Role of acid efflux during growth promotion of primary leaves of Phaseolus vulgaris L. by hormones and light

The white-light-(WL) induced enlargement of dicotyledonous leaf cells is known to occur via an acid-growth mechanism; i.e., WL causes leaf cells to excrete protons which lead to an increase in wall extensibility and thus cell enlargement. Gibberellic acid (GA₃) and N⁶-benzyladenine (BA) also induce leaf cell enlargement. To see if they also act via acid-induced cell wall loosening, a comparison has been made of WL-, GA₃-and BA-induced growth of strips, taken from primary leaves of bean (Phaseolus vulgaris L.) plants raised in continuous red light for 10 d. White light, GA₃ and BA all increased wall extensibility as measured by the Instron technique, and this change preceded the increase in growth rate. However, whereas WL induced significant proton excretion, neither GA₃ nor BA caused any acidification of the apoplast. Furthermore, neutral buffers, which effectively inhibited the growth induced by WL, were without effect on growth promoted by either GA₃ or BA. These results indicate that while WL, GA₃ and BA all initiate growth in bean leaves by altering cell-wall properties, GA₃ and BA do so through some wall loosening mechanism other than wall acidification. Neither gibberellin nor cytokinin is likely to play a major role in light-induced cell enlargement of dicotyledonous leaves.Abbreviations BA N^o-benzyladenine - FC fusicoccin - GA₃ gibberellic acid - RL red light - SK medium 10 mM sucrose+10mM KCl - WL white light     

Loss of capacity for acid-induced wall loosening as the principal cause of the cessation of cell enlargement in light-grown bean leaves

Cell enlargement in primary leaves of bean (Phaseolus vulgaris L.) can be induced, free of cell divisions, by exposure of 10-d-old, red-light-grown seedlings to white light. The absolute rate of leaf expansion increases until day 12, then decreases until the leaves reached mature size on day 18. The cause of the reduction in growth rate following day 12 has been investigated. Turgor calculated from measurements of leaf water and osmotic potential fell from 6.5 to 3.5 bar before day 12, but remained constant thereafter. The decline of growth after day 12 is not caused by a decrease in turgor. On the other hand, Instron-measured cell-wall extensibility decreased in parallel with growth rate after day 12. Two parameters influencing extensibility were examined. Light-induced acidification of cell walls, which has been shown to initiate wall extension, remained constant over the growth period (days 10–18). Furthermore, cells of any age could be stimulated to excrete H⁺ by fusicoccin. However, older tissue was not able to grow in response to fusicoccin or light. Measurements of acid-induced extension on preparations of isolated cell walls showed that as cells matured, the cell walls became less able to extend when acidified. These data indicate that it is a decline in the capacity for acid-induced wall loosening that reduces wall extensibility and thus cell enlargement in maturing leaves.Abbreviations and symbols FC fusicoccin - P turgor pressure - RL red light - WEx wall extensibility - WL white light - P _w leaf water potential - P _s osmotic potential     

Stimulation of Pisum sativum epicotyl elongation by gibberellin and auxin. – Different effects of two hormones on osmoregulation and cell walls

The possible involvement of auxin in the action of gibberellin in stimulating cell elongation was examined by comparing the effects of gibberellic acid (GA) and IAA on the growth, osmoregulation and cell wall properties of the Alaska pea ( Pisum sativum L. cv. Alaska) subhook. Both GA and IAA stimulated cell elongation in the subhook region of derooted cuttings. Cotyledon excision decreased the stimulating effect of GA on the growth of the subhook region, but did not affect that of IAA. As the subhook region elongated, the osmotic potential of the cell sap and the total amount of osmotic solutes increased. Cotyledon excision accelerated the increase in the osmotic potential and suppressed the accumulation of osmotic solutes. In cuttings with cotyledons. GA partly counteracted the increase in the osmotic potential and substantially promoted the accumulation of osmotic solutes. On the other hand, in cuttings without cotyledons. GA did not affect the change in the osmotic potential although it slightly promoted the accumulation of osmotic solutes. IAA accelerated the increase in the osmotic potential, but did not affect the accumulation of osmotic solutes. IAA enhanced the extensibility of the cell wall, while GA did not affect it. These results suggest that at least in the Alaksa pea subhook region. GA does not stimulate cell elongation by affecting the level of auxin.     

