Light-induced inhibition of elongation growth in sunflower hypocotyls (original) (raw)
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Physiologia Plantarum, 1992
Inhibition of Pisum sativum epicotyl elongation by white light-Differeni effects of light on the mechanical properties of cell walls in the epidermal and inner tissues,-PhysioL Plant, 84: 380-385, White fluorescent light (5 W m^-) inhibited subhook growth in derooted Alaska pea cuttings, in the inner tisstie of the subhook, it inhibited the increase in osmotic potential during 18 h incubation, in the epidermis, on the other hand, hght did not affect the osmotic potential. Light increased the minimum-stress relaxation time (T)) of the inner tissue cell walls, but did not change T,, of the epidermal cell wall. Light decreased tissue stress determined by the split test and the ability of the inner tissue to extend by water absorption. The short-term light effect on subhook growth. T,. and the tissue stress almost disappeared when pea cuttings were transferred to darkness. These facts soggest that light changes the mechanical properties of the cell wall in the inner tissue of shoots, and decreases tissue stress, which is considered to be the driving force of shoot growth.
Plants
This study presents the hypocotyl elongation of sunflower seedlings germinated under different light conditions. Elongation was rhythmic under diurnal (LD) photoperiods but uniform (arrhythmic) under free-running conditions of white light (LL) or darkness (DD). On the sixth day after the onset of germination, seedlings were entrained in all diurnal photoperiods. Their hypocotyl elongation was dual, showing different kinetics in daytime and nighttime periods. The daytime elongation peak was around midday and 1–2 h after dusk in the nighttime. Plantlets compensated for the differences in the daytime and nighttime durations and exhibited similar overall elongation rates, centered around the uniform elongation in LL conditions. Thus, plants from diurnal photoperiods and LL could be grouped together as white-light treatments that suppressed hypocotyl elongation. Hypocotyl elongation was significantly higher under DD than under white-light photoperiods. In continuous monochromatic blue, y...
Interaction between Wall Deposition and Cell Elongation in Dark-Grown Hypocotyl Cells in Arabidopsis
PLANT PHYSIOLOGY, 2004
A central problem in plant biology is how cell expansion is coordinated with wall synthesis. We have studied growth and wall deposition in epidermal cells of dark-grown Arabidopsis hypocotyls. Cells elongated in a biphasic pattern, slowly first and rapidly thereafter. The growth acceleration was initiated at the hypocotyl base and propagated acropetally. Using transmission and scanning electron microscopy, we analyzed walls in slowly and rapidly growing cells in 4-d-old dark-grown seedlings. We observed thick walls in slowly growing cells and thin walls in rapidly growing cells, which indicates that the rate of cell wall synthesis was not coupled to the cell elongation rate. The thick walls showed a polylamellated architecture, whereas polysaccharides in thin walls were axially oriented. Interestingly, innermost cellulose microfibrils were transversely oriented in both slowly and rapidly growing cells. This suggested that transversely deposited microfibrils reoriented in deeper layers of the expanding wall. No growth acceleration, only slow growth, was observed in the cellulose synthase mutant cesA6 prc1-1 or in seedlings, which had been treated with the cellulose synthesis inhibitor isoxaben. In these seedlings, innermost microfibrils were transversely oriented and not randomized as has been reported for other cellulose-deficient mutants or following treatment with dichlorobenzonitrile. Interestingly, isoxaben treatment after the initiation of the growth acceleration in the hypocotyl did not affect subsequent cell elongation. Together, these results show that rapid cell elongation, which involves extensive remodeling of the cell wall polymer network, depends on normal cellulose deposition during the slow growth phase. fax 33-1-30833099.
PLANT PHYSIOLOGY, 1991
The underlying mechanism of photoinhibition of stem elongation by blue (BL) and red light (RL) was studied in etiolated seedlings of pea (Pisum sativum L. cv Alaska). Brief BL irradiations resulted in fast transient inhibition of elongation, while a delayed (lag approximately 60 minutes) but prolonged inhibition was observed after brief RL. Possible changes in the hydraulic and wall properties of the growing cells during photoinhibition were examined. Cell sap osmotic pressure was unaffected by BL and RL, but both irradiations increased turgor pressure by approximately 0.05 megapascal (pressure-probe technique). Cell wall yielding was analyzed by in vivo stress relaxation (pressureblock technique). BL and RL reduced the initial rate of relaxation by 38 and 54%, while the final amount of relaxation was decreased by 48 and 10%, respectively. These results indicate that RL inhibits elongation mainly by lowering the wall yield coefficient, while most of the inhibitory effect of BL was due to an increase of the yield threshold. Mechanical extensibility of cell walls (Instron technique) was decreased by BL and RL, mainly due to a reduction in the plastic component of extensibility. Thus, photoinhibitions of elongation by both BL and RL are achieved through changes in cell wall properties, and are not due to effects on the hydraulic properties of the cell.
