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Plant Shoots (plant + shoot)
Selected AbstractsEffects of Salinity and Mixed Ammonium and Nitrate Nutrition on the Growth and Nitrogen Utilization of BarleyJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 4 2001A. Ali The absorption and utilization of nitrogen (N) by plants are affected by salinity and the form of N in the root medium. A hydroponic study was conducted under controlled conditions to investigate growth and N uptake by barley (Hordeum vulgare L.) supplied with five different NH4+ -N/NO3, -N ratios at electrical conductivity of 0 and 8 dS m,1. The five NH4+ -N/NO3 -N ratios were 0/100, 25/75, 50/50, 75/25 and 100/0, each giving a total N supply of 100 mg N l,1 in the root medium. A mixed N supply of NH4+ and NO3, resulted in greater accumulation of N in plants than either NO3, or NH4+ as the sole N source. Plants produced a significantly higher dry matter yield when grown with mixed N nutrition than with NH4+ or NO3, alone. Total dry matter production and root and shoot N contents decreased with increasing salinity in the root medium. The interaction between salinity and N nutrition was found to be significant for all the variables. A significant positive correlation (r=0.97) was found between nitrogen level in the plant shoot and its dry matter yield. Wachstum und Stickstoffausnutzung bei Gerste in Abhängigkeit von Versalzung und Michungen von Ammonium und Nitrat Aufnahme und Nutzung von N durch Pflanzen wird von der Versalzung und N-Form im Wurzelbereich bestimmt. Es wurde in Hydrokultur unter kontrollierten Bedingungen Wachstum und N-Aufnahme durch Gerste (Hordeum vulgare L.) bei Anwendung von fünf unterschiedlichen NH4+ -N/NO3, -N Verhältnissen bei einer elektrischen Konduktivität von 0 und 8 dS m,1 untersucht. Die Gesamtmenge von 100 mg N l,1 im Wurzelmedium wies NH4+ -N/NO3, -N Verhältnisse von 0/100, 25/75, 50/50, 75/25 und 100/0 auf. Mischungen von NH4+ und NO3, führten zu einer größeren Aufnahme durch die Pflanzen als bei alleiniger Anwendung von NO3, oder NH4+. Die Pflanzen produzierten signifikant mehr Gesamttrockenmasse mit Mischungen der beiden N-Formen im Vergleich zu alleiniger Anwendung von NH4+ oder NO3,. Die Gesamttrockenmasse sowie die N-Gehalte von Wurzel und Sproß nahmen mit steigender Versalzung ab. Versalzungs- und N-Versorgungs-Interaktion war signifikant in allen Versuchsbedingungen. Eine signifikante positive Korrelation (r=0,97) wurde zwischen Stickstoffkonzentration und der Trockenmasseproduktion der Pflanze gefunden. [source] Xylem Flow and its Driving Forces in a Tropical Liana: Concomitant Flow-Sensitive NMR Imaging and Pressure Probe MeasurementsPLANT BIOLOGY, Issue 6 2000N. Wistuba Abstract: Flow-sensitive NMR imaging and pressure probe techniques were used for measuring xylem water flow and its driving forces (i.e., xylem pressure as well as cell turgor and osmotic pressure gradients) in a tropical liana, Epipremnum aureum. Selection of tall specimens allowed continuous and simultaneous measurements of all parameters at various distances from the root under diurnally changing environmental conditions. Well hydrated plants exhibited exactly linearly correlated dynamic changes in xylem tension and flow velocity. Concomitant multiple-probe insertions along the plant shoot revealed xylem and turgor pressure gradients with changing magnitudes due to environmental changes and plant orientation (upright, apex-down, or horizontal). The data suggest that in upright and - to a lesser extent - in horizontal plants the transpirational water loss by the cells towards the apex during the day is not fully compensated by water uptake through the night. Thus, longitudinal cellular osmotic pressure gradients exist. Due to the tight hydraulic coupling of the xylem and the tissue cells these gradients represent (besides the transpiration-induced tension in the xylem) an additional tension component for anti-gravitational water movement from the roots through the vessels to the apex. [source] Nitrogen fertilization effects on Myzus persicae aphid dynamics on peach: vegetative growth allocation or chemical defence?ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2010Marie-Hélène Sauge Abstract Plant nitrogen (N) fertilization is a common cropping practice that is expected to serve as a pest management tool. Its effects on the dynamics of the aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) were examined on young peach [Prunus persica (L.) Batsch (Rosaceae)] trees grown under five N treatments, ranging from N shortage to supra-optimal supply for growth. Aphid population increased over time at the three intermediate N levels. It remained stable at the lowest N level and decreased at the highest N level. Four weeks after the start of infestation, the number of aphids displayed a parabolic response to N level. The relationships between N status and parameters of plant vegetative growth (stem diameter) or biomass allocation (lateral-total leaf area and root-shoot ratio) were consistent with responses proposed by models of adaptive plasticity in resource allocation patterns. However, the variation in plant growth predicted aphid population dynamics only partially. Whereas aphid number was positively correlated with plant N status and vegetative growth up to the intermediate N level, it was negatively correlated with plant N status above this level, but not with vegetative growth. The concentrations of primary and secondary (plant defence-related) metabolites in the plant shoots were modified by N treatments: amino acids (main nutritional resource of aphids) and prunasin increased, whereas chlorogenic acid decreased with increasing N availability. Constitutive changes in plant chemistry in response to N fertilization could not directly explain