Effect of red light on coleoptile growth

The effects of red light in reducing the growth of the oat (Avena sativa L.) coleoptile and the synthesis of auxin in the coleoptile tip are detectable 2 hours after treatment and become more pronounced with time. When the coleoptile tip is supplied with additional tryptophan the synthesis of auxin is doubled both in darkness and when exposed to red light. Treatment of the tip with gibberellic acid or pyridoxal phosphate overcomes the reduction of auxin synthesis caused by red light. The uptake of exogenous indoleacetic acid, at pH 6.5, by coleoptile tissue is doubled by exposure to red light. The effect of red light on coleoptile growth appears to be mediated by phytochrome in the cell membrane which delocalizes the tryptophan utilized for auxin synthesis.     

Influence of boric acid on somatic embryogenesis of a cytosterile line of indica rice

The effect of boric acid on somatic embryo induction in rice was investigated using mature seeds of a widely used cytoplasmic male sterile line of indica rice IR-58025. Boric acid was added at a concentration of 100.00, 161.29, 241.93, 322.58 and 403.22 μM to the embryo induction medium containing basal salts, with 9.84 μM 2,4-dichlorophenoxyacetic acid. Boric acid was found to exert different effects on scutellum, coleoptile and root tissues. Increased growth of embryogenic masses with increasing boric acid concentrations was observed on coleoptile tissues of mature seed. Embryogenic response was observed at 161.29 μM boric acid on coleoptile and 241.93 μM boric acid on root tissue. Scutellum tissue showed embryonic response in 161.29 and 241.93 μM boric acid. The results indicate that the boric acid used in standard Murashige and Skoog medium is not sufficient to support induction of somatic embryogenesis in IR-58025 A. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biogenesis of auxin in the coleptile of a semi-brachytic barley, uzu

The coleoptile of a semi-brachytic barley, uzu(Hordeum vulgareL. cv. Akashinriki), elongated ca 1/2 as much as the coleoptileof the contrasting normal form which is isogenic excepting theuz gene. This retarded growth of the uzu coleoptile, as comparedto the normal coleoptile, is not due to changes in the rateof basipetal transport of auxin, neither to the destructionof auxin during transport, nor to sensitivity to auxin. Furthermore,less of the extractable and bound auxins were found in the uzu(uzuz)coleoptile than in the normal(UZUZ)coleoptile, suggesting thatthe retarded growth of uzu coleoptile may be due to less auxinproduction. Apical tips of the normal coleoptile grown under sterile conditionsresponded to both tryptophan and tryptamine, but uzu coleoptiletips responded only to tryptamine. Thus, growth retardationof the uzu coleoptile may be due to lower activity of the enzymewhich converts tryptophan to tryptamine in the uzu coleoptile. (Received August 20, 1973; )     

Influence of gibberellic acid on auxin biosynthesis and their effects on coleoptile elongation in garlic

To demonstrate the effect of auxin on intact coleoptile growth, garlic (Allium sativum L.) cloves were inoculated in agar supplemented with DW (control), GA₃ and GA₃+tryptophan (a precursor of IAA, GA₃+T). The coleoptiles were harvested at 24 h intervals to measure growth in terms of length, activities of IAAld DH (which convert tryptophan to IAA) and peroxidase (that oxidizes IAA). Contents of endogenous IAA and PAA were also measured by indirect ELISA. Peroxidase activity was suppressed by GA₃ treatment and increased by GA₃+T treatment. Although endogenous contents of IAA were increased by the addition of GA₃ and even more by GA₃+T in the media, there was no further increase in coleoptile length, suggesting that garlic coleoptiles are sufficient in their production of IAA.     

