THE GROWTH AND RESPIRATION OF THE AVENA COLEOPTILE

1. Transport of the plant growth hormone into the Avena coleoptile as well as the action of the hormone on cell elongation in the coleoptile are shown to depend upon aerobic metabolism. 2. Crystalline auxine, in contrast with impure preparations, affects neither the magnitude nor the respiratory quotient of coleoptile respiration. 3. Increasing age of the coleoptile cell decreases its rate of elongation much more than its rate of respiration. HCN or phenylurethane on the other hand decrease the two processes to the same extent, in spite of the fact that only a small portion of the energy liberated by respiration can be used in the mechanical process of growth. 4. From 2 and 3 it is concluded that processes of a respiratory nature but of relatively small magnitude form one or more integral steps in the chain of reactions by which the plant growth hormone brings about cell elongation.     

Oxygen Dependence of Elongation Growth and Oxygen Uptake in Maize Coleoptiles

Auxin-mediated elongation growth of maize coleoptile segments is inhibited by reducing the O₂ concentration in the incubation medium to GT 100 μmol . 1^?1. The half-maximal elongation rate is reached at 40 μmol . 1^?1 O₂, i.e. about two orders of magnitude higher than with mitochondrial respiration. O₂ uptake of the segments measured under similar conditions with an O₂ electrode shows a very similar dependence on O₂ concentration. Auxin increases O₂ uptake by 5–10% when it induces growth. About 40% of the O₂ uptake is insensitive to inhibition by KCN. Auxin has no effect on O₂ uptake in the presence of KCN. The possibility that auxin-mediated elongation growth depends on a KCN-sensitive oxidative process, other than cytochrome c oxidase-catalyzed respiration, is discussed.     

THE EFFECT OF AUXINS UPON PROTOPLASMIC STREAMING

1. Evidence has accumulated that the action of auxins in promoting growth is exerted not upon the cell wall but upon the cell contents; i.e., the protoplasm. Following indications previously obtained, therefore, the effect of auxins on the rate of protoplasm streaming in the Avena coleoptile was studied. 2. Indole-3-acetic acid, the most active auxin available in pure form, was found to increase the rate of streaming in the epidermal cells of the Avena coleoptile at concentrations between 0.5 and 0.002 mg. per liter, the maximum increase being brought about at 0.01 mg. per liter. This concentration is approximately that which, applied in agar to one side of the decapitated coleoptile, would give a curvature of 1°; i.e., it is well within the range of concentrations active in growth promotion. It is, however, much less than that which produces maximum elongation in immersed sections of Avena coleoptiles. 3. This accelerating effect is readily determined quantitatively by comparison with the streaming in control coleoptiles in pure water, which, if thoroughly aerated, maintain a constant rate for over an hour. The accelerating effect takes place immediately and is over within about 30 minutes. 4. Concentrations of indole-3-acetic acid greater than 0.5 mg.per liter inhibit the streaming, the effect being also over in about 30 minutes, and its extent increasing with increasing auxin concentration. This parallels the effect of high auxin concentrations in inhibiting elongation, although the inhibition of streaming is obtained at much lower concentrations than inhibit elongation. 5. The effects of indole-3-acetic acid on streaming are not specific for that substance, but appear to be common to auxins in general. Thus coumaryl-3-acetic acid and allocinnamic acid, both of which bring about cell enlargement, root formation, and bud inhibition, i.e. are typical auxins, also cause an immediate acceleration of the rate of streaming, and as with indole-acetic add the effect is over in about 30 minutes. The concentrations of these two substances which produce the maximum effect are about ten times that of indole-acetic acid, which approximately corresponds with their relative auxin activities. The curves relating concentrations of these substances to their effects on streaming are very similar to that for indole-acetic acid. 6. On the other hand, certain substances which are known to affect streaming in other materials do not produce any effect comparable to that of auxin. Ethylene chlorhydrin, histidine, and urea in all concentrations were without effect on streaming in the Avena coleoptile within the first 30 minutes of treatment. 7. The effects produced by the auxins were not due to pH. 8. The action on streaming here studied is evidently quite different from the re-starting of streaming after its cessation, studied by Fitting in Vallisneria. Correspondingly histidine, which in Fitting''s experiments showed activity down to 10^–7 M, is inactive here. 9. Per contra, the effect of auxin here studied is on normal streaming. It takes place immediately and at concentrations in the same range as those which produce growth. The curve of effect against concentration parallels that for growth although the actual concentration values differ. It is therefore reasonable to suppose that the effect of auxin on streaming is closely connected with one of the first stages of its effect on the growth process.     

