The inhibition of kohlrabi chloroplast degeneration by kinetin

Summary Detached kohlrabi leaves of late autumn material yellowed completely after 6 days in weak light. This process was accompanied by a decrease in chlorophyll, protein, and ribonucleic acid levels. In the chloroplasts, degeneration symptoms such as reduction in chloroplast volume, the decay of grana, development of the long thylakoid system, disappearance of chloroplast ribosomes, increase in the volume of plastoglobuli, and finally a complete breakdown of plastids in the digesting vacuoles, were observed. The ultrastructural changes in degenerating kohlrabi chloroplasts resembled those described earlier for brussels sprouts (Dennis et al. 1967), which suggests that the plastid degeneration model may be specific for speciesBrassica oleracea L.Kinetin inhibited the fall in the level of chlorophyll, proteins, and RNA in relation to the control material, and even stimulated chlorophyll and protein synthesis to a level higher than that of the initial material. Treatment with kinetin also markedly delayed the loss of chloroplast ribosomes. The most evident effect of the kinetin influence on the plastid ultrastructure was the stimulation of the formation and maintenance of grana. A possible mechanism for these processes in the light of the recent studies on the chloroplast membranes is discussed.     

小麦黄化突变体叶绿体超微结构研究

利用透射电镜对小麦自然黄化突变体及其突变亲本(西农1718)叶片细胞叶绿体的数目、形态及超微结构进行比较分析。结果发现:(1)3种不同黄化程度突变体的叶绿体分布、数目、形状及大小与突变亲本无明显差异;(2)突变体叶绿素含量为野生型58%的黄绿植株与其突变亲本叶绿体超微结构无明显差异,基质类囊体与基粒类囊体高度分化,基粒数目以及基粒片层数目较多;(3)突变体金黄和绿黄植株的叶绿素含量分别为野生型的17%、24%,其叶绿体超微结构与突变亲本明显不同,突变体的叶绿体发育存在明显缺陷,其中突变体金黄植株的叶绿体内无基粒、基质片层清晰可见,有淀粉粒,嗜锇颗粒较多,而突变体绿黄植株的叶绿体内有基粒,但明显少于突变亲本,且基粒片层较少,基质类囊体较发达。结果表明该黄化突变体叶绿体超微结构的改变,是由于叶绿素含量降低造成,推测,该黄化突变是由于叶绿素合成受阻导致的。     

Uptake and Growth-promoting Activity of Indoleacetic Acid in Segments of Cold-hardened Wheat Coleoptiles

Seedings of winter wheat (Triticum aestivum L. cv. Kharkov MC 22) were grown at 24 C (unhardened) and 4 C (hardened). Indoleacetic acid (IAA) was added to excised coleoptile segments after lengthy incubation and their responses were determined by photometric auxanometry at both 25 C and 5 C. The segments' rates of uptake of ¹⁴CIAA were also compared at both temperatures. Cold hardening had no significant effect on the rates of elongation and uptake in a saturating concentration of IAA (2 to 10 μM) at either temperature. Elongation was more sensitive to temperature of measurement than was uptake. At suboptimal concentrations of IAA and 25 C, hardened coleoptiles took up [2-¹⁴C]-IAA twice as fast but elongated half as fast as unhardened coleoptiles. This and the lack of effect of cold hardening on apparent uptake of [1-¹⁴C]-IAA raised the possibility that a higher rate of IAA-decarboxylation was coupled with the higher rate of uptake of IAA by hardened coleoptiles. Homeostatic hormonal regulation was also evident in the same endogenous rates of elongation of segments of cold-hardened and unhardened coleoptiles.     

The antagonism of IAA-induced hydrogen ion extrusion and coleoptile growth by diclofop-methyl

Diclofop-methyl (DM) (ester) was readily absorbed by peeled and unpeeled coleoptiles of wheat, Triticum aestivum L. cv. Waldron, and oat, Avena sativa L. cv. Garry. Substantial absorption of diclofop (acid) occurred only in peeled coleoptiles of the two species. IAA-induced acidification in peeled coleoptiles of both species was inhibited by 100 μ M DM or diclofop (acid) during a 3 to 4 h period. There was no recovery of acidification after DM or diclofop inhibition in oat coleoptiles; however, acidification in wheat coleoptiles recovered from inhibition by DM but not from diclofop. The recovery from DM inhibition may be due to a reduction in the diclofop pool derived from DM by efflux and metabolism (detoxification) in peeled wheat coleoptiles. Diclofop was not detoxified in oat coleoptiles. IAA-induced elongation of unpeeled oat coleoptiles was inhibited totally by 100 μ M DM but not by 100 μ M diclofop after 3.3 h of treatment. Wheat coleoptile elongation was relatively unaffected by either DM or diclofop. Basal elongation (no IAA) of both wheat and oat coleoptiles was inhibited by DM and diclofop. The inhibition by DM appeared to be irreversible, whereas the inhibition by diclofop was overcome by the addition of 10 μ M IAA.     

