Radish Hypocotyls Research Articles

Effects of High Temperature and Growth Retardant on Dry Matter Accumulation, Hypocotyl Thickening, Photosynthesis, and Sugar Content in Radish (Raphanus sativus L.) Plants

Radial thickening of radish hypocotyls is inhibited by high temperature, but the inhibition is reversed by the application of growth retardants. To study these phenomena, dry weight accumulation, net photosynthesis (Pn), and sugar contents of developing plants were determined. These results showed that photosynthetic ability of leaves and glucose and fructose contents decreased in the hypocotyls of plants grown at an elevated temperature. Growth parameters for quantitative growth were unaffected by the high temperature, whereas reducing sugar content was slightly increased by the application of the growth retardant uniconazole P. These results indicate that the growth retardant affected the process of reducing sugar accumulation, but not Pn directly.

FLOATING SYSTEM CULTIVATION OF RADISH (RAPHANUS SATIVUS L.): PRODUCTION AND QUALITY

FLOATING SYSTEM CULTIVATION OF RADISH (RAPHANUS SATIVUS L.): PRODUCTION AND QUALITY

A major factor in gravitropism in radish hypocotyls is the suppression of growth on the upper side of hypocotyls

The changes in length on the two opposite sides of etiolated radish (Raphanus sativus) hypocotyls prior to, and following gravitropic stimulation, were measured using an infrared-imaging system. It was observed that the growth suppression on the upper side began first at least 10 min after the onset of gravitropic stimulation, and after 30 min the acceleration in growth on the lower side started. The gravitropic curvature was steadily induced from 10 min. When radish hypocotyls were switched from a vertical to horizontal position for different durations and then replaced to the vertical position, the growth suppression on the gravity-stimulated (upper) side was observed in all cases, but the acceleration in growth on the opposite (lower) side appeared only in continuously gravity-stimulated seedlings, although it occurred later than the growth suppression on the upper side. These results suggest that the suppression in growth on the upper side of the hypocotyls is a direct effect of gravitropic stimulation, but not the acceleration on the lower side. When 4-methylthio-3-butenyl isothiocyanate (4-MTBI), which has an inhibitory activity against radish hypocotyl growth, was applied on the one side of radish hypocotyls and then the 4-MTBI-applied side or opposite side was placed in a horizontal position, the former showed greater bending than the control, suggesting that the growth suppression on the upper side is enhanced and maintained with MTBI application there. In the latter case, the seedlings showed less bending than the control, suggesting a decrease in growth on the lower side with MTBI application. All the results suggest that gravitropism of radish hypocotyls may be caused by an increase in growth-inhibiting substance(s) induced with gravitropic stimulation in the upper side, inducing growth inhibition there.

Synthesis and preliminary bioactivity evaluation of new pregnane brassinosteroid-like compounds

Seven new pregnane compounds bearing some representative A- and B-ring brassinosteroid functions, as well as hydrogen bond donor and acceptor ones on the D ring, were efficiently synthesized. The obtained compounds did not show remarkable plant growth-promoting activity in the radish hypocotyl elongation and cotyledon expansion bioassays, however, introducing oxygen and amino functions on the D ring led to an enhancement of the bioactivity. The 16β-functionalized pregnane brassinosteroid-like compounds were slightly more active than the 16α-functionalized ones.Key words: steroids, brassinosteroids, pregnane analogues.

4. Gravity-induced differential growth in radish hypocotyls

4. Gravity-induced differential growth in radish hypocotyls

Induction of myrosinase gene expression and myrosinase activity in radish hypocotyls by phototropic stimulation

The role of myrosinase (beta-thioglucoside glucohydrolase, EC 3.2.3.1) in the phototropic response in radish hypocotyls was investigated. Unilateral illumination with blue light abruptly up-regulated the activity of myrosinase, which releases bioactive 4-methylthio-3-butenyl isothiocyanate (MTBI) from inactive 4-methylthio-3-butenyl glucosinolate (MTBG), in the illuminated halves of radish hypocotyls 10 min after onset of phototropic stimulation, peaking after 30 min and decreasing thereafter. The myrosinase activity in the shaded halves also increased, but was significantly lower than that in the illuminated halves. Furthermore, whether blue light illumination induces myrosinase gene expression was studied. Northern blotting analysis indicated that myrosinase mRNA levels were increased markedly in unilaterally illuminated hypocotyls, reaching maximum signal intensity within 10 min after onset of blue illumination, declining nearly to the control level thereafter. These results suggested that phototropic stimulation promotes myrosinase gene expression and myrosinase activity in the illuminated side, resulting in the conversion of inactive MTBG to active MTBI and simultaneously producing more active raphanusanins, causing a phototropic response.