Effect of white light on cell expansion and lipid netabolism in sunflower cotyledons
Journal of Plant Physiology, 1997
The growth of the cotyledons of etiolated sunflower seedlings (Helianthus annuus L.) is promoted by white light (WL). This process is due to an enhancement in the rate of cell expansion. The degradation of lipid reserves is stimulated by WL. An analysis of different fractions of homogenized cotyledons revealed rhat rhe enzyme lipase is exclusively localized in the oil bodies (oleosomes) of rhe cells. In WL-treated seedlings, lipolytic activity was higher rhan in dark-grown controls. In contrast, the specific activity of isocitrate lyase, a key enzyme of the glyoxylate cycle, was reduced upon exposure to WL. The results are discussed with respect to rhe relationship between sugar accumulation and cell expansion in the cotyledons and rhe hypocotyl of the developing sunflower seedling.
Plant Physiology, 2000
Spontaneous growth of isolated inner tissue from the etiolated sunflower (Helianthus annuus L.) hypocotyl growing zone was investigated. A new preparation technique allowed measurements starting 3 s after excision. Elongation with respect to the turgescent and plasmolized state was quantified in terms of relative growth rates, facilitating comparison to growth in situ. Turgor and turgor-induced strain were determined. Overall longitudinal strain in inner tissues in situ was positive, indicating that compressive forces exerted by peripheral tissues are outweighed by turgor-dependent tensile stress. Inner tissue expansion following isolation depended on water uptake. Extreme plastic extension rates occurred immediately after excision, suggesting that mechanical parameters of inner tissue in situ cannot be extrapolated from the mechanics of excised sections. In the long term, excised inner tissue autonomously established values of turgor, turgor-induced strain, and relative growth rates similar to values in the living plant. These results support historic models of tissue cooperation during organ growth, in which inner tissues actively participate in the control of growth rates.
The epidermal-growth-control theory of stem elongation: An old and a new perspective
Journal of Plant Physiology, 2007
The botanist G. Kraus postulated in 1867 that the peripheral cell layers determine the rate of organ elongation based on the observation that the separated outer and inner tissues of growing stems spontaneously change their lengths upon isolation from each other. Here, we summarize the modern version of this classical concept, the ''epidermal-growth-control'' or ''tensile skin'' theory of stem elongation. First, we present newly acquired data from sunflower hypocotyls, which demonstrate that the expansion of the isolated inner tissues is not an experimental artefact, as recently claimed, but rather the result of metabolism-independent cell elongation caused by the removal of the growth-controlling peripheral walls. Second, we present data showing that auxin-induced elongation of excised stem segments is attributable to the loosening of the thick epidermal walls, which provides additional evidence for the ''epidermal-growth-control concept''. Third, we show that the cuticle of aerial organs can be thin and mechanically weak in seedlings raised at high humidity, but thick and mechanically important for organs growing under relatively dry air conditions. Finally, we present a modified model of the ''tensile skin-theory'' that draws attention to the mechanical and physiological roles of (a) the thickened, helicoidal outer cell walls, (b) the mechanical constraint of a cuticle, and (c) the interactions among outer and inner cell layers as growth is coordinated by hormonal signals.
Cell elongation in Arabidopsis hypocotyls involves dynamic changes in cell wall thickness
Journal of Experimental Botany, 2007
Field-emission scanning electron microscopy was used to measure wall thicknesses of different cell types in freeze-fractured hypocotyls of Arabidopsis thaliana. Measurements of uronic acid content, wall mass, and wall volume suggest that cell wall biosynthesis in this organ does not always keep pace with, and is not always tightly coupled to, elongation. In light-grown hypocotyls, walls thicken, maintain a constant thickness, or become thinner during elongation, depending upon the cell type and the stage of growth. In lightgrown hypocotyls, exogenous gibberellic acid represses the extent of thickening and promotes cell elongation by both wall thinning and increased anisotropy during the early stages of hypocotyl elongation, and by increased wall deposition in the latter stages. Dark-grown hypocotyls, in the 48 h period between cold imbibition and seedling emergence, deposit very thick walls that subsequently thin in a narrow developmental window as the hypocotyl rapidly elongates. The rate of wall deposition is then maintained and keeps pace with cell elongation. The outer epidermal wall is always the thickest (~1 mm) whereas the thinnest walls, about 50 nm, are found in inner cell layers. It is concluded that control of wall thickness in different cell types is tightly regulated during hypocotyl development, and that wall deposition and cell elongation are not invariably coupled.
Acta Scientiarum. Agronomy, 2014
The purpose of this study was to evaluate the effects of light restriction on the growth of benghal dayflower (Commelina benghalensis). The experiment was conducted in pots under full sunlight and with 18.5, 30, 40, 50, 60 and 70% artificial light restriction treatments. Plant growth was evaluated up to 90 days after planting (DAP), and mathematical models of the major shoot length, internode length, individual area of the first leaf completely expanded, number of leaves and shoot and root dry mass weights were established depending on increasing light restriction levels. The elevation of the light gradient promoted reductions in the number of leaves and fasciculate root dry mass weight. Light restriction did not induce alterations in the plasticity of performance (alterations in total biomass accumulation) of the C. benghalensis plants, the stability of which was related to an integration of the expected morphological, anatomical and physiological adjustments, constituting in a strong evidence of shading tolerance.