Showing papers on "Kinetin published in 1978"

Modification of disease resistance of tobacco callus tissues by cytokinins.

Abstract: The effects of differing cytokinin and auxin concentrations on resistance of tobacco (Nicotiana tabacum L.) tissue cultures to race 0 of Phytophthora parasitica var. nicotianae were examined. With 1 micromolar kinetin and either 11.5 micromolar indoleacetic acid or 1 micromolar 2,4-dichlorophen-oxyacetic acid, tissues from resistant cultivars exhibited a “hypersensitive” reaction to zoospores of the fungus and subsequently were colonized only slightly. With susceptible cultivars or with tissues from resistant cultivars supplied with higher cytokinin levels (e.g. 10 micromolar kinetin), this hypersensitive reaction did not occur and tissues were heavily colonized. Benzylaminopurine and kinetin were particularly effective in eliminating both the hypersensitive reaction and disease resistance. Zeatin and 6-(3-methyl-2-butenylamino)purine were less effective. Increases in indoleacetic acid levels reversed the effects of high cytokinin concentrations. The balance of phytohormones apparently controls the host response to the fungus; thus, in this system, resistance or susceptibility can be studied without changing either host or fungal genotype.

In vitro induction of androgenic plantlets inAesculus hippocastanum

Abstract: Horsechestnut anthers were isolated from flower buds in various stages of development and cultivated in the presence of auxin and kinetin. The anthers showed the capacity for androgenesis and evidence is presented that the plantlets developed from single microspores. Haploid karyotypes were observed in the root menstem cells in three plantlets.

Abscisic Acid Induces Formation of Floating Leaves in the Heterophyllous Aquatic Angiosperm Potamogeton nodosus.

Abstract: Potamogeton nodosus tubers produce floating-type instead of submersed-type leaves when exposed to 10 –5 molar synthetic abscisic acid. Abscisic acid-induced leaves have stomata on upper leaf surfaces and higher width/length ratios than controls. These effects are wholly or partially overcome by simultaneous exposure to abscisic acid combined with gibberellic acid, kinetin, or benzyladenine.

The hormonal control of organ formation in callus of medicago sativa l. cultured in vitro

Abstract: Organogenesis in alfalfa callus (Medicago sativa L. cv. 'Regen S') has been obtained by the transfer of callus from an induction medium containing growth regulators to a regeneration medium lacking growth regulators. The transfer of callus from induction medium containing high levels of 2,4-D and low levels of kinetin to regeneration medium resulted in the formation of shoots. Conversely, the transfer of callus from induction medium containing low levels of 2,4-D and high levels of kinetin resulted in the formation of roots. The pattern of organogenesis on regeneration medium was modified by the nutritional composition of that medium. When Blaydes medium supplemented with inositol and yeast extract was employed as regeneration medium, root organogenesis was inhibited. Root organogenesis was not inhibited by either Shenk and Hildebrandt medium or Gamborg's B5 medium. Shoot formation occurred on all of these media. A survey of the in vitro organ-forming capacity of 14 genotypic clones from the cv. 'Regen S' was conducted. The capacity to form organs differed quantitatively among the clones analyzed. A more detailed analysis of a highly responsive clone (RA3) and a poorly responsive clone (RA5) revealed no significant qualitative difference in their organogenic responses. THE regeneration of shoots from in vitro cultures

Properties of a high-affinity cytokinin-binding protein from wheat germ.

Abstract: A soluble protein that interacts with a range of cytokinins was extensively purified from wheat (Triticum aestivum L.) germ. This protein has a K d for kinetin of 2×10-7 M. The binding of kinetin to the protein is inhibited by low concentrations of synthetic and naturally-occurring cytokinins including N6-benzyladenine, N6-benzyladenosine, kinetin riboside, N6-dimethylallyladenine, N6-dimethylallyladenosine, zeatin, zeatin riboside, N6-dimethyladenine and N6-dimethyladenosine. Adenine, adenosine and several non-N6-substituted adenine derivatives were ineffective as inhibitors of kinetin binding. While N6-butyryl-3′,5′-cyclic AMP, N6,2-O′-dibutyryl-3′,5′-cyclic AMP and 2′,3′-cyclic AMP inhibited binding of kinetin to the protein, 3′,5′-cyclic AMP was ineffective. The kinetin-binding protein is heat-labile and pronase-sensitive. Kinetin-binding activity exactly co-chromatographs with a single peak of carbohydrate and protein on gel-filtration and is displaced from concanavalin A-Sepharose 4B by α-methylglucoside. On gel filtration, the kinetin-binding protein behaves as a soluble protein with an apparent molecular weight of 180,000 daltons.

