Adventitious Bud Initiation Research Articles

Studies on the Initial Process of Adventitious Bud Differentiation in Torenia Stem Segments Cultured in vitro I. Effects of Cytokinin

Summary The effects of mineral nutrients and growth regulators added to culture medium on the initial stages of adventitious bud differentiation were investigated using Torenia internodal segments cultured In vitro. Meristematic zones (MZ) appeared prior to adventitious bud formation in the epidermal Cell layers of stem segments. Adventitious bud and Mz formation was rarely noted in the explants Cultured on the MS medium without benzyladenine (BA). When explants were cultured on a medium composed of only BA and sucrose, MZ were formed but no adventitious bud initiation was observed. While, both MZ and bud formation was strongly promoted when a medium consisting of mineral nutrients and BA was used. Applications of indole-3-acetic acid and gibberellic acid stimulated neither MZ nor bud formation. When explants were cultured on a medium containing only BA (1.0 mg/l) and sucrose during the first 6 d and then transferred to nutrient medium without BA, adventitious buds were differentiated at a high rate. Consequently, it seems that BA strongly promoted MZ formation (bud initiation) during initial period of culture and mineral nutrients play major role in subsequent development of MZ to bud primordia.

Initiation of adventitious buds in tuberous roots ofIpomoea batatas

The anatomical development of adventitious buds in the tuberous roots ofIpomoea batatas has been studied. Only the detached tubers regenerate. The bud primordia develop from the procambium-like cells adjoining lateral root scars. Initially, the buds grow away from the surface of the tuber but, later, they turn almost 180°, towards the surface of the tuber, before bursting out of the tuber. The growth of the bud is largely contributed by random periclinal divisions of parenchymatous cells of the bud primordium. The basipetally developed vasculature of the bud is connected to the vasculature of the lateral root.

In vitro initiation of adventitious buds and its modification by high concentration of benzyladenine in leaf tissues of mulberry (Morus alba)

Leaf explants of mulberry (Mortis alba L.) derived from aseptically grown shoots and seedlings were cultured on Murashige and Skoog's medium. Normal and abnormal leaves were grown by varying the concentration of benzyladenine. They differed in the way of forming adventitious buds. In normal leaves bud initiation occurred exclusively at the cut ends of midribs after removing petioles, while in abnormal ones buds formed at any region on midribs and petioles. Histological observations were made to study different patterns of bud initiation.

生体上および人工培地上でのタマネギ花床からの子球再生

Onion bulblet formation on receptacles in vivo and in vitro was studied histologically.Onion bulblet formation in vivo was induced by clipping immature florets and pedicels and spraying 10mg/l N6-benzyladenine (BA) or water daily for two weeks. BA spray produced larger bulblets than water spray.Histologically, adventitious buds had been initiated from pedicel bases and receptacles at the termination of treatment. Then, they developed scaly leaves successively, and 5 weeks later bulblets were completed, and fell down from receptacles. These bulblets seemed to be in a state of relative rest.For in vitro culture, receptacles were cut in 2 or 4 pieces and cultured on the modified Murashige and Skoog′s medium (the basal medium) with or without α-naphthaleneacetic acid (NAA) and BA. The addition of NAA and BA increased the number of plantlets regenerated. Plantlets were produced on younger receptacles as a result of development of the primordia of floral organs into leaves, while on older receptacles, from which florets were removed at the explanting time, as a result of initiation of adventitious buds on them. Leaf sheathes in all plantlets swelled and formed bulb scales 30 to 90 days after explanting. Plantlets regenerated from receptacles of younger stages needed a longer period for bulbing. Callus formation was induced when florets were planted, and then plantlets were initiated from callus.The number of plantlets regenerated per receptacle was different according to the varied concentrations of NAA and BA incorporated into the medium. At 1mg/l NAA, higher concentrations of BA increased the number of plantlets. At 10mg/l NAA, however, the number of plantlets did not differ with the concentrations of BA.