Action of red light on indole-3-acetic-acid status and growth in coleoptiles of etiolated maize seedlings

Brief irradiation of intact etiolated seedlings of maize (Zea mays L.) with red light (R; 30 W cm^-2, 10 min) reduces the amounts of diffusible and free (solvent-extractable) indole-3-acetic acid (IAA) obtainable from excised coleoptile tips. The effect is transient, the lowest level (30% of the dark control) occurring at about 3 h after irradiation. The free-IAA content of the whole coleoptile and the diffusible-IAA yield from the base of the same organ are similarly reduced, whereas the conjugated-IAA content of the coleoptile is not affected. These results support the view that R inhibits the production of IAA at the coleoptile tip. It is further shown that R inhibits biosynthesis of [³H]IAA from [³H]tryptophan supplied to the coleoptile tip. The shapes of the fluence-response curves obtained for the reduction of the diffusible-IAA yield by R and far-red light (FR) indicate the participation of two photoreactive systems. One has thresholds at 10^-3 W s cm² of R, five orders of magnitude less than the minimum required for the appearance of spectrophotometrically measurable far-red-absorbing form of phytochrome (Pfr) in vivo, and 10^-1 W s cm^-2 of FR; its response is linear to the logarithm of fluence exceeding five orders of magnitude. The other system is seen above 10² W s cm^-2 as an increase in the slope of the fluenceresponse curve; its response is FR reversible and related to the Pfr level of total photoreversible phytochrome. Both systems inhibit biosynthesis of IAA from tryptophan. Elongation of the coleoptile is stimulated by R; the stimulation is most apparent in the apical region, and is saturated with a fluence at which bo detectable pfr is formed. Farred light can also saturate this response. Since the endogenous IAA concentration in the coleoptile appears not to be in the inhibitory range, it is concluded that the stimulation of coleoptile elongation is not the result of changes in free-IAA levels.Abbreviations FR far-red light - IAA indole-3-acetic acid - Pfr phytochrome in the far-red-absorbing form - Pr phytochrome in the red-absorbing form - R red light     

Maize based diets and possible neurobehavioural after-effects among some populations in the world

Maize is a cereal particularly lacking in tryptophan, which is the precursor of serotonin, an important neurotransmitter. Altough complementary foods may eliminate tryptophan deficiency, serotonin deficiency may often continue to exist because of competition made by other Large Neutral Amino Acids (LNAA) against tryptophan for neuron access, since they use the same carrier to cross the blood-brain barrier. Thus serotonin synthesis depends on two variables: the amount of tryptophan and the trp/LNAA ratio (R). “R” is lowest for common maize, low for beans and, as a rule, for most vegetable foods, higher for meat. So, when maize is the preponderant food in the meal, the “R” value lowers and so in parallel serotonin synthesis does. Serotonin deficiency involves several behavioural consequences, such as the tendency towards aggressive behaviour or the religious fanaticism. Among native american populations, these consequences appear, as a rule, positively correlated with maize alimentary dependence (Aztecs appear as those who greatly suffered from serotonin deficiency). In the world these are thinkable for some african populations (i.e. Zulu) or european (i.e. Balkan peoples).     

Alteration of plasmalemma H<Superscript>+</Superscript>-ATPase activity in maize coleoptile cells at different age of seedlings

An irregular alteration of the activity and character of the distribution of plasmalemma H⁺-ATPase has been shown in parenchymal cells of the coleoptile subapical zone within the period from the third to fifth day of ethiolated maize seedling development. The study was carried out by the cytochemical method. The highest enzyme activity was determined in the cells of four-day-old coleoptiles. The revealed change in H⁺-ATPase activity does not correspond to the dynamics of the growth intensity of the elongation of coleoptile cells within the studied period of seedling development.     

The Effect of Gibberellin on Tryptophan Conversion and Elongation of the Avena Coleoptile

Gibberellic acid (GA₃) enhanced directly the release of ¹⁴CO₂ from tryptophan-1-^l4C by cell free preparations of Avena coleoptile tips. The rate of tryptophan metabolism in the presence of GA₃ was increased by approximately 100 per cent. The addition of auxin synthesis inhibitors to incubation flasks nullified the enhancement effect of GA₃ on elongation of the coleoptile tips. These studies implicate tryptamine as an intermediate in the formation of auxin from tryptophan. The possibility of GA₃-IAA interaction in the elongation processes was also investigated. Combination treatments of these growth-promoting substances did not induce a synergistic growth response by the coleoptile tissue.     