Comparative analysis of the action of cytokinin and light on the formation of ribulosebisphosphate carboxylase and plastid biogenesis

Abstract: The role of cytokinin in plastid biogenesis was investigated in etiolated rye leaves (Secale cereale L.) and compared with the effect of white light. Cytokinin deficiency of the leaves was induced by early excision of the seedling roots and reversed by the application of kinetin. The cytokinin supply had a much greater influence on plastid biogenesis than on leaf growth in general. The activities of several chloroplastic enzymes were increased 200%–400% after kinetin treatment of cytokinin-depleted leaves. The activity of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and the amount of fraction-I protein even showed a sevenfold increase. In cytokinin-depleted leaves the development of ribulose-1,5-bisphosphate carboxylase and NADP-glyceraldehydephosphate dehydrogenase was specifically, and markedly inhibited by actinomycin D. The inhibition was partially or even completely overcome after treatment with kinetin. However, under all conditions, RNA synthesis of the leaves, was only partially inhibited by actinomycin D. According to immunologic studies, all dark-grown leaves, in addition to the complete enzyme, contained an excess of free small subunit of ribulose-1,5-bisphosphate carboxylase that was absent in mature light-grown leaves. The most striking accumulation of free small subunit, protein occurred in cytokinin-depleted dark-grown leaves, indicating a deficiency of the plastidic synthesis of the large subunit. The capacity as well as the activity of plastidic protein synthesis was preferentially increased by cytokinin and light. Cytokinin increased, the amount of plastidic ribosomes per leaf and relative to the amount of cytoplasmic ribosomes. While the percentage of cytoplasmic ribosomes bound as polyribosomes was little affected by the cytokinin supply, the proportion of plastidic polyribosomes was increased from 11% to 18% after kinetin treatment of cytokinin-depleted leaves. In the light, the proportion of plastidic polyribosomes reached 39% of the total plastidic ribosomes.

The Effect of Potassium on Cotyledon Expansion Induced by Cytokinins

Abstract: Potassium has been found to enhance greatly the expansion response of cucumber cotyledons to cytokinins. A reduction of the response to kinetin is obtained with increasing age of the cotyledons. The lesser response is associated with lower levels of potassium remaining in the cotyledon. A high level of KCI in the incubation medium offsets the lower potassium content of the tissue and enables a much larger response to the cytokinins. At 40 mM KCI the response to kinetin is 4.2 times greater than in the absence of KCI. Calcium increases the effect of potassium on the response to kinetin. When incubated in 40 mM KCI and 10 mM CaCI2 with 10 mg/I 6-benzylamino-purine, the final weight of the cotyledons is 6.8 times the initial weight after just 4 days. This KCI-CaCI2 combination is also found to promote chlorophyll synthesis in the usual cucumber cotyledon bioassay.

Nuclear cytology of callus induction and developmentin vitro

Abstract: Expiants of immature cotyledons (2 cm in length) ofVicia Raba (2 n=12) were grownin vitro onMitchell andGildow's (1975) medium supplemented with auxin (either IAA or 2,4-D) alone or auxin and kinetin in many possible combinations of concentrations.

