Temperature-induced phase shifting of circadian rhythms in cotton seedlings as related to variations in chilling resistance

The relationship between the degree of chilling resistance and phase shifting caused by low-temperature pulses was examined in two circadian rhythms in cotton (Gossypium hirsutum L. cv. Deltapine 50) seedlings grown under light-dark cycles of 1212 h at 33° C. The seedlings showed a circadian rhythm of chilling resistance and of cotyledon movement. A pulse of 19° C for 12 h during the chilling-sensitive phase (light period) caused a phase delay of 6 h, while a similar temperature pulse during the chilling-resistant phase (dark period) did not cause any phase shift. Exposure to 19° C, 85% RH (relative humidity) for 12 h during the dark period induced chilling resistance in the following otherwise chilling-sensitive light period. In this light period a 12-h 19° C pulse did not cause a phase shift of chilling resistance. Pulses of low temperatures (5–19° C) were more effective in causing phase delays in the rhythm of cotyledon movement when given during the chilling-sensitive phase than when given during the chilling-resistant phase. A 12-h pulse of 5° C, 100% RH during the light period caused a phase delay of cotyledon movement of 12 h. However, when that pulse had been preceded by a chill-acclimating exposure to 19° C, 85% RH for 12 h during the dark period the phase delay was shortened to 6 h. The correlation between higher degree of chilling resistance and the prevention or shortening of the phase delay caused by low temperatures indicates that the mechanism that increases chilling resistance directly or indirectly confers greater ability for prevention of phase shifting by low temperatures in circadian rhythms.Abbreviations CT circadian time - LDC light-dark cycle of 24 h - RH relative humidity     

Changes in respiration of mitochondria isolated from cotyledons of ethylene-treated pea seedlings

Treatment of intact, germinating pea (Pisum sativum L. cv. Homesteader) seedlings with ethylene enhanced the cyanide-resistant respiration of mitochondria isolated from the cotyledons. The level of enhancement depended on the concentration of ethylene. Thus, exposure to 0.9 l·l^-1 of ethylene in air for days 4–6 of germination had little effect on cyanide-resistant respiration, while exposure to 130 l·l^-1 increased it from 10 to 50 nmol O₂·min^-1·(mg protein)^-1. The length of exposure to ethylene also affected the degree of enhancement. According to some literature data, lipoxygenase (EC 1.13.11.12) activity can be mistaken for cyanide-resistant respiration, but in our preparations of purified pea mitochondria ethylene had no effect on lipoxygenase activity, nor did the gas disrupt the outer mitochondrial membrane. Bahr and Bonner plots of respiration in the presence of salicylhydroxamic acid (SHAM) indicated that ethylene did not affect respiration proceeding via the cytochrome pathway. Thus, increases in total respiration in mitochondria from cotyledons of ethylene-treated pea seedlings reflect increases in cyanide-resistant respiration.Abbreviations Cyt c cytochrome c - SHAM salicylhydroxamic acid     

Temporal organization of chilling resistance in cotton seedlings: effects of low temperature and relative humidity

The effect of temperature and relative humidity (RH) on the time course of the rhythmic endogenous changes of chilling resistance was studied in cotton (Gossypium hirsutum L. cv. Deltapine 50) seedlings grown under light-dark cycles of 12:12 h. The resistant phase to 5° C, 85% RH lasted during most of the dark period while to 5° C, 100% RH it was longer and extended into the last half of the light period because a transient phase advance occurred when chilling started at the middle of the light period. Seedlings acclimated by low temperature were resistant throughout the light-dark cycle. A treatment with 100% RH before chilling to acclimated seedlings introduced a sensitive phase that corresponded to that of non-acclimated seedlings. In non-acclimated seedlings, this treatment decreased the resistance but the basic pattern of the rhythm was sustained. Changes in chilling resistance were analyzed under fluctuating temperatures and RHs, and explained taking into consideration the functioning of the circadian clock and environmental induction of resistance.Abbreviations CR chilling resistance - LDC light-dark cycle of 24 h - RH relative humidity     

Ethylene metabolism in Pisum sativum L.