The Lazy Mutation in Rice Affects a Step between Statoliths and Gravity-Induced Lateral Auxin Transport

Abstract: Compared to wild type, the lazy mutant in Oryza sati-va L. shows a reduced gravitropic response. In order to locate the lesion in the stimulus-response chain, coleoptile segments of lazy rice were investigated with respect to auxin transport. Gravity-induced lateral movement of radiolabelled indoleacetic acid (IAA) was strongly inhibited by the lazy mutation compared to wild type while uptake and longitudinal transport of IAA, as well as amyloplast sedimentation, were not significantly affected. These findings suggest that LAZY controls a step in the signalling chain between statoliths and auxin secretion.     

Salt tolerance of two differently drought-tolerant wheat genotypes during germination and early seedling growth

Summary Osmotic and specific ion effect are the most frequently mentioned mechanisms by which saline substrates reduce plant growth. However, the relative importance of osmotic and specific ion effect on plant growth seems to vary depending on the drought and/or salt tolerance of the plant under study. We studied the effects of several single salts of Na⁺ and Ca²⁺−NaCl, NaNO₃, Na₂SO₄, NaHCO₃, Na₂CO₃, and Ca(NO₃)₂—on the germination and root and coleoptile growth of two wheat (Triticum aestivum L.) cultivars, TAM W-101 and Sturdy, the former being more drought tolerant than the latter. The concentrations used were: 0, 0.02, 0.04, 0.08, 0.16, and 0.32 mol L⁻¹. Significant two- and three-way interactions were observed between cultivar, kind of salt, and salt concentration for germination, growth of coleoptile and root, and root/coleoptile ratio. Salts differed significantly (P<0.001) in their effect on seed germination, coleoptile and root growth of both cultivars. Germination of TAM W-101 seeds was consistently more tolerant than that of Sturdy to NaCl, CaCl₂, Ca(NO₃)₂, and NaHCO₃ salts at concentrations of 0.02, 0.04, 0.08, 0.16 mol L⁻¹. The osmotic potential, at which the germination of wheat seeds was reduced to 50% of that of the control, was different depending on the kind of salt used in the germination medium. NaCl at low concentrations (0.02 and 0.04 mol L⁻¹) stimulated the germination of both wheat cultivars. At concentrations of 0.02 to 0.16 mol L⁻¹, Ca²⁺ salts (CaCl₂ and Ca(NO₃)₂) were consistently more inhibitory than the respective Na⁺ salts (NaCl and NaNO₃) for germination of Sturdy. This did not consistently hold true for TAM W-101. Among the Na⁺ salts, NaCl was the least toxic and NaHCO₃ and Na₂CO₃ were the most toxic for seed germination. Root and coleoptile (in both wheat cultivars) differed in their response to salts. This differential response of coleoptile and root to each salt resulted in seedlings with a wide range of root/coleoptile ratios. For example, the root/coleoptile ratio of cultivar TAM W-101 changed from 2.09 (in the control) to 3.77, 3.19, 2.8, 2.44, 1.31, 0.32, and 0.0 when subjected to 0.08 mol L⁻¹ of Na₂SO₄, NaCl, CaCl₂, NaNO₃, Ca(NO₃)₂, NaHCO₃, and Na₂CO₃, respectively. Na₂CO₃ at 0.08 mol L⁻¹ inhibited root growth to such an extent that germinated wheat seeds contained coleoptile but no roots. The data indicate that, apart from the clear and more toxic effects of NaHCO₃ and Na₂CO₃ and lesser toxic effect of NaCl on germination and seedling growth, any toxicity-ranking of other salts done at a given concentration and for a given tissue growth may not hold true for other salt concentrations, other tissues and/or other cultivars. The more drought-tolerant TAM W-101, when compared to the less drought tolerant Sturdy, showed higher tolerance (at most concentrations) to NaCl, CaCl₂, Ca(NO₃)₂ and NaHCO₃ during its seed germination and to Na₂SO₄ and CaCl₂ for its root growth. This supports other reports that some drought-tolerant wheat cultivars are more tolerant to NaCl. In contrast, the coleoptile growth of drought-sensitive Sturdy was noticeably more tolerant to NaNO₃, Ca(NO₃)₂ and NaHCO₃ than that of drought-tolerant TAM W-101. Based on the above and the different root/coleoptile ratios observed in the presence of various salts, it is concluded that in these wheat cultivars: a) coleoptile and root tissues are differently sensitive to various salts, and b) at the germination stage, tolerance to certain salts is higher in the more drought-tolerant cultivar.     