Growth and pigment content of wheat as influenced by the combined effects of salinity and growth regulators

A field experiment was conducted to investigate the effects of presoaking the wheat grains (Triticum aestivum L.) in different levels of salinity (33 or 66 mM) and in growth regulators (indolyl-3-acetic acid, IAA at SO g m^-3, gibberellic acid, GA₃ at 100 g m^-3, or kinetin at 100 g m_-3) on the shoot growth and pigment content of the developing wheat flag leaf. Salinity at 33 or 66 mM led to an insignificant increase in the fresh and dry masses as well as in the shoot diameter and shoot length, but it attenuated the flag leaf area. In the majority of cases, salinity increased the chlorophyll (Chla, Chlb) and carotenoid contents as well as the number of chloroplasts per a mesophyll cell. The growth in the wheat shoot of the saline-treated plants was, in general, stimulated in response to presoaking the grains in kinetin or GA₃. On the other hand, IAA + salinity led to a negligible effect on the growth in the wheat plants particularly at the early stages of growth. The presoaking of grains in NaCl at 33 mM + IAA or 66 mM + kinetin induced a marked increase in the pigment content of the wheat flag leaf particularly at the early stages of growth. The interaction between salinity and phytohormones increased the number of chloroplasts; kinetin was the most effective.     

Structural and functional properties of the coleoptile chloroplast: Photosynthesis and photosensory transduction

Recent studies have shown that guard cell and coleoptile chloroplasts appear to be involved in blue light photoreception during blue light-dependent stomatal opening and phototropic bending. The guard cell chloroplast has been studied in detail but the coleoptile chloroplast is poorly understood. The present study was aimed at the characterization of the corn coleoptile chloroplast, and its comparison with mesophyll and guard cell chloroplasts. Coleoptile chloroplasts operated the xanthophyll cycle, and their zeaxanthin content tracked incident rates of solar radiation throughout the day. Zeaxanthin formation was very sensitive to low incident fluence rates, and saturated at around 800–1000 mol m^–2 s^–1. Zeaxanthin formation in corn mesophyll chloroplasts was insensitive to low fluence rates and saturated at around 1800 mol m^–2 s^–1. Quenching rates of chlorophyll a fluorescence transients from coleoptile chloroplasts induced by saturating fluence rates of actinic red light increased as a function of zeaxanthin content. This implies that zeaxanthin plays a photoprotective role in the coleoptile chloroplast. Addition of low fluence rates of blue light to saturating red light also increased quenching rates in a zeaxanthin-dependent fashion. This blue light response of the coleoptile chloroplast is analogous to that of the guard cell chloroplast, and implicates these organelles in the sensory transduction of blue light. On a chlorophyll basis, coleoptile chloroplasts had high rates of photosynthetic oxygen evolution and low rates of photosynthetic carbon fixation, as compared with mesophyll chloroplasts. In contrast with the uniform chloroplast distribution in the leaf, coleoptile chloroplasts were predominately found in the outer cell layers of the coleoptile cortex, and had large starch grains and a moderate amount of stacked grana and stroma lamellae. Several key properties of the coleoptile chloroplast were different from those of mesophyll chloroplasts and resembled those of guard cell chloroplasts. We propose that the common properties of guard cell and coleoptile chloroplasts define a functional pattern characteristic of chloroplasts specialized in photosensory transduction.Abbreviations Ant or A antheraxanthin - dv/dt fluorescence quenching rate - Fm maximum yield of fluorescence with all PS II reaction centers closed - Fo yield of instantaneous fluorescence with all PS II reaction centers open - Vio or V violaxanthin - Zea or Z zeaxanthin     

Effect of cytokinins on <Emphasis Type="BoldItalic">in vitro</Emphasis> development of autotrophism and acclimatization of <Emphasis Type="Italic">Annona glabra</Emphasis> L.