Effect of calmodulin antagonists on auxin-induced elongation

Coleoptile segments of oat (Avena sativa var Cayuse) and corn (Zea mays L. var Patriot) were incubated in different concentrations of calmodulin antagonists in the presence and absence of α-naphthaleneacetic acid. The calmodulin antgonists (chlorpromazine (CP), trifluoperazine, and fluphenazine) inhibited the auxin-induced elongation at 5 to 50 micromolar concentrations. Chlorpromazine sulfoxide, an analog of chlorpromazine, did not have significant effect on the elongation of oat and corn coleoptiles. A specific inhibitor of calmodulin N-(6-aminohexyl)5-chloro-1-naphthalenesulfonamide hydrochloride (W-7, a naphthalenesulfonamide derivative) inhibited coleoptile elongation, while its inactive analog N-(6-aminohexyl)-1-naphthalenesulfonamide hydrochloride (W-5) was ineffective at similar concentrations. During a 4-hour incubation period, coleoptile segments accumulated significant quantities of ³H-CP. About 85 to 90% of auxin-induced growth was recovered after 4 hours of preincubation with CP or 12 hours with W-7 and transferring coleoptiles to buffer containing NAA. Leakage of amino acids from coleoptiles increased with increasing concentration of CP, showing a rapid and significant increase above 20 micromolar CP. The amount of amino acids released in the presence of W-7 and W-5 was significantly lower than the amount released in the presence of CP. Both W-5 and W-7 increased amino acid release but only W-7 inhibited auxin-induced growth. Calmodulin activity measured by phosphodiesterase activation did not differ significantly between auxin-treated and control coleoptile segments. These results suggest the possible involvement of calmodulin in auxin-induced coleoptile elongation.     

COMPARATIVE STUDIES ON RESPIRATION : IX. THE EFFECTS OF ANTAGONISTIC SALTS ON THE RESPIRATION OF ASPERGILLUS NIGER.

1. In the presence of 0.05 per cent dextrose the respiration of Aspergillus niger is increased by NaCl in concentrations of 0.25 to 0.5M, and by 0.5M CaCl₂. 2. Stronger concentrations, as 2M NaCl and 1.25M CaCl₂, decrease the respiration. The decrease in the higher concentrations is probably an osmotic effect of these salts. 3. A mixture of 19 cc. of NaCl and 1 cc. of CaCl₂ (both 0.5M) showed antagonism, in that the respiration was normal, although each salt alone caused an increase. 4. Spores of Aspergillus niger did not germinate on 0.5M NaCl (plus 0.05 per cent dextrose) while they did on 0.5M CaCl₂ (plus 0.05 per cent dextrose) and on various mixtures of the two. This shows that a substance may have different effects on respiration from those which it has upon growth.     

CYANIDE-SENSITIVE BACTERIAL RESPIRATORY SYSTEMS DIFFERENT FROM THE USUAL CYTOCHROME-CYTOCHROME OXIDASE SYSTEM

Aerobic respiration of Streptococcus pyogenes and pneumococcus Type 1 are strongly inhibited by KCN, NaN₃, and Na₂S. The anaerobic glycolysis of glucose by pneumococcus is also inhibited by KCN and NaN₃. Streptococcus pyogenes, E. coli, pneumococcus Type 1, B. subtilis, B. proteus, and Staphylococcus aureus did not catalyze the oxygen uptake by p-phenylenediamine in the presence of added cytochrome c or in its absence. Yeast cells, B. subtilis, and B. pyocyaneus oxidized p-phenylenediamine to a dark purple meriquinoid substance in contrast to the other bacteria mentioned above. Streptococcus pyogenes in contrast to pneumococcus Type 1 catalyzed the oxygen uptake by cysteine. Neither of these bacteria catalyzed the oxygen uptake by tyrosine, adrenaline, pyrocatechin, xanthine, and hypoxanthine. Streptococcus pyogenes, pneumococcus Type 1, and E. coli, boiled and not boiled, gave positive peroxidative tests with benzidine showing the presence of hematin compounds. The results discussed in the light of the interpretations offered by Keilin and Harpley show that Streptococcus pyogenes and pneumococcus Type 1 contain cyanide-sensitive respiratory systems which are different from the cytochrome c-cytochrome oxidase system.     

