Coleoptiles

Various assay methods have been used to detect the presence of inhibitory substances. These include some of the classical tests used by investigators of growth-promoting substances—i.e., the various Avena coleoptile assays which utilize intact, decapitated, or isolated cylinders and the split pea stem test. Effects on seed germination and seedling shoot or root growth and development have also been measured in addition to other visible expressions of inhibition. Details of many of these tests have been compiled by Mitchell et al. (99). Tests have been carried out in Petri dishes, with various solution culture techniques, and by sand and soil culture. Effects so measured may or may not be similar to those obtained under field situations— i.e., the establishment of inhibition under controlled conditions pro-... 

Naringenin (5, 7, 4 -trihydroxyflavanone), isolated in pure form from dormant peach flower buds, strongly inhibited the growth of Avena coleoptiles at 4.6 X 10-4 M (71). Naringenin is the aglycone of the glycoside naringin. 

Coumarin, the lactone of o-hydroxycinnamic acid, and some of its derivatives have been isolated from many plant species 31). Thimann and Bonner 141) attributed the growth-inhibiting effects of coumarin to its action on enzyme sulfhydryl groups. Inhibitory effects of coumarin on Avena coleoptiles and pea stem sections could be overcome by 2,3-dimercaptopropanol (BAL). Coumarin has also been reported to disrupt mitosis 29,30). 

Protoanemonin, which has been isolated from Anemone pulsatilla and Ranunculus spp., was reported to inhibit root growth by slowing down metabolism and blocking mitosis 35). Erickson and Rosen 35) observed cytological effects in corn root tips at concentrations of 10M and lower. Cells undergoing division appeared to accumulate in the interphase or prophase stages. Metaphase, anaphase, and telophase stages were not observed. Cytoplasmic and vacuolar structures were disturbed and the presence of mitochondria could not be demonstrated in treated tissue. Thimann and Bonner 141) reported that protoanemonin was 10 to 30 times more inhibitory than coumarin in coleoptile and split pea stem tests, and that BAL prevented the inhibitory action. 

Rothwell and Wain (126) have isolated in crystalline form a growth inhibitor from Lupinus luteus (yellow lupine) pods which they have partially characterized. Analytical data suggested that the inhibitor possessed the characteristics of an unsaturated hydroxyketo acid. Inhibition in the wheat coleoptile cylinder test was obtained with concentrations of 0.25 to 1.0 p.p.m. 

Yusupova Z.R. Akhmetova I.E. Khairullin R.M. Maksimov I.V. (2005) The effect of chitooligosaccharides on hydrogen peroxide production and anionic peroxidase activity in wheat coleoptiles / / Rus. J. of Plant Physiol. V. 52. P. 209-212. 

Pierce, W.S. Higinbothom, N. (1970). Compartments and fluxes of and Cl" in Avena coleoptile cells. Plant Physiology, 46, 666-73. 

In the presence of air, the roots, coleoptile, mesocotyl, endosperm, scutellum, and anther wall of maize synthesise a tissue-specific spectrum of polypeptides. The scutellum and endosperm of the immature kernel synthesise many or all of the ANPs constitutively, along with many other proteins under aerobic conditions. Under anaerobic conditions all of the above organs selectively synthesise only the ANPs. Moreover, except for a few characteristic qualitative and quantitative differences, the patterns of anaerobic protein synthesis in these diverse organs are remarkably similar (Okimoto et al., 1980). On the other hand, maize leaves, which have emerged from the coleoptile, do not incorporate labelled amino acids under anaerobic conditions and do not survive even a brief exposure to anaerobiosis (Okimoto et al., 1980). 

Immunogold localization of the pectic epitope has been performed on different types of cells cell suspensions, roots, shoots, meristems, coleoptiles, pollen grains, protoplasts from different species carrot, sugar beet, tobacco, oat... The pattern of labeling was always the same polygalacturonic acid was essentially located on the material expanded at three-way junctions between cells or lining intercellular space, but was not found in primary walls. No epitope could be located close to the plasma membrane (Fig. lO.a). Middle lamellae far from junction zones and walls of meristematic cells were never labeled. 

Kim, J-B., Caipita, N.C. (1992), Changes in esterification of the uronic acid groups of cell wall polysaccharides during elongation of maize coleoptiles. Plant Physiol. 98, 646-653. 

