Untreated Control Seedlings Research Articles

Sulfometuron methyl influences seedling growth and leaf function of three conifer species

Seedling growth and gas exchange responses were measured for two potted seedling trials testing herbicide phytotoxicity to three important tree species of the Inland Northwest, USA. Media-filled pots were treated with sulfometuron methyl (Oust®) in varying concentrations and planted with seedlings of Larix occidentalis Nutt., Pseudotsuga menziesii var. glauca (Beissn.) Franco, and Pinus monticola Dougl. ex D. Don. Seedlings were grown in two trials to determine the effects of two important residue breakdown factors, substrate moisture and pH, relative to that of herbicide application rate on seedling health. Changes in seedling height, root-collar diameter, and root volume were morphologic variables of interest, and physiological variables measured were net photosynthetic assimilation, stomatal conductance, and transpiration rate. While three levels of media moisture and four levels of media pH had no effect on seedling performance, most growth and leaf function variables were hindered across application rate treatments of all three species. Label-recommended dosages resulted in growth suppression levels potentially detrimental to seedling establishment for all three species. This was most pronounced for Pinus monticola, in particular for root growth, where untreated control seedlings showed 109% more root volume growth than treated seedlings. We conclude that when possible, a species-specific application rate might be found that balances the benefits of vegetation control with the phytotoxicity to promote optimal growth gains.

Effects of 24-epibrassinolide and 28-homobrassinolide on the growth and antioxidant enzyme activities in the seedlings of Brassica juncea L.

The present paper deals with the effects of two active forms of brassinosteroids (BRs) as epibrassinosteroid (24-EBL) and homobrassinosteroid (28-HBL) on percentage germination, growth in the form of shoot length, activities of auxinase (IAAO), polyphenol oxidase (PPO), superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APOX) in 10 day old seedlings of Brassica juncea L. (RCM 619) under field conditions. Exogenous application of 240-EBL and 28-HBL significantly ameliorate the total protein content as compared to untreated control seedlings. 10(-8) M 28-HBL helps in enhancing the PPO activity very significantly, as compared to all other concentrations of EBL and HBL and also to that of untreated control. Similar trend was observed in IAAO activity. It was observed that all the concentrations of EBL were unable to enhance the APOX activity as compared to untreated control seedlings but 10(-8) M HBL significantly ameliorates APOX activity. CAT and SOD activities ameliorate significantly with exogenous application of EBL and HBL. Out of two active forms of BRs, 28-HBL was more effective at germination stage in scavenging the free radicals, which are produced in greater amount during germination from basic metabolic processes, whereas 28-EBL was effective in the initial growth of seedlings in the form of increase in shoot length.

Heat acelimation and chemical pre-treatments induccd thermotolerancc in chickpea

Induced heat-tolerance triggered by heat acclimation treatment and foliar application of salicylic acid and abscisic acid were evaluated in three different genotypes of chickpea (Cicer arietinum L.) distinctly differing in their sensitivity to heat stress. Seedlings pre-treated with 100uM salicylic acid (SA) and 50 uM abscisic acid (ABA) showed improved heat tolerance to a lethal temperature of 46°C than the untreated control seedlings. Heat stress increased lipid peroxidation of membranes and reduced plant survival. Protein and proline contents increased significantly in pre-treated seedlings. Cell membrane stability also increased remarkably in pre-treated seedlings of all three genotypes. Changes in activities of antioxidative enzymes like peroxidase, ascorbate peroxidase in pre-treated seedlings revealed increase in enzymatic activities which declined sharply at lethal temperuturc. Quantum of increase in enzymatic activity was however higher in thermotolerant genotype in comparison to heat susceptible genotype. Thermotolerant genotype also exhibited constitutively higher antioxidative activities. Catalase activity, in contrast, showed a significant decrease in its activity in pre-treated seedlings following exposure to lethal temperature. These results indicate that heat acclimation treatment and application of SA and ABA show great potential in inducing heat tolerance in chickpea seedlings and these can be further analyzed to understand their role in thermoprotection.

