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Results for “Plant Stems/physiology”

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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4 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Cytoplasmic pH dynamics in maize pulvinal cells induced by gravity vector changes

In maize (Zea mays) and other grasses, changes in orientation of stems are perceived by pulvinal tissue, which responds to the stimulus by differential growth resulting in upward bending of the stem. The amyloplast-containing bundle sheath cells are the sites of gravity perception, although the initial steps of gravity perception and transmission remain unclear. In columella cells of Arabidopsis roots, we previously found that cytoplasmic pH (pH(c)) is a mediator in early gravitropic signaling (A.C. Scott, N.S. Allen [1999] Plant Physiol 121: 1291-1298). The question arises whether pH(c) has a more general role in signaling gravity vector changes. Using confocal ratiometric imaging and the fluorescent pH indicator carboxy seminaphtorhodafluor acetoxymethyl ester acetate, we measured pH(c) in the cells composing the maize pulvinus. When stem slices were gravistimulated and imaged on a horizontally mounted confocal microscope, pH(c) changes were only apparent within the bundle sheath cells, and not in the parenchyma cells. After turning, cytoplasmic acidification was observed at the sides of the cells, whereas the cytoplasm at the base of the cells where plastids slowly accumulated became more basic. These changes were most apparent in cells exhibiting net amyloplast sedimentation. Parenchyma cells and isolated bundle sheath cells did not show any gravity-induced pH(c) changes although all cell types responded to external stimuli in the predicted way: Propionic acid and auxin treatments induced acidification, whereas raising the external pH caused alkalinization. The results suggest that pH(c) has an important role in the early signaling pathways of maize stem gravitropism.

Non-NASA Center↗
NASA NTRS1989

On the role of calcium in indole-3-acetic acid movement and graviresponse in etiolated pea epicotyls

To determine whether Ca2+ plays a special role in the early graviresponse of shoots, as has been reported for roots, we treated etiolated pea epicotyls with substances known to antagonize Ca2+ (La3+), to remove Ca2+ from the wall (spermidine, EGTA), to inhibit calmodulin mediated reactions (chlorpromazine), or to inhibit IAA transport (TIBA). We studied the effect of these substances on IAA and Ca2+ uptake into 7 mm long subapical 3rd internode etiolated pea epicotyl sections and pea leaf protoplasts, on pea epicotyl growth, and graviresponse and on lateral IAA redistribution during gravistimulation. Our results support the view that adequate Ca2+ in the apoplast is required for normal IAA uptake, transport and graviresponse. Experiments with protoplasts indicate that Ca2+ may be controlling a labile membrane porter, possibly located on the external surface of cell membrane, while inhibitor experiments suggest that calmodulin is also implicated in both the movement of IAA and graviresponse. Since a major transfer of Ca2+ through free space during graviresponse has not yet been demonstrated, and since inhibition of calcium channels does not affect IAA redistribution (Migliaccio and Galston, 1987, Plant Physiology 85:542), we conclude that no clear evidence links prior Ca2+ movement with IAA redistribution during graviresponse in stems.

Non-NASA Center↗
NASA NTRS1988

Mechanism of rapid suppression of cell expansion in cucumber hypocotyls after blue-light irradiation

Rapid suppression of hypocotyl elongation by blue light in cucumber (Cucumis sativus L.) was studied to examine possible hydraulic and wall changes responsible for diminished growth. Cell-sap osmotic pressure, measured by vapor-pressure osmometry, was not decreased by blue light; turgor pressure, measured by the pressure-probe technique, remained constant during the growth inhibition; and stem hydraulic conductance, measured by dynamic and static methods, was likewise unaffected by blue light. Wall yielding properties were assessed by the pressure-block technique for in-vivo stress relaxation. Blue light reduced the initial rate of relaxation by 77%, but had little effect on the final amount of relaxation. The results demonstrate that blue irradiation acts to decrease the wall yielding coefficient, but not the yield threshold. Stress-strain (Instron) analysis showed that irradiation of the seedlings had little effect on the mechanical extensibilities of the isolated wall. The results indicate that blue light can reduce cell-wall loosening without affecting bulk viscoelastic properties, and indicate a chemorheological mechanism of cell-wall expansion.

NASA Discipline Number 40-30↗
NASA NTRS2001

Induced compression wood formation in Douglas fir (Pseudotsuga menziesii) in microgravity

In the microgravity environment of the Space Shuttle Columbia (Life and Microgravity Mission STS-78), were grown 1-year-old Douglas fir and loblolly pine plants in a NASA plant growth facility. Several plants were harnessed (at 45 degrees ) to establish if compression wood biosynthesis, involving altered cellulose and lignin deposition and cell wall structure would occur under those conditions of induced mechanical stress. Selected plants were harnessed at day 2 in orbit, with stem sections of specific plants harvested and fixed for subsequent microscopic analyses on days 8, 10 and 15. At the end of the total space mission period (17 days), the remaining healthy harnessed plants and their vertical (upright) controls were harvested and fixed on earth. All harnessed (at 45 degrees ) plant specimens, whether grown at 1 g or in microgravity, formed compression wood. Moreover, not only the cambial cells but also the developing tracheid cells underwent significant morphological changes. This indicated that the developing tracheids from the primary cell wall expansion stage to the fully lignified maturation stage are involved in the perception and transduction of the stimuli stipulating the need for alteration of cell wall architecture. It is thus apparent that, even in a microgravity environment, woody plants can make appropriate corrections to compensate for stress gradients introduced by mechanical bending, thereby enabling compression wood to be formed. The evolutionary implications of these findings are discussed in terms of "variability" in cell wall biosynthesis.

manned↗