Endogenous Cytokinins and the Breaking of Dormancy and Apical Dominance in Potato Tubers

Abstract: Cytokinins are present in all parts of potato tubers, and are equally distributed between the apical, lateral, and internodal tissue when dormant. However, the breaking of dormancy coincided with a rapid increase in the free base cytokinin levels in the apical buds and the tissue adjacent to it. These high levels Of cytokinin in the apical tissue were maintained while apical dominance was displayed. Once apical:dominance was overcome the cytokinin levels in the lateral buds and the tissue adjacent to them were similar to the levels in the apical regions. The present evidence suggests that cytokinin glucosides are transported to the meristematic regions of the tubers where they are hydrolysed to their free bases. Amounts of free bases in excess of those required for growth are apparently again converted to storage forms (particularly zeatin glucoside) in the meristematic regions of the tubers and in the sprouts. INTRODUCTION Recent reviews (Guern and Usciati, 1972; Phillips, 1975) have emphasized that there is a large body of conflicting data with regard to the regulation of apical dominance. It is recognized that the process is probably controlled by complex interactions between nutritional factors, growth promoters, and growth inhibitors. Although the hormonal regulation of apical dominance has been studied extensively, results obtained with exogenously applied hormones are not always supported by those in which endogenous hormone levels were investigated. From work with applied hormones it would appear as if lateral bud development is inhibited by high auxin levels (Thimann and Skoog, 1934) and that the inhibition can be overcome by cytokinins (Wickson and Thimann, 1958; Ali and Fletcher, 1970; Lee, Kessler, and Thimann, 1974). Endogenous hormone studies however, do not support this hypothesis but seem to indicate that the opposite situation prevails. In the majority of situations investigated inhibited buds were found to contain low auxin (Thomas, 1972; Jablanovic and Neskovic, 1977) and high cytokinin levels (Tucker and Mansfield, 1973; Jablanovic and Neskovic, 1977). Before the exact role of the different hormones in the release of buds from apical dominance can be evaluated it is essential that many more non-manipulated plant systems be investigated. The present report describes changes in the endogenous This content downloaded from 157.55.39.58 on Fri, 26 Aug 2016 05:14:56 UTC All use subject to http://about.jstor.org/terms 1078 Van Staden and Dimalla—Cytokinins and Potato Growth cytokinin levels of potatoes stored under conditions which promoted sprouting and under which lateral buds were released from apical dominance. MATERIALS AND METHODS Plant material Freshly harvested potato tubers Solanum tuberosum L. (cv. BP 1) were kept at I6 °C for 7 d and thereafter stored in darkness at 10 °C. At five sampling times (Fig. 1) tissue sections, 10 mm in diameter and 10 mm in length, were collected from 300 randomly selected tubers. At each sampling, material was collected from the apical bud cortex, lateral bud cortex, internodal cortex (the material analysed consisted primarily of periderm and cortical tissue with traces of adjoining xylem, outer phloem, and perimedullary parenchyma), and the internal medullary regions of the tubers (Fig. 1). In the sampling periods before sprouting, apical and lateral buds were included in the material assayed. Except for the material collected from the centre of the tubers, which consisted mainly of parenchyma tissue, the material analysed was composed of periderm and cortical tissue with traces of adjoining xylem, outer phloem, and perimedullary parenchyma. During the periods when sprouting occurred the sprouts were detached and assayed separately. All excised material was immediately deep-frozen and stored for analysis at —20 °C. Extraction, purification, and bioassay for cytokinins The frozen plant material was homogenized with 80% (v/v) ethanol and extracted for 24 h. After filtration the extracts were reduced to dryness in vacuo at 40 °C and the residues redissolved in 100 ml 70% ethanol. The pH of the ethanolic extracts was adjusted to 2-5 with HC1 and the extracts were then passed through cation-exchange columns (25 g Dowex 50W-X8, 200-400 mesh, H+ form, 2 cm x 26 cm). The columns were washed with 100 ml distilled water, followed by 200 ml 80% ethanol and the adsorbed cytokinins subsequently eluted with 300 ml 5 N NH4 OH. After removal of the ammonia the residues were taken up in small volumes of 80% ethanol and the equivalent of 50 g of plant material streaked onto a sheet (46 cm x 54 cm) of Whatman No. 1 chromatography paper and then separated with iso-propanol : 25% ammonium hydroxide : water (10:1:1, by vol). The dried chromatograms were divided into 10 Rf strips and the equivalent of 50 g fresh material assayed for cell division activity with the soybean callus bioassay (Miller, 1965). All assays were repeated and the means for the two separate bioassays plotted in the histograms. In order to obtain more information about the nature of the cytokinins present in the tubers the Rt zones 0-2-0-8 were eluted from the paper chromatograms and fractionated oh a Sephadex LH 20 column (2-5 cm x 90 cm) eluted with 20% ethanol at a flow rate of 15 ml tr1. Additional information about the possible identity of the endogenous cytokinins was obtained by treating the extracts with /?-glucosidase (Van Staden, 1976) and 0-1% potassium permanganate (Miller, 1965) respectively before fractionation on the Sephadex LH-20 column. Fractions (40 ml) were collected in 50 ml Erlenmeyer flasks, the ethanol evaporated in a stream of air, and the different fractions assayed for cytokinin activity. RESULTS The buds of the potato tubers were collected at the commencement of the experiment and after 8 weeks of storage at 10 °C were considered to be dormant as they showed no visible signs of growth. After 13 weeks at 10 °C the apical buds of all tubers had started to swell and in 10% of the tubers which were analysed the apical shoot had already elongated to a length of 3-5 mm. Ten weeks later (23 weeks) the tubers showed full apical dominance. The apical sprouts were well developed (30-90 mm long) and the lateral buds were just beginning to swell. After 28 weeks in storage the tubers were in the multiple sprout stage, at which time both the apical and lateral sprouts were well developed (Fig. 1). Cytokinin activity which, on paper, co-chromatographed with zeatin, dihydro zeatin, and their respective ribosides (Fig. 2) was detected in all the potato material This content downloaded from 157.55.39.58 on Fri, 26 Aug 2016 05:14:56 UTC All use subject to http://about.jstor.org/terms Van Staden and Dimalla—Cytokinins and Potato Growth 1079 1 8 13 Weeks of storage Fig. 1. Diagr'am showing the development of potato tubers during storage. Sampling procedure: A = apical bud cortex; B = lateral bud cortex; C = internodal cortex; D = internal tissue. analysed. For purposes of comparison this activity (which co-chromatographed with the free bases) was expressed as jig kinetin equivalents kg-1 fresh material. The data obtained in this manner indicated that material taken from the internal medullary regions of the potatoes contained low levels of free base cytokinins during the course of the experiment (Fig. 3). Although higher than in the internal regions of the potatoes, the cytokinin levels in the internodal cortical tissue also remained fairly constant during storage. Up to 8 weeks after storage similar levels of cytokinin were recorded in the apical, lateral, and internodal regions of the potatoes. After 13 weeks, however, cytokinin levels increased markedly in and

