Studies on soluble RNA binding indoleacetic acid in etiolated mung bean hypocotyl sections

Nucleic acid was extracted by the SLS-phenol method from Phaseolusaureus hypocotyl treated with IAA-2-¹⁴C. Radioactivity in thenucleic acid fraction was found at the positions of sRNA andrRNA on an MAK column. IAA-¹⁴C was released from the radioactivecompound(s) in the sRNA fraction, by alkaline hydrolysis, butnot by ethanol extraction, or by dialysis to 2 M NaCl, 8 M urea,and 0.1 M EDTA. When the radioactive compound at the positionof sRNA on an MAK column was further re-chromatographed on aDEAE-cellulose column and on a BD-cellulose column, it was alwayslocalized only in a settled part of the fraction of each column.From this fraction IAA-¹⁴C was released by alkaline hydrolysis.Also, IAA-¹⁴C was released from the radioactive compound insRNA fraction, by RNase digestion, but not by pronase treatment.Results of these experiments suggest the existence of some kindsof sRNA binding IAA. The genesis of this sRNA binding IAA-¹⁴Cwas observed within 30 min after the supply of IAA-¹⁴C, andthe sRNA became saturated with IAA-¹⁴C about 2 hr after thebeginning of incubation. The behavior of sRNA binding IAA, representedby sRNA binding IAA-¹⁴C, may have a role in IAA induced growthof mung bean hypocotyl sections. (Received July 6, 1971; )     

Phytochrome and potassium uptake by mung bean hypocotyl sections

Uptake of potassium (K) and ⁸⁶rubidiumlabelled potassium (⁸⁶Rb) by sub-hypocotyl hook sections of Phaseolus aureus L. was inhibited by red light. The effect was reversible with far red light. Using short exposures of high irradiance the effect on ⁸⁶Rb-labelled K uptake was observed after 5 min. The response showed no specificity for a particular anion. Uptake of ⁸⁶Rb-labelled K by sections cut immediately below the cotyledons was enhanced by red light after 10 min incubation and was also far red reversible. These results are interpreted as a rapid phytochrome-induced change in membrane properties resulting in modified K uptake.Abbreviations P Phytochrome - Pr red absorbing form of P - Pfr far red absorbing form of P - R red light - F far red light     

The stimulation of indoleacetic acid synthesis in bush bean plants (Phaseolus vulgaris L.) by naphthenates

A 12 hr seed soak in a solution of 100 ppm of potassium naphthenatesresulted in 140.5% stimulation of IAA synthesis determined in5–8 cm tips of epicotyls of 14-day-old dark-grown Phaseolusvulgaris seedlings. (Received September 1, 1973; )     

Regulation of sterol biosynthesis in etiolated mung bean hypocotyl sections

The incorporation of radioactivity into sterols by transmethylation of methionine-[¹⁴C-methyl] was studied in mung bean hypocotyl sections. Young hypocotyl sections (1 cm) synthesized 4 times more radioactive sterols than older sections (5 cm). The transmethylation reactions may be rate limiting in older tissues. Wounding has only a quantitative effect on sterol biosynthesis, as seen by incorporation experiments with MVA-[2-¹⁴C]. Naphthalene acetic acid (NAA) stimulates sterol biosynthesis in both wounded surfaces and intact tissues of mung bean hypocotyl sections.     

Development of isoperoxidases along the growth gradient in the mung bean hypocotyl

Cytoplasmic and wall bound peroxidases were extracted from successive segments of decreasing growth potential along the mung bean hypocotyl. Active wall bound peroxidases were present in the epidermis and external parenchyma layers at the end of the elongation phase. Two fast migrating anionic isoperoxidases covalently bound to the cell walls increased when the cell walls lost their plasticity. These isoenzymes were characterized by a high affinity for several peroxidase substrates and high thermal stability.     