Effects of KCN and Salicylhydroxamic Acid on Respiration of Soybean Leaves at Different Ages

Measurements of respiration were made on leaf discs from glasshouse-grown soybean (Glycine max [L.] Merr. cv `Corsoy') plants in the presence and absence of cyanide (KCN) and salicylhydroxamic acid (SHAM). O₂ uptake by mature leaves measured at 25°C was stimulated by 1 millimolar KCN (63%) and also by 5 millimolar azide (79%). SHAM, an inhibitor of the alternative oxidase and a selection of other enzymes, also stimulated O₂ uptake by itself at concentration of 10 millimolar. However, in combination, KCN and SHAM were inhibitory. The rate of O₂ uptake declined consistently with leaf age. The stimulation of O₂ uptake by KCN and by SHAM occurred only after a certain stage of leaf development had been reached and was more pronounced in fully expanded leaves. In young leaves, O₂ uptake was inhibited by both KCN and SHAM individually. The uncoupler, p-trifluoromethoxy carbonylcyanide phenylhydrazone, stimulated leaf respiration at all ages studied, the stimulation being more pronounced in fully expanded leaves. The uncoupled rate was inhibited by KCN and SHAM individually. The capacity of the cytochrome path declined with leaf age, paralleling the decline in total respiration. However, the capacity of the alternative path peaked at about full leaf expansion, exceeding the cytochrome capacity and remaining relatively constant. These results are consistent with the presence in soybean leaves of an alternative path capacity that seems to increase with age, and they suggest that the stimulation of O₂ uptake by KCN and NaN₃ in mature leaves was mainly by the SHAM-sensitive alternative path. The stimulation of O₂ uptake by SHAM was not expected, and the reason for it is not clear.     

Alternative respiration and antibiotic production of Acremonium chrysogenum

The influence of potassium cyanide (KCN), dissolved O₂ concentration and medium composition on alternative respiration (AR) of Acremonium chrysogenum were investigated. The respiration of the fungus was only partially inhibited by KCN, but completely inhibited by the combination of KCN with salicylhydroxamic acid. It has been proved by in-situ measurements of the NADH-dependent fluorescence that the AR is active at low dissolved O₂ concentrations. The influence of the medium composition and the age of the fungus on the specific oxygen uptake rate is considered. Correpondence to: K. Schügerl     

THE EFFECT OF AUXINS ON PROTOPLASMIC STREAMING. III

1. A new method is described which gives a continuous record of the absolute rate of protoplasmic streaming in epidermal cells of the Avena coleoptile. 2. With this method a study was made of the influence of malate and iodoacetate on streaming velocity, in order to make correlations with the previously established effects of these substances on growth and respiration. 3. In the presence of optimum concentrations of indole-3-acetic acid in freshly cut sections, malate had no effect on streaming. In the presence of very low concentrations of the auxin, however, malate increased the range of response, so that the threshold of auxin sensitivity was lowered some ten times by the malate. Malate alone had no effect on streaming. 4. In coleoptile sections, soaked overnight in sugar solution or in water, the acceleration of streaming normally caused by auxin almost disappears, but the presence of malate causes large accelerations of streaming by the auxin. 5. Similarly, in sections from old coleoptiles, which no longer show acceleration of streaming by auxin, the acceleration is restored when malate is added together with the auxin. 6. Malate does not enter the cell as rapidly as does auxin, but easily detectable amounts penetrate within 30 minutes. 7. Iodoacetate in the concentration which inhibits growth (5 x 10^–5 M) completely inhibits the acceleration of streaming by auxin. In still lower concentrations iodoacetate slightly accelerates streaming. Higher concentrations, up to 2 x 10^–4 M, did not reduce the rate of streaming below that of controls without auxin. The effect of iodoacetate is therefore to inhibit the acceleration caused by auxin and not to affect the basal streaming rate. 8. It is concluded that, just as for growth and respiration, malate is necessary for the response to auxin shown by acceleration of streaming. This further strengthens the triple parallel between the effects of auxin on streaming, growth, and respiration, all of which are apparently mediated by the 4-carbon acid system.     