The role of cytokinins in the differentiation of the photosynthetic apparatus in micropropagated plants and their effect on the plant’s ability to transition from a heterotrophic to an autotrophic condition during acclimatization was investigated. Annona glabra L. shoots were cultured on woody plant medium supplemented with sucrose and different cytokinins to evaluate leaf tissue for chloroplast development, chloroplast numbers, photosynthetic pigmentation, total photosynthetic potential, and soluble sugar content. Plants were transferred to the rooting medium in the presence or absence of sucrose and then acclimatized. Kinetin and benzyladenine (BAP) stimulated chloroplast differentiation. Inclusion of zeatin in the medium induced the formation of greater numbers of chloroplasts in the leaves, while plants cultivated in the presence of only kinetin and BAP demonstrated greater chlorophyll a and carotenoid content. The use of kinetin and BAP during in vitro culture promoted accumulation of dry matter during the acclimatization phase, especially in plants rooted under autotrophic conditions (without sucrose). Kinetin and BAP promoted development of more leaf area and greater plant survival rates in plant acclimatization on both autotrophic and heterotrophic media. The inhibitory effects of thidiazuron on the differentiation of chloroplasts, accumulation of chlorophyll a, and photosynthetic potential were examined.     

Effects of the steroidal alkaloid tomatine in auxin bioassays and its interaction with indole-3-acetic acid

Summary The steroidal alkaloid tomatine did not enhance elongation of oat coleoptile and first internode sections, or of wheat coleoptile sections. Higher concentrations of the alkaloid inhibited elongation and interacted antagonistically with IAA. Although 10^-4 M tomatine alone did not influence elongation of oat coleoptile sections, it did reduce growth response to exogenous IAA. Tomatine concentrations less than 10^-4 M did not influence response to IAA. The auxin activity of tomatine, reported by Vendrig, was therefore not confirmed.     

THE EFFECT OF LIGHT INTENSITY AND TEMPERATURE ON PLANT GROWTH AND CHLOROPLAST ULTRASTRUCTURE IN SOYBEAN

Soybean plants grown in controlled environment cabinets under light intensities of 220 w/m² or 90 w/m² (400–700 nm) and day to night temperatures of 27.5–22.5 C or 20.0–12.5 C in all combinations, exhibited differences in growth rate, leaf anatomy, chloroplast ultrastructure, and leaf starch, chlorophyll, and chloroplast lipid contents. Leaves grown under the lower light intensity at both temperatures had palisade mesophyll chloroplasts containing well-formed grana. The corresponding leaves developed under the higher light intensity had very rudimentary grana. Chloroplasts from high temperature and high light had grana consisting of two or three appressed thylakoids, while grana from the low temperature were confined to occasional thylakoid overlap. Spongy mesophyll chloroplasts were less sensitive to growth conditions. Transfer experiments showed that the ultrastructure of chloroplasts from mature leaves could be modified by changing the conditions, though the effect was less marked than when the leaf was growing.     

THE GREENING OF ETIOLATED BEAN LEAVES AND THE DEVELOPMENT OF CHLOROPLAST FINE STRUCTURE IN ABSENCE OF PHOTOSYNTHESIS

CMU inhibits oxygen evolution in greening etiolated bean leaves.In the presence of this compound chlorophyll content is reducedand fine structure development of the chloroplasts is markedlyaffected. The number of grana per chloroplast is reduced butthe grana are larger and contain more thylakoids than the granain chloroplasts of the greening control leaves. Sucrose reversesthe effect of CMU on pigment content and fine structure developmentof chloroplasts. (Received September 14, 1965; )     

Cultivar Differences in Growth and Chloroplast Ultrastructure in Rice as Affected by Nitrogen