Initiation of Adventitious Bud in Root of Sweet Potato, Ipomoea batatas Poiret

Shooting from the root-cuttings have been known in many plant species, and this phenomenon is very important in agriculture with regard to the vegetative propagation of crops and the regeneration of weeds. In this paper some observations on adventitious bud-initiation in root of sweet potato were undertaken to clarify the factors controlling the initiation of adventitious bud. It has been said that adventitious buds initiate in the tissue such as phellogen or parenchyma of cortex from parent root and in a part adjacent to the base of lateral root. In the present observation, the meristem regarded as adventitious bud-primordium was observed only in the cortex of the lateral roots which was surrounded by the cortex tissue of parent root (fig. 1A∼C, fig. 2). Many adventitious buds bearing leaf-primordia were observed in the cortex of parent root, and the vascular system of the adventitious bud connected with that of the lateral root, not of the parent root. From these observations, it is considered that the primordium initiated in lateral root develops to adventitious bud and intrudes into the cortex tissue of the parent root and then grows bigger and bigger which ultimately bears several leaf-primordia (fig. 1). In rare cases, the meristematic cell-aggregate was recognized in the cambium layer of parent root adjacent to the base of lateral root, and this meristem was observed always in a longitudinal row with the lateral root along the parent root (fig. 3A). In a scar, several lateral roots of which vascular system individually connected with that of parent root were found in a longitudinal row along the parent root, and some of them were newly formed ones (fig. 3B, C). Therefore, it seemed that these meristematic cell-aggregates developed to the new lateral roots and not to the adventitious buds. It can be concluded that the meristem in the cortex of lateral root develops to adventitious bud and that of the cambium layer of parent root develops to lateral root. This conclusion differs from the opinion that the meristem initiated in root is undetermined one, namely it will become that of a root or a shoot. There are a few different opinions about the stage of development of root when an adventitious bud initiates, and it has also been thought that the stage varies with the varieties of sweet potato. In this observation, the adventitious bud-primordium was observed in the juvenile root such as 1 mm in diameter in all the varieties examined (table 1). Therefore, it is confirmed that an adventitious bud generally initiates in the juvenile atage of root development in sweet potato. It was reported that the damage of a lateral root causes the initiation of adventitious bud from the near part to the base of that lateral root. In an experiment where lateral roots were cut off from parent root, no tendency to promote the initiation of adventitious bud by such damage was recognized, however, the promotion of the development of the adventitious bud already initiated was observed slightly (table 2). These findings suggest that the initiation of adventitious bud in sweet potato is caused, by the endogenous factors existing in the root itself.

ORIGIN OF BUDS IN TOBACCO STEM SEGMENTS CULTURED IN VITRO

DESPITE THE great wealth of botanical literature concerned with the initiation of adventitious buds (Priestley and Swingle, 1929; Buvat, 1944-45; Peeters, 1947), there have been relatively few anatomical studies on bud initiation in tissues cultured in synthetic media. Buvat (1944-45) has summarized these and has, himself, added considerably to an understanding of the problem of dedifferentiation2 of plant cells. However, his investigations concern principally the cytological aspects of primordium formation. Although Camus (1949) has studied the changes in subjacent tissues during bud development, he has not considered the details of initiation of the shoot primordia. Previous communications (Skoog, 1944; Skoog and Tsui, 1948, 1951; Sterling, 1950) have shown a marked correlation between relatively high levels of adenine, supplied through a culture medium, and bud initiation in tobacco stem segments. Obviously, the establishment of such a relationship makes possible the chemical control of bud formation. It is, therefore, of interest to place on record the successive steps in this controlled initiation of shoot primordia in vitro. This paper presents an anatomical description of such development and considers the latter in relation to the general problems of meristematic activity and dedifferentiation. MATERIALS AND METHODS.-The materials and methods used are those reported earlier (Sterling, 1950), with the limitation that this account deals only with the tobacco stem segments which received adenine sulfate (40 mg./l.) in the basal medium. The material is representative of the samples used in physiological studies on growth and tissue composition. Segments grown on control media were described in the earlier paper. SITES OF BUD ORIGIN.-In these cultures, there are three maj or regions of bud formation, Viz., cambium-external phloem, internal phloem, and callus. The region of the cambium and its young phloic derivatives produces the maj ority of bud primordia. In most instances, no sharp distinction can be made between these two classes of cells in the rapidly dividing cambial zone; therefore, this source of buds was previously reported as cambial (Sterling, 1950). However, in some cases bud primordia are found exclusively in the external phloem, with differentiated sieve tubes lying be-

Inhibition of Adventitious Bud Initiation in Hypocotyls of Flax by Indole-3-Acetic Acid and Flax Extract

HYPOCOTYLS of intact flax plants (Linum usit-atissimum L.) rarely develop buds. If decapitated, the young hypocotyl initiates adventitious buds some of which develop into flowering shoots1. The result is the same if both the cotyledonary buds and the epicotyl are removed, but the cotyledons are allowed to remain. Hypocotyls of plants with cotyledons and the young epicotyl enclosed in a plaster cast remain budless. Segments of hypocotyls2and of internodes occasionally initiate buds. These findings suggested that bud initiation is under hormonal control which is disturbed by partial or complete isolation.