Kinetin and Auxin Activity

The cytokinin benzyladenine inhibited endogenous hypocotyl elongation in intact etiolated seedlings of cucumber (Cucumis sativus L.). In hypocotyl segments, the inhibitory effect of benzyladenine on growth was clearly detectable in the presence of indoleacetic acid. Fusicoccin-induced elongation was unaffected by the presence of cytokinin. The effect of cytokinin on elongation of the segments was determined by measuring changes in fresh weight, a linear function of extension growth. The effect of benzyladenine on hypocotyl growth was at least as large in segments prepared from red-light-grown seedlings as in those from seedlings grown in total darkness. A comparison was made between the inhibitory effects of cytokinin and blue light. The use of the calcium chelator ethyleneglycol-bis(jB-aminoethyl ether)-N, N'-tetraacetic acid indicated that calcium ions are required for manifestation of benzyladenine-induced inhibition.on cucumber cotyledon expansion, and on inhibition of greening, than either inducer alone (4). In the same system, red light or cytokinin alone caused maximal acceleration of greening (4). The presence of cytokinin in the incubation medium was found to inhibit auxin-promoted extension growth of segments in several different species (7,18,24,26).We have studied the effects of BA3, a synthetic cytokinin, on stem elongation in dark-grown cucumber seedlings. We investigated whether BA would inhibit IAA-induced extension growth of hypocotyl segments. In addition, we compared suppression of growth by cytokinin and by blue light. Furthermore, we examined whether the cytokinin-induced inhibition of hypocotyl elongation depends on calcium, as reported for inhibition by blue light (23). In all these studies we adopted the technically easy and accurate method developed for assaying the effect of IAA on elongation based on cucumber hypocotyl weight increase (10). MATERIALS AND METHODSThe suggestion that plant hormones might serve as second messengers in the signal response cascade is supported by the fact that many light-regulated plant growth responses are reported either to involve changes in hormone level or to be mimicked by hormone application (for review, see 6,15,17). Photocontrol of stem elongation has been widely explored and documented (see refs. 6, 13). The effect of cytokinins on shoot elongation is less well known. Photoinhibition of stem elongation operates through at least two photoreceptors, phytochrome and cryptochrome(s) (1,5,11,12,14

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Similarity between Cytokinin and Blue Light Inhibition of Cucumber Hypocotyl Elongation

Cohen

Gepstein²,

Horwitz³

1991

“…Reexposure to high-intensity light following induction is asserted to be necessary both to stabilize the stimulus and to promote its translocation to the buds (3, 4, 6, 7). Other reports suggest that flowering may result from an interaction between endogenous and environmental rhythms (1,2,4), and still others indicate that Xanthium can become florally induced in continuous darkness (7,10).…”

Section: Sum Marymentioning

confidence: 99%

“…Inhibitors of root development from hypocotyls are known, e.g. kinetin inhibits root development by sunflower and bean hypocotyls (7,10). Lateral root formation in the segments is essentially polar, so it is likely on the basis of distribution that most of the root primordia were initiated after the cuts were made.…”

mentioning

confidence: 99%

Certain properties of hypocotyl of Impatiens balsamina reflecting physiological complexity

Arnold¹,

Alston²

1961

In the course of a studly of leucoanthocyanin synthesis in balsam hypocotyls (1) certain properties of specific regions of the hypocotyl were noted which were of particular interest. For example, if 5 cm hypocotyls from dark-grown plants were cut into ten segments of equal length and transferred to White's medium with agar and sucrose in light, the time-rate -of appearance of anthocyanin pigment was correlated with the origin of the segment. The upper segments (nearest the cotyledons) were the first in which anthocyanin appeared. Little or no anthocvanin formed, even in strong light, in the absence of sugar, but when sugar was present some pigment appeared in the absence of light. The combination light + sugar (sucrose, in this instance) yielded the most pigment. Surprisingly, in darkness with sugar, the pigment was not formed in segment 1 (adjacent to the cotyledons) which, in light, was the most efficient anthocyanin producer. Furthermore, segments of the hypocotyl differed in their ability to form hairs or lateral roots. Other manifestations, similar to the above, of the responsiveness of the balsam hypocotyl, together with additional practical advantages which will be enumerated, suggested that this species would be a good choice for a comprehensive study of growth and differentiation of the hypocotyl. The hypocotyl has been relatively neglected in favor of simple linear systems such as the root, but the complexity of the hypocotyl provides some problems of peculiar interest. For example, the hypocotyl is transitional between root and shoots, and undergoes extensive growth of essentially intercalary nature. Noel (13) has studied the site of growth in the balsam hypocotyl, using india ink markings. He also studied lateral root and epidermal hair formation in this species. He reported that at any stage 90 % of all subsequent growth occurred in the first 5 or 6 mm below the cotyledons. The region of active growth includes the hypoootyl arch which remains curved in darkness. Noel referred to the region as a pseudo-meristem. In our own investigation, numerous mitotic figures were observed through the hypocotyl arch of 10-day old seedlings. I Received Feb. 23, 1961.The balsam hypocotyl is a rich source of leucoanthocyanins; genetic strains are available w\vhich are anthocyanin-free or which differ qualitatively in the form of anthocyanin present (2). The hypocotyl therefore provides an excellent system for studving the physiology and biochemistry of anthocyanin synthesis while anthocyanin represents a labile overt physiological indicator, i.e. anthocyanin synthesis is quantitatively affected by numerous and diverse environmental factors.This initial paper includes information of essentially descriptive nature plus a series of experiments on pigmentation and root and hair formation in hypocotyl segments in light and darkness with and without addition of the sugars, sucrose and glucose. All data reported here are from seedlings with a hypocotyl length of about 50 mm. METHODSVaughan Seed Company's Scarlet Balsam (f1;...