Enhancement of anthocyanin biosynthesis by sugar in radish ( Raphanus sativus) hypocotyl

Radish ( Raphanus sativus) hypocotyl accumulates anthocyanins as the plant grows. Although anthocyanins were detected in both the peripheral cortex and pericycle, the major site of accumulation was the pericycle. Detached hypocotyls of radish seedlings produced large amounts of anthocyanins using exogenous glucose, fructose, or sucrose, but little anthocyanin using mannose or 3- O-methyl- d-glucose. Treatment with 175 mM sucrose was most effective in inducing anthocyanin biosynthesis in the hypocotyl system. Two anthocyanin biosynthetic genes, chalcone synthase and anthocyanidin synthase, were significantly activated by sucrose, whereas these genes were expressed weakly in the control. These results suggested that sugars transported into hypocotyls promote anthocyanin biosynthesis by inducing expression of the biosynthetic genes in radish.

Spatial and temporal distribution of sucrose synthase in the radish hypocotyl in relation to thickening growth.

Sucrose synthase (SuSy) is a key enzyme in the development of storage root of radish. Clarification of its spatial and temporal expression during the thickening growth of radish hypocotyl, which later develops into storage root, was carried out immunologically using light microscopy. Sequential harvests at 3, 7, 11 and 13 d after sowing (DAS) were performed on two radish cultivars having different sink capacity. A very low level of SuSy was observed 3 DAS for both cultivars. White Cherrish (WC; strong storage root) showed the maximum level of SuSy between 7 and 11 DAS with increased cell development (thickening), while in Kosena (K; low storage root) the level remained high after 13 d of growth. A high level of SuSy was found in companion cells, which was consistent with previous observations, but SuSy was also found in the xylem parenchyma and in some cortical cells. The level of SuSy differed according to the localization and depended highly on cell development. Both cell division and cell enlargement were stimulated in WC compared with K. The role of SuSy during thickening growth of radish hypocotyl is discussed in terms of utilizing photosynthates.

Chemistry and biology of phototropism-regulating substances in higher plants.

Most people are familiar with the sight of a young seedling bending towards a window or the brightest source of light to which it is exposed. This directional growth response is known as phototropism, which is caused by a lateral growth-promoting auxin in the bending organ (Cholodny-Went theory, cited in high school textbook). Recently, however, Bruinsma et al., Weiler et al., and Hasegawa et al. independently found that the shaded half did not contain more auxin than the illuminated one. Instead it was found that the even distribution of auxin was accompanied by a lateral gradient of growth inhibiting substances during phototropic curvature (Bruinsma-Hasegawa theory). We have isolated some photo-induced growth inhibitory substances related to phototropism, benzoxazolinones from light-grown maize shoots (Zea mays L.), raphanusanins from radish hypocotyl (Raphanus sativus var. hortensis f. gigantissimus M.), indolyacetonitrile from light-grown shoots (Brassica oleacea L.), 8-epixanthatin from sunflower hypocotyl (Helianthus annus L.), and quite recently uridine from oat coleoptile (Avena sativa L.). Chemical analyses have shown phototropic stimulations to cause curvature by inducing a local unequal distribution of growth-inhibiting substances that antagonize auxin in its cell-elongating activity. Finally, a model is presented for further studies on phototropism.

Phototropic stimulation induces the conversion of glucosinolate to phototropism-regulating substances of radish hypocotyls

The distribution of natural growth inhibitors, the raphanusanins (isomers of 3-(methylthio)methylene-2-pyrrolidinethione) and their precursors (4-methylthio-3-butenyl glucosinolate (MTBG) and 4-methylthio-3-butenyl isothiocyanate (MTBI)), between illuminated and shaded halves of radish hypocotyls during phototropic curvature was analyzed using a physicochemical assay. Phototropic stimulation rapidly decreased MTBG content, and abruptly increased contents of MTBI and raphanusanins in the illuminated halves of radish hypocotyls within 30 min after the onset of unilateral illumination. Content in the shaded halves was similar to that in dark controls. When MTBG, MTBI, and raphanusanins at endogenous levels were applied unilaterally to etiolated hypocotyls, MTBI and raphanusanins caused hypocotyls to bend but MTBG showed no activity. Blue illumination promoted myrosinase (thioglucosidase) activity, which releases MTBI from MTBG, in hypocotyls after 10 min, although enzyme activity in dark controls did not change. These results suggest that phototropic stimulation promotes myrosinase activity in the illuminated side of radish hypocotyls, releasing bioactive MTBI from inactive MTBG and simultaneously producing bioactive raphanusanins.