Short-day treatment enhances root egress of summer-planted Picea abies seedlings under dry conditions

Second year Norway spruce [Picea abies (L.) Karst.] container seedlings, short-day (SD) treated for 3 weeks in July, were exposed together with untreated control seedlings (Co) to three different drought treatments for 5 weeks after planting in early August. The treatments were: (1) regular watering (0 week drought); (2) 2 weeks of drought and 3 weeks of watering; and (3) no watering (5 week drought). No difference was found in the vigour and shoot xylem water potential between the SD-treated and the Co seedlings after the drought treatments. The root growth decreased less for the SD seedlings than for the Co seedlings along with the increase in the length of the drought period.

Intraspecific variability of cadmium tolerance in hydroponically grown Indian mustard (Brassica juncea (L.) Czern.) seedlings

Indian mustard (Brassica juncea (L.) Czern.) is a promising plant species for phytoremediation of heavy metal polluted soils. However, genetic variability of metal tolerance in Indian mustard has not been studied. We evaluated intraspecific variation of Cd tolerance of this species by screening 64 varieties in hydroponics. The tolerance index (TI), calculated as percentage of root length of Cd-treated (7 μM CdCl2) over untreated control seedlings, significantly varied from 34 to 79%, depending on the variety. Information about phenotypic and economic traits of the studied varieties was taken from the literature and subjected to a cluster analysis. The varieties were distributed into three clusters and most of the varieties characterized by the highest TI values (TI > 65%) were grouped together in one cluster. Moreover, TI negatively correlated with the following characteristics: yellow seed colour (R = −0.35, P = 0.005), total oil content (R = −0.33, P = 0.008), oleic acid (R = −0.25, P = 0.047) and linoleic acid (R = −0.36, P = 0.004) contents in seeds. The results showed the presence of significant variability for Cd tolerance in Indian mustard. The knowledge about correlations between Cd tolerance and phenotypic characteristics of plants might be utilized for rapid selection of cultivars to be used for phytoremediation of polluted soils.

Effect of kinetin on early stages of chlorophyll biosynthesis in streptomycin-treated barley seedlings

Treatment of barley seeds (Hordeum vulgare L.) with streptomycin, an inhibitor of plastid protein synthesis, resulted in growth of the albino phenotype seedlings with ribosome-deficient undifferentiated plastids and chlorophyll (Chl) level as low as 0.1% of that in control plant leaves. A major effect of the antibiotic was almost complete suppression of the ability of plants to synthesize 5-aminolevulinic acid (ALA) intended for Chl biosynthesis. The activity of synthesis of ALA intended for heme porphyrin biosynthesis in etiolated and greening seedlings and in light-grown albinophenotype plants was insensitive to light and cytokinins. In the upper parts of leaves of streptomycin-treated plants, exhibiting 60% Chl deficit, the cells with three types of chloroplasts could be observed: normally developed chloroplasts, chloroplasts composed of single thylakoids and grana, and completely undifferentiated plastids. In this Chl-deficient tissue, ALA synthesis was found to be stimulated by kinetin but much less than in leaves of the control plants. The endogenous cytokinin content in etiolated and greening seedlings treated with streptomycin was almost the same as it was in untreated control seedlings. The cytokinin level in the white tissue of plants grown in the light was on average twice as high as that in green leaves of the control plants. The capability of kinetin to stimulate the synthesis of ALA used for Chl biosynthesis was found to correlate with the Chl content and organization of the chloroplast internal structure. This correlation confirms the hypothesis that the normally developed internal structure of plastids is essential for the adequate phytohormone response in plants.

Post-transplant root and shoot development inAbies nordmannianaSpach. seedlings after whorl bud and branch pruning

After lifting in a nursery, 3-year-old seedlings ofAbies nordmanniana were treated for improvement in new leader growth after transplanting. The treatments were: (A) whorl (subapical) buds, lateral buds at the stem and whorl branch tips removed; (B) as (A), but with whorl branches removed at their junction to the stem; and (C) untreated control seedlings. After transplanting in April, plant samples were lifted in June, July and September to determine the effect of treatments on root and shoot development. Root length and number of root tips were determined by scanning and computed image analysis. Height, dry weight of shoot and root and ratio between these were determined. Removal of whorl and lateral buds and whorl branch tips had a negative effect on root and shoot growth after transplanting. Root length, number of root tips and shoot dry weight were reduced, but by September equaled the untreated control seedlings. Removal of whorl branches caused a significant reduction in both root length and shoot dry weight compared to untreated control seedlings. root length / root:shoot / root tip scanning

Effect of Bioplex™ on Transplant Success of Non-Dormant Red Oak (Quercus rubra L.)

