Shoot

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

Uptake of Selenium and its antioxidant activity in ryegrass when applied as selenate and selenite forms

Abstract: Selenium (Se) is an essential micronutrient for animal and human nutrition, but whether it is essential to plants remains controversial. However, there are increasing experimental evidences that indicate a protective role of Se against the oxidative stress in higher plants through Se-dependent glutathione peroxidase (GSH-Px) activity. The effects of the Se chemical forms, selenite and selenate, the rate of their application on shoot Se concentration and their influence on the antioxidative system of ryegrass (Lolium perenne cv. Aries), through the measurement of GSH-Px activity and lipid peroxidation, were evaluated in an Andisol of Southern Chile. Moreover, a soil–plant relationship for Se was determined and a simple method to extract available Se from acid soils is proposed. In a 55-day experiment ryegrass seeds were sown in pots and soil was treated with sodium selenite or sodium selenate (0–10 mg Se kg−1). The results showed that the Se concentration in shoots increased with the application of both selenite and selenate. However, the highest shoot Se concentrations were obtained in selenate-treated plants. For both sources of Se, there was a significant positive correlation between the shoot Se concentration and the GSH-Px activity; and the Se-dependence of this enzymatic activity was related especially with the chemical form of applied Se rather than the Se concentration in plant tissues. Furthermore, the lipid peroxidation, as measured by Thiobarbituric Acid Reactive Substances (TBARS), decreased at low levels of shoot Se concentration, reaching the lowest level at approximately 20 mg Se kg−1 in plants and then increased steadily above this level. In addition, the acid extraction method used to evaluate available Se in soil showed a positive good correlation between soil Se and shoot Se concentrations irrespective of chemical form of Se applied.

Short‐term effects of boron, germanium and high light intensity on membrane permeability in boron deficient leaves of sunflower

Abstract: The effects of varied boron (B) supply (0.01-50 μM) and light intensity (100-580 μmol m -1 s -1 ) on plant growth, leaf symptoms and membrane permeability of leaves were studied in sunflower plants over a 10-day-period of growth in nutrient solution. Membrane permeability was measured by incubating isolated young leaves in aerated distilled water. Additional experiments showed the effect of short-term supply (20 min to 2 h) of B and germanium (Ge) on membrane permeability of B-deficient leaves incubated in distilled water. Low supply of B decreased shoot and root growth and caused brown-purple pigmentation of young leaves, particularly under high light intensities. Leakage of K + from leaves increased with severity of B deficiency whereas, in B-sufficient leaves, leakage of solutes was low. Also leakage of phenolics, amino acids and sucrose was enhanced by B deficiency. Compared to B-sufficient leaves, the leakage from B-deficient leaves was 35-fold higher for K + , 45-fold higher for sucrose and 7-fold higher for phenolics and amino acids. Increases in solute leakage were marked in leaf areas with brown-purple pigmentation and particularly pronounced by increasing light intensity or by exposure of leaves to continuous light. In severely B-deficient leaves grown under high light intensity, treatment with B and Ge up to 1 000 μM for 20 min resulted in an immediate decrease in K + efflux to about the same levels as in B-sufficient leaves. Similar rapid decreases in K + efflux were also found in B-deficient leaves when exposed to darkness for 16 h or 30 h before the leakage measurement. The results demonstrate a particular role for B in maintaining the integrity of plasma membranes. Boron presumably stabilizes the structure of the plasma membrane by complexing membrane constituents. It also has a protective effect on membrane constituents by complexing phenolics, so that oxidation of phenolics to highly toxic quinones and oxygen free radicals is prevented or limited. In these functions, boron seems to be to a large extent replaceable by germanium.

The homeobox genes ATHB12 and ATHB7 encode potential regulators of growth in response to water deficit in Arabidopsis

Abstract: The Arabidopsisthaliana homeodomain leucine-zipper gene ATHB7, which is active specifically under water deficit conditions, is proposed to act as a negative regulator of growth (Soderman et al., 1996, Plant J. 10: 375 381; Hjellstrom et al., 2003, Plant Cell Environ 26: 1127 1136). In this report we demonstrate that the paralogous gene, ATHB12, has a similar expression pattern and function. ATHB12,like ATHB7,was up-regulated during water deficit conditions, the up-regulation being dependent on abscisic acid (ABA) and on the activity of the Ser/Thr phosphatases ABI1 and ABI2. Plants that are mutant for ATHB12, as a result of T-DNA insertions in the ATHB12 gene, showed a reduced sensitivity to ABA in root elongation assays, whereas transgenic Arabidopsis plants expressing ATHB12 and/orATHB7 as driven by the CaMV 35S promoter were hypersensitive in this response compared to wild-type. High-level expression of either gene also resulted in a delay in inflorescence stem elongation growth and caused plants to develop rosette leaves with a more rounded shape, shorter petioles, and increased branching of the inflorescence stem. Transgenic Arabidopsisplants expressing the reporter geneuidA under the control of the ATHB12promoter showed marker gene activity in axillary shoot primordia, lateral root primordia, inflorescence stems and in flower organs. Treatment of plants with ABA or water deficit conditions caused the activity of ATHB12to increase in the inflorescence stem, the flower organs and the leaves, and to expand into the vasculature of roots and the differentiation/elongation zone of root tips. Taken together, these results indicate that ATHB12 and ATHB7 act to mediate a growth response to water deficit by similar mechanisms.