Studies on the initiation of adventitious roots on mung bean hypocotyl

During the early stages of root induction in hypocotyls of mungbean cuttings, four new peroxidase isoenzymes are formed inthat part of the cutting that produces roots. These isoenzymesare in addition to and different from the three already presentin the hypocotyl. Forty-eight hr is required for the changeto take place from the original three to seven isoenzymes. Thechange in isoenzyme pattern and root initiation itself are retardedwhen streptomycin is applied during the very early stages ofroot induction. However, during the latter part of the first24-hr period after the cutting is made and when some of thenew isoenzymes have already been formed, the rooting processbecomes insensitive to this antibiotic. Cytologically, the occurrenceof cell division is paralleled by the formation of the fournew peroxidase isoenzymes. The delay in the occurrence of celldivision caused by the presence of streptomycin is paralleledby a similar delay in the formation of the four new isoenzymes. (Received November 27, 1970; )     

Heat shock increases chilling tolerance of mung bean hypocotyl tissue

The effects of heat shock on the chilling tolerance of mung bean [Vigna radiata (L.) Wilczek] seedling tissue were studied by using two measurements of chilling injury: increased 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity and solute leakage. ACC oxidase activity (measured as ACC-induced ethylene production) of freshly excised mung bean hypocotyl segments was highly dependent on the temperature at which the seedlings were grown. However, this highly temperature-dependent level of ACC oxidase activity was probably a wound response since it was almost entirely eliminated by incubating the excised segments at 20°C for 3 h. In contrast, heating of excised segments to 40°C for up to 4 h resulted in a time-dependent increase in ACC oxidase activity which was sensitive to cycloheximide, indicating rapid protein synthesis during the heat treatment. ACC oxidase activity fell sharply during subsequent chilling at 2. 5°C. After 3 days of chilling, all treated segments, regardless of their initial ACC oxidase activity, showed a decline to the same low activity level and ACC oxidase activity continued to fall slowly for up to 9 days at 2. 5°C. Hypocotyl segments excised from seedlings held at 15°C showed no change in solute leakage, but leakage increased rapidly when seedlings were either chilled at 2. 5°C or heated to 32°C (just below the heat shock temperature). Chill-induced leakage from non-heat-shocked segments increased steadily with chilling duration and was unaffected by cycloheximide concentration up to day 6. Within the elevated rate of leakage on day 9, however, leakage was lower from segments exposed to 10 and 50 μM cycloheximide. Solute leakage was markedly reduced for up to 9 days when segments were heat shocked at 40°C for 3 or 4 h with or without 10 M cycloheximide, but the presence of 50 μM cycloheximide caused an initial doubling of solute leakage and a 3-fold increase after 3 days of chilling. Cycloheximide prevented formation of heat shock protection against chilling from the start at 50 μM and after 9 days at 10 μM. These results indicate that the protection afforded by heat shock against chilling damage is quantitative and probably involves protein synthesis.     

Influence of ethylene on adventitious root formation in mung bean hypocotyl cuttings

The relationship between ethylene and adventitious root formation in mung bean hypocotyl cuttings was studied.Ethephon, an ethylene-releasing compound, at 5 x 10 -5 M increased root number and root dry weight on hypo-cotyl cuttings. When ethephon was applied to hypocotyl at different times after excision, there were two effectivetimes for root production i.e. between 06 h and 18-24 h. These two time periods correspond to the induction phase and the late initiation phase of root development, respectively. After excision, three peaks of ethylene productionwere observed. The first peak commencing at 6 h started the sequence of reactions leading root formation, the second peak appearing at 12 h coincided with the beginning of the increase of the IAA level during primordia initiation, and the third peak showing at 48 h played a role in root differentiation and growth. Ethylene stimulated rooting by enhancing the increase in auxins. Thus it appears that the IAA-induced ethylene production may be a factor involved in the stimulation of adventitious root formation.     

A rapid gravitational effect on the translocation of fluorescein in mung bean hypocotyl sections

Geotropic stimulation of excised stems of dark-grown mung bean seedlings (Vigna radiata L., Wilczek) results in a rapid increase in the movement of fluorescein in phloem cells of the hypocotyl. A significant effect is observed after subjecting stems to geotropic stimulation for 2.5 min. Maximum increase occurs after about 15 or more min of geotropic stimulation. The increase is confined to the lower side of the hypocotyl. Pretreatment with a 5x10^-4 M concentration of 2,4-dinitrophenol prevents the gravity-induced increase in fluorescein movement. It is suggested that the increased movement of fluorescein is due to the generation of a positive electrostatic charge in the plasma membrane of receptor cells by some unknown action of gravity on membrane molecules. The charge is presumed to be the causative factor that increases the movement of auxin and other negatively-charged substances into receptor cells.     