Control of light-induced bean leaf expansion: Role of osmotic potential,wall yield stress,and hydraulic conductivity

The role of three-turgor-related cellular parameters, the osmotic potential ( _s), the wall yield stress (Y) and the apparent hydraulic conductivity (L'p), in the initiation of ligh-induced expansion of bean (Phaseolus vulgaris L.) leaves has been determined. Although light causes an increase in the total solute content of leaf cells, the water uptake accompanying growth results in a slight increase in _s. Y is about 4 bar; and is unaffected by light. L'p, as calculated from growth rates and isopiestic measurements of leaf water potential, is only slightly greater in rapidly-growing leaves. The turgor pressure of growing cells is lower than that of the controls by about 35%. We conclude that light does not induce cell enlargement in the leaf by altering any of the above parameters, but does so primarily by increasing wall extensibility.Abbreviations and symbols RL red light - WL white light - L'p apparent hydraulic conductivity - OC osmotic concentration - Y wall yield stress - _s osmotic potential     

Osmotic relations during elongation growth in hypocotyls of Helianthus annum L.

The relationship between growth, change in cell osmotic pressure and accumulation of osmotic solutes was investigated in hypocotyls of sunflower (Helianthus annum L.) seedlings. During growth in darkness the osmotic pressure decreased by 50% between days 2 and 6 after sowing. After irradiation of dark-grown seedlings with continuous white light (WL) an inhibition of hypocotyl growth was measured, but the osmotic pressure of the growing cells was not lower than in the dark-grown control. Growth in darkness and after WL irradiation was accompanied by an increase in the amount of osmotic substances (soluble sugars) which was proportional to the increase in length of the organ. During growth in continuous WL the cell osmotic pressure decreased by 45 % between days 2 and 6 after sowing. The transfer of WL-grown seedlings to darkness (“re-etiolation”) resulted in a rapid acceleration of hypocotyl growth, but the cell osmotic pressure was the same as that of the WL grown control. Growth in continuous WL was accompanied by a corresponding accumulation of osmotic substances (soluble sugars). The transition from WL to darkness resulted in an enhanced accumulation of osmotica and an increase in cell-wall extensibility. The results indicate that the relative maintenance of cell osmotic pressure during rapid hypocotyl growth in darkness is caused by an enhanced accumulation of soluble sugars into the growing cells of the organ.     

Salinity Stress Inhibits Bean Leaf Expansion by Reducing Turgor, Not Wall Extensibility

Treatment of bean (Phaseolus vulgaris L.) seedlings with low levels of salinity (50 or 100 millimolar NaCl) decreased the rate of light-induced leaf cell expansion in the primary leaves over a 3 day period. This decrease could be due to a reduction in one or both of the primary cellular growth parameters: wall extensibility and cell turgor. Wall extensibility was assessed by the Instron technique. Salinity did not decrease extensibility and caused small increases relative to the controls after 72 hours. On the other hand, 50 millimolar NaCl caused a significant reduction in leaf bulk turgor at 24 hours; adaptive decreases in leaf osmotic potential (osmotic adjustment) were more than compensated by parallel decreases in the xylem tension potential and the leaf apoplastic solute potential, resulting in a decreased leaf water potential. It is concluded that in bean seedlings, mild salinity initially affects leaf growth rate by a decrease in turgor rather than by a reduction in wall extensibility. Moreover, longterm salinization (10 days) resulted in an apparent mechanical adjustment, i.e. an increase in wall extensibility, which may help counteract reductions in turgor and maintain leaf growth rates.     

Light-stimulated cell expansion in bean (Phaseolus vulgaris L.) leaves

Cell expansion in dicotyledonous leaves is strongly stimulated by bright white light (WL), at least in part as a result of light-induced acidification of the cell walls. It has been proposed that photosynthetic reactions are required for light-stimulated transport processes across plasma membranes of leaf cells, including proton excretion. The involvement of photosynthesis in growth and wall acidification of primary leaves of bean has been tested by inhibiting photosynthesis in two ways: by reducing chlorophyll content of intact plants with tentoxin (TX) and by treating leaf discs with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Exposure to bright WL stimulated growth of intact leaves of TX-treated plants. Discs excised from green as well as from TX-or DCMU-treated leaves also responded by growing faster in WL, as long as exogenous sucrose was supplied to the photosynthetically inhibited tissues. The WL caused acidification of the epidermal surface of intact TX-leaves, but acidification of the incubation medium by mesophyll cells only occurred when photosynthesis was not inhibited. It is concluded that light-stimulated cell enlargement of bean leaves, and the necessary acidification of epidermal cell walls, are mediated by a pigment other than chlorophyll. Light-induced proton excretion by mesophyll cells, on the other hand, may require both a photosynthetic product (or exogenous sugars) and a non-photosynthetic light effect.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1 -dimethylurea - OC osmotic concentration - RL red light - TX tentoxin - WL white light We thank Dr. G.E. Templeton, University of Arkansas, Fayetteville, USA, for initially supplying us with TX, and also Dr. Stephen O. Duke, Southern Weend Science Laboratory, Stoneville, Miss., USA, for suggesting this compound for our experiments. We are grateful to Professor E. Ballio for his generous gift of fusicoccin.     