the reduced aphid performance for the highest N level. Nevertheless, the indirect effect of N on the induction of plant defence compounds by aphid feeding warrants further investigation. The study focuses on the feasibility of handling N fertilization to control M. persicae in orchards, but findings may also be relevant for our understanding of the physiological relationships between the host's nutritional status and the requirements of the insect. [source] Responses of shoot growth and survival to water stress gradient in diploid and tetraploid populations of Lolium multiflorum and L. perenneGRASSLAND SCIENCE, Issue 4 2006Shu-ichi Sugiyama Abstract Drought stress is one of the critical environmental factors in determining growth and survival of herbage grasses. In this study, by using a hydroponic culture system including different amounts of polyethylene glycol (PEG), responses of plant shoots to water stress in four different intensities (0 Mpa, ,0.6 Mpa, ,1.2 Mpa and ,1.8 Mpa) were examined in diploid and tetraploid cultivars of Italian ryegrass (Lolium multiflorum) and perennial ryegrass (L. perenne). Since freezing injury is caused by cell dehydration, freezing tolerance was also examined for six subzero temperatures (,11, ,12, ,14, ,16, ,18 and ,20°C) in both species. L. multiflorum had a larger shoot biomass at all stress intensities and a lower survival rate under severe water stress and freezing stress conditions than L. perenne. Thus, there was a trade-off (negative correlation) between potential growth under a stress-free condition and survival under a severe stress condition in diploid and tetraploid cultivars of both species. This trade-off was mediated by tissue water content. High water content led to a high growth rate through increasing specific leaf area, while low water content resulted in a high tissue osmotic potential that could confer high cell dehydration tolerance. [source] Nitrogen and phosphorus availability limit N2 fixation in beanNEW PHYTOLOGIST, Issue 2 2000E. O. LEIDI Availability of nitrogen (N) and phosphorus (P) might significantly affect N2 fixation in legumes. The interaction of N and P was studied in common bean (Phaseolus vulgaris), considering their effects on nodulation and N2 fixation, nitrate reductase activity, and the composition of N compounds in xylem sap. The effect of N on the uptake of P by plants was estimated by analysing rhizospheric pH and P concentration in xylem sap and in plant shoots. Inoculated bean plants were grown in pots containing perlite/vermiculite in two experiments with different amounts of P and N. In a third experiment, bean plants were grown on two soil types or on river sand supplied with different concentrations of N. At harvest, shoot growth, number of nodules and mass, and nitrogenase activity were determined. Xylem sap was collected for the determination of ureides, amino acids, nitrate and phosphate concentration. At low nitrate concentration (1 mM), increasing amounts of P promoted both nodule formation and N2 fixation, measured as ureide content in the xylem sap. However, at high nitrate concentration (10 mM), nodulation and N2 fixation did not improve with increased P supply. Glutamine and aspartate were the main organic N compounds transported in the xylem sap of plants grown in low nitrate, whereas asparagine was the dominant N compound in xylem sap from plants grown in high nitrate. Nitrate reductase activity in roots was higher than in shoots of plants grown with low P and high N. In both soils and in the sand experiment, increased application of N decreased nodule mass and number, nitrogenase activity and xylem ureides but increased the concentration of asparagine in xylem sap. Increasing P nutrition improved symbiotic N2 fixation in bean only at low N concentrations. It did not alleviate the inhibitory effect of high nitrate concentration on N2 fixation. A decrease in plant P uptake was observed, as indicated by a lower concentration of P in the xylem sap and shoots, correlating with the amount of N supplied. Simultaneously with the specific inhibition of N2 fixation, high nitrate concentrations might decrease P availability, thus inhibiting even further the symbiotic association because of the high P requirement for nodulation and N2 fixation. [source] Short episodes of water stress increase barley root resistance to radial shrinkage in a dehydrating environmentPHYSIOLOGIA PLANTARUM, Issue 4 2006Jorge Hugo Lemcoff Although plant shoots can be ,hardened' by abiotic stresses, little is known about such changes in roots. In order to investigate possible induction of root-hardening in response to short water-stress episodes, barley seedlings (Hordeum vulgare L) hydroponically grown under a controlled environment were moderately water-stressed by addition of a non-penetrating osmoticum, polyethylene glycol (PEG) 6000 at ,0.4 MPa water potential, to the aerated nutrient solution. Seedlings were then hydrated in dilute nutrient solution without PEG before excision and assay of the seminal roots. Previous water stress treatments for 72 h, 12 h, or even 6 h induced an apparent root-hardening process. Thus, root radial shrinkage during subsequent exposure to strongly dehydrating conditions was remarkably decreased. The root hardening was related to biophysical adjustments: turgor-pressure increased while osmotic potential decreased from ,0.45 ± 0.02 MPa to ,0.60 ± 0.02 MPa. Moreover, the maximum bulk volumetric modulus of elasticity, ?max determined by pressure,volume analysis, increased from 2.1 ± 0.4 MPa to 3.7 ± 0.4 MPa, i.e. root elasticity was decreased. Root hardening in response to episodes of water stress may have ecological significance for barley plants in regions where intermittent drought episodes are frequent. [source] | |||||||||||||