Plant growth, leaf protein and chlorophyll content, and chloroplastultrastructure as affected by nitrogen (N) were examined infour rice (Oryza sativa L.) cultivars grown in culture solutionunder controlled conditions. Increasing N concentration generallyincreased height and shoot dry weight of all cultivars. Cultivardifferences were significant at normal N level (40 ppm). Amongcultivars, IR8 was most responsive to increasing N, having thesignificantly highest shoot dry weight and protein content.Total chlorophyll and protein contents varied with cultivarand N, but chlorophyll a/b ratio remained constant. At the ultrastructurallevel, chloroplasts had generally well-developed grana and stromalamellae at 40 ppm.N. Chloroplasts at high N had from one tofour times as many grana as the N-deficient chloroplasts. Nitrogendeficiency reduced the size of the chloroplast, grana-stromalamellae and resulted in fewer poorly stacked grana. Increasingthe N level (120 ppm) above the normal level did not significantlyaffect chloroplast size of any cultivar, except for IR8 whichhad the largest chloroplast. A reduction in the number of starchgrains was observed in IR8, but more were present in ER36 underN-deficient conditions. The size of starch grains was not affectedby N and did not differ among cultivars. Plastoglobuli appearedto be larger under N-deficient conditions. Nitrogen had no effecton the number of plastoglobuli but cultivar differences existed.The highly N-responsive IR8 (based on dry weight) had the largestchloroplast which increased with N level. The increase in chloroplastsize accounted for the increase in both chlorophyll and proteincontents and, consequently, dry weight. Key words: Oryza sativa L., chloroplast, chlorophyll, protein     

Auxin-induced elongation growth and expressions of cell wall-bound exo- and endo-beta-glucanases in barley coleoptiles

When auxin stimulates rapid cell elongation growth of cereal coleoptiles, it causes a degradation of 1,3:1,4-beta-glucan in hemicellulosic polysaccharides. We examined gene expressions of endo-1,3:1,4-beta-glucanase (EI) and exo-beta-glucanase (ExoII), of which optimum pH are about 5, and molecular distribution of hemicellulosic polysaccharides in barley (Hordeum vulgare L.) coleoptile segments treated with or without IAA. IAA (10(-5) M) stimulated the gene expression of EI, while it did not affect that of ExoII. IAA induced gene expression of EI after 4 h and increased wall-bound glucanase activity after 8 h. The molecular weight distribution of hemicellulosic polysaccharides from coleoptile cell walls was shifted to lower molecular weight region by 2 h of IAA treatment. Fusicoccin (10(-6) M) mimicked IAA-induced elongation growth and the decrease in molecular weight of hemicellulosic 1,3:1,4-beta-glucan of coleoptiles in the first 4 h, but it did not promote elongation growth thereafter. These facts suggest that acidification of barley cell walls by IAA action enhances pre-existing cell wall-bound glucanase activity in the early first phase of IAA-induced growth and the late second phase involves the gene expression of EI by IAA.     

Effect of auxin on mesocotyl elongation of dark-grown maize under different seeding depths

In order to elucidate the physiological mechanism of maize mesocotyl elongation induced by auxin under different seeding depths, seeds of five maize inbred lines, including 3681-4 line tolerant to deep seeding, were treated with IAA and triiodobenzoic acid (TIBA) under seeding depths of 20 or 2 cm. Under deep seeding conditions, maize mesocotyls grew by 1.5–2.0 times faster than under shallow seeding conditions. IAA (10⁻⁶ to 10⁻⁴ M) applied to roots stimulated mesocotyl elongation only of 3681-4 line and only under deep seeding conditions. TIBA (10⁻⁵ and 10⁻⁴ M) applied to roots inhibited mesocotyl elongation in all lines, but only 3681-4 was sensitive to 10⁻⁶ M TIBA. IAA promoted only cell elongation, and TIBA inhibited both cell elongation and cell division. After IAA and TIBA treatments, endogenous IAA content changed in parallel with the mesocotyl growth rate under different seeding depths. Furthermore, ABP1 gene expression changed in parallel with the mesocotyl growth rate under deep seeding conditions. Therefore, deep seeding tolerance of 3681-4 line was achieved due to auxin-regulated rapid mesocotyl elongation.     

Critical study of coleoptile elongation controlled by IAA and ABA I. Growth kinetics and distribution

The elongation rate of wheat coleoptiles, treated with IAA andABA, was already affected during the first 8 hr of culture.The most sensitive zone of the material—for hormonal treatments—wasfirst localized and then comparatively cultured both in situand in vitro. Growth stimulation by IAA was nearly proportionalto its concentration up to 10^–4 M, while ABA always inducedan significant inhibition. (Received January 31, 1977; )     

Carbonic Anhydrase,Photosynthesis, and Seed Yield in Mustard Plants Treated with Phytohormones

