Continuous shoot growth monitoring in hydroponics

A weighing apparatus for automatic recording of fresh weight of shoots of spinach plants ( Spinacia oleracea L., cv. Subito) growing in nutrient solution is described. The system was tested for 17 days in a controlled environment and enabled the determination of the relative growth rate (RGR) of the shoot fresh weight. Results from three consecutive growth experiments demonstrated diurnal fluctuations in the relative growth rate of the shoot fresh weight. In general, relative growth rates were between 0.32 and 0.36 day⁻¹ 16 days after sowing and decreased to between 0.11 and 0.18 day⁻¹ during the 12 following days. The variance between three replicate growth curves was compared with the variance of a growth function fitted through destructively obtained spinach shoot weight data.     

Inhibition of auxin-induced elongation and xyloglucan breakdown in azuki bean epicotyl segments by fucose-binding lectins

Auxin-induced elongation of epicotyl segments of azuki bean ( Vigna angularis Ohwi and Ohashi cv. Takara) was suppressed by fucose-binding lectins from Tetragonolobus purpureus Moench and Ulex europaeus L. These lectins also inhibited auxin-induced cell wall loosening (decrease in the minimum stress-relaxation time of the cell walls) of segments. Auxin caused a decrease in molecular mass of xyloglucans extracted with 24% KOH from the cell walls. The lectins inhibited auxin-induced changes in molecular mass of the xyloglucans. The autolytic release of xylose-containing products from the pectinase-treated cell walls was also suppressed by the lectins. Fucose-binding lectins pretreated with fucose exhibited little or no inhibitory effect on auxin-induced elongation, cell wall loosning, or breakdown of xyloglucans. These results support the view that the breakdown of xyloglucans is involved in the cell wall loosening responsible for auxin-induced elongation in dicotyledons.     

Changes in invertase activities precede ovary growth induced by gibberellic acid in

Developing pods of pea ( Pisum sativum L. cv. Alaska no 7) were used to study the enzymes of sucrose metabolism. Acid and neutral invertase (EC 3.2.1.26). sucrose synthase (SS, EC 2.4.1.13) and sucrose phosphate synthase (SPS, EC 2.4.1.14) have been localized in the soluble fraction. Acid invertase activity was also present in the insoluble fraction and in pea ovary apoplast. In pea pods, sucrose breakdown was dominated by the invertase pathway. SS specific activity only increased at late stages of parthenocarpic pod development, while SPS did so in pods obtained by pollination. Changes in time course of invertase activities have been correlated with the growth rate of fruits induced to develop either by fertilization or by exogenous application of giberellic acid (GA), 2,4-dichloro-phenoxy acetic acid (2,4-D) or 6-benzylaminopurine (6-BAP). The soluble neutral activities might be associated with pod elongation, while the acid ones were rather related to assimilate import by the induced fruits. Application of gibberellic acid to non-pollinated ovaries significantly enhanced the soluble neutral invertase activity before any ovary outgrowth was detected (up to 2 h after treatment). Within the same period of time. GA-treated ovaries showed a decrease in the acid invertase activity of the soluble fraction and an increase of the acid invertase activity in the apopiast. preceding in time the increment of the acid invertase activity associated with the insoluble fraction. Our results suggest that the early GA response may be mediated through a promotion of processes of protein secretion.     

Ammonium and nitrate uptake by barley genotypes in diurnally fluctuating root temperatures simulating till and no-till conditions