Influence of Different Cytokinins on the Transpiration and Senescence of Excised Oat Leaves

Abstract: In order to investigate the possibility that cytokinins control transpiration indirectly through affecting leaf senescence, a direct comparison was made of the effect of different cytokinins on transpiration and senescence of oat leaves (Avena sativa L. cv. Forward). Senescence was assessed by measuring chlorophyll loss. The synthetic cytokinins N6 benzyladenine (BA) and kinetin delayed senescence and increased transpiration of oat leaves to a greater extent than did the naturally occurring compounds zeatin, Nb-Δ2 isopentenyladenine (i6 Ade) and 6-o-hydroxybenzyladenosine (hyd-BA riboside). During the early stages of the transpiration experiment zeatin showed similar or greater activity than BA. This period was longest when freshly excised leaves were used, was reduced when leaves were used after incubation in distilled water in the dark for 20 h and was eliminated by incubation in cytokinin solution in the dark. After this period the activity of zeatin declined relative to BA. The effect of cytokinins in increasing transpiration occurred only in the light; no effect was observed in the dark. BA showed higher activity than zeatin in senescence tests but both cytokinins were less effective as the tests progressed, this decrease in activity being more rapid when older leaves were used. The results are discussed in relation to the mechanisms by which endogenous cytokinins might control sensecence and transpiration in oat leaves and to the value of the oat leaf senscence and transpiration bioassays as tests for cytokinin activity of plant extracts.