Inhibition of Cyanide-Insensitive Respiration in <Emphasis Type="Italic">Klebsiella oxytoca</Emphasis> SYSU-011 by 8-Hydroxyquinolone

The inhibition of the cyanide (KCN)-insensitive respiration of Klebsiella oxytoca SYSU-011 by 8-hydroxyquinoline (8-HQ) was determined. Results showed that the profile of the rate of oxygen uptake of normal-grown and 8-HQ–grown K. oxytoca SYSU-011 was biphasic and similar, suggesting that 8-HQ did not inhibit the respiration of normal-grown K. oxytoca SYSU-011. A different biphasic KCN inhibition profile of respiration was observed for KCN-grown cells treated with and without 8-HQ. No decrease in respiration rate of KCN-grown cells and a 40% decrease in respiration rate of KCN-grown cells treated with 8-HQ were observed when KCN concentration was 10^–1 mM. Comparing differences of the profiles of oxygen uptake in KCN-grown cells with and without 8-HQ addition indicated that 8-HQ inhibited expression of the KCN-insensitive pathway carried out by nonheme oxidase. Greater inhibition of NADH oxidase activity by 2-n-heptyl-4-hydroxyquinoline-N-oxide from the cell membrane of the KCN-grown cells treated with 8-HQ, and more H₂O₂ production from these cells with than without 8-HQ, suggest that the function of the cyanide-insensitive pathway can stabilize the respiration of the cyanide-grown cells to prevent the production of H₂O₂.     

Light-dependent Elongation of Anaerobically Maintained Green Pea Stem Segments and Its Implications

Anaerobic conditions reversibly inhibit the elongation of isolated green pea (Pisum sativum L. var Alaska) stem segments. Illumination of segments maintained under anoxia causes a resumption of growth. Polarographic studies show pea stem segments are photosynthetically competent as determined by O₂ evolution. Although O₂ production is totally inhibited by dichlorophenyldimethylurea (DCMU) and dinitrophenol (DNP) inhibits O₂-dependent growth, neither DCMU nor DNP completely abolishes light-dependent growth, although both reduce the effect markedly. Phenazine methosulfate promotes the growth of anaerobically maintained, illuminated, DCMU-treated segments. The data indicate that the principal effect of light in inducing growth under anaerobic conditions is the photosynthetic provision of O₂ for respiration. There is also some evidence that, at least in the absence of O₂, a small amount of elongation is due to some other light-driven process, perhaps cyclic photophosphorylation.     

THE EFFECT OF AUXINS ON PROTOPLASMIC STREAMING. II

1. A further study has been made of the effect of indole-3-acetic acid (auxin) on protoplasmic streaming in the epidermal cells of the Avena coleoptile. 2. The transient nature of the effect of auxin, both in accelerating and retarding streaming, is due to the temporary exhaustion of carbohydrate from the tissues. In presence of 1 per cent fructose or some other sugars the acceleration or retardation of streaming by auxin is not transient, but is maintained for at least 2 hours. 3. The retardation of streaming brought about by concentrations of auxin above 0.5 mg. per liter is due to oxygen deficiency This has been confirmed in several ways. 4. It follows that the effect of auxin is to increase the respiration of the coleoptile tissue. 5. Younger coleoptiles, 3 cm. long, are sensitive to lower concentrations of auxin than those 5 cm. long, and more readily exhibit oxygen deficiency as a result of the action of auxin. However, after decapitation their response to auxin more closely resembles that of 5 cm. coleoptiles. 6. The retardation of streaming in such coleoptiles, resulting from oxygen deficiency, is delayed by very dilute solutions of histidine. On this basis an explanation is suggested for the results of Fitting on streaming in Vallisneria leaves. 7. The mean rate of streaming in control untreated coleoptiles in pure water varies with the time of year, but not with the time of day. 8. The results support the view that auxin accelerates an oxygen-consuming process which controls the rate of protoplasmic streaming, and that the latter controls growth. The substrate for this process is probably sugar. 9. It is suggested that auxin also accelerates another oxygen-consuming process, which may withdraw oxygen from the process which controls streaming rate and hence cause retardation of the latter.     