Development of Sink Capacity of the "Storage Root" in a Radish Cultivar with a High Ratio of "Storage Root" to Shoot

The mechanisms that control sink capacity are poorly understood. In radish, a major sink is the storage root, which begins to thicken early in development, mainly as a result of thickening of the hypocotyl. We investigated changes in the accumulation of dry matter, sink activity (increase in dry weight of the hypocotyl per unit of dry weight present per unit of time), carbohydrate content, levels of metabolites, activities of enzymes related to the breakdown of sucrose, and the profile of soluble proteins, as well as changes in anatomy, using hypocotyls of a cultivar with a high ratio of storage root to shoot. We found that sink activity was strongly related to the level and activity of sucrose synthase but not to the activity of invertase. We also found a significant correlation between sucrose content and the level and activity of sucrose synthase. Our results suggest that sucrose synthase, but not invertase, might be critical for the development of the sink activity of the radish hypocotyl and that the level of sucrose might regulate the expression of sucrose synthase. A discussion of sink capacity is presented that includes consideration of structural changes in the hypocotyl.

Soluble sinapoyl esters are converted to wall-bound esters in phenylalanine ammonia-lyase-inhibited radish seedlings

Between the third and eighth day of radish seedling growth, wall-bound esters of (E)-sinapic and (E)-p-coumaric acids increase about fourfold, (E)-ferulic acid about sixfold, in the cotyledons. In the hypocotyl plus roots, wall-bound ferulic and p-coumaric acids increase twofold but wall-bound sinapic acid levels are unchanged. When grown with 100 μM 2-aminoindan-2-phosphonic acid (AIP), a competitive inhibitor of phenylalanine ammonia-lyase (PAL), cotyledons had levels of wall-bound sinapic acid similar to controls but there was no detectable wall-bound p-coumaric acid and only traces of wall-bound ferulic acid. As seedlings developed, their decrease in soluble sinapoyl esters greatly exceeded levels of wall bound sinapic acid accumulated. We interpret this as evidence that de novo hydroxycinnamic acid synthesis was blocked and preformed soluble sinapoyl esters stored in the cotyledons were mobilized and esterified into developing cell walls. Growth with 5 μM AIP inhibited wall-bound p-coumaric and ferulic acid accumulation more than 90% in the hypocotyl plus roots and slightly increased hypocotyl elongation, suggesting that wall-bound phenolics may normally play a role in restricting radish hypocotyl cell wall extensibility.

Water channel does not limit evaporation of water from plant cells

Evaporation of water from the cell surface of the internode ofChara corallina was not affected by HgCl2 which is known to inhibit water channels. This makes a sharp contrast to the fact that most of osmotically driven water transport is inhibited by HgCl2. Also in radish hypocotyls whose epidermis had been peeled off, evaporation of water was not inhibited by HgCl2, while osmotic water transport was significantly inhibited.

Enzymatic formation of plant cerebroside: properties of UDP-glucose: ceramide glucosyltransferase in radish seedlings.

The activity of cerebroside synthase (UDP-glucose: ceramide glucosyltransferase) was found in the microsomal fraction of radish hypocotyls, and was studied. One % of the radioactivity due to UDP-[3H]glucose added to the membrane fraction was incorporated into cerebroside within 60 min. Optimum pH and temperature of the activity were pH 7.8 and 30 degrees C, respectively. No metal ions enhanced the cerebroside synthase activity, dissimilar to that in animal tissues. The apparent Km for UDP-glucose was approximately 200 microM. The same activity was also observed in radish roots and cotyledons, but proportions of UDP-[3H]glucose incorporation were slightly lower than that in hypocotyls. Exogenous ceramide species having trihydroxy sphingoid bases, which were major ceramide components of radish cerebrosides, usually stimulated cerebroside formation in microsomal fractions from radish seedlings, while any ceramide types having dihydroxy sphingoid bases were ineffective on the glucosylation reaction. It was assumed, therefore, that cerebroside synthase in radish seedlings would have substrate selectivity for ceramide species.

Starch content of etiolated radish (Raphanus sativus L.) hypocotyls as affected by chloramphenicol and external sucrose

Abstract Starch was enzymatically assayed in the hypocotyls of radish (Raphanus sativus L.) seedlings grown in water or chloramphenicol (CAP) 1 × 104. CAP inhibits starch formation and its effect is related to the concentration. Both CAP- and water-grown hypocotyls are able to accumulate starch when sucrose is supplied in the medium, thus suggesting that the damage caused by CAP to the amyloplast is not irreversible. Apical segments of both water- and CAP- grown hypocotyls accumulate starch upon incubation in sucrose solutions while basal segments are unable to accumulate starch even in the presence of sucrose. The authors suggest that the basal segments are unable to perform sucrose uptake or that the amyloplast is incapable to starch synthesis. In any case the inability of the basal segment to perform sucrose uptake is independent of CAP. These findings confirm that the radish hypocotyls is not homogeneous along its axes.