Cellular basis of growth suppression by submergence in azuki bean epicotyls

Background and Aims

Complete submergence severely reduces growth rate and productivity of terrestrial plants, but much remains to be elucidated regarding the mechanisms involved. The aim of this study was to clarify the cellular basis of growth suppression by submergence in stems.

Methods

The effects of submergence on the viscoelastic extensibility of the cell wall and the cellular osmotic concentration were studied in azuki bean epicotyls. Modifications by submergence to chemical properties of the cell wall; levels of osmotic solutes and their translocation from the seed to epicotyls; and apoplastic pH and levels of ATP and ethanol were also examined. These cellular events underwater were compared in etiolated and in light-grown seedlings.

Key Results

Under submergence, the osmotic concentration of the cell sap was substantially decreased via decreased concentrations of organic compounds including sugars and amino acids. In contrast, the viscoelastic extensibility of the cell wall was kept high. Submergence also decreased ATP and increased the pH of the apoplastic solution. Alcoholic fermentation was stimulated underwater, but the resulting accumulated ethanol was not directly involved in growth suppression. Light partially relieved the inhibitory effects of submergence on growth, osmoregulation and sugar translocation.

Conclusions

A decrease in the levels of osmotic solutes is a main cause of underwater growth suppression in azuki bean epicotyls. This may be brought about by suppression of solute uptake via breakdown of the H⁺ gradient across the plasma membrane due to a decrease in ATP. The involvement of cell wall properties in underwater growth suppression remains to be fully elucidated.Key words: Apoplastic pH, cell wall extensibility, growth suppression, osmoregulation, osmotic concentration, submergence, sugar translocation, Vigna angularis     

Promotion of leaf sheath growth by gibberellic acid in a dwarf mutant of rice

The mechanism of gibberellin (GA)-induced leaf sheath growth was examined using a dwarf mutant of rice (Oryza sativa L. cv. Tan-ginbozu) treated in advance with an inhibitor of GA biosynthesis. Gibberellic acid (GA₃) enhanced the growth of the second leaf sheath, but auxins did not. Measurement of the mitotic index and cell size revealed that cell elongation rather than cell division is promoted by GA₃. Gibberellic acid increased the extensibility of cell walls in the elongation zone of the leaf sheath. It also increased the total amount of osmotic solutes including sugars in the leaf sheath, but did not increase the osmotic concentration of the cell sap, due to an accompanying increase in cell volume by water absorption. In the later stage of GA₃-induced growth, starch granules completely disappeared from leaf sheath cells, whereas dense granules remained in control plants. These findings indicate that GA enhances cell elongation by increasing wall extensibility, osmotic concentration being kept unchanged by starch degradation. Received: 28 August 1997 / Accepted: 16 October 1997     

Comparative effects of gibberellic acid and N6-benzyladenine on dry matter partitioning and osmotic and water potentials in seedling organs of dwarf watermelon

Apical applications of 0.2 μg N⁶-benzyladenine (BA), a synthetic cytokinin, or 5 μg of gibberellic acid (GA₃) significantly enhanced hypocotyl elongation in intact dwarf watermelon seedlings over a 48-h period. Accompanying the increase in hypocotyl length was marked expansion of cotyledons in BA-treated seedlings and inhibition of root growth by both compounds. A study on dry matter partitioning indicated that both growth regulators caused a preferential accumulation of dry matter in hypocotyls at the expense of the roots; however, GA₃ elicited a more rapid and greater change than did BA. In comparison to untreated seedlings, BA decreased total translocation of metabolites out of the cotyledons. Water potentials of cotyledons and hypocotyls were determined by allowing organs to equilibrate for 2 h in serial concentrations of polyethylene glycol 4000. Osmotic potentials were determined by thermocouple psychrometry. During periods of rapid growth in cotyledons and hypocotyls of BA-treated seedlings and in hypocotyls of GA-treated seedlings, the osmotic potential increased and the turgor pressure decreased in relation to untreated seedlings, indicating that cell wall extensibility was being increased. Osmotic potentials were lower in hypocotyls of GA-treated than in those of BA-treated seedlings, even though growth rates were higher in GA-treated seedlings, indicating that the latter treatment was generating more osmotically active solutes in hypocotyls.     