The possible role of C₂H₄ metabolism in mediating the responses of plants to C₂H₄ is re-examined. It is demonstrated that (i) the effects of inhibitors upon C₂H₄ action do not correspond with their effects on metabolism, (ii) elicitors of C₂H₄ effects do not have appropriate effects on C₂H₄ metabolism, (iii) inhibitors of C₂H₄ metabolism do not affect the response of plants to C₂H₄. It is concluded that metabolism of C₂H₄ is not linked to the mode of action of the growth regulator.Abbreviations DTC sodium diethyldithiocarbamate - FW fresh weight     

Phytochrome-controlled ethylene biosynthesis of intact etiolated bean seedlings

Intact etiolated bean (Phaseolus vulgaris L. cv. Limburgse vroege) seedlings were illuminated with red light (10.5 W·m^-2) for 10 min. After different time intervals ethylene production, and contents of 1-aminocyclopropane-1-carboxylic acid (ACC) and 1-(malonylamino)cyclopropane-1-carboxylic acid were measured. The red-light-induced decrease of ethylene production in 8-d-old intact etiolated bean seedlings was fast, strong and long-lasting ad was mediated through the phytochrome system. This effect appeared to be strictly age-dependent, as it could not be detected in plants younger than 6 d or older than 11 d.The capacity for the conversion of ACC to ethylene was not affected by red light. The inhibitory effect of the light treatment on ethylene production could be related to a reduced free-ACC content. This reduction was a consequence of a temporary non-reversible increase of ACC malonylation and a long-lasting, for a certain time reversible, inhibition of ACC synthesis. The effect of a brief irradiation with red light on the decrease of ethylene production and free-ACC content was completed after about 2 h. Reversibility by far-red, however, persisted for at least 3 h, and was lost between 3 and 6 h.Abbrevation ACC 1-aminocyclopropane-1-carboxylic acid - M-ACC 1-(malonylamino)cyclopropane-1-carboxylic acid     

The measurement of ethylene binding and metabolism in plant tissue

Methods are described for the rigorous measurement of C₂H₄ metabolism and C₂H₄ binding in plant tissue. Comparisons are drawn between the results obtained using other methods and those which emerge from our studies, indicating that significant misapprehensions may have arisen in relation both to the distribution of metabolism and binding.     

The effect of light and dark periods on the production of ethylene from water-stressed wheat leaves

Light was found to inhibit substantially (i.e. up to 88%) the production of ethylene induced by water stress in excised wheat leaves and from the shoots of intact plants. The relatively small amounts of ethylene emanating fron non-stressed leaves were also inhibited by light but to a smaller degree (i.e. up to 61%). In water-stressed leaves the degree of light inhibition of ethylene production was shown to be related to the age of the leaves; the amounts of ethylene diffusing from young leaves (i.e. 6-days old) was inhibited 52% by light whereas in older leaves (i.e. 9-days old) it was inhibited by 85%. Previous studies [Wright (1979) Planta 144, 179–188 and (1980) Planta 148, 381–388] had shown that application of 6-benzyladenine (BA) to leaves a day before wilting, greatly increases the amount of ethylene diffusing from the leaves following wilting (e.g. 8-fold), and to smaller degrees do applications of indole-3-acetic acid (IAA) and gibberellic acid (GA₃). On the other hand abscisic acid (ABA) treatment reduces the amount of ethylene produced. In these earlier experiments the ethylene was collected from leaves held under dark or near-dark conditions, so in the present study the activities of these growth regulators (10^-4 mol l^-1 solutions) under dark and light conditions were compared. It was found that they maintained the same relative activities on ethylene emanation (i.e. BA>IAA>GA₃>water controls>ABA) under both light and dark conditions. However, because of the inhibitory effect of light, the absolute amounts of ethylene produced from all treatments were always much higher in the dark than in the light (usually about a 6-fold difference). An interesting effect of light treatment on ethylene biosynthesis was found when water-stressed leaves were kept in dark chambers for 41/2 h and then transferred to light. Quite unexpectedly, instead of the rate of ethylene production falling immediately, it continued to be produced at the dark rate (i.e. no light inhibition!) for over 2 h before the rate began to decline, and for a much longer period (i.e. in excess of 41/2 h) if the leaves had previously been sprayed with BA. Predictably, leaves placed in the light (i.e. in leaf chambers) and then transferred to darkness, immediately or very soon produced ethylene at the dark rate. One explanation of these results, which is discussed, would be that the biosynthesis of an ethylene precursor requires an obligatory dark stage. The possible implications of these studies to a survival role of ethylene in plants during periods of water stress is discussed.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - BA 6-benzyladenine - GA₃ gibberellic acid - GLC gas-liquid chromatography - IAA indole-3-acetic acid - TLC thin-layer chromatography - _leaf leaf water potential     