“…The growth of the basal callus was also inhibited by kinetin. Other reports demonstrate the inhibitory effect of kinetin on buds, roots, and shoot formation in intact plant and plant tissues (4,5,8,23).In general, substances with cytokinin activity stimulated the growth of tobacco callus tissue, but high concentrations of them inhibited the growth of the same tissue (10,19). Cytokinins stimulate the synthesis of RNA and protein in plant tissue (16,21,22), in isolated nuclei (3, 17), and isolated mitochondria (1).…”

mentioning

confidence: 99%

Kinetin Inhibition of ³H-Uracil and ¹⁴C-Leucine Incorporation by Tobacco Cells in Suspension Culture

Nudel

Bamberger

1971

The rate of "4C-leucine and 3H-uracil incorporation by tobacco cells (Nicotiana tabaccum var. Samsun N.N.) in suspension culture was simultaneously decreased by the addition of kinetin at concentrations above 2.5 X 10-5 M.Ribosomal RNA was the first RNA species affected by kinetin. The purine derivatives, adenine and N6-methylaminopurine, which exhibit low cytokinin activity overcame the inhibitory effects of kinetin. However, purine derivatives without cytokinin activity, guanine, N6. -dimethylaminopurine, and 2-aminopurine, did not relieve kinetin inhibition.Since the early studies of cytokinins, it has been shown that in addition to their stimulatory effect on the growth of plant tissues they exhibited some inhibitory effects. Skoog and Miller (20) have shown that tobacco stem segments which were plated on medium containing 0.5 mg/l of kinetin formed only few buds, and that these buds were retarded in their growth. The growth of the basal callus was also inhibited by kinetin. Other reports demonstrate the inhibitory effect of kinetin on buds, roots, and shoot formation in intact plant and plant tissues (4,5,8,23).In general, substances with cytokinin activity stimulated the growth of tobacco callus tissue, but high concentrations of them inhibited the growth of the same tissue (10,19). Cytokinins stimulate the synthesis of RNA and protein in plant tissue (16,21,22), in isolated nuclei (3, 17), and isolated mitochondria (1). In this paper we studied the kinetics of the inhibition by high concentration of kinetin, of 3H-uracil, and '4C-leucine incorporation by tobacco cells in suspension culture. A preliminary report has been published elsewhere (14 3H-Uracil and 14C-Leucine Incorporation. The rate of incorporation of 3H-uracil and '4C-leucine was determined in suspensions of single cells and very small cell clusters. These suspensions were obtained by precipitating the large clusters and collecting the supernatant of the stock cultures. Unless otherwise mentioned in the text, radioactive precursors, hormones, or drugs were added to the suspensions at zero time. After varying periods of time, aliquots of the suspensions were transferred into trichloroacetic acid (10% final concentration) for 20 min. The cells were precipitated on Whatman fiberglass filters and washed with 5% trichloroacetic acid. Radioactivity was measured in a Packard Tricarb liquid scintillation spectrometer. Most of the 3H-and '4C radioactivity could be removed from the filters by treatment with ribonuclease A (Worthington) and pronase (Calbiochem), respectively.Labeling ofRNA with 32P, Extraction and Separation on Methylated Albumin Kieselguhr Columns. Four days prior to the labeling experiments, the cultures were transferred into a phosphate-poor medium (one-eighth of its concentration in the growth medium). Following the incubation of the cultures with 1 mc of carrier-free 32PO43-(Amersham) the tissue (10 g fresh wt) was collected on a precooled Buchner funnel and washed with an excess of ice cold water. The tissue was then froze...