Kinetin

About: Kinetin is a research topic. Over the lifetime, 7856 publications have been published within this topic receiving 135550 citations. The topic is also known as: Kinetin.

Role of Protein Synthesis in the Senescence of Leaves: II. The Influence of Amino Acids on Senescence.

Abstract: When the first leaf of the oat (Avena sativa) seedling is detached and placed in the dark, yellowing and proteolysis take place rapidly. The earlier finding that d-serine promotes this process has led to a further study of the controlling roles of several amino acids. Since the action of serine was found to be more powerful in presence of kinetin than alone, the effects of other amino acids have been restudied in presence of kinetin. Cysteine emerges as a moderately strong promotor of senescence, with glycine and alanine having definite but weaker effects. The serine effect is antagonized by arginine, especially in presence of kinetin, and so is the cysteine effect. This is considered to indicate that these two amino acids act in the same way. The antagonism exerted by arginine is in turn antagonized by canavanine. The protease activities at two pH regions which increase in the oat leaf during senescence react to both p-chlorimercuri-phenylsulfonate and to phenylmethyl-sulfonyl fluoride, and thus may contain both SH and OH groups. The amounts of both these enzyme activities formed in the leaf during 3 days in the dark are increased over 50% by pretreatment with serine, and this increase is very largely prevented by arginine. The amounts of soluble proteins left in the leaf vary as expected in the opposite sense. It is deduced that control of the new formation of proteases plays an important part in senescence. A suggestion is made as to the mechanism of control of senescence in leaves.

Plant regeneration from indica rice (Oryza sativa L.) protoplasts.

Abstract: Rice (Oryza sativa L.) plants of the indica cultivar IR54 were regenerated from protoplasts. Conditions were developed for isolating and purifying protoplasts from suspension cultures with protoplast yields ranging from 1·106 to 15·106 viable protoplasts/1 g fresh weight. Protoplast viability after purification was generally over 90%. Protoplasts were cultured in a slightly modified Kao medium in a Petri plate by placing them onto a Millipore filter positioned on top of a feeder (nurse) culture containing cells from a suspension culture of the japonica rice, Calrose 76. Plating efficiencies of protoplasts ranged from 0.5 to 3.0%; it was zero in the absence of the nurse culture. Protoplast preparations usually contained no contaminating cells, and when present, the number of cells never exceeded 0.1% of the protoplasts. After three weeks the Millipore filter with callus colonies were transferred off feeder cells and onto a Linsmaier and Skoog-type medium for an additional three weeks. Selected callus colonies that had embryo-like structures were then transferred to regeneration medium containing cytokinins, and regeneration frequencies up to 80% were obtained. Small shoots emerged and were transferred to jars for root development prior to transferring to pots of soil and growing the plants to maturity in growth chambers. Of the cytokinins evaluated, N6-benzylaminopurine was the most effective in promoting shoot formation; however, kinetin was also somewhat effective. Regeneration medium could be either an N6 or Murashige and Skoog basal medium. Of 76 plants grown to maturity, 62 were fertile, and the plant heights averaged about three-fourths the height of seed-grown plants. Two other suspension cultures of IR54, one developed from the protoplast callus of the initial IR54 line, and the other developed from callus produced by mature seeds, have yielded protoplasts capable of regenerating plants when using cells of the Calrose 76 suspension as a nurse culture. In addition, protoplasts obtained from three-week-old primary callus of immature embryos of IR54 were capable of regenerating plants when using the same culture conditions.

Improved growth and taxol yield in developing calli of Taxus cuspidata by medium composition modification.

Abstract: Cell culture of Taxus spp. represents a potential alternative source of taxol and related taxanes used in cancer chemotherapy. We have analyzed the effect of different culture media components on growth and production of taxol in developing callus cultures of T. cuspidata. Several sequential modifications were made to the basal B5 medium, which included addition and/or variation in the concentration of sucrose, B5 organic supplements, gibberellic acid, 36 combinations of 2,4-D/kinetin ratios, media salts and organic supplements, phenylalanine, casein hydrolysate and medium pH. The experiments were conducted during a 55 day-growth period followed by taxane extraction and analysis. Significant increases in taxol yield and growth over basal medium grown calli were observed with some of the modified media.

Somatic embryogenesis in cotton ( Gossypium ). II. Requirements for embryo development and plant regeneration

Abstract: Calli of cotton (Gossypium hirsutum L) initiated from seedling hypocotyl tissue were placed in liquid suspension and maintained by serial subculture in hormone-free Murashige and Skoog (MS) medium Suspensions were sieved and globular embryos collected, washed, resuspended in basal medium and plated onto various semi-solid media High inorganic salts (MS), low salt (2/3 MS), excess KNO3, and the growth regulators napthaleneacetic acid (NAA), gibberellic acid (GA3) and kinetin were tested for their effects on somatic embryo maturation Long-term embryo proliferation and maturation were best on medium containing MS plus 19g/l KNO3 Embryos 3 mm to 10 mm in size were removed from this plating medium and placed on sterile vermiculite saturated with Stewart and Hsu's medium plus 01 mg/l indoleacetic acid (IAA) Plants were recovered from 106% of the embryos When ≥5 mm embryos were placed on this medium, 30% of the embryos formed plants within six weeks Smaller embryos required a longer period of development on the vermiculite and the addition of fresh medium supplemented with 01 mg/l GA3 Plants with an extensive root system and two true leaves were removed from sterile culture and potted in either one-to-one peat and sand, or vermiculite Eighty percent of the regenerants were successfully hardened when glass beakers of increasing size (10 to 150 ml) were sequentially placed over the young plants during a two-week period

The effect of kinetin on nucleic acids and nucleases of excised barley leaves.

Abstract: Recent work from several laboratories (6, 7, 9, 11, 12, 13) has shown that in excised green leaves floated on water there are rapid declines in the level of RNA, DNA, protein and chlorophyll which are retarded if the leaves *are floated on kinetin solution. Furthermore, the local application of kinetin on detached tobacco leaf causes the maintenance of the protein level and color of the treated area which has been suggested to act as a metabolic sink (6). The stimulation of both RNA and protein synthesis by kinetin in tobacco (8) and Xanthiumwl (7) leaves has been reported, and McCalla, Moore and Osborne (5) using another kinin, the benzyladenine-CG4, have obtained tentative evidence that label was incorporated into RNA although at a very low rate. Wollgiehn and Parthier (13) have recently shown that chloramphenicol and thiouracil accelerated the yellowing of detached tobacco leaves and the breakdown of RNA and protein which was prevented by kinetin. All these findings have indicated that kinetin in some way maintains the level of RNA and thus keeps protein synthesis going in detached leaves. Since the level of RNA and DNA in detached leaves may depend not only on the rate of synthesis, but also on the rate of breakdown, it was thought desirable to investigate the effect of kinetin on the amount of RNA, DNA and chlorophyll, on the rate of incorporation of p32 into RNA and DNA, and on the activity of soluble ribonuclease and deoxyribonuclease in excised barley leaves. The present paper describes the results of this investigation. Materials and Methods