Showing papers by "Kenneth V. Thimann published in 1964"

Release of Lateral Buds from Apical Dominance

Abstract: IT has been shown with isolated stem sections bearing a single bud that the development of this bud can be inhibited by indolyl-3-acetic acid (IAA) or other auxins, and this inhibition released by kinetin1. The concentrations of IAA needed are physiological, and the whole phenomenon appears identical with that of normal apical dominance. Nevertheless, the question remains as to whether the same release can be obtained in the intact plant, that is, under conditions of apical dominance sensu stricto.

Transport and Distribution of Auxin during Tropistic Response. II. The Lateral Migration of Auxin in Phototropism of Coleoptiles.

Abstract: It was found that the process of cellular absorption of Rb in corn leaf tissue resembles that in excised roots of barley in the following respects: absorption at the concentration used is a linear function of time for at least 1 hour; the accumulation ratio reached in 1 hour, with an external concentration of 0.02 mM Rb, is over 250: 1; the rate of absorption at 4.50 is 10 % or less of the rate at 300.

On a crystal-containing body in cells of the oat coleoptile.

Abstract: In the course of an experimental study of phototropism in seedlings (1, 2) attention has been directed to the plastids as possible participants in the light-detection process. This led to a microscopic study of the cells of the oat coleoptile and thence to the discovery of the body which is the subject of this note. The materials were chosen for their phototropic sensitivity. Avena sativa (oats) var. segerhavre (Victory) coleoptiles, grown in the dark after being given 5 hours' red light from the initial soaking, were used when 25 to 35 mm long. Hordeum vulgare (barley) and Zea mays (corn) coleoptiles, also grown in the dark, were used at the same length; the corn was given 3 hours' exposure to red light at the start. Phycomyces blakesleeanus was grown as described by Gruen (3) and harvested in stage 4. Subepidermal cells of the Avena coleoptile, especially at and near the apex (0.1 to 0.5 mm from the tip), contain a number of small bodies, a little less than 1 # in diameter. Each body consists of a single (probably 3-layered) membrane (Figs. 2 to 5) enclosing a matrix denser than the ground cytoplasm of the cell. In this matrix is embedded a single, usually rhomboidal, crystal; the outline of the crystal is sometimes irregularly polyhedral, occasionally rectangular or even hexagonal. Since the lattice lines sometimes appear to cross at right angles, it is not excluded that the crystal packing may be cubic. Usually the crystal is free from the membrane, but in a few cases it appears attached or adherent at one or more sides, and little or none of the matrix may be present at those sides (Fig. 2). In only one instance has any other defined structure appeared in the matrix, and in this case the included material was not lamellar. Thus, a clear distinction exists

The histological basis for inhibition of axillary buds inPisum sativum and the effects of auxins and kinetin on xylem development

Abstract: This investigation continues the s tudy of the effects of auxins and kinet in on growth regulat ion and xy l em differentiat ion in the second internode of the pea epicotyl (S o r o k i n, M a t h u r and T h i m a n n 1962). The earlier p a p e r descr,ibed the ana t om y of the internode and its changes during growth, while the present wort~ concerns the ana tomica l development of the t ranspor t sys tem between the int 'ernode and the la teral bud. The growth of the bud was ini t iated b y releasing it ei ther f rom na tu ra l apical dominance b y decapi ta t ion, or f rom auxininduced inhibit ion b y app ly ing kinetin. There will be described, first, the ana t omy of the inhibi ted ax i l l a ry buds on excised pea stem segments, and, second, the changes which occur dur~ing growth on a simple medium containing sucrose, auxins and kinetin, alone or in combination. These changes concern pa r t i cu la r ly the development of vascular connections, which have been studied ( for convenience ~in microscopic identification) as xy lem. Whether the format ion of ph loem accompanies that of xy l em was not determined, but t h e funct ion herein ascribed to x y l e m m a y ac tua l ly be pe r fo rmed b y the combined xy lemphloem structure in a vascular bundle.

Interactions between daylength and light intensity in the growth and chlorophyll content ofAcetabularia crenulata

Abstract: Of the environmental variables regulating the development of higher plants one of the most important is the daylength. Research with algae, however, has given the impression that their performance is remarkably unaffected by the length of the daily light period, the few observed effects being, for the most part, explainable in other ways. True photoperiodism is typically characterized by: (a) induction, or continuation of the effect after transference to non-inducing photo periods, and (b) sensitivity to short breaks in the light or dark periods. Several reports of effects exerted on algae by the lengths of light and dark periods occur in the literature. League and Gketxlach (1955) found that the number of gametangium pairs counted in randomly selected microscope fields of Vaucheria cultures was considerably higher in those given 18-hour photoperiods than in those given 8-hour photo periods. Similarly, Muller (1962) found that the ratio of plurilocular to unilocular sporangia produced by the brown alga, Ectocarpus, could be increased by increasing the daylength at 16° C. However, both authors were able to raise the performance of their short-day cultures to that of the respective long-day cultures, in the first instance by adding glucose and meat peptone to the medium, and in the second by increasing the light intensity. In neither case was it possible to alter the short-day behavior by introducing light-breaks in the middle of the dark period. The effects of daylength on gamete germination in Ulothrix flacca and on gamete production in Ulva lactuca and U. thuretti reported by Hygen

Pesticides And The P.S.A.C.

Abstract: vigorous discussions, both formal and informal, on the pesticide problem. In its simplest form, of course, the problem sets a classical example of one of the best-known kinds of incompatibility, namely, that between eating your cake and having it. If the farmer wants maximum yields from his land and his labor, the housewife wants clean and unspeckled fruits and vegetables, and the politician wants surpluses with which to belabor the government or to wow the Russians, then there is no getting away from the necessity of cleaning up the insects, fungi, and weeds that are attacking the crops. On the other hand, if the fisherman wants the biggest and most numerous catch, and the enthusiastic Auduboner hopes to see the prothonatory warbler or the peregrine falcon, then no "chemicals" must be spread anywhere. As always in such problems, the solution lies in the middle