Seed Dormancy Mechanisms in Wild Rice (Zizania aquatica)1

Abstract: Freshly harvested seeds of wild rice (Zizania aquatica L.) require 3 to 5 months of moist storage at 1 to 3 to induce germination. Dormancy lasting more than 1 year has been noted. These periods of dormancy pose problems to plant breeders desiring multiple generations per year and to growers desiring to change varieties in establish fields. The purpose of this research was to determine the role of the pericarp in seed dormancy, the existence of germination inhibitors, and the influence of gibberellin and kinetin on germination of dormant wild rice seeds. The pericarp of seeds harvested the previous day was scraped off, punctured, or cut at several locations on the seed. Germination occurred only when the treatments were made directly over or very near the embryo, indicating mechanical resistance by the pericarp. Soil collected from fields 1 and 2 years out of production was screened for seed. The pericarps of nongerminating seeds were randomly punctured, increasing germination 33 and 79% respectively. This suggests an impermeable pericarp. Freshly harvested seeds from which the pericarp was either scraped or not scraped were germinated in aqueous extracts of the pericarp, and hulls (lemma and palea) from freshly harvested seeds. Aqueous extracts of the pericarp reduced germination 77% while aqueous extracts of the hulls reduced germination 84%, compared to scraped seed germinated in water. Aqueous extracts of the hulls from seeds stored for 1 year had little influence on germination when used as germination media for freshly harvested scraped seeds. The hulls were removed from some freshly harvested seeds and not from others before storing for 1, 2, and 4 weeks in water at 1.5 C. Seedling survival after 30 days was significantly reduced when lemmas and paleas were left on the seeds 1 or 2 weeks during storage in water at 1.5 C. These experiments support the contention of growth regulators in the hulls of freshly harvested seed. All combinations of 0, 0.01, 0.1, 1, and 5μM solutions of gibberellic acid (GA₃) and kinetin were applied germinated dehulled, punctured seeds. Before seeds were dehulled and punctured, they were stored in plastic containers at 1.5 C for 90 days. Germination increased from 36 to 51% as GA₃ concentrations increased. Kinetin alone had little influence on germination except in combination with GA₃. Less etiolated seedlings were obtained when kinetin was included in GA₃ treatments. The addition of 5μM GA₃ + 1μM kinetin increased germination of freshly harvested, scraped seeds from 29 to 76%. Wild rice appears to have multiple mechanisms of seed dormancy. The seed pericarp exhibits mechanical resistance and impermeability. Water soluble germination inhibitors appear to be present in hulls and pericarp, and gibberellic acid concentrations are low in freshly harvested seed. Freshly harvested seed can be germinated by dehulling and scraping, permitting multiple generations per year in breeding programs. Persistence of dormant seeds in fields will present problems in introducing new varieties.

Rapid Effects of Abscisic Acid on Ion Uptake in Sunflower Roots

Abstract: Short-term effects of ABA, ABA + kinetin and kinetin on ion (86Rb-potassium and phosphate) and water uptake in sunflower plants (Helianthus annuus var. californicus) were examined with a continuous-recording technique. Ion uptake in the roots and transport to the shoots were also investigated by conventional tracer uptake experiments and by sap bleeding experiments with excised roots. After addition of 5 × 10−6-4 × 10−5M ABA to the root medium there was an immediate decrease (30–70%) in the rate of ion uptake which lasted 30–70 min. The rate of water uptake was not significantly affected as measured with this method. Ion transport to the shoots and to the bleeding sap of excised roots was decreased by ABA. ABA-induced inhibition of ion uptake was abolished by the presence of kinetin, and uptake was slightly stimulated by 2 × 10−5M kinetin alone. We suggest that concentration gradients of ABA or rapid changes in the ABA-kinetin balance in the roots affect ion uptake and transport.

