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Results for “Plant Growth Regulators/metabolism”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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43 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

How cereal grass shoots perceive and respond to gravity

The leaf-sheath pulvinus of grasses presents a unique system for studying gravitropism, primarily because of its differences from other organs. The mature pulvinus is a discrete organ specialized for gravitropism: it is nongrowing in the absence of gravistimulation and capable of displaying a graviresponse independent of the rest of the plant. In this paper we present a model for gravitropism in pulvini based on recent findings from studies on the mechanisms of graviperception and graviresponse. According to this model, amyloplasts play an essential role in perceiving a change in the orientation of the pulvinus. The perception of this reorientation leads to the enhanced synthesis and release from conjugate of the auxin IAA, and the increased conjugation of gibberellin, on a localized basis. Because there is a graded growth promotion across the gravistimulated pulvinus, it is suggested that the observed hormonal asymmetry is actually an indication of a linear gradient of hormone concentration, as well as hormone response, across the pulvinus. It is further suggested that the linear gradient of hormone concentration may be predominantly the result of local changes in hormone level, rather than a product of hormonal movement into or across the pulvinus.

NASA Discipline Number 40-99↗
NASA NTRS1990

Biophysical basis of growth promotion in primary leaves of Phaseolus vulgaris L. by hormones versus light: solute accumulation and the growth potential

Rapid cell enlargement in primary leaves of bean is induced by bright white light (WL), gibberellic acid (GA3) or the cytokinin N6-benzyladenine (BA). In previous studies it has been show that all three agents cause an increase in wall extensibility, although by different mechanisms. Here we examine the effects of the three growth promoters on the osmotic potential difference (delta Psi), the accumulation of solutes (delta TSC), the wall yield threshold (Y) and the growth potential (delta Psi -Y). With GA3 and BA, but not WL, there was a rapid decline in delta Psi as measured by the osmotic concentration of expressed sap. Unlike WL, neither GA3 nor BA promoted the accumulation of osmotic solutes. The decline in delta Psi, however, was apparently counteracted by a decline in Y since the growth potential, as measured by the external-osmoticum method, remained unchanged. It is concluded that WL, GA3 and BA all promote cell enlargement of bean leaves by increasing one cellular growth parameter, wall extensibility. Only WL, however, promotes osmotic adjustment during growth.

Non-NASA Center↗
NASA NTRS1988

Molecular and cellular aspects of calcium action in plants

Calcium is known to be a second messenger in many developmental processes in animal systems, but it has only recently become evident that Ca is an important intracellular messenger in plants as well. The level of free Ca concentration in the cytoplasm is extremely low, and it is influenced by extracellular signals such as light, gravity, and hormones. Investigations from our laboratory indicated that Ca and its binding protein, calmodulin, play an important role in stimulus-response coupling by regulating enzyme activities, especially through protein phosphorylation. In vivo and in vitro protein phosphorylation studies have revealed Ca-dependent changes in various plant tissues. We have also been able to influence various physiological processes such as cell elongation, abscission, senescence, and tuberization by altering extracellular and intracellular Ca levels. Other examples of Ca-mediated processes in plants are as follows: a) cell division, b) geotropism, c) protoplasmic streaming, d) stomatal control, e) chloroplast movement, f) secretion, g) hormone-dependent changes, h) enzyme activation, and i) protein phosphorylation.

NASA Program Space Biology↗
NASA NTRS1988

Enzymic synthesis of indole-3-acetyl-1-O-beta-d-glucose. I. Partial purification and characterization of the enzyme from Zea mays

The first enzyme-catalyzed reaction leading from indole-3-acetic acid (IAA) to the myo-inositol esters of IAA is the synthesis of indole-3-acetyl-1-O-beta-D-glucose from uridine-5'-diphosphoglucose (UDPG) and IAA. The reaction is catalyzed by the enzyme, UDPG-indol-3-ylacetyl glucosyl transferase (IAA-glucose-synthase). This work reports methods for the assay of the enzyme and for the extraction and partial purification of the enzyme from kernels of Zea mays sweet corn. The enzyme has an apparent molecular weight of 46,500 an isoelectric point of 5.5, and its pH optimum lies between 7.3 and 7.6. The enzyme is stable to storage at zero degrees but loses activity during column chromatographic procedures which can be restored only fractionally by addition of column eluates. The data suggest either multiple unknown cofactors or conformational changes leading to activity loss.

NASA Discipline Number 40-10↗
NASA NTRS1984

Cell wall pH and auxin transport velocity

According to the chemiosmotic polar diffusion hypothesis, auxin pulse velocity and basal secretion should increase with decreasing cell wall pH. Experiments were designed to test this prediction. Avena coleoptile sections were preincubated in either fusicoccin (FC), cycloheximide, pH 4.0, or pH 8.0 buffer and subsequently their polar transport capacities were determined. Relative to controls, FC enhanced auxin (IAA) uptake while CHI and pH 8.0 buffer reduced IAA uptake. Nevertheless, FC reduced IAA pulse velocity while cycloheximide increased velocity. Additional experiments showed that delivery of auxin to receivers is enhanced by increased receiver pH. This phenomenon was overcome by a pretreatment of the tissue with IAA. Our data suggest that while acidic wall pH values facilitate cellular IAA uptake, they do not enhance pulse velocity or basal secretion. These findings are inconsistent with the chemiosmotic hypothesis for auxin transport.

Plant Growth Regulators/metabolism↗
NASA NTRS1999

The influence of microgravity and spaceflight on columella cell ultrastructure in starch-deficient mutants of Arabidopsis

The ultrastructure of root cap columella cells was studied by morphometric analysis in wild-type, a reduced-starch mutant, and a starchless mutant of Arabidopsis grown in microgravity (F-microgravity) and compared to ground 1g (G-1g) and flight 1g (F-1g) controls. Seedlings of the wild-type and reduced-starch mutant that developed during an experiment on the Space Shuttle (both the F-microgravity samples and the F-lg control) exhibited a decreased starch content in comparison to the G-1g control. These results suggest that some factor associated with spaceflight (and not microgravity per se) affects starch metabolism. Elevated levels of ethylene were found during the experiments on the Space Shuttle, and analysis of ground controls with added ethylene demonstrated that this gas was responsible for decreased starch levels in the columella cells. This is the first study to use an on-board centrifuge as a control when quantifying starch in spaceflight-grown plants. Furthermore, our results show that ethylene levels must be carefully considered and controlled when designing experiments with plants for the International Space Station.

manned↗