Changes in cellular osmotic potential and mechanical properties of cell walls during light-induced inhibition of cell elongation in maize coleoptiles

The growth rate of maize ( Zea mays L. cv. Cross Bantam T51) coleoptiles in the dark was highest at the basal zone and decreased towards the tip. Growth was strongly inhibited by white fluorescent light (5 W m⁻²), especially in the basal zone of coleoptiles. Light irradiation caused an increase in the values of stress-relaxation parameters, the minimum stress-relaxation time and the relaxation rate and a decrease in the extensibility (strain/stress) of the cell walls at all zones. In addition, during growth, the accumulation of osmotic solutes was strongly inhibited by white light irradiation, resulting in an increased osmotic potential. The influences of white light on the mechanical properties of the cell wall and the osmotic potential of the tissue sap were most prominent in the basal zone. Significant correlations were observed between the increment of coleoptile length and the mechanical properties of the cell walls or the osmotic potential of the tissue sap and osmotic solutes content. Furthermore, light inhibited the outward bending of split coleoptile segments. These facts suggest that white light inhibits elongation of maize coleoptiles by modifying both the mechanical properties of the cell walls and cellular osmotic potential, which control the rate of water uptake.     

Growth-induced water potentials and the growth of maize leaves

Profiles of water potential (Psi(w)) were measured from the soil through the plant to the tip of growing leaves of fully established maize (Zea mays L.). The profiles revealed gradients in transpiration-induced Psi(w) extending upward along the transpiration path, and growth-induced Psi(w) extending radially between the veins in the elongating region of the leaf base. Water moving upward required a small gradient while that moving radially required a much larger gradient primarily because the protoxylem vessels were encased in many small, undifferentiated cells that were likely to act as a barrier to radial flow. Upon maturation, these small cells enlarged and some began to conduct water, probably decreasing the barrier. In the mature leaf, the growth-induced Psi(w) were absent but the transpiration-induced Psi(w) remained. When leaves were growing, the growth-induced Psi(w) moved water into the elongating cells during the day and night, and it shifted with changes in transpiration-induced Psi(w). The shift involved solutes accumulating in the growing region. When water was withheld, the growth-induced Psi(w) disappeared and leaf elongation ceased even though turgor pressure was at its highest. Turgor was maintained by osmotic adjustment that doubled the osmotic potential of the elongating cells. If elongation resumed at night or with rewatering, the growth-induced Psi(w) reappeared. If pressure was applied to the soil/root system to cause guttation and re-establish the growth-induced Psi(w), elongation resumed immediately. These findings support the hypothesis that the primary control of growth is the disappearance and reappearance of the growth-induced Psi(w) because the potential changed in the xylem and nearby cells, blocking or permitting radial water movement and thus blocking or permitting growth.     

Proton excretion and cell expansion in bean leaves

Light-induced expansion of Phaseolus vulgaris L. leaf cells is accompanied by increased cell-wall plasticity. The possibility that leaf-cell walls are loosened by excreted protons has been investigated. First, light causes acidification, detected at the leaf surface, within 5–15 min. Growth starts 10–20 min after exposure to light. Second, exogenous acid induces loosening of isolated leaf cell walls. Third, infiltration of the tissue with a neutral buffer inhibits light-induced growth. Fourth, fusicoccin stimulates growth of as well as H⁺ excretion by bean leaf cells, without light. These findings show that the acid-growth theory is applicable to light-induced growth of leaf cells, and indicate that light-induced proton excretion initiates cell enlargement in leaves.Abbreviations FC fusicoccin - RL red light - WEx wall extensibility - WL white light     

Factors controlling plasticity of leaf morphology in Robinia pseudoacacia: III. biophysical constraints on leaf expansion under long-term water stress

