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Absence of Parallelism Between Polyamine and Nucleic Acid Contents During Induced Growth of Cucumber Cotyledons by M

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Absence of Parallelism Between Polyamine and Nucleic Acid Contents During Induced Growth of Cucumber Cotyledons by M Biochem. J. (1978) 172,185-188 185 Printed in Great Britain Absence of Parallelism between Polyamine and Nucleic Acid Contents during Induced Growth of Cucumber Cotyledons By M. RANGARAJAN SURESH and P. RADHAKANTHA ADIGA Department ofBiochemistry, Indian Institute ofScience, Bangalore-560012, India (Received 7 February 1978) The cytokinins (benzyladenine or benzyladenosine) decreased spermidine and spermine contents despite increasing putrescine content, when administered to isolated cotyledons of Cucumis sativus L. var. Guntur in organ culture. KCI decreased putrescine contents, although marginally increasing polyamine contents. The cytokinins and/or KCl augmented nucleic acid biosynthesis and accumulation, resulting in enhanced growth and differentiation of the isolated cotyledons. These observations show that polyamine accumulation and growth are not always coupled. It has become common to relate the increase in prepared hormone and/or KC1 solutions or 5 ml polyamine concentrations with enhanced growth, of water as control. The Petri dishes were incubated cell proliferation and augmented macromolecular under continuous fluorescent light of approx. 13001x biosynthesis. Studies with microbial, animal and for various times at 23 ± 2°C. No detectable bacterial plant systems show that (a) di- and poly-amines contamination was observed during the period of stimulate growth per se (Tabor & Tabor, 1964; Clo the culture. The cotyledons were subsequently et al., 1976; Bagni & Fracassini, 1974) and (b) in- washed, homogenized at 0°C with cold HC104 (final creases occur in the activities of both ornithine concn. 0.2M) and cooled overnight. The acid-soluble decarboxylase and S-adenosyl-L-methionine decarb- supernatant was processed for di- and poly-amine oxylase accompanied by increased amine concen- analysis (Ramakrishna & Adiga, 1973). From the trations after hormone and drug administration acid-insoluble pellet, lipids were extracted and the (Raina & Janne, 1975), and in rapidly growing tissues, macromolecules fractionated and estimated (Rama- including natural or induced neoplasias (Snyder & krishna & Adiga, 1975a). Russell, 1970; Bachrach, 1976). A close parallelism between polyamine and macromolecular biosyn- Results and Discussion thesis, particularly the relationship of spermidine to RNA synthesis, was observed in a number of those The administration of cytokinins, namely benzyl- systems (Raina & Janne, 1975). These observations adenine or benzyladenosine, to the isolated cotyledons led to the generalization that 'no growth processes of Cucumis sativus in culture led to pronounced occur without prior stimulation of polyamine morphological changes and growth and differen- biosynthesis' (Russell, 1973a) and that 'biosynthesis tiation into leaf-like structures. The changes form the and accumulation of polyamines appear to be a basis of a bioassay for cytokinins (Udayakumar & universal prerequisite for growth' (Russell, 1973b). Krishnasastry, 1973). This effect ofcytokinin was also In the present paper we report the lack of corre- simulated by KCl. The effect of combined treatment lation between growth, RNA and DNA synthesis on with cytokinin and KCl on growth was additive. the one hand and the concentrations of putrescine, Addition of putrescine, spermidine or spermine to the spermidine and spermine on the other in a higher- culture medium in the range 0.01-100mM did not plant system induced to grow in organ culture under bring about the growth-promoting effect; in fact the influence of growth promoters. concentrations above I mm were inhibitory. This growth and differentiation induced by cytokinin Materials and Methods and/or KCI involve the biogenesis of the chloroplast, increase in cell size and number, vascularization ofthe The sources of the seeds (Cucumis sativus L. var. tissue and multicellular trichome formation on the Guntur), biochemicals and details of culture con- adaxial surface resulting in a dorsiventral leaf from ditions have been described elsewhere (Suresh et al., the embryonic cotyledon (Suresh, 1978). It may be 1978). Briefly, about 50 pairs of cotyledons from emphasized that this growth and differentiation also 60h-etiolated seedlings were washed and transferred occur during the normal course of germination of to a sterile Petri dish containing a Whatman no. 1 the seed and that the cotyledonary leafphotosynthesis filter-paper disc moistened with 5ml of the freshly has a profound influence on the subsequent growth Vol. 172 186 M. R. SURESH AND P. R. ADIGA 24 48 Duration of culture (h) 24 48 Duration of culture (h) Fig. 2. Changes in putrescine (a), spermidine (b) and sper- Fig. 1. Changes in DNA (a), RNA (b) and protein (c) mine (c) contents with time duringgrowth anddifferentiation contents with time during growth and differentiation of of cotyledons of Cucumis sativus L. var Guntur induced by cotyledons of Cucumis sativus L. var. Guntur induced by benzyladenosine and/or KCI in organ culture benzyladenosine and/or KCI in organ culture o, Control; *, 13.4puM-benzyladenosine; C], 50mM- 0, Control; *, 13.4.uM-benzyladenosine; a-I, 50mM- KCI; *, benzyladenosine+KCI. The experimental KCI; *, benzyladenosine+KCI. The experimental points represent means±S.D. (n = 4). points represent means+s.D. (n = 4). For other details see the text. treatments, although a uniform decrease (approx. of the cucumber seedling (Penny et al., 1976). It is 50%) was observed by 72h. Despite this mobilization pertinent that in Cucumis sativus L. var. Delicatess of the reserve protein, a significantly increased increased RNA and protein synthesis on administra- incorporation (25%) of '4C-labelled amino acids tion of benzyladenine and KCl respectively have was observed after 6h in the presence of the growth been reported (Knypl, 1971). stimulators (results not given). The changes in total DNA and RNA contents The changes in the amounts of putrescine, induced by benzyladenosine and/or KCl are shown spermidine and spermine during growth and in Figs. 1(a) and 1(b). Significant increases (P <0.001) differentiation ofcotyledons are depicted in Figs. 2(a), in RNA by 8 h and DNA by 24h were observed after 2(b) and 2(c). The modulation of arginine decarb- treatment with cytokinin or KCI. The nucleic acid oxylase, the first enzyme in the polyamine bio- contents were consistently higher on combined synthesis in higher plants (Ramakrishna & Adiga, treatment with cytokinin and KCl, a feature that was 1975b), and changes in the putrescine concentrations in agreement with the morphological observations. by various growth promoters, inhibitors, KCl and A similar response in the concentrations of nucleic H+ have been studied in detail (Suresh et al., 1978). acids was observed when either KCI, benzyladenine Unlike the dramatic early changes in ornithine or benzyladenosine was added. A 50 % increase in decarboxylase of mammalian systems, the increase 32p incorporation into RNA was evident by 3 h after in arginine decarboxylase was not as rapid. This may administration of the growth promoters even after be related to the longer half-life of arginine decarb- correction for the enhanced intracellular pool size oxylase (3-4h) compared with ornithine decarb- of the precursor (results not given). The total protein oxylase (1 1-20min) (Raina & Janne, 1975). It is content (Fig. ic) did not alter with the different evident from Fig. 2 that the cytokinin decreases 1978 RAPID PAPERS 187 spermidine concentrations despite the large increase These observations, including those now described in putrescine. However, KCl marginally decreased on the lack of association between polyamine and the amount of putrescine (Fig. 2), whereas nucleic acid concentrations during stimulated growth, significantly increasing polyamines. KCl-induced do not, however, argue against the role played by decrease in putrescine content has been observed polyamines in growth and related processes. It is earlier in tobacco (Smith, 1975). On the other hand, conceivable that, under conditions of limited avail- K+ deficiency is known to be associated with sub- ability of one of these amines, others could effec- stantial putrescine accumulation in several plant tively substitute for the physiological function systems (Smith, 1971, 1975). The decrease in poly- (Fillingame & Morris, 1973; Fillingame et al., 1975). amines was observed even when benzyladenosine- Alternatively a redistribution of the available amines treated tissue was extracted in 6 M-HCI, super- present at the basal concentrations could perform natants hydrolysed at 110°C for 18h before amine the essential function under such conditions. The determination (Russell, 1971). This excludes the amine concentrations fluctuate on treatment with possibility that the cytokinin elicits the synthesis and hormones, inhibitors and stress; a true physiological storage of any acid-labile polyamine derivative. An effect due to amine deficiency would precipitate only essentially similar but magnified pattern was obtained after decrease below a certain critical threshold (especially with cytokinin treatment) when the amine value. Thus it would appear that an emphasis on the content was expressed per unit amount of RNA or strict parallelism between polyamines and growth is DNA (see Figs. 1 and 2). In view of a comparable unwarranted at present, although the two are degree of stimulatory influence on growth and nucleic adventitiously coupled in a number ofsystems. acid synthesis, the opposite effects of cytokinin and KCl on amine accumulation were unexpected.
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