Biochemical Requirements for Seed Germination and Shoot Development of Witchweed (Striga asiatica)

Abstract: Germination of witchweed [Striga asiatica (L.) Kuntze] seeds was induced by treating air-dry seeds with kinetin (6-furfuryl-aminopurine) at 1.16 × 10−4 M and 2.32 × 10−4 M without subjecting the seeds to the conventional preconditioning procedures. Rudimentary shoot development of the seedlings also was promoted. Tissue culture techniques were used also to study growth regulator and nutritional requirements for witchweed seedling development. Seedlings with normal leaves and stems were obtained under aseptic conditions in synthetic media at pH 5.4 in the absence of a host plant when cultured in the presence of kinetin, indole-3-acetic acid (IAA), sucrose, casein hydrolysate and mineral salts. No shoot development occurred in the absence of kinetin or zeatin [6-(trans-4-hydroxy-3-methylbut-2-enylamino)purine]. Shoot development was more advanced if IAA or gibberellic acid (GA3) was used in combination with the cytokinins. Witchweed seedlings are dependent on a host plant not only for their nutrition, but also for plant hormones such as a cytokinin required for the promotion of shoot development.

Effects of Post-Harvest Treatment of Fruit and Vegetables with Cytokinin-Active Seaweed Extracts and Kinetin Solutions

Abstract: Samples of aubergines, avocados, bananas, capsicums, Junes, mangoes and pears were immersed for l or 2 h in tither diluted commercial seaweed extracts of known cytokinin activity or in aqueous kinetin Solutions. In comparison with controls immersed in water for the same time, no significant effect was produced on the rate of ripening of aubergines, avocados and pears, Significant increases in the rates of ripening of bananas and mangoes were obtained by immersion in diluted seaweed extracts. The shelf-Iife of capsicums was significantly increased by immersion in seaweed extracts, but kinetin Solutions increased the rate of ripening, The most noticeable effect was with Hmes, the rate of \"degreening\" of fruits after immersion in either seaweed extracts or kinetin Solutions betng reduced. Optimum cytokinin concentration varied between different batches of limes. Introduction Post-harvest treatment with cytokinins, in particular Nbenzyl-adenine, of fruit and vegetables to increase their shelf-life has been recorded by several workers; this work was reviewed by Salunkhe and Wu (1974), Commercial seaweed extracts have been demonstrated to have high cytokinin activities (Brain et al. 1973, Williams et al., in press), and there are several reports that fruits colJected from plants treated with seaweed extracts have increased shelf-lives in comparison with fruits from untreated plants (Blunden 1972, Skelton and Senn 1969, Povolny 1966, 1969 and 1972). This communication reports a preliminary study on the post-harvest treatment of various fruits and vegetables by immersion in either seaweed extracts of known cytokinin activity or in kinetin Solutions. The purpose of the work, undertaken on a smali scaJe, was to ascertain possible benefits of treatment, the commercial applications of which would be determlned in future large-scale trials. Materials and Methods Materials Two commercial seaweed extracts, S.M, 3 (supplied by Chase Organics Ltd.) and Marinure (supplied by Wilfred Smith (Horticultural) Ltd.), were used in all trials, except that with bananas and in the first Urne trial, in which only S.M.3 was used. In the trial with pears a third commercial seaweed extract, Algistim (supplied by Glenorganic Ltd.) was also used. All three extracts were assayed for cytokinin activity using the radish leaf expansion bioassay, with kinetin äs the reference compound (Kuraishi and Okumura 1956, Bentley-Mowat and Reid 1968). Plant material was obtained either directly from growers in the U.K. (pears, aubergines, capsicums) or, shortly after import, from wholesalers at Nine Elms Market, London. Treatments and storage conditions Test material was completely immersed for l h, or occasionally for either l or 2 h, in either aqueous dilutions of seaweed extract having a final cytokinin activity equivalent to 30,15,7.5 or 15 ppm kinetin, when assayed by the radish leaf expansion bioassay, or in equivalent concentrations of aqueous kinetin Solutions. As a control, material was also immersed in water for the same period. When the available numbers of fruit were small, fewer seaweed extract concentrations were used. For bananas and mangoes, onJy the effects of seaweed extracts were studied. In the banana trial, the seaweed extract was used in dÜutions equivalent in activity to Botanka Marina / VoL XXI / 1978 / Fase. 4 238 Blunden, Jones and Passam: Post-Harvest Treatment of Pruit and Vegetables with Seaweed Extracts and Kinetin 30, 15 and 7.5 p p m kinetin equivalents. In the various experiments the numbers of fruit per treatment were äs follows: aubergines 5, avocados 5, bananas 10, capsicums 5. limes 10, mangoes 5 and pears 7. After immersion, surface liquid was wiped from the samples which were then stored äs follows: Aubergines were kept at 15 °C and 90-95% r.h. in continuous light, and examined daily for any change in firmness or appearance, which was recorded on an arbitrary scale ranging from l (firm) to 7 (very soft and wrinkled). Avocados were stored at 17 °C and at 95% r.h. under continuous light, and examined daily for changes from green and hard (1) to dark reddish-brown and soft (5). Bananas were kept in darkness at 15 °C and at 85-90% r.h. and examined daily for any colour changes, which were recorded using the scale of von Loesecke (1949); i.e. l (green) to 8 (yellow and blackening). They were not treated with ethylene. Capsicums were stored in concinuous light at 12 °C and 80-90% r.h. and examined daily for any colour change from green (1) to red/orange (6). Limes were stored at 10 °C and at 85% r.h. in subdued lighting, They were examined daily for colour changes from green (1) to 95-100% yellow (10). Mangoes were stored at 23 °C and at 90% r.h. under a normal daylight-darkness regime and examined daily. Changes were recorded on a scale from l (green and hard) to 6 (yellow/orange and soft). Pears were kept at 15 °C and at 80-90% r.h. in constant light. Changes in firmness were recorded daily on an arbitrary scale from l (green and hard) to 5 (yellow and very soft). Significant effects of the treatments (P = 0.05) were determined by the Mann Whitney U test. Results and Discussion No significant effect on ripening time was observed äs a result of dipping aubergines, avocados and pears in either diluted seaweed extracts, of known cytokinin activities, or in aqueous Solutions of kinetin (Tab. 1). Immersion of bananas for 2 h in seaweed extract with a cytokinin activity equivalent to 30 ppm kinetin showed a significant increase in the ripening rate after 8 days when compared to control fruit (Tab. 2). This difference was maintained until the end of the experiment. There was n o significant difference between control fruit and that immersed for 2 h in extract dilutions equivalent to 15 and 7.5 ppm kinetin. Immersion of bananas in extract dilutions of equivalent activities for l h only showed a significant increase in the rate of ripening with the 7.5 ppm dilution from 22 days. These results are Tab. 1. Mean times taken after Immersion in either diluted seaweed extracts or in kinetin Solutions for aubergines, avocados and pears to become soft and unmarketable Test fruit or vegetable Immersion solution Mean time (days) for fruit to become soft and unmarketable Cytokinin concentration (ppm), calculated äs kinetin

