No abstract

Eliasson, L. and Bollmark, M. 1988. Ethylene as a possible mediator of light-induced inhibition of root growth. -Physiol. Plant. 72: 605409.Pea seedlings (Pisum sativum L. cv. Weibull's Marma) were used to investigate the possible role of ethylene in light-induced inhibition of root elongation. Illumination of the roots with white light inhibited root elongation by 4&50°/0 and increased ethylene production by the roots about 4-fold. Our main approach was to use exogenous 1-aminocyclopropane-1-carboxylic acid (ACC), supplied in the growth solution, to monitor ethylene production of the roots independent of light treatment. Ethylene production of excised root tips increased with increasing ACC concentrations. The rate of ethylene production in dark-grown roots treated with 0.1 pM ACC was similar to that caused by illumination. Low ACC concentrations (0.01-0.1 pM) decreased the rate of root elongation, especially in seedlings grown in the dark, and 0.1 pM ACC inhibited elongation to about the same extent as light. In light the roots curved and grew partly plagiogravitropically. This effect was also simulated by the 0.1 pM ACC treatment. At 1 pM and higher concentrations, ACC inhibited root growth almost completely and caused conspicuous curvatures of the root tips both in light and darkness. Inhibitors of ethylene synthesis and action partially counteracted the inhibition of root elongation caused by light. These observations suggest that the increase in ethylene production caused by light is at least partly responsible for the decreased growth of light-exposed roots.

BoUtnark, M. and Eliasson, L., 1986. Effects of exogenous cytokinins on root formation in pea cuttings. -Physiol. Piantarum 68: 662-666.Abbreviation -BAP, benzylaminopurine; IAA, indole-3-acetic acid.

Cuttings were taken from 4‐week‐old seedlings of Norway spruce (Picea abies L. Karst.) raised at two different irradiation levels. Rooting experiments showed that root formation was increased by the ethylene formed by adding 1‐aminocyclopropane‐1‐carboxylic acid ACC or Ethrel, especially in the slowly rooting cuttings grown under high light (HL). Cobaltousion. an ethylene synthesis inhibitor, delayed rooting, especially in the easily rooted cuttings grown under low light (LL). Compounds isolated from the cuttings using immunoaffinity chromatography, on a column with antibodies against cytokinins, and separated by HPLC decreased in amount during the first week of the rooting period. An increase in ethylene production accelerated this process, especially in cuttings grown under HL, whereas cobaltous ion delayed it. We suggest that ethylene stimulates rooting by enhancing the degradation of cytokinins.

In conifers such as Norway spruce, the extent of shoot growth is predetermined by the size and number of embryonal organs of the buds laid down the previous year. As it is known that cytokinins have a key role in bud development a possible hypothesis is that the level of cytokinin in the buds during their formation determines their size and complexity. As a first step to test this hypothesis we compared cytokinin levels in buds of different size of annual shoots from 15‐ to 20‐year‐old trees of Picea abies (L.) Karst. Apical buds from the leaders, and from branches in lower parts of the trees, were collected in April, July and August. The difference in size of the buds and the shoots growing from them was considerable in these three positions. Extracts were purified by immunoaffinity columns, and the retained compounds were separated by high‐performance liquid chromatography (HPLC). Quantification was made by enzyme‐linked immunosorbent assay (ELISA), and the accuracy of this method was checked by measurements with liquid chromatography‐mass spectrometry (LC‐MS) and UV absorption. Zeatin riboside (ZR) was the most abundant cytokinin, but isopentenyladenosine (iPA) was also present in all samples. The large apical bud of the leader contained much higher cytokinin concentrations than the considerably smaller buds from lower positions, and during the period of secondary growth in July, similar relationships were found for annual stem tissue from different positions. The possible role of ZR as a controlling factor in bud development and apical control is discussed. Our conclusion is that the level of zeatin‐type cytokinins appears to play an important role in the establishment of differences in bud size and, thereby, the architecture of the tree crown.