In this article, we measured the relative growth rate (RGR) of leaves of Robinia pseudoacacia seedlings under well-watered and water-stressed conditions (mid-day Ψ(w) = leaf water potential estimated with a pressure bomb of -0.48 and -0.98 MPa, respectively). Pressure-volume (PV) curves were done on growing leaves at 25, 50 and 95% of the mature size (growth stage) in order to compute solute potential (Ψ) and turgor pressure (Ψ(P) ) as a function of Ψ(w) . The PV curves and diurnal measurements of Ψ(w) and RGR allowed us to evaluate the parameters (cell wall extensibility m and growth turgor threshold Y) of the Lockhart equation, RGR = m(Ψ(P)-Y), at each growth stage. Our data showed that m and Y did change with leaf age, but the changes were slow enough to evaluate m and Y on any given day. We believe this is the first study to provide evidence that the Lockhart equation adequately quantifies leaf growth of trees over a range of time domains. The value of m linearly declined and Y linearly increased with growth stage. Also, mild drought stress caused a decline in m and increase in Y relative to controls. Although water stress caused an osmotic adjustment which, in turn, increased Ψ(P) in stressed plants relative to controls, the RGR and final leaf sizes were reduced in water-stressed plants because of the impact of water stress on decreased m and increased Y.     

Comparative effects of gibberellic acid and N6-benzyladenine on dry matter partitioning and osmotic and water potentials in seedling organs of dwarf watermelon

Apical applications of 0.2 g N⁶-benzyladenine (BA), a synthetic cytokinin, or 5 g of gibberellic acid (GA₃) significantly enhanced hypocotyl elongation in intact dwarf watermelon seedlings over a 48-h period. Accompanying the increase in hypocotyl length was marked expansion of cotyledons in BA-treated seedlings and inhibition of root growth by both compounds. A study on dry matter partitioning indicated that both growth regulators caused a preferential accumulation of dry matter in hypocotyls at the expense of the roots; however, GA₃ elicited a more rapid and greater change than did BA. In comparison to untreated seedlings, BA decreased total translocation of metabolites out of the cotyledons. Water potentials of cotyledons and hypocotyls were determined by allowing organs to equilibrate for 2 h in serial concentrations of polyethylene glycol 4000. Osmotic potentials were determined by thermocouple psychrometry. During periods of rapid growth in cotyledons and hypocotyls of BA-treated seedlings and in hypocotyls of GA-treated seedlings, the osmotic potential increased and the turgor pressure decreased in relation to untreated seedlings, indicating that cell wall extensibility was being increased. Osmotic potentials were lower in hypocotyls of GA-treated than in those of BA-treated seedlings, even though growth rates were higher in GA-treated seedlings, indicating that the latter treatment was generating more osmotically active solutes in hypocotyls.Scientific Contribution No. 1219 from the New Hampshire Agricultural Experiment Station.     

Primary events regulating stem growth at low water potentials

Cell enlargement is inhibited by inadequate water. As a first step toward understanding the mechanism, all the physical parameters affecting enlargement were monitored to identify those that changed first, particularly in coincidence with the inhibition. The osmotic potential, turgor, yield threshold turgor, growth-induced water potential, wall extensibility, and conductance to water were measured in the elongating region, and the water potential was measured in the xylem of stems of dark-grown soybean (Glycine max [L.] Merr.) seedlings. A stepdown in water potential was achieved around the roots by transplanting the seedlings to vermiculite of low water content, and each of the parameters was measured simultaneously in the same plants while intact or within a few minutes of being intact using a newly developed guillotine psychrometer. The gradient of decreasing water potential from the xylem to the enlarging cells (growth-induced water potential) was the first of the parameters to decrease to a growth-limiting level. The kinetics were the same as for the inhibition of growth. The decreased gradient was caused mostly by a decreased water potential of the xylem. This was followed after 5 to 10 hours by a similar decrease in cell wall extensibility and tissue conductance for water. Later, the growth-induced water potential recovered as a result of osmotic adjustment and a rise in the water potential of the xylem. Still later, moderate growth resumed at a rate apparently determined by the low wall extensibility and tissue conductance for water. The turgor did not change significantly during the experiment. These results indicate that the primary event during the growth inhibition was the change in the growth-induced water potential. Because the growth limitation subsequently shifted to the low wall extensibility and tissue conductance for water, the initial change in potential may have set in motion subsequent metabolic changes that altered the characteristics of the wall and cell membranes.     