Abstract Biostimulants are used to reduce the stress associated with non-dormant (summer dug) harvest of field-grown nursery stock; however, the effectiveness of biostimulant treatment is uncertain. This study tested the effects of three application methods of Bioplex™ (a commonly used biostimulant) to container-grown red oak seedlings on whole plant transpirational water use and growth before and after root pruning. Root pruning was used to simulate field harvest; it removed 59% of the seedling's total root surface area. Bioplex™ application by foliar spray, soil drench or a combination of foliar spray and soil drench, significantly reduced whole plant transpirational water use by 15% for three days after application, relative to untreated control seedlings. Root pruning significantly reduced whole plant transpiration, compared to non-root-pruned seedlings, and had a greater effect on transpiration than any Bioplex™ treatment. The previous season's Bioplex treatment had no effect on the spring growth flush following fall root pruning. Root pruning in fall significantly reduced root and total plant dry weights the following spring. Although Bioplex™ applications significantly reduced transpiration for three days after application, there does not seem to be any long-term beneficial effect when used to mediate summer digging transplant stress.

Reversibility of the Action of 2, 4-dichlorobenzoic acid, a Synthetic Herbicide, on Cucumber Seedlings by Strains of Soil Microorganisms

The herbicide, 2, 4-dichlorobenzoic acid (DCLBA), was administered through the nutrient solution to six cucumber seedlings grown hydroponically. DCLBA, which is also a synthetic auxin, stunts cucumber plants at a low concentration but kills at a higher one. Roots of six comparable seedlings, treated with DCLBA, were exposed to two strains of microorganisms, TS-22 and TS-29, and Rhizoplane AC1, which were isolated from soils and cucumber roots. The control cucumber seedlings, unexposed to DCLBA and the different strains of microorganisms grew vigorously, whereas those exposed to DCLBA were stunted. The stature of seedlings, exposed simultaneously to DCLBA and TS-22, TS-29, and Rhizoplane AC1, was nearly that of the control, but their fresh and dry weights were approximately 2/3 and 1/2, respectively, of the untreated control seedlings. These results demonstrate that there are microorganisms in the soil and on cucumber roots which, if added to the nutrient solution, can catabolize DCLBA.

Paclobutrazol affects the resistance of black spruce to high light and thermal stress.

Detached needles from 20-week-old black spruce (Picea mariana (Mill.) B.S.P.) seedlings root-drenched with 60 mg of paclobutrazol were exposed to two temperatures (22 and 50 degrees C) and two light treatments (100 and 1900 &mgr;mol m(-2) s(-1) PAR) in a factorial combination for 4 h in vitro. Mean dry weights of individual needles from paclobutrazol-treated plants were approximately 1.9 times heavier than that of needles from untreated controls at 22 degrees C, but no differences were observed following incubation at 50 degrees C. Numbers of cells per needle remained constant in all treatments. Chlorophyll and carotenoid contents per needle were higher in seedlings treated with paclobutrazol than in untreated control seedlings, and the differences were most pronounced in the high temperature plus high light treatment. In low light at 50 degrees C, quantum efficiency of photosystem II was 45% higher in needles of paclobutrazol-treated seedlings than in needles of untreated control seedlings, but quantum efficiency of needles from treated seedlings declined when needles were exposed to high light at either temperature. Peroxidase and superoxide dismutase activities were up-regulated by paclobutrazol, whereas catalase activities were depressed and no significant differences were observed between treated and control needles at 50 degrees C in either light treatment. Paclobutrazol treatment did not moderate the depressive effects of high temperature on total soluble protein or on the activity of ribulose-1,5-bisphosphate carboxylase. In contrast, high activities of phosphoenolpyruvate carboxylase were maintained in paclobutrazol-treated needles under all stress conditions, whereas large losses in activity were recorded in untreated needles at 50 degrees C. Collectively, these observations suggest that paclobutrazol treatment may convey resistance to excessive light and high temperatures by increasing the potential of conifers to limit damage caused by oxidative stress.