Phytochrome-mediated induction of phenylalanine ammonia-lyase in the cotyledons of tomato (Lycopersicon esculentum Mill.) plants

Phenylalanine ammonia-lyase (PAL; EC 4.3.1.5.) induction in cotyledons from 96-h dark-grown Lycopersicon esculentum Mill. was studied in response to continuous light and hourly light pulses (blue, red, far red). The increases of PAL promoted by blue and red pulses are reversed completely by immediately following 758 nm irradiations. The response to continuous red light could be substituted for by hourly 6-min red light pulses. The effect of continuous red treatments is mainly due to a multiple induction effect of phytochrome. In contrast to red light, hourly light pulses with far red and blue, light can only partially substitute for continuous irradiation. The continuous blue response could be due to a combination of a multiple induction response and of a high irradiance response of phytochrome. The continuous far red response, could represent a high irradiance response of phytochrome. Dichromatic irradiations indicate that phytochrome is the photoreceptor controlling the light response (PAL) in tomato seedlings.Abbreviations Norflurazon NF-4-chloro-5-(methylamino)-2-(,,,-trifluoro-m-tolyl)-3 (2H) pyridazinone - PAL phenylalanine ammonia-lyase - phytochrome photoequilibrium P_fr/P_tot - P_fr far-red absorbing form of phytochrome - P_r red absorbing form of phytochrome - P_tot total phytochrome: P_r+P_fr     

Subcellular localization of the sites of conversion of 1-aminocyclopropane-1-carboxylic acid into ethylene in plant cells

The subcellular localization of the sites of 1-aminocyclopropane-1-carboxylic acid (ACC) conversion into ethylene was studied by comparing the specific radioactivity of ethylene evolved from the whole cells with that of intra- and extracellular pools of labelled ACC. We demonstrate that some cells cultured in vitro (Vitis vinifera L. cv. Muscat) or leaf tissues (Hordeum vulgare L. and Triticum aestivum L.) have two sites of ethylene production: (i) an external site, converting apoplastic ACC, located at the plasma membrane, and very sensitive to high osmotica and, (ii) an intracellular site, converting internal ACC and remaining unaffected even under severe plasmolysis. In other cells cultured in vitro (Vitis vinifera L. cv. Gamay) and pea leaves (Pisum sativum L.), only the intracellular site operates and ethylene production is almost unaffected by plasmolysis. Protoplasts obtained from plasmolysis-sensitive Muscat cells lose 97% of their capacity for ethylene production compared with the parent cell, while those from plasmolysisinsensitive Gamay cells retain up to 50%. Protoplasts from both Gamay and Muscat cells cultured for 8 d in vitro, recover the full capacity of ethylene production of the initial whole cells, whether or not they are allowed to reform their cell wall. Therefore, we exclude a cooperation between the cell wall and the plasma membrane in ethylene production.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene-forming enzyme We are grateful to Dr. Philip John (Reading, UK) for useful discus sions made possible by a North Atlantic Treaty Organization Colla borative Grant (No. 0383/88) and Dr. Yves Meyer (Perpignan, France) for his collaboration in culturing protoplasts.     