Effect of Carbon Dioxide on Growth of Meat Spoilage Bacteria

The ability of CO₂ to inhibit respiration and growth of representative strains of seven species of meat spoilage bacteria was examined. Enterobacter and Microbacterium thermosphactum were unaffected by CO₂. Both respiration and growth of the other species were inhibited. With four of the species (fluorescent and nonfluorescent Pseudomonas, Alteromonas putrefaciens, and Yersinia enterocolitica), the inhibition pattern in a complex medium was similar, and inhibition was incomplete and reached a maximum level at comparatively low concentrations of CO₂. With Acinetobacter, inhibition continued to increase with increasing CO₂ concentration. The degree of inhibition with a constant concentration of CO₂ in solution increased with decreasing temperature for all CO₂-susceptible species except the nonfluorescent Pseudomonas. Anaerobic growth of CO₂-susceptible facultative anaerobes was unaffected by CO₂.     

Cyanide-resistant respiration in light- and dark-grown soybean cotyledons

Measurements of respiration were made on intact tissue and mitochondria isolated from soybean (Glycine max [L.] Merr. cv `Corsoy') cotyledons from seedlings of different ages grown in light and darkness. Effects of cyanide (KCN) and salicylhydroxamic acid (SHAM) on O₂ uptake rates were determined. O₂ uptake was faster in light-grown tissue and was inhibited by both KCN and SHAM in all except light-grown tissue older than 9 days. Both inhibitors stimulated O₂ uptake in tissues more than 9 days old. Mitochondria in which O₂ uptake was coupled to ATP synthesis were isolated from all tissues. O₂ uptake by mitochondrial preparations from light- and dark-grown cotyledons was equally sensitive to KCN. Similarly, age did not affect KCN sensitivity, but sensitivity to SHAM declined with age both in the presence and absence of KCN. Estimated capacities of the cytochrome and alternative pathways of the mitochondrial preparations indicated considerably larger cytochrome than alternative pathway capacities. The cytochrome pathway capacities paralleled the state 3 mitochondrial respiration rates, which increased from day 5 to day 7 then declined thereafter. The alternative pathway capacities were not affected by light. The uncoupler, p-trifluoromethoxycarbonylcyanide phenylhydrazone (FCCP), increased the flow of electrons through the cytochrome pathway at the expense of flow through the alternative pathway in isolated mitochondria. However, the combined capacities did not exceed the rate in the presence of FCCP. The results are interpreted to indicate that the stimulation of respiration by KCN and SHAM observed in the 12-day-old green cotyledons and previously observed in older soybean leaves is not explained by characteristics of the mitochondria.     

Respiratory inhibitors of a magnetic bacterium Magnetospirillum sp. AMB-1 capable of growing aerobically

Respiratory inhibitors of a magnetic bacterium Magnetospirillum sp. AMB-1, which is able to grow aerobically, were investigated using a microbial electrode system. The respiration of strain AMB-1 was inhibited by 2-heptyl-4-hydroxyquinoline N-oxide (HQNO), KCN and dicumarol. Strain AMB-1 cannot grow in the presence of these inhibitors under aerobic conditions. On the other hand, strain AMB-1 can grow and form magnetite (Fe₃O₄) particles with HQNO and KCN under anaerobic conditions. Growth and magnetite formation of strain AMB-1 were reduced by dicumarol, which also inhibited iron reduction under anaerobic conditions, whereas iron reduction was not inhibited by HQNO and KCN.     

Stimulation of coleoptile elongation in zea mays by p-hydroxybenzoic acid

Based on the biochemistry of coenzyme Q and plastoquinone, corn coleoptile sections were treated with p-hydroxybenzoic acid (HBA) and p-hydroxyphenylpyruvic acid (HPPA), which are biosynthetic precursors of the essential coenzyme Q₁₀ and plastoquinone-9, respectively. HBA at low concentrations stimulated growth; higher concentrations inhibited elongation. HPPA did not stimulate growth, but inhibited growth. HBA could promote growth by benefiting respiration particularly if a deficiency of HBA existed and there were a depressed biosynthesis of coenzyme Q₁₀ for electron transfer in respiration.     

A sequential response to growth substances in coleoptiles from γ-irradiated wheat

Summary -irradiated wheat seed (500 kr) produces coleoptiles that grow without cell division or DNA synthesis. Apart from an initial 24-hr delay in growth, intact coleoptiles have a pattern of cell elongation similar to normal coleoptiles. The elongation of coleoptiles excised at a size of 2 mm, when the cells are small and just prior to entering a rapid elongation phase, is promoted by kinetin and gibberellic acid (GA₃). Elongation of coleoptiles excised at 8 mm, when the cells are larger and in the rapid elongation phase, is promoted by indoleacetic acid (IAA). This sequential response to growth substances in coleoptiles is remarkably similar to that in normal coleoptiles. The GA₃ response in excised coleoptiles is not inhibited by FUDR, confirming that DNA synthesis is not required for GA₃-induced elongation in coleoptiles.     