Evaluation of Natural Products as Antifeedants for the Pales Weevil (Coleoptera: Curculionidae) and as Fungitoxins for Leptographium procerum

Four natural plant compounds (limonin, S (+) and R (−) carvone, and cucurbitacin) and one insect pheromone (verbenone) were evaluated for antifeedant activity against the pales weevil, Hylobius pales (Herbst), on Pinus strobus seedlings and for toxic activity against the pathogenic fungus, Leptographium procerum (Kendrick) Wingfield, which is vectored by H. pales to P. strobus. All compounds demonstrated significant antifeedant activity in a choice test on treated pine seedlings, but none completely eliminated feeding. Only cucurbitacin elicited a linear dose-response relationship, with significant activity occurring at concentrations as low as 0.10 μg/ml. The other compounds significantly reduced feeding at concentrations as low as 1 μg/ml (the lowest concentration at which they were tested). Total feeding activity was unaffected for all but one treatment (S (+) carvone at 1 μg/ml) when compared with feeding on the untreated control seedlings. It is, therefore, unlikely that the compounds in this study were toxic to the weevils during the 2 d evaluation period. In the fungitoxin test, all compounds except cucurbitacin suppressed germination of L. procerum spores. R (−) carvone was the most effective, allowing only 5% germination at 1 μg/ml, compared to 96% germination in the water solvent.

The effect of aluminium on respiration of wheat roots

The effects of aluminium ions on respiration of excised root apices from wheat (Triticum aestivum L. cv. Vulcan) and on isolated mitochondria have been investigated. Addition of 75μ M aluminium to the growth medium of 4‐day‐old seedlings inhibited O2 uptake by excised root apices by 23 and 35% after 12 and 24 h, respectively. This decreased rate of respiration was initially caused by inhibition of the cytochrome pathway of mitochondrial electron transport. The cyanide‐insensitive, alternative pathway was inhibited only after more prolonged exposure to aluminium. Mitochondria isolated from roots of aluminium‐treated seedlings had reduced oxidative capacity with substrates that supply electrons to Complexes I and II, compared with mitochondria from roots of untreated control seedlings. The state 3 and state 4 rates of O2 uptake and the uncoupled rates with these substrates were also inhibited when aluminium was added directly to reaction mixtures containing mitochondria isolated from untreated plants. In contrast, when aluminium was added to reaction mixtures oxidizing exogenous NADH, state 4 O2 uptake was stimulated, whereas no effect was observed on the state 3 rate or the rate in the presence of uncoupler. The results suggest that aluminium initially affects electron flow through Complexes I and II, and that after more prolonged exposure, aluminium may also interact with other sites in mitochondria.

Stockings for protection of containerized conifer seedlings against pine weevil (Hylobius abietis L.) damage

The effectiveness of a stocking, constructed of nylon and cotton netting, in protecting containerized conifer seedlings against pine weevil attack was evaluated in field tests on 37 clear‐cut reforestation areas in southern and central Sweden. The stockings significantly reduced pine weevil feeding on treated seedlings as well as seedling mortality. The protective effect of the stockings was similar to that of an insecticide (permethrin) treatment. In most experiments the survival of stocking‐enclosed seedlings was satisfactory from a practical point of view, whereas untreated control seedlings suffered heavy mortality.

Plant Growth-Regulating Activities of 3-Hydroxy-5-Methylisoxazole : II. Effect of 3-hydroxy-5-methylisoxazole on the geotropic response of rice seedlings

The results of the investigation showed that 3-hydroxy-5-methylisoxazole (HMI) accelerated the geotropic response of rice seedlings. In general, the horizontally placed rice seedlings gradually revert to a nearly vertical positon. This response to gravity is referred to as the geotropic curvature of rice seedlings. The extent of this response by rice seedlings is important in determining their physiological status which influences future growth and development. The HMI-treated seedlings had a high geotropic curvature response. The effect of HMI on the geotropic curvature could also be observed when untreated control seedlings were soaked in HMI solution. The rate of geotropic curvature response of rice seedlings increased with increasing HMI dosage. HMI showed no auxin activity in the rice lamina joint test. However, the auxin activity of indoleacetic acid was increased in the presence of HMI. Therefore, the increased geotropic curvature response of rice seedlings caused by HMI may be due to a synergistic effect of HMI on endogenoud auxin.