Red light causes a reduction in IAA levels at the apical tip by inhibiting de novo biosynthesis from tryptophan in maize coleoptiles

When maize coleoptiles were unilaterally exposed to red light (7.9 μmol m⁻²s⁻¹ for 5 min), 3 h after treatment IAA levels in coleoptiles decreased in all regions, from top to basal, with levels about 60% of dark controls. Localized irradiation in the 5 mm top zone was sufficient to cause the same extent of IAA reduction in the tips to that in the tips of whole irradiated shoots. When coleoptiles were treated with N-1-naphthylphthalamic acid (NPA), an accumulation of IAA in the tip and a decrease of diffusible IAA from tips were simultaneously detected. IAA accumulation in red-light treated coleoptiles by NPA was much lower than that of dark controls. NPA treatment did not affect the content of conjugated IAA in either dark or light treated coleoptile tips. When ¹³C₁₁ ¹⁵N₂-tryptophan (Trp) was applied to the top of coleoptiles, substantial amounts of stable isotope were incorporated into free IAA in dark and red-light treated coleoptile tips. The ratio of incorporation was slightly lower in red-light treated coleoptile tips than that in dark controls. The label could not be detected in conjugated IAA. The rate of basipetal transport of IAA was about 10 mm h⁻¹ and the velocity was not affected by red light. These results strongly suggest that red light does not affect the rates of conversion of free IAA to the conjugate form or of the basipetal transport, but just reduces the IAA level in the tips, probably inhibited by IAA biosynthesis from Trp in this region.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

A QTL on chromosome 6A in bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>) is associated with longer coleoptiles,greater seedling vigour and final plant height

Wheat crops with greater early vigour shade the soil surface more rapidly and reduce water loss. Evaporative losses affect water-use efficiency particularly in drier regions where most of the rainfall occurs early in the growing season before canopy closure. Greater seedling leaf area and longer coleoptiles are major determinants of increased vigour and better crop establishment. A previously developed high vigour breeding line ‘Vigour 18’ was used to establish a large recombinant inbred family and framework map to identify a QTL on chromosome 6A that accounted for up to 8% of the variation for coleoptile length, 14% of seedling leaf width and was associated with increased plant height. The SSR marker NW3106, nearest to the 6A QTL, was also associated with greater leaf width in a breeding population that was also derived from a cross involving the high vigour donor line ‘Vigour18’. The association between the NW3106 marker and coleoptile length was validated in a second breeding population which was developed using an unrelated long coleoptile donor line. The ‘Vigour18’ allele of the QTL on chromosome 6A promoted coleoptile length and leaf width during early plant growth but was also associated with increased plant height at maturity. Markers linked to the QTL are being used to increase the frequency of increased vigour and long coleoptile alleles in early generations of breeding populations.     