Chemical studies on 4-methylthio-3-butenyl isothiocyanate from roots of japanese radish(Raphanus sativus L.) in connection with raphanusanins, phototropism-regulating substances of radish hypocotyls

4-Methylthio-3-butenyl isothiocyanate as the direct precursor of raphanusanins has been isolated from the commercially available radish (Raphanus sativus L.), and some chemical studies on 4-methylthio-3-butenyl isothiocyanate (MTB-ITC) have been carried out, where it has been spontaneously converted into raphanusanins, phototropism-regulating substances of radish hypocotyls, in MeOH-H2O as well as in H2O solution.

Study on the Allelopathy of Alfalfa(Medicago sativa L.). I. Observation of allelopathy and survey for substances inducing growth inhibition.

Allelopathic effects of alfalfa (Medicago sativa L.) plants were investigated using soil previously grown with alfalfa (alfalfa soil). Alfalfa soil inhibited the emergence of alfalfa seeds and also the growth of alfalfa and radish. Methanol extracts from the alfalfa soil markedly inhibited the elongation of radish hypocotyl and alfalfa radicle, suggesting the presence of allelopathic substances. The incorporation of cut pieces of alfalfa shoots in the soil reduced seed emergence, hypocotyl elongation and dry weight in radish seedlings to 65, 73 and 81%, respectively, compared to the control. Aqueous extracts of alfalfa plants inhibited the elongation of radish hypocotyl and alfalfa radicle. Inhibition increased with increasing concentrations. Inhibition of radish hypocotyl and alfalfa radicle elongation was greater in root extracts than in shoot extracts. The presence of phenolic compounds as allelopathic substances in alfalfa soil, as well as in the alfalfa plant, was suggested using color reaction with diazotized sulfanilic acid.

Mode of action of natural growth inhibitors in radish hypocotyl elongation – influence of raphanusanin on auxin‐mediated microtubule orientation

Raphanusanin is a plant growth‐inhibiting substance which plays an important role in light growth inhibition and phototropism of radish hypocotyls. We investigated the effect of raphanusanin on indole‐3‐acetic acid (IAA)‐mediated orientation of microtubules (MT) in the outer epidermal cells of radish hypocotyl segments using immunofluorescence microscopy. IAA‐mediated MT reorientation preceded cell elongation induced by IAA. A change of IAA‐mediated MT orientation from longitudinal to transverse started within less than 15 min after IAA treatment, while significant growth promotion induced by IAA was found within about 30 min. The IAA‐mediated transverse MT orientations were significantly inhibited by simultaneously added raphanusanin. We also investigated the effect of raphanusanin on the MT orientation of the segments pretreated with IAA. The change of MT orientation induced by raphanusanin preceded growth inhibition of the segments. Within about 60 min after its application, raphanusanin initiated inhibition of the steady‐state elongation pre‐induced by IAA, while IAA‐mediated transverse MT orientations started to change into longitudinal orientations within less than 30 min after application of raphanusanin. Based on these results, it is suggested that raphanusanin induces growth inhibition through interference with the auxin‐mediated MT orientations.

Mode of action of natural growth inhibitors in radish hypocotyl elongation - influence of raphanusanin on auxin-mediated microtubule orientation

Mode of action of natural growth inhibitors in radish hypocotyl elongation - influence of raphanusanin on auxin-mediated microtubule orientation

The Site of Reception of Phototropic Stimulation and the Occurrence of Growth Inhibitors in Radish Seedlings

Summary To investigate whether the cotyledons and/or apex of seedlings of radish (Raphanus sativus var. hortensis f. gigantissimus Makino) are necessary for the perception of phototropic stimulus, they were removed immediately before unilateral illumination that induced the curvature. Their excision did not significantly reduce the phototropic curvature of the hypocotyls. The influence of removal of cotyledons and apex on the distribution of the growth inhibitors, cis- and trans-raphanusanins and raphanusamide, between lighted and shaded halves of hypocotyls was investigated using a physicochemical assay. The lateral gradient of the growth inhibitors between the lighted and shaded halves was little influenced by the removal. The gradient was caused by light-induced biosynthesis at the lighted side. These results show that in radish hypocotyls the phototropic stimulus is absorbed directly by the hypocotyl and that the inhibitors that induce the curvature in this plant increase at the lighted side of the hypocotyls.