Morphogenesis in Cultured Floral Parts of African Violet

Abstract: Callus tissue was induced from floral parts of African violet cultured on MS medium containing NAA (2 mg l-1) and BAP (0-2 mg l-1). When maintained on this medium in the presence of light, the callus produced many shoots and roots. Large numbers of adventitious shoot buds were formed apparently in the absence of callusing when ovary, sepal, and petal tissue was cultured on MS medium supplemented with BAP (1 mg 1_1) and NAA (1 mg 1_1). In contrast, culturing the same floral parts on MS medium augmented with kinetin (1 mg l-1) and NAA (0-5 mg I"1) led to the profuse development of roots. Organs seemed to be initiated from the epidermis of cultured floral parts and did not appear to be related to particular cells or loci. Transfer of shoots to MS medium devoid of growth substances resulted in the formation of plantlets, which at a height of 3 cm could be transferred to soil and grown to maturity without variation in morphology or cytology.

Investigations on the cell cycle of haploid and diploid tissue cultures of Datura innoxia Mill. and its synchronization.

Abstract: Using a 14C/3H double-labelling technique, the influence of kinetic on the length of the cell cycle of meristematic cells in haploid and diploid callus cultures of Datura innoxia was determined. The total length of the cell cycle of haploid cells as compared to that of diploid cells was reduced by 2.3 h (-kinetin) or 1.4 h (+kinetin). Furthermore, the addition of kinetin to the nutrient solution also reduces cell cycle duration at both ploidy levels. For synchronization of the cell cycle, a fluorodesoxyuridine/thymidine system was successfully employed. Apparently, the reduction of total cell cycle duration of cycling cells due to treatment with kinetin occurred at the expense of the G1phase. Nevertheless, kinetin seems to exert an influence on the transition of cells from the G2 into the M phase as well.