Regulation of growth in stem sections of deep-water rice

Submergence in water greatly stimulates internodal elongation in excised stem sections of deep-water rice (Oryza sativa L. cv. Habiganj Aman II) and inhibits growth of leaf blades and leaf sheaths. The highest rates of internodal growth have been observed in continuous light. Very little growth occurs in submerged sections kept in darkness or incubated under N₂ in the light. The effect of submergence on the growth of deep-water rice is, at least in part, mediated by C₂H₄, which accumulates in the air spaces of submerged sections. This accumulation results from increased C₂H₄ synthesis in the internodes of submerged sections and reduced diffusion of C₂H₄ from the tissue into the water. Increased C₂H₄ levels accelerate internodal elongation and inhibit the growth of leaves. Compounds capable of changing the rate of C₂H₄ synthesis, namely aminoethoxyvinylglycine, an inhibitor of C₂H₄ synthesis, and 1-aminocyclopropane-1-carboxylic acid, the immediate, precursor of C₂H₄, have opposite effects on growth of internodes and leaves. The enhancement of internodal elongation by C₂H₄ is particularly pronounced in an atmosphere of high CO₂ and low O₂. The increase in C₂H₄ synthesis in internodes of submerged sections is primarily triggered by reduced atmospheric concentrations of O₂. The rate of C₂H₄ evolution by internodes isolated from stem sections and incubated in an atmosphere of low O₂ is up to four times greater than that of isolated internodes incubated in air. In contrast, C₂H₄ evolution from the leaves is reduced under hypoxic conditions. The effect of submergence on growth of stem sections of deep-water rice can be mimicked by exposing non-submerged sections to a gas mixture which is similar to the gaseous atmosphere in the internodal lacunae of submerged sections, namely 3% O₂, 6% CO₂, 91% N₂ (by vol.) and 1 l l^-1 C₂H₄. Our results indicate that growth responses obtained with isolated rice stem sections are similar to those of intact deep-water rice plants.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine     

玉米苗中DIMBOA与几种酚酸类物质抑菌活性比较

本文从室内培养的7日龄玉米幼苗中提取、分离、鉴定了抗性次生化合物丁布(2,4-d ihydroxy-7-m ethoxy-2H-1,4-benzoxazin-3(4H)-one,D IMBOA),并就该物质对玉米纹枯病病原菌立枯丝核菌(Rhizoctonia solani)的活性与三种酚酸类物质(阿魏酸、对羟基肉桂酸和咖啡酸)进行了离体比较研究。结果表明,丁布(D IMBOA),对立枯丝核菌有很强的生物活性,在浓度为50μg/mL时即可抑制立枯丝核菌菌丝的生长,抑制率为18.52%。阿魏酸、对羟基肉桂酸和咖啡酸,这三种酚酸在浓度250μg/mL时对立枯丝核菌菌丝的生长有抑制作用,抑制率分别为26.30%、8.50%和6.30%。不仅如此,丁布与对羟基肉桂酸之间、以及三种酚酸两两组合之间还存在一定的协同作用。在浓度相等的情况下,丁布与对羟基肉桂酸的等量混合液的抑菌率显著高于这两种物质单独存在时的抑菌率之和;同样,对羟基肉桂酸与阿魏酸的等量混合液的抑菌率比单一的对羟基肉桂酸溶液的抑菌率高18.89%,比单一的阿魏酸溶液的抑菌率高13.33%;对羟基肉桂酸与咖啡酸的等量混合液,抑菌率比两者单独试验时分别高9.63%和14.83%;阿魏酸与咖啡酸的混合液,抑菌率比两酸单独试验时分别高11.48%和22.23%。这一结果提示植物体内产生适当比例不同次生化合物的组合对植物抗病性的提高是至关重要的。     

Absence of red-light enhancement of phototropism in pea seedlings at limiting irradiances of blue light