Effect of the defoliant thidiazuron on ethylene evolution from mung bean hypocotyl segments

The effect of the defoliant thidiazuron (N-phenyl-N′1,2,3-thiadiazol-5-ylurea) on ethylene evolution from etiolated mung bean hypocotyl segments was examined. Treatment of hypocotyl segments with concentrations of thidiazuron equal to or greater than 30 nanomolar stimulated ethylene evolution. Increased rates of ethylene evolution from thidiazuron-treated tissues could be detected within 90 minutes of treatment and persisted up to 30 hours after treatment. Radioactive methionine was readily taken up by thidiazuron-treated tissues and was converted to ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) and an acidic conjugate of ACC. Aminoethoxyvinylglycine, aminooxyacetic acid, cobalt chloride, and α-aminoisobutyric acid reduced ethylene evolution from treated tissues. An increase in the endogenous content of free ACC coincided with the increase in ethylene evolution following thidiazuron treatment. Uptake and conversion of exogenous ACC to ethylene were not affected by thidiazuron treatment. No increases in the extractable activities of ACC synthase were detected following thidiazuron treatment.     

硝普钠（SNP）对绿豆下胚轴插条生根的影响

研究了SNP对绿豆下胚轴插条生根的影响.结果表明,SNP促进下胚轴插条生根的最适浓度和最佳时间分别为300μmol*L-1和24 h,最适浓度SNP对6 d龄幼苗下胚轴插条生根促进效果最好,对下胚轴插条的生根促进效应显著大于其余插条.同时就SNP、IBA和NAA对不定根发生的影响进行了比较研究.     

Effect of 6-benzyladenine on the initiation of adventitious roots on mung bean hypocotyl

Cuttings incubated with 6-benzyladenine showed extensive celldivision and tracheid differentiation in the cortex and rootprimordia did not form. The histological and enzyme data suggestthat the formation of isoperoxidases is associated with theearly differentiation of specialized parenchyma cells involvedin the formation of root primordia. (Received June 13, 1973; )     

甘蔗废糖蜜对绿豆插条下胚轴生根的影响

本文研究甘蔗废糖蜜对绿豆插条下胚轴生根的影响,结果表明,1000~7000mg/L浓度范围内的甘蔗废糖蜜能明显增加绿豆插条下胚轴不定根的数目、根长、根干重及生根范围,并促进不定根内可溶性糖含量和不定根系活力提高。     

Caffeic acid affects early growth, and morphogenetic response of hypocotyl cuttings of mung bean (Phaseolus aureus)

Caffeic acid (CA) is one of the most common cinnamic acids ubiquitously present in plants and implicated in a variety of interactions including allelopathy among plants and microbes. This study investigated the possible interference of CA with root growth and the process of rhizogenesis in hypocotyl cuttings of mung bean (Phaseolus aureus=Vigna radiata). Results indicated that CA (0-1000 microM) significantly suppressed root growth of mung bean, and impaired adventitious root formation and root length in the mung bean hypocotyl cuttings. Further investigations into the role of CA in hampering root formation indicated its interference with the biochemical processes involved in rooting process at the three stages - root initiation (third day; RI), root expression (fifth day; RE), and post-expression (seventh day; PE) - of rhizogenesis. CA caused significant changes in the activities of proteases, peroxidases (PODs), and polyphenol oxidases (PPOs) during root development and decreased the content of total endogenous phenolics (TP) in the hypocotyl cuttings. The enhanced activity of PODs and PPOs, though, relates to lignification and/or phenolic metabolism during rhizogenesis; yet their protective role to CA-induced stress, especially during the PE phase, is not ruled out. At 1000 microM CA, where rooting was significantly affected, TP content was very high during the RI phase, thus indicating its non-utilization. The study concludes that CA interferes with the rooting potential of mung bean hypocotyl cuttings by altering the activities of PODs and PPOs and the endogenous TP content that play a key role in rhizogenesis.     