Chromosaponin I increases mechanical extensibility of lettuce root cell walls

Chromosaponin I (CSI), at 3 m M , stimulates the growth of lettuce roots ( Lactuca sativa L. cv. Grand Rapids) with increasing fresh weight and decreasing root diameter compared with control. To analyze the mechanism of action of CSI, mechanical properties of lettuce root cell walls were examined with a tensiometer and the osmotic potential of the cell sap was measured with a vapor pressure osmometer. The mechanical extensibility of the cell wall was increased by CSI treatment, while the osmotic potential remained constant. Under osmotic stress, through addition of 0.225 M mannitol, the mechanical extensibility of the cell wall was increased before stimulation of growth was observed. These results suggest that cell wall-loosening is involved in the growth stimulation induced by CSI.     

盐分和水分胁迫对芦荟幼苗渗透调节和渗调物质积累的影响

用不同浓度NaCl和等渗聚乙二醇(PEG 6000)处理芦荟(Aloe vera L.)幼苗,10 d后测定叶片相对生长速率和厚度、叶片中主要有机溶质、无机离子含量及渗透调节能力.结果表明,-0.44、-0.88 MPa NaCl和PEG处理使芦荟叶片的相对生长速率和叶片厚度明显下降,且盐胁迫对幼苗生长的抑制和叶片含水量降低的效应明显高于等渗的水分胁迫,其叶片渗透调节能力随处理渗透势的降低而增加, -0.88 MPa PEG胁迫的芦荟幼苗的渗透调节能力高于等渗盐分胁迫.在主要渗透调节物质可溶性糖、有机酸、K 、Ca2 和Cl-中,-0.88 MPa PEG处理下含量比相同渗透势的NaCl处理下显著增加的是有机溶质,因此推断有机溶质含量高是PEG胁迫下渗透调节能力较强的主要因素.     

The role of organic and inorganic solutes in the osmotic adjustment of drought-stressed Jatropha curcas plants

This study aimed to assess the accumulation of organic and inorganic solutes and their relative contribution to osmotic adjustment in roots and leaves of Jatropha curcas subjected to different water deficit intensity. Plants were grown in vermiculite 50% (control), 40%, 30%, 20% and 10% expressed in gravimetric water content. The water potential, osmotic potential and turgor potential of leaves decreased progressively in parallel to CO₂ photosynthetic assimilation, transpiration and stomatal conductance, as the water deficit increased. However, the relative water content, succulence and water content in the leaves did not show differences between the control and stressed plants, indicating osmotic adjustment associated with an efficient mechanisms to prevent water loss by transpiration through stomatal closure. The K⁺ ions had greater quantitative participation in the osmotic adjustment in both leaves and roots followed by Na⁺ and Cl⁻, while the NO₃⁻ ion only showed minor involvement. Of the organic solutes studied, the total soluble sugars showed the highest relative contribution to the osmotic adjustment in both organs and its concentration positively increased with more severe water deficit. The free amino acids and glycinebetaine also effectively contributed to the osmotic potential reduction of both the root and leaves. The role of proline was quantitatively insignificant in terms of osmotic adjustment, in both the control and stressed roots and leaves. Our data reveal that roots and leaves of J. curcas young plants display osmotic adjustment in response to drought stress linked with mechanisms to prevent water loss by transpiration by means of the participation of inorganic and organic solutes and stomatal closure. Of all the solutes studied, soluble sugars uniquely display a prominent drought-induced synthesis and/or accumulation in both roots and leaves.     

Effects of temperature on the cell wall and osmotic properties in dark-grown rice and azuki bean seedlings

The mechanism inducing the difference in growth rate under various temperature (10–50 °C) conditions was analyzed using rice and azuki bean seedlings. The growth rate of rice coleoptiles and azuki bean epicotyls increased as temperature increased up to 40 and 30 °C, respectively, and the elongation was retarded at a higher temperature. The cell wall extensibility of rice coleoptiles and azuki bean epicotyls also showed the highest value at 40 and 30 °C, respectively, and became smaller as the temperature rose or dropped from the optimum. The opposite tendency was observed in the minimum stress-relaxation time of the cell wall. On the other hand, the cellular osmotic concentration of rice coleoptiles and azuki bean epicotyls was lower at the temperature optimum for growth at 40 and 30 °C, respectively. When rice and azuki bean seedlings grown at 10, 20, 40, or 50 °C were transferred to the initial temperature (30 °C), the growth rate of coleoptiles and epicotyls was mostly elevated, concomitant with an increase in the cell wall extensibility. The growth rate was correlated with the cell wall mechanical parameters in both materials. These results suggest that the environmental temperature modulates the growth rate of plant shoots by affecting mainly the mechanical properties of the cell wall. Electronic Publication