The effect of different light qualities (blue, green, white, red and far-red) on ethylene production in leaf discs and flower petal discs of Begonia × hiemalis cv. Schwabenland Red was studied. All the light qualities, except far-red, reduced the ACC-conversion to ethylene in leaf discs by about 70% at a photosynthetic photon flux density (PPFD) of 20 mol m^–2s^–1.Blue and green light were less inhibitory than white and red light at lower PPFD. In all treatments far-red light at 0.5 mol m^–2s^–1 of photon flux density (PFD) stimulated the ACC-conversion to ethylene in leaf discs by about 60–90% compared to the dark-incubated control. White and red light strongly inhibited the -naphthalene-acetic acid (NAA) stimulated ethylene synthesis in leaf discs. The results may suggest that the ethylene production is controlled by phytochrome in the leaves but not in the petals. Lack of coaction of any light quality with silver ions on ethylene production in leaf and petal discs was also observed.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene forming enzyme - NAA -naphthalene-acetic acid - PFD photon flux density - PPFD photosynthetic photon flux density - RH relative air humidity - SAM S-adenosylmethionine - STS silver thiosulphate     

Tissue and subcellular immunolocalisation of enzymes of lignin synthesis in differentiating and wounded hypocotyl tissue of French bean (Phaseolus vulgaris L.)

Antisera raised againstl-phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H), and a cationic cell-wall peroxidase, which had all been purified from suspension-cultured cells of French bean, have been used to carry out immunogold localisations in the growing plant. Immunoglobulin-G fractions were prepared from each antiserum and used to study the distribution of the enzymes in differentiating and wounded hypocotyls by immunogold techniques and visualisation by both light and electron microscopy. Following silver enhancement to amplify the signal, proteins were detected by confocal microscopy in both developing (pre-xylem/ phloem) and later metaxylem stelar tissue.l-Phenylalanine ammonia-lyase and C4H also accumulated in cells adjacent to metaxylem, presumably involved in maintaining a supply of phenylpropanoid precursors to the enucleated xylem for further lignin synthesis. In these cells, PAL subunits were cytosolic although some were associated with endomembrane. Cinnamate-4-hydroxylase was wholly associated with membrane and particularly high concentrations were found in the Golgi bodies. The cationic peroxidase accumulated in xylem at sites of secondary thickening and in the middle lamella. The three proteins are also involved in defensive lignification. Thus when visualised by light microscopy, PAL and C4H were seen to accumulate to high levels throughout the cell types in wound sites and especially in the epidermal cells. An even more intense general distribution was found upon hyperinduction of wounded cells with-aminooxy--phenylpropionic acid. At the subcellular level, PAL was found to be localised in the cytosol in the wounded cells; however, because of the loss of membrane through mechanical damage, association with membrane structures, particularly endoplasmic reticulum, in unwounded cells is not entirely ruled out. Cinnamate-4-hydroxylase was associated with membranes when these were preserved. In wounded tissue, the peroxidase was found at the growing edges of tylose-like structures in the vascular xylem.Abbreviations AOPP -aminooxy--phenylpropionic acid - C4H cinnamic acid-4-hydroxylase - CHS chalcone synthase - GRP glycine-rich glycoprotein - HRGP hydroxyproline-rich glycoprotein - Ig immunoglobulin - PAL phenylalanine ammonia-lyase G.P.B. thanks the Agicultural and Food Research Council for support.     

Light-dependent production of ethylene in Tillandsia usneoides L.