Promotion of rooting in mung bean hypocotyl cuttings with ethrel, an ethylene releasing compound

Ethrel increased the number of roots on mung bean hypocotylcuttings under continuous illumination but decreased their length.IAA, GA₃) kinetin and TIBA inhibited both the number and length.Inhibitory effect of GA3 and kinetin on root number was overcomeby ethrel but on root length was enhanced. Ethrel in combinationwith IAA promoted the number and length of roots synergisticallybut enhanced the inhibitory effect of TIBA on both. (Received June 27, 1970; )     

Inhibition of IAA-induced ethylene production in etiolated mung bean hypocotyl segments by 2,3,5-triiodobenzoic acid and 2-(p-chlorophenoxy)-2-methyl propionic acid

The effect of two auxin antagonists, 2,3,5-triiodobenzoic acid (TIBA) and 2-( p -chlorophenoxy)-2-methyl propionic acid (CMPA) on IAA-induced ethylene production in etiolated mung bean hypocotyl ( Vigna radiata L. Rwilcz cv. Berken) segments was studied. Both TIBA and CMPA inhibited IAA-induced ethylene production and CO₂ production at concentrations from 0.001 m M to 0.1 m M and 0.01 m M to 1.0 m M , respectively. The optimum concentration for inhibition of ethylene production by TIBA was 0.05 m M and CMPA was 0.5 m M . At the optimum concentration of TIBA and CMPA, there was a significant decrease in IAA-induced ethylene production without a decrease in respiration rates below control levels. After 18 h, mung bean hypocotyl segments treated with 0.05 m M TIBA for 6 h or 0.5 m M CMPA for 8 h showed a maximum inhibition of IAA-induced ethylene production. Treatments longer than 8 h caused no further inhibition. The uptake of [¹⁴C]-naphthaleneacetic acid by mung bean segments was greatly reduced by the addition of either TIBA (0.05m M ) or CMPA (0.5 m M ) to the incubation media. The results of treatment sequences showed that TIBA needed to be applied prior to IAA in order to inhibit IAA-induced ethylene production, but CMPA caused the same inhibitory effect whether applied before or after IAA treatment. These findings provide evidence that TIBA inhibits auxin-induced ethylene production in etiolated mung bean hypocotyl segments by blocking auxin movement into the tissue whereas CMPA may work on both auxin transport and action.     

Inhibition of auxin-induced ethylene production by salicylic acid in mung bean hypocotyls

Salicylic acid (SA), a common plant phenolic compound, influences diverse physiological and biochemical processes in plants. To gain insight into the mode of interaction between auxin, ethylene, and SA, the effect of SA on auxininduced ethylene production in mung bean hypocotyls was investigated. Auxin markedly induced ethylene production, while SA inhibited the auxin-induced ethylene synthesis in a dose-dependent manner. At 1 mM of SA, auxininduced ethylene production decreased more than 60% in hypocotyls. Results showed that the accumulation of ACC was not affected by SA during the entire period of auxin treatment, indicating that the inhibition of auxin-induced ethylene production by SA was not due to the decrease in ACC synthase activity, the rate-limiting step for ethylene biosynthesis. By contrast, SA effectively reduced not only the basal level of ACC oxidase activity but also the wound-and ethylene-induced ACC oxidase activity, the last step of ethylene production, in a dose-dependent manner. Northern and immuno blot analyses indicate that SA does not exert any inhibitory effect on the ACC oxidase gene expression, whereas it effectively inhibits both the in vivo and in vitro ACC oxidase enzyme activity, thereby abolishing auxin-induced ethylene production in mung bean hypocotyl tissue. It appears that SA inhibits ACC oxidase enzyme activity through the reversible interaction with Fe²⁺, an essential cofactor of this enzyme. These results are consistent with the notion that ethylene production is controlled by an intimate regulatory interaction between auxin and SA in mung bean hypocotyl tissue.