The leaves of 30-d-old plants of Brassica juncea Czern & Coss cv. Varuna were sprayed with 10^–6 M aqueous solutions of indole-3-yl-acetic acid (IAA), gibberellic acid (GA₃), kinetin (KIN), and abscisic acid (ABA) or 10^–8 M of 28-homobrassinolide (HBR). All the phytohormones, except ABA, improved the vegetative growth and seed yield at harvest, compared with those sprayed with deionised water (control). HBR was most prominent in its effect, generating 32, 30, 36, 70, 25, and 29 % higher values for dry mass, chlorophyll content, carbonic anhydrase (E.C. 4.2.1.1) activity, and net photosynthetic rate in 60-d-old plants, pods per plant, and seed yield at harvest, over the control, respectively. The order of response to various hormones was HBR > GA₃ > IAA > KIN > control > ABA.     

Strong light elevates thermotolerance of photosynthetic apparatus and the content of membranes and polar lipids in wheat leaves

The influence of excess irradiance on resistance of wheat (Triticum aestivum L.) photosynthetic apparatus to heating in darkness and in the light was investigated and compared with changes in leaf cell ultra-structure and composition of cell lipids and fatty acids. The leaves of 14- to 16-day-old plants grown at low irradiance (about 20 W/m²) were exposed for 1 h to irradiance of 370 or 600 W/m² PAR. Using infrared gas analysis, we found that the preexposure of leaves to excess irradiation elevated resistance of apparent photosynthesis to 10-min heat treatment at 40–45°C. The rate of Hill reaction (reduction of 2,6-dichlorophenolindophenol by isolated chloroplasts) was higher for leaves heated at high irradiance than for leaves heated in darkness. During illumination of leaves with strong light, mesophyll cells became more abundant in mitochondria and peroxysomes, as well as in cisternae of endoplasmic reticulum and Golgi complex. The chloroplast thylakoids and grana became more extensive and numerous. At the same time, the leaf content of main classes of membrane glycerolipids increased in parallel with the increase in the phospholipid/glycolipid and lipid/chlorophyll ratios. The unsaturation index of fatty acids of membrane lipids increased because of the elevated content of linolenic acid. Thus, excessive light (not fully utilized in photosynthesis) induced in wheat leaves a series of nonspecific adaptive changes that were similar to those occurring under the action of other environmental factors, such as heat shock, cooling, salinity, and osmotic stresses.     

Comparative ultrastructural properties of pallisade tissue and spongy tissue chloroplasts from normal and mutant leaves of Pisum sativum L.*

Abstract. The ultrastructure of chloroplasts from palisade and spongy tissue was studied in order to analyse the adaptation of chloroplasts to the light gradient within the bifacial leaves of pea. Chloroplasts of two nuclear gene mutants of Pisum sativum (chlorotica-29 and chlorophyll b-less 130A), grown under normal light conditions, were compared with the wild type (WT) garden-pea cv. ‘Dippes Gelbe Viktoria’. The differentiation of the thylakoid membrane system of plastids from normal pea leaves exhibited nearly the same degree of grana formation in palisade and in spongy tissue. Using morphometrical measurements, only a slight increase in grana stacking capacity was found in chloroplasts of spongy tissue. In contrast, chloroplasts of mutant leaves differed in grana development in palisade and spongy tissue, respectively. Their thylakoid systems appeared to be disorganized and not developed as much as in chloroplasts from normal pea leaves. Grana contained fewer lamellae per granum, the number of grana per chloroplast section was reduced and the length of appressed thylakoid regions was decreased. Nevertheless, chloroplasts of the mutants were always differentiated into grana and stroma thylakoids. The structural changes observed and the reduction of the total chlorophyll content correlated with alterations in the polypeptide composition of thylakoid membrane preparations from mutant chloroplasts. In sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), polypeptide bands with a relative molecular mass of 27 and 26 kilodalton (kD) were markedly reduced in mutant chloroplasts. These two polypeptides represented the major apoproteins of the light harvesting chlorophyll a/b complex from photosystem II (LHC-II) as inferred from a comparison with the electrophoretic mobility of polypeptides isolated from the LHC-II.     