Tillandsia usneoides L. is a favorite model plant for investigating ethylene biosynthesis because no soil is needed for cultivation (important for long-term measurements) and small plants and different clones are available. We investigated the endogenous production of ethylene in relation to temperature, light, daylength and CO₂ concentration. Using a novel and most sensitive technique to measure ethylene, laser-driven photoacoustic spectroscopy, real-time online measurements were performed. Since T. usneoides is a crassulacean acid metabolism (CAM) plant and does not take up CO₂ during the day we could show that ethylene production is strictly light dependent and does not follow any endogenous rhythm. In contrast to reports on other plants, CO₂ concentration did not influence the production of ethylene by T. usneoides. However, high ethylene production was obtained after application of 1-aminoacyclopropane-1-carboxylic acid (ACC). Received: 10 September 1997 / Accepted: 27 November 1997     

Rapid induction of ethylene biosynthesis in cultured parsley cells by fungal elicitor and its relationship to the induction of phenylalanine ammonia-lyase

The biosynthesis of ethylene was examined in suspension-cultured cells of parsley (Petroselinum hortense) treated with an elicitor from cell walls of Phytophthora megasperma. Untreated cells contained 50 nmol g^-1 of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), and produced ethylene at a rate of about 0.5 nmol g^-1 h^-1. Within 2 h after addition of elicitor to the culture medium, the cells started to produce more ethylene and accumulated more ACC. Exogenously added ACC did not increase the rate of ethylene production in control or elicitor-treated cells, indicating that the enzyme converting ACC to ethylene was limiting in both cases. The first enzyme in ethylene biosynthesis, ACC synthase, was very rapidly and transiently induced by the elicitor treatment. Its activity increased more than tenfold within 60 min. Density labelling with ²H₂O showed that this increase was caused by the denovo synthesis of the enzyme protein. Cordycepin and actinomycin D did not affect the induction of ACC synthase, indicating that the synthesis of new mRNA was not required. The peak of ACC-synthase activity preceded the maximal phenylalanine ammonia-lyase (PAL) activity by several hours. Exogenously supplied ethylene or ACC did not induce PAL. However, aminoethoxyvinylglycine, an inhibitor of ACC synthase, suppressed the rise in ethylene production in elicitor-treated cells and partially inhibited the induction of PAL. Exogenously supplied ACC reversed this inhibition. It is concluded that induction of the ethylene biosynthetic pathway is a very early symptom of elicitor action. Although ethylene alone is not a sufficient signal for PAL induction, the enhanced activity of ACC synthase and the ethylene biosynthetic pathway may be important for the subsequent induction of PAL.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - PAL phenylalanine ammonia-lyase     

The apoplastic pool of abscisic acid in cotton leaves in relation to stomatal closure

Suboptimal nitrogen nutrition, leaf aging, and prior exposure to water stress all increased stomatal closure in excised cotton (Gossypium hirsutum L.) leaves supplied abscisic acid (ABA) through the transpiration stream. The effects of water stress and N stress were partially reversed by simultaneous application of kinetin (N⁶-furfurylaminopurine) with the ABA, but the effect of leaf aging was not. These enhanced responses to ABA could have resulted either from altered rates of ABA release from symplast to apoplast, or from some post-release effect involving ABA transport to, or detection by, the guard cells. Excised leaves were preloaded with [¹⁴C]ABA and subjected to overpressures in a pressure chamber to isolate apoplastic solutes in the exudate. Small quantities of ¹⁴C were released into the exudate, with the amount increasing greatly with increasing pressure. Over the range of pressures from 1 to 2.5 MPa, ABA in the exudate contained about 70% of the total ¹⁴C, and a compound co-chromatographing with phaseic acid contained over half of the remainder. At a low balancing pressure (1 MPa), release of ¹⁴C into the exudate was increased by N stress, prior water stress, and leaf aging. Kinetin did not affect ¹⁴C release in leaves of any age, N status, or water status. Distribution of ABA between pools can account in part for the effects of water stress, N stress, and leaf age on stomatal behavior, but in the cases of water stress and N stress there are additional kinetinreversible effects, presumably at the guard cells.Abbreviations and symbols ABA abscisic acid - PA phaseic acid - _w water potential     