The morphological development and N uptake patterns of spring barley (Hordeum vulgare L.) genotypes of Northern European (Nordic) and Pacific Northwest US (PNW) origin were compared under two diurnally fluctuating root temperature regimes in solution culture. The two regimes, 15/5°C and 9/5°C day maximum/night minimum temperatures, simulated soil temperature differences between tilled vs. heavy-residue, no-till conditions, respectively, observed during early spring in eastern Washington. Previous field experiments indicated that some of the Nordic genotypes accumulated more N and dry matter than the PNW cultivars during early spring under no-till conditions. The objective of this experiment was to determined whether these differences 1) are dependent on the temperature of the rooting environment, and 2) are correlated with genotypic differences in NH₄ ⁺ and NO₃ ^– uptake. Overall, shoot N and dry matter accumulation was reduced by 40% due to lower root temperatures during illumination. Leaf emergence was slowed by 14 to 22%, and tiller production was also inhibited. All genotypes absorbed more ammonium than nitrate from equimolar solutions, and the proportion of total N absorbed as NH₄ ⁺ was slightly higher in the 9/5°C than the 15/5°C regime. A Finnish genotype, HJA80201, accumulated significantly more shoot N than the PNW cultivars, Clark and Steptoe, and also more than a Swedish cultivar, Pernilla, in the 9/5°C regime. In the 15/5°C regime Steptoe did not differ in shoot N from the Nordic genotypes, while Clark remained significantly lower. These differences were not correlated to relative propensity for N form. Root lengths of the Nordic genotypes were significantly greater than the PNW genotypes grown under the 9/5°C regime, while the root lengths in the warmer root temperture regime were not significantly different among genotypes. Higher root elongation rates under low soil temperature conditions may be an inherent adaptive mechanism of the Nordic genotypes. Overall, the data indicate that lower maximum daytime temperatures of the soil surface layer likely account for a significant portion of the growth reductions and lower N uptake observed in no-till systems.     

An inflatable minirhizotron system for root observations with improved soil/tube contact

Commonly used minirhizotrons consisting of a transparent tube inserted into the soil seldom attain good contact between the tube and the soil, which leads to root growth occurring in a gap rather than in the soil. A new system is described involving an inflatable flexible rubber wall, made from a modified motorcycle tube. Pressure ensures a proper tube/soil contact so that the environmental circumstances for root growth along the tube more closely correspond to those in the undisturbed soil. Before the endoscope slide is introduced into the minirhizotron for taking pictures, the inflatable tube is removed, so that there is no-often opaque-wall between the endoscope and the roots. This improves the picture quality and facilitates the analysis of root images.     

Metabolic activities of the sugarbeet pathogens Fusarium solani (Mart.) Sacc. and Sclerotium rolfsii Sacc. under pyramin stress

Effects of different concentrations of active ingredient of the herbicide pyramin on metabolic activities of Fusarium solani and Sclerotium rolfsii were examined. High concentrations of this herbicide (1000 and 2000 g mL^-1 for F. solani and 100 and 200 g mL^-1 for S. rolfsii) had inhibitory effects on the metabolic activities of both fungi. These were demonstrated by significant decreases in growth, and increases in rates of CO₂ evolved, O₂ consumed and keto acids produced. These were accompanied by increased rates of sugar, nitrate and inorganic phosphorus absorption as well as lowered rates of synthesis of carbohydrates and insoluble nitrogenous (including protein) and phosphorus (including RNA-P and DNA-P) compounds. In addition, rates of excretion of both nitrogen and phosphorus fractions by the mycelial mats were increased.A concentration of 25 g mL^-1 exerted little or no effect on the metabolic activities of these fungi, although S. rolfsii was somewhat sensitive to this concentration.     

Penetrometer resistance,root penetration resistance and root elongation rate in two sandy loam soils

Root penetration resistance and elongation of maize seedling roots were measured directly in undisturbed cores of two sandy loam soils. Root elongation rate was negatively correlated with root penetration resistance, and was reduced to about 50 to 60% of that of unimpeded controls by a resistance of between 0.26 and 0.47 MPa. Resistance to a 30° semiangle, 1 mm diameter penetrometer was between about 4.5 and 7.5 times greater than the measured root penetration resistance. However, resistance to a 5° semiangle, 1 mm diameter probe was approximately the same as the resistnace to root penetration after subtracting the frictional component of resistance. The diameter of roots grown in the undisturbed cores was greater than that of roots grown in loose soil, probably as a direct result of the larger mechanical impedance in the cores.     

