatal resistance of clone 457 was almost half that measured for clone 456 under all experimental conditions; however, increasing the leaf-air vapour pressure difference resulted in increased stomatal resistances in both clones. The photosynthetic response to CO2 concentration was also determined. The measured rates for clone 457 were twice those of clone 456 and both clones gave maximum rates of apparent photosynthesis above about 700 ng cm-3 internal CO2 concentration (corresponding to about 1400 ng cm-3 external concentration). The differences in photosynthetic rate could be accounted for by the greater than twofold difference in mesophyll resistance between the clones. Mesophyll resistance was not affected by altering the leaf-air vapour pressure difference. It is suggested that a factor in determining the relative survival rate of the two clones is the greater ability of clone 456 to limit transpiration water loss and that this more than compensates for the reduced rate of photosynthesis of this clone compared with clone 457.

Movement of the Column of Stylidium crassifolium as a Function of Temperature

Abstract: The column of the flower of S. crassifolium when mechanically stimulated moves through an angle of about 4 rad in 15 ms and then resets more slowly in several hundred seconds. The rates of the firing and resetting as a function of temperature have been investigated. Arrhenius plots of these rates are approximately straight lines yielding energies of activation of ~ 8 kJ mol-1 for firing and ~72 kJ mol-1 for resetting. These results suggest that resetting is the 'active' part of the movement, and is closely linked to the metabolic energy supply. The rate of firing is more likely limited by friction within the cell walls of the motor tissue, or possibly by the viscosity of extracellular water.