Parthenin (19) has at a concentration of 50 ppm no effect on the germination of the bean Phaseolus vulgaris but inhibits the development of radicles and hypocotyls (41). Similar effects were observed by Kanchan for Parthenlum hysteropherus and Eleusine coracana coleoptiles (42) and it was shown that besides parthenin (19), caffeic acid, vanillic acid, ferulic acid, chlorogenic acid an3 anisic acid were major constituents in P. hysteropherus (43). 

Other lipophilic weak acids have been shown to alter PD in plant cells. Benzoic and butyric acids (1 PM) rapidly depolarized the PD In oat coleoptile cells at pH 6.0 to about -100 mV (43). Higher concentrations (10 mM) of butyrate produced hyperpolarization. Butyrate also hyperpolarized apical cortical cells of maize roots... 

Mitochondria from cucumber roots, pea (Plsum sativum L.) roots, and maize coleoptiles reacted in a manner similar to mitochondria from cucumber hypocotyls. Hence, it appears that various allelochemlcals can produce different effects on ATP production. 

Fig. 2. Phototropic dosage response curves for oat coleoptiles at three intensities of blue light (440 nm) (7) 1.4 10-11, (2)...

The defenders of the carotenoid-photoreceptor-hypothesis have always understood the shape of these action spectra in the blue to mean that the bluelight receptor is a carotenoid. Indeed, in Fig. 6 3 it can be observed, that the three-peak absorption spectrum of trans-0-carotenoid (in hexene) agrees well with the observed action spectrum of the avena coleoptile (Fig. 3 5). However, there remains one loose end which has been the crucial point of controversy in this field, ever since Galston and Baker66 suggested in 1949 that the photoreceptor for phototropism might be a flavin Flavin absorbs in the near UV, /3-carotenoid does not. 

Nevertheless, the avena coleoptile exhibits a curvature to unilateral UV-illumina-tion with a satisfactory log-linear response/time relationship38) (the bending mode is similar to that observed for the second positive curvature which develops from the coleoptile base cf. 2.2). Fig. 5 338) shows that the double-peaked action spectrum does not match neither flavin (Fig. 5 5,16S)) nor carotenoid absorption (Fig. 5 4,183)), most likely excluding both as photoreceptors. The growth hormone auxin (cf. 2.4 and Scheme 1) has been discussed to be a possible photoreceptor. However, in this case, this is not supported by the action spectrum either. 

Table 1. Bluelight induced bending of decapitated avena coleoptiles with different fillings, with and without application of the growth-hormone auxin (cf. Sect. 2.4). Clearly the quantity of bending depends on the intrinsic light gradient (after v. Guttenberg75)).

The most photosensitive part of the coleoptile with respect to phototropism is the apical 50 qm-zone. The first millimeter of the tip is 160 times more sensitive than the second, and the second millimeter 1,800 times more sensitive than the third 108h In 1937, Bunning29 showed by microchemical method that there is a high concentration of carotenoid (lutein) below the tip of the avena coleoptile, from 250 jum to 2 mm below this point and just in the extreme tip no carotenoid is found. This calls in question whether the enormous local differences in sensitivity can solely be caused by corresponding different absorption gradients. This doubt is further substantiated by the fact, that carotenoid deficient mutants (containing 5 to 10% of the normal siblings) show normal phototropic sensitivity. 

If only the extreme apex of the oat coleoptile is irradiated unilaterally, curvature nevertheless develops normally, migrating down to the light shielded region (first positive curvature). This observation led to the demonstration by Boysen-Jensen in 191018), showing that the principle causing curvature could be transmitted across... 

Fig. 10. Diffusion of auxin into agar blocks in three hours from corn coleoptile tips. The numbers given are curvatures obtained from a standard auxin test, i,.e. a measure for the auxin diffused into the agar. (A) dark control bisecting does not significantly reduce the total amount of auxin. Unilateral bluelight (B) the total amount of flavin is not significantly reduced by irradiation (C) partial bisecting indicates strong lateral-basipetal auxin transport23). (D) Radio-actively labeled auxin, symmetrically applied to the coleoptile tip, proves the conclusion drawn from experiment (C)13 G...

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