成熟和褐变荔枝果实呼吸作用和脂氧合酶活性

荔枝果实完全成熟和果皮变鮮红时,呼吸速率降低,仅相当于果皮带绿时的39.4％。此时果皮和果肉的脂氧合酶活性亦明显降低,分别相当于后者的60.2％和49.1％。成熟荔枝果实果皮呼吸作用对KCN抑制敏感。2mM KCN抑制果皮总呼吸的91.8％,而仅抑制果肉的56.9％。荔枝果皮呼吸的电了传递主要是通过细胞色素氧化酶途径,而果肉則可能一半是通过其它氧化酶途径。2mKCN和1.5mM SHAM抑制成熟果皮总呼吸97.9％,为SHAM抑制的交替途径呼吸占总呼吸5.28％。相同浓度KCN和SHAM抑制褐变果皮总呼吸79.7％,则SHAM抑制的交替途径呼吸占27.1％。果实褐变时,果成交替途径呼吸比例增高。这一变化可能促进H_2O_2积累、乙烯产生和果皮褐变深化。     

Respiration during Postharvest Development of Soursop Fruit, Annona muricata L

Fruit of soursop, Annona muricata L., showed increased CO₂ production 2 days after harvest, preceding the respiratory increase that coincided with autocatalytic ethylene evolution and other ripening phenomena. Experiments to alter gas exchange patterns of postharvest fruit parts and tissue cylinders had little success.

The respiratory quotient of tissue discs was near unity throughout development. 2,4-Dinitrophenol uncoupled respiration more effectively than carbonylcyanide m-chlorophenylhydrazone; 0.4 millimolar KCN stimulated, 4 millimolar salicylhydroxamic acid slightly inhibited, and their combination strongly inhibited respiration, as did 10 millimolar NaN₃. Tricarboxylic acid cycle members and ascorbate were more effective substrates than sugars, but acetate and glutarate strongly inhibited.

Disc respiration showed the same early peak as whole fruit respiration; this peak is thus an inherent characteristic of postharvest development and cannot be ascribed to differences between ovaries of the aggregatetype fruit. The capacity of the respiratory apparatus did not change during this preclimacteric peak, but the contents of rate-limiting malate and citrate increased after harvest.

It is concluded that the preclimacteric rise in CO₂ evolution reflects increased mitochondrial respiration because of enhanced supply of carboxylates as a substrate, probably induced by detachment from the tree. The second rise corresponds with the respiration during ripening of other climacteric fruits.

     

Xyloglucan antibodies inhibit auxin-induced elongation and cell wall loosening of azuki bean epicotyls but not of oat coleoptiles

Polyclonal antibodies were raised in rabbits against isoprimeverose (Xyl₁Glc₁), xyloglucan heptasaccharides (Xyl₃Glc₄), and octasaccharides (Gal₁Xyl₃Glc₄). Antibodies specific for hepta- and octasaccharides suppressed auxin-induced elongation of epicotyl segments of azuki bean (Vigna angularis Ohwi and Ohashi cv Takara). These antibodies also inhibited auxin-induced cell wall loosening (decrease in the minimum stress-relaxation time and the relaxation rate of the cell walls) of azuki segments. However, none of the antibodies influenced auxin-induced elongation or cell wall loosening of coleoptile segments of oat (Avena sativa L. cv Victory). Auxin caused a decrease in molecular mass of xyloglucans in the cell walls of azuki epicotyls and oat coleoptiles. The antibodies inhibited such a change in molecular mass of xyloglucans in both species. Preimmune serum exhibited little or no inhibitory effect on auxin-induced elongation, cell wall loosening, or breakdown of xyloglucans. The results support the view that the breakdown of xyloglucans is associated with the cell wall loosening responsible for auxin-induced elongation in dicotyledons. The view does not appear to be applicable to poaceae, because the inhibition of xyloglucan breakdown by the antibodies did not influence auxin-induced elongation or cell wall loosening of oat coleoptiles.