Survival of inoculated Laccaria bicolor in competition with native ectomycorrhizal fungi and effects on the growth of outplanted Douglasfir seedlings

The survival, development and mycorrhizal efficiency of a selected strain of Laccaria bicolor along with naturally occurring ectomycorrhizal fungi in a young plantation of Douglas fir was examined. Symbionts were identified and their respective colonization abilities were determined. Eight species of symbiotic fungi, which may have originated in adjacent coniferous forests, were observed on the root systems. Mycorrhizal diversity differed between inoculated (5 taxa) and control (8 taxa) seedlings. Ectomycorrhizal fungi which occurred naturally in the nursery on control seedlings (Thelephora terrestris and Suillus sp.) did not survive after outplanting. Both inoculated and naturally occurring Laccaria species, as well as Cenococcum geophilum, survived on the old roots and colonized the newly formed roots, limiting the colonization by other naturally occurring fungi. Other fungi, such as Paxillus involutus, Scleroderma citrinum and Hebeloma sp. preferentially colonized the old roots near the seedling's collar. Russulaceae were found mainly in the middle section of the root system. Mycorrhizal colonization by Laccaria species on inoculated seedlings (54%) was significantly greater than on controls (13%) which were consequently dominated by the native fungi. Significant differences (up to 239%) were found in the growth of inoculated seedlings, especially in root and shoot weight, which developed mainly during the second year after outplanting. Seedling growth varied with the species of mycorrhizae and with the degree of root colonization. Competitiveness and effectiveness of the introduced strain on improving growth performances of seedlings are discussed.     

Role of magnesium in combination with liming in alleviating acid-soil stress with the aluminium-sensitive sorghum genotype CV323

An experiment to study the effects of Mg nutrition on root and shoot development of the Al-sensitive sorghum (Sorghum bicolor (L.) Moench) genotype CV323 grown in pots of sandy loam under different acid soil stress is reported. This experiment had a factorial design: four rates of liming were combined with four rates of Mg fertilization. When no Mg was added, the pH of the soil solutions (collected in ceramic cups) increased from 4.0 (unlimed) to 4.2, 4.7 and 5.9 at the increasing rates of liming. After 30 days of growth dry matter yields of the limed treatments were 40%, 115% and 199% higher than that of the unlimed treatment. Without liming and at the highest liming rate, adding Mg did not affect plant biomass significantly. At the two intermediate levels of liming, however, 11.3 mg extra Mg per kg soil increased dry matter yield to the same levels as found at the highest liming rate. Concentrations of Mg in the soil solution rose after Mg was added and fell when lime was added, but adding both Mg and lime increased Mg concentrations in the plant shoots. In plants of the limed treatments, dry matter yield was correlated closely with the Mg concentration in the shoot. This was not so in the unlimed treatment. Furthermore, in the unlimed treatments root development was inhibited, but reduced Mg uptake by the plants resulted mainly from the direct effect of Al- (or H-) ions in the soil solution rather than from impaired root development. It is concluded that Mg fertilization counteracted the interfering effects of Al- and H ions on Mg uptake.     

The pH profile for acid-induced elongation of coleoptile and epicotyl sections is consistent with the acid-growth theory

The acid-growth theory predicts that a solution with a pH identical to that of the apoplast of auxintreated tissues (4.5–5.0) should induce elongation at a rate comparable to that of auxin. Different pH profiles for elongation have been obtained, however, depending on the type of pretreatment between harvest of the sections and the start of the pH-incubations. To determine the acid sensitivity under in vivo conditions, oat (Avena sativa L.) coleoptile, maize (Zea mays L.) coleoptile and pea (Pisum sativum L.) epicotyl sections were abraded so that exogenous buffers could penetrate the free space, and placed in buffered solutions of pH 3.5–6.5 without any preincubation. The extension, without auxin, was measured over the first 3 h. Experiments conducted in three laboratories produced similar results. For all three species, sections placed in buffer without pretreatment elongated at least threefold faster at pH 5.0 than at 6.0 or 6.5, and the rate elongation at pH 5.0 was comparable to that induced by auxin. Pretreatment of abraded sections with pH-6.5 buffer or distilled water adjusted to pH 6.5 or above gave similar results. We conclude that the pH present in the apoplast of auxin-treated coleoptile and stems is sufficiently low to account for the initial growth response to auxin.Abbreviations FS free space - IAA indole-3-acetic acid This research was supported by a grant from the National Adonautics and space Administration (NASA), NAGW 1394 to R.E.C., NASA grant NAGW-297 to M.L.E., and NASA grant NAG 1849 to D.L.R.