Benzyladenine effects on the development of the photosynthetic apparatus in Zea mays: Studies on photosynthetic activity, enzymes and (etio)chloroplast ultrastructure

Primary leaf segments from 8-day-old dark-grown, and from 4- and 8-day-old light-grown seedlings of Zea mays L. cv. Fronica, were treated with 10^-bM benzyladenine (BA) in the dark for 14 h. The segments were then studied after an exposure to light for 14 h. Photosynthetic activity (O₂ evolution and CO₂ fixation) and chlorophyll accumulation were stimulated by BA in dark-grown leaf segments with etioplastids in the earliest stage of development. In these segments BA stimulated the activities of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39), phosphoenolpyruvate carboxylase (EC 4.1.1.31), NADP⁺-malic enzyme (EC 1.1.1.40) and pyruvate, orthophosphate dikinase (EC 2.7.9.1). In segments taken from 4- and 8-day light-grown seedlings, BA did not enhance the photosynthetic activity nor the chlorophyll accumulation. The activity of the enzymes mentioned above, was significantly enhanced by the BA-treatment. BA mainly affected grana stacking in mesophyll cell chloroplasts in primary leaf segments taken from 3- to 5-day light-grown seedlings. Stroma thylakoid development was stimulated only in leaf segments from 3-day-old plants. At the same time BA accelerated grana loss in chloroplasts of bundle sheath cells, a typical phenomenon of development in such chloroplasts. Stroma thylakoid length in these chloroplasts increased by a BA treatment in segments from 3- and 4-day light-grown plants. A significantly higher number of chloroplasts was only observed with segments taken from 8-day light-grown seedlings and treated with BA. The etiochloroplast number in segments taken from 8-day etiolated plants was significantly higher in BA-treated segments after 26 h illumination. In etiochloroplasts from both mesophyll and bundle sheath cells, BA enhanced grana stacking after illumination for 4 h or more, whereas stroma membrane length was significantly higher only after 26 h light. It is concluded that the effects of BA depend on the developmental stage. BA accelerates the development of mesophyll and bundle sheath cell (etio)chloroplasts, but does not affect the ultrastructure of mature chloroplasts.     

Heat shock increases thermotolerance of photosynthetic electron transport and the content of chloroplast membranes and lipids in wheat leaves

Preliminary heating of 15-16-day-old wheat (Triticum aestivum L.) plants for 3 h at 37–38°C (heat shock, HS) increased the tolerance of photosynthetic electron transport (determined as the reduction of 2,6-dichlorophenol indophenol by isolated chloroplasts) toward heating of leaves at 42–48°C in high light (100 klx). At the same time, HS did not affect the activity of the xanthophyll cycle reactions in the 30–48°C temperature range. HS exposure induced an increase in the thylakoid length, the number of grana, and the average number of thylakoids per granum. The volume of the thylakoid system increased 1.4-fold. Such indices as the total content of chlorophylls (a + b), the chlorophyll a/b ratio, as well as the contents of individual carotenoids, chloroplast membrane proteins, and the soluble leaf proteins remained unchanged. The de novo photosynthetic membrane formation was accompanied by the 1.5-fold increase in major chloroplast lipids. It was concluded that, in mature wheat chloroplasts, HS induced the formation of thylakoids characterized by a changed molecular structure and by increased lipid/protein and lipid/chlorophyll ratios.     

Effect of Ecdysterone on Morphological and Physiological Processes in Plants

In order to elucidate the physiological role of phytoecdysteroids in plants, we investigated the effects of exogenous ecdysterone (ECD) and phytohormones (IAA, GA₃, and 24-epibrassinolide (EBL)) on the growth of wheat coleoptiles and Arabidopsis thaliana seedlings (wild-type ecotype Columbia (Col) and its det2 mutant), on -amylase activity in the barley aleurone layer, and on the pigment content in the kidney bean senescent leaves. The range of effective ECD concentrations depended on the type of a reaction to be regulated. The regulation of growth processes was affected by a wide range of ECD concentrations (10^–13–10^–5 M), whereas some metabolic processes, such as the activation of -amylase and the retardation of leaf yellowing, by a narrow range, that is, 10^–9–10^–7 M and 10^–9–10^–8 M, respectively. We noted the synergetic effect of ECD and IAA on coleoptile elongation, the antagonistic effect of ECD and EBL on coleoptile elongation, as well as the antagonistic action of ECD and GA₃ on coleoptile elongation and -amylase activity. The data obtained demonstrate that ECD is a physiologically active compound. ECD might be supposed to act as a source of sterols or a regulator of IAA and protein synthesis. The effects of this regulator seems to be brought about by its interaction with the EBL and GA₃ receptors.