Calcium and phytochrome control of leaf unrolling in dark-grown barley seedlings

The red light-stimulated component of unrolling in sections from 7-d-old dark-grown barley (Hordeum vulgare L.) leaves is inhibited by ethyleneglycol-bis-(-aminoethyl ether)-N,N,N,N-tetracetic acid (EGTA). A free-Ca²⁺ activity of less than 40 M restores the ability to respond to red light, but only if supplied within 1 h of red light. Magnesium ions are an ineffective substitute. At least two processes in unrolling appear to be Ca²⁺-sensitive.Fluence-response measurements indicate that the levels of the far-red-absorbing from of phytochrome (Pfr) still present 4 h after red-light treatment should be above saturation for the unrolling response; consequently, loss of Pfr does not explain the loss in effectiveness of Ca²⁺ during prolonged EGTA treatment. However, if a further red-light treatment is given simultaneously with Ca²⁺ addition 4 h after the initial light stimulus, then full unrolling occurs in EGTA-treated sections. These data indicate that, under normal circumstances, a functional change in the properties of Pfr must occur, uncoupling it from the transduction chain.Abbreviations EGTA ethyleneglycol-bis-(-aminoethylether)-N,N,N,N,-tetracetic acid - FR far-red light - Mes 2-(N-morpholino)ethanesulphonic, acid - Pfr far-red absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light     

Influence of external factors on callose and cellulose synthesis during incubation in vitro of intact cotton fibres with [14C]sucrose

Seed clusters, with adhering fibres, from individual locules of 36-d-old fruit capsules of Gossypium arboreum L. were fed with [¹⁴C]sucrose in vitro. The fibres synthesised, under standard conditions, (13)--D-glucan (callose) and (14)--D-glucan (cellulose) in the ratio of approx. 2:1. Under a great variety of different conditions this product ratio remained more or less constant, even when total glucan synthesis was strongly inhibited with 2,4-dinitrophenol or phloretin, or when stimulated with abscisic acid. In attempts to favour cellulose synthesis, no conditions were found where the ratio was substantially reduced. On the other hand, the ratio could be appreciably increased by inhibiting cellulose synthesis, e.g. with 2,6-dichlorobenzonitrile or coumarin, by anionic detergents such as sodium dodecyl sulphate, by low temperatures, or by increasing the osmotic strength of the incubation medium up to conditions causing plasmolysis. Specific degradation of callose, during incubation of the seed clusters, by exogenous exo-(13)--D-glucanase significantly diminished incorporation of radioactivity into cellulose.Abbreviations DMSO dimethyl sulphoxide - EDTA ethylenediaminetetraacetic acid     

Promotion of mesocotyl growth in etiolated rice seedlings by 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione

4-Ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione (TA) promoted mesocotyl growth in dark-grown rice (Oryza sativa L.) seedlings. In cultivars of the japonica type TA alone showed a small promotive effect and TA+gibberellic acid(GA₃) had a marked synergistic effect, while in other cultivars, mostly of the indica type, TA alone showed a great promotive effect and TA+GA₃ had only an additive effect. In cv. Nato, a typical representative of cultivars showing the second type of response, the concentration of TA giving the greatest growth promotion was around 0.1–0.2 mM. In Nato seedlings treated with TA at 0.1 mM, the mesocotyls continued to elongate for 6 days and reached about 75 mm in length, while the mesocotyls of control seedlings grew to a maximum of about 10 mm and growth was limited to the first 3 days after planting. The TA-induced mesocotyl elongation was mainly the consequence of increased cell multiplication in the meristematic area immediately below the coleoptilar node. GA₃, abscisic acid (ABA) and ethylene also stimulated mesocotyl growth in dark-grown Nato seedlings but their effects were much smaller than those of TA. ABA, like GA₃, had an additive effect with TA, but ethylene suppressed the effect of TA and resulted in increased lateral expansion in the upper region of the mesocotyls of TA-treated seedlings.Abbreviations ABA abscisic acid - GA(s) gibberellin(s) - GA₃ gibberellic acid - TA 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione Part 5 in the series Plant Growth-regulating Activities of Isourea Derivatives and Related Compounds; Part 4=Ogawa et al. (1978)