Suppression of (1→3),(1→4)-β-d-Glucan Turnover during Light-Induced Inhibition of Rice Coleoptile Growth

d -Glucan contents and (1→3),(1→4)-β-d-glucan hydrolase activity increased in the faster phase of coleoptile growth, then declined under both light and dark conditions. The relative glucan content in the cell wall showed a good correlation with the increment of coleoptile length. Strong correlations were also observed among the increment of coleoptile length, the decrease in the level of the glucans, and the relative activity of the glucanase in the cell wall of light- and dark-grown coleoptiles except for those values in the early stage of coleoptile growth, supporting a hypothesis that the turnover of the glucans is one of the important factors which regulate rice coleoptile growth. The levels of the glucans and the glucanase activity were always lower in the cell wall of coleoptiles grown in the light than those in darkness during the experimental period. These results suggest that light irradiation inhibits both the synthesis and the breakdown of the glucans, causing a decrease in the capacity of the cell wall to extend, thereby inducing growth suppression in rice coleoptiles. Received 24 September 1998/ Accepted in revised form 28 December 1998     

Growth and Cellular Differentiation in the Wheat Coleoptile (Triticum vulgare L.): I. ESTIMATION OF CELL NUMBER, CELL VOLUME, AND CERTAIN NITROGENOUS CONSTITUENTS

The numbers and volumes of cells were determined for consecutivestages in the growth and development of the wheat coleoptile(var. ‘King II’) when grown at 25° C. in darknessfrom soon after germination to senescence. Cell expansion occurredthroughout growth and development up to 96 hours, and was accompaniedby cell division between 18–60 hours. Evidence is presentedthat suggests there are two phases of cell expansion concernedin coleoptile growth. Determinations were made at daily intervals from 24 to 120 hoursafter sowing of protein nitrogen, trichloroacetic acid solublenitrogen (TCA-sol. N), ribonucleic acid (RNA), and deoxyribonucleicacid (DNA) in the coleoptile, and the results expressed on aper-coleoptile and per-cell basis. The maximum rate of net proteinsynthesis took place during or after the cell-multiplicationphase of growth, depending on whether the results were expressedper coleoptile or per cell respectively. The ratio of proteinnitrogen to TCA-sol. N changed considerably during growth, from4·7 for young cells to 0·68 for mature cells. The fluctuations in the values for RNA and protein are consistentwith the template theory of protein synthesis and the DNA dataare discussed in relation to polyploidy in differentiated cells.No significant difference was found in the nucleotide compositionof RNA during the growth and development of the coleoptile.     

Anoxia tolerance and α-amylase activity in four rice cultivars

The relationship between anoxia tolerance and reserved carbohydrate catabolism was investigated in four rice (Oryza sativa L.) cultivars subjected to a 48-h anoxic stress. The coleoptile elongation of all cultivars was suppressed by anoxic stress, however, the elongation of cvs Koshihikari and Awa-akamai was much greater than that of cvs Touzoumochi and Asahimochi. The anoxic coleoptiles of cvs Koshihikari and Awa-akamai contained about 2-fold as much ATP as those of cvs Touzoumochi and Asahimochi. Ethanol production in the anoxic coleoptiles of cvs Koshihikari and Awa-akamai was about 2-fold as much as that of cvs Touzoumochi and Asahimochi, which suggests that ethanolic fermentation is probably more active in cvs Koshihikari and Awa-akamai than in cvs Asahimochi and Touzoumochi. Activity of α-amylase, which catabolizes starch to soluble sugars, in endosperms of cvs Koshihikari and Awa-akamai was about 2-fold that of cvs Touzoumochi and Asahimochi, and soluble sugar concentration in the coleoptiles of cvs Koshihikari and Awa-akamai was about 3-fold greater than that of cvs Touzoumochi and Asahimochi. Soluble sugar concentration and ethanol production rate in the coleoptiles of rice seedlings were correlated well with α-amylase activity in their endosperms, which were also correlated well with anoxia tolerance with respect to the coleoptile elongation and ATP concentration in the coleoptiles. These results suggest that the ability to degrade starch to soluble sugar by α-amylase in endosperm may be important for the anoxia tolerance in rice coleoptiles and it may serve to distinguish the anoxia tolerance of rice coleoptiles.     

