Shoot

About: Shoot is a research topic. Over the lifetime, 32188 publications have been published within this topic receiving 693348 citations.

Impact of Fe and Ag nanoparticles on seed germination and differences in bioavailability during exposure in aqueous suspension and soil

Abstract: The potential environmental toxicity of zero-valent iron nanoparticles (nZVI) and three types of nanosilver differing in average particle size from 1 to 20 nm was evaluated using seed germination tests with ryegrass, barley, and flax exposed to 0-5000 mg L(-1) nZVI or 0-100 mg L(-1) Ag. For nZVI, germination tests were conducted both in water and in two contrasting soils to test the impact of assumed differences in bioavailability of nanoparticles. Inhibitory effects were observed in aqueous suspensions at 250 mg L(-1) for nZVI and 10 mg L(-1) for Ag. Reduction in shoot growth was a more sensitive endpoint than germination percentage. Complete inhibition of germination was observed at 1000-2000 mg L(-1) for nZVI. For Ag, complete inhibition was not achieved. The presence of soil had a modest influence on toxicity, and inhibitory effects were observed at 300 mg nZVI L(-1) water in soil (equivalent to 1000 mg nZVI kg(-1) soil). Complete inhibition was observed at 750 and 1500 mg L(-1) in sandy soil for flax and ryegrass, respectively, while for barley 13% germination still occurred at 1500 mg L(-1) . In clay soil, inhibition was less pronounced. Our results indicate that nZVI at low concentrations can be used without detrimental effects on plants and thus be suitable for combined remediation where plants are involved. Silver nanoparticles inhibited seed germination at lower concentrations, but showed no clear size-dependent effects, and never completely impeded germination. Thus, seed germination tests seem less suited for estimation of environmental impact of

Interactions between selenium and sulphur nutrition in Arabidopsis thaliana

Abstract: Selenium (Se) is an essential plant micronutrient, but is toxic at high tissue concentrations. It is chemically similar to sulphur (S), an essential plant macronutrient. The interactions between Se and S nutrition were investigated in the model plant Arabidopsis thaliana (L.) Heynh. Arabidopsis plants were grown on agar containing a complete mineral complement and various concentrations of selenate and sulphate. The Se/S concentration ratio in the shoot ([Se](shoot)/[S](shoot)) showed a complex dependence on the ratio of selenate to sulphate concentration in the agar ([Se](agar)/[S](agar)). Increasing [S](agar) increased shoot fresh weight (FW) and [S](shoot), but decreased [Se](shoot). Increasing [Se](agar) increased both [Se](shoot) and [S](shoot), but reduced shoot FW. The reduction in shoot FW in the presence of Se was linearly related to the shoot Se/S concentration ratio. These data suggest (i) that Se and S enter Arabidopsis through multiple transport pathways with contrasting sulphate/selenate selectivities, whose activities vary between plants of contrasting nutritional status, (ii) that rhizosphere sulphate inhibits selenate uptake, (iii) that rhizosphere selenate promotes sulphate uptake, possibly by preventing the reduction in the abundance and/or activity of sulphate transporters by sulphate and/or its metabolites, and (iv) that Se toxicity occurs because Se and S compete for a biochemical process, such as assimilation into amino acids of essential proteins.

Influence of Phosphorus Nutrition on Growth and Carbon Partitioning in Glycine max

Abstract: Soybean plants (Glycine max [L.] Merr var Amsoy 71) were grown in growth chambers with high-phosphorus (high-P) and low-phosphorus (low-P) culture solutions. Low-P treatment reduced shoot growth significantly 7 days after treatment began. Root growth was much less affected by low-P, there being no significant reduction in root growth rate until 17 days had elapsed. The results suggest that low-P treatment decreased soybean growth primarily through an effect on the expansion of the leaf surface which was diminished by 85%, the main effect of low-P being on the rate of expansion of individual leaves. Low-P had a lesser effect on photosynthesis; light saturated photosynthetic rates at ambient and saturating CO2 levels were lowered by 55 and 45%, respectively, after 19 days of low-P treatment. Low-P treatment increased starch concentrations in mature leaves, expanding leaves and fibrous roots; sucrose concentrations, however, were reduced by low-P in leaves and increased in roots. Foliar F-2,6-BP levels were not affected by P treatment in the light but in darkness they increased with high-P and decreased with low-P. The increase in the starch/sucrose ratio in low-P leaves was correlated primarily with changes in the total activities of enzymes of starch and sucrose metabolism.

The role of auxins and cytokinins in the release of buds from dominance

Abstract: The paper deals with the general problem of the physiological basis of branching, and the roles of known and unexplored factors in sensitivity to apical domirnance. It is shown that when pea seedling shoots are completely or partially inhibited by other shoots on the same plant auxin can promote their elongation, even though it does not have this effect on inhibited buds. This influence of auxin is only exerted on internodal elongation and not on apical growth. When kinetin in a solution of alcohol and carbowax is applied directly to the lateral buds of pea seedlings, it releases them from inhibition by the growing apex. It is shown that the role of alcohol in this solution is to act as a surfactant, permitting good contact with the buds, while that of carbowax, being hygroscopic, is to maintain a thin film of solution over the buds. Buds thus released from apical dominance by kinetin do not elongate as much as do uninhibited control buds. Such kinetintreated buds can, however, be made to elongate normally by the application of auxin locally to their apices. It is concluded that growing shoots are relatively insensitive to correlative inhibition because they synthesize two types of growth substances, namely, auxin, which antagonizes the inhibitory effect on internodal elongation, and cytokinins, which permit the apex itself to develop. In the discussion it is brought out that many cases of branching, which appear at first to bear little relation to one another, can be understood on the basis of two principles, namely: (1) Any reduction in the growth rate of a dominant apex reduces its inhibitory effect on other apices, and (2) once an apex starts growing it becomes less sensitive to inhibition by other apices These generalizations and the experimental results are tentatively interpreted in terms of an interaction between the syntheses of auxin and of cytokinin.

The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source‐sink relations and respiration

Abstract: . Herbaceous C3 plants grown in elevated CO2 show increases in carbon assimilation and carbohydrate accumulation (particularly starch) within source leaves. Although changes in the partitioning of biomass between root and shoot occur, the proportion of this extra assimilate made available for sink growth is not known. Root:shoot ratios tend to increase for CO2-enriched herbaceous plants and decrease for CO2-enriched trees. Root:shoot ratios for cereals tend to remain constant. In contrast, elevated temperatures decrease carbohydrate accumulation within source and sink regions of a plant and decrease root:shoot ratios. Allometric analysis of at least two species showing changes in root: shoot ratios due to elevated CO2 show no alteration in the whole-plant partitioning of biomass. Little information is available for interactions between temperature and CO2. Cold-adapted plants show little response to elevated levels of CO2, with some species showing a decline in biomass accumulation. In general though, increasing temperature will increase sucrose synthesis, transport and utilization for CO2-enriched plants and decrease carbohydrate accumulation within the leaf. Literature reports are discussed in relation to the hypothesis that sucrose is a major factor in the control of plant carbon partitioning. A model is presented in support.