The effect of kinetin and auxin on the chloroplast structure and chlorophyll content in wheat coleoptiles

Abstract: Kinetin and auxin when applied to excised segments of wheat coleoptiles bring about changes in chloroplast structure and chlorophyll content of parenchymatous cells. Auxin (IAA) alone at a concentration of 10-5M stimulated the elongation (growth), but the chloroplast membrane system was less developed and the chlorophyll content was lowest in comparison with control and other variants. Kinetin (KIN) exhibited various effects depending on the concentration used. 10-6M KIN somehow stimulated the elongation and enhanced the amount of grana coming to one chloroplast section, but the individual grana were relatively small and the chlorophyll content a little higher than in the control. On the other hand 10-5M KIN which did not promote the elongation of wheat coleoptiles, had the maximum stimulatory effect on the chloroplast membrane system, especially on the occurrence of large grana, and the chlorophyll content was highest in comparison with the other variants. The occurrence of starch grains in chloroplasts was lower than in the other variants. The effect of a joint treatment of KIN and IAA did not exceed that of KIN (10-5M) alone. Thus the development of chloroplasts and the accumulation of chlorophyll in wheat coleoptiles are stimulated by the concentration of KIN which does not promote the elongation of coleoptiles.

Regeneration of plants from mesophyll protoplasts of Nicotiana plumbaginifolia Viv

Abstract: Protoplasts ofNicotiana plumbaginifolia were isolated by a one step enzymatic method. They were cultured in Ohyama and Nitsch's medium supplemented with 2,4-D (1.0 mg/l), benzylaminopurine (1.0 mg/l) and 14% sucrose. Cell divisions were initiated after 5 days and within 3 weeks colonies were discernible without the microscope. After transfer to Murashige and Skoog's medium containing IAA and kinetin the colonies differentiated into plantlets.

Kinetin Reversal of NaCl Effects.

Abstract: Leaf discs of Nicotiana rustica L. were floated on NaCl in the presence of kinetin or abscisic acid. On the 5th day 14CO2 fixation, [3H]leucine incorporation, stomatal conductance, and chlorophyll content were determined. Kinetin either partially or completely reversed the inhibitory effects of NaCl while ABA had no effect.

Thiourea, a Growth Promoter of Callus Tissues1

Abstract: Thiourea (TU) promoted growth in cytokinin-requiring soybean, tobacco, and apple callus tissues, in the absence of kinetin. The increase in fresh and dry weight obtained was a result of cell multiplication. Callus tissues grew well when repeatedly subcultured in kinetin-free medium containing TU. The best growth was obtained with 10~4-10~3 M TU. At these concentrations synergism was demonstrated between TU and the cytokinins, kinetin, benzyladenine, and zeatin. TU caused greater growth than diphenylurea and phenylthiourea. The possibility that a breakdown product of TU is responsible for the enhanced growth was not excluded. The dormancy-breaking effect of TU was suggested to be related to its growth-enhancing effect.

Callus formation versus differentiation of cultured barley embryos: hormonal and osmotic interactions.

Abstract: The effect of various plant growth substances as single agents was evaluated in a complex tissue culture system: whole embryo culture of early differentiating barley embryos. Callus formation in unsupplemented medium derives from the mesocotyl and is uniquely characteristic of cultures initiated at this stage of embryonic development. This phenomenon could be prevented or reversed by incorporation of gibberellic acid in the medium resulting in plantlet formation. Indoleacetic acid enhanced callus growth, whereas kinetin did not promote either callus or meristematic development. Callus tissue markedly accumulated starch, effectively lowering the cellular osmolarity, while inducing a corresponding rise in the osmolarity of the culture medium. This osmotic pattern was reversed by gibberellic acid induction of shoot formation. These osmotic-hormonal interactions are interpreted relative to in vivo, in situ normal embryogeny or developmental lesions such as tumors.