Effect of temperature on the dose–response curves for auxin-induced elongation growth in maize coleoptile segments

The dose–response curves for IAA-induced growth in maize coleoptile segments were studied as a function of time and temperature. In addition, the kinetics of growth rate responses at some auxin concentrations and temperatures was also compared. It was found that the dose–response curves for IAA-induced elongation growth were, independently of time and temperature, bell-shaped with an optimal concentration at 10⁻⁵ M IAA. The kinetics of IAA-induced growth rate responses depended on IAA concentration and temperature, and could be separated into two phases (biphasic reaction). The first phase (very rapid) was followed by a long lasting one (second phase), which began about 30 min after auxin addition. For coleoptile segments incubated at 30°C, the amplitudes of the first and second phase were significantly higher, when compared with 25°C, at all IAA concentrations studied. However, when coleoptile segments were incubated at 20°C, the elongation growth of coleoptile segments treated with suboptimal IAA concentrations was diminished, mainly as a result of both phases reduction. In conclusion, we propose that the shape of the dose–response curves for IAA-induced growth in maize coleoptile segments is connected with biphasic kinetic of growth rate response.     

Interactions between Plants and Epiphytic Bacteria Regarding Their Auxin Metabolism

More “diffusible” auxin is received from nonsterile than from sterile corn coleoptile tips. An artificial reinfection of sterile coleoptiles with epiphytic, IAA-producing bacteria strains does, a superinfection of nonsterile coleoptiles does not increase the auxin amount. The difference between sterile and nonsterile tips persists if diffusion from the coleoptile surface is excluded by covering the surface with a paraffin layer. The greater the distance from the apex, the higher becomes the superiority of nonsterile tips. An artificial bacterial contamination of the contact face between tip and receiver agar block, or addition of glucose and tryptophan to the agar block, do not influence the received auxin amount. Consequently the additional, bacteria-produced auxin delivered by the nonsterile tip is not produced at the cut surface or in the agar but is present in the tissues of the coleoptile tip.     

The Role of the Coleoptile Apex in Controlling Organ Elongation: I. THE EFFECTS OF DECAPITATION AND APICAL INCISIONS

It has been widely accepted for over 50 years that the elongationrate of a coleoptile is dependent on the supply of auxin fromthe apex. The original coleoptile decapitation experiments whichprovided support for this view have been repeated but the measurementsof coleoptile elongation were made with greater temporal andspatial precision. The experiments confirm that Avena and Zeacoleoptile elongation is retarded by decapitation but the locationand timing of the growth rate changes are not consistent withthe hypothesis that decapitation reduces growth rate solelyby removing the major supply of auxin. Evidence is presentedthat wounding is the prime cause of the effects of decapitation.Data are also presented showing that the recovery of growthrate of coleoptiles after decapitation or wounding is not dearlyassociated with any events near the cut surface and hence thetraditional explanation of this phenomenon (‘regenerationof the physiological tip’) is misleading. Key words: Coleoptile, decapitation, apex     

Tryptophan supplementation and pH adjustment for optimizing the sporulation of <Emphasis Type="Italic">Coniothyrium minitans</Emphasis>

To determine the effect of tryptophan and pH on sporulation of Coniothyrium minitans, the fungus was cultivated using a two-stage, agar plate method in which addition of tryptophan and pH were controlled at the sporulation stage. The spore yield was enhanced by 4 times with 0.1 g tryptophan/l addition after 72 h. The optimal pH values were 4 for mycelia growth and 5.8–6 for sporulation. Mycelia grown at pH 6 had a higher productivity of spore production than did those grown at pH 4.