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In vitro cultivated pear, Pyrus communis L. cv. Beurré Hardy, pedicels cut above their primary abscission layer can form a secondary abscission layer, especially under the influence of auxins or cytokinins in the culture medium. The maximum percentage of abscission reached by auxin application was always higher than that by cytokinin. The presence of the flower was of no consequence to the abscission. Characteristic differences in abscission were observed between pear and apple pedicels. In contrast to apple (1) secondary abscission in pear could also be induced by cytokinins, and (2) the site of abscission in pear was dependent on the auxin concentration. At lower auxin concentrations abscission was induced in the basal parts of the pedicels inserted in the medium, whereas at higher auxin concentrations the abscission layer was formed in the terminal parts of the pedicels above the culture medium. A clear effect of gibberellins, ABA and CEPA could not be detected. [ABSTRACT FROM AUTHOR]

In vitro cultivated apple pedicels without a primary abscission layer can form a secondary (adventitious) abscission layer, especially under the influence of auxins. In the apple cv. Cox's Orange Pippin abscission can only be induced by auxins, while the site of the abscission layer, a few millimetres from the basal ends of the pedicels, is fixed and independent of the auxin concentration. The auxin treatment has to last at least 5-6 days to induce abscission, which is not affected by the presence of a flower. A secondary layer does not occur when pedicels are placed inverted on the media. Although abscission occurs both in light and in darkness, it is strongly promoted by light. Abscission is also accelerated by raising the temperature from 9°C to 21-25°C. High concentrations of 2,3,5-triiodobenzoic acid reduce the percentage of auxin-induced abscission. Sugar is required, but the presence of macro-elements is not essential. [ABSTRACT FROM AUTHOR]

The effect of various growth substances on regeneration and growth of bulblets on excised bulb scale segments of Hyacinthus orientalis L. cv. Pink Pearl was studied. Bulblet formation was promoted by the auxins IAA and IBA but was inhibited by NAA at high concentrations. IAA hardly affected bulblet weight, whereas IBA and NAA at high concentrations decreased it. Cytokinins bad hardly any effect on bulblet regeneration and bulblet weight. Gibberellins inhibited both bulblet regeneration and bulblet weight; GA4+7 acted much stronger than GA3. ABA and ethephon decreased bulblet regeneration and bulblet growth. [ABSTRACT FROM AUTHOR]

During the last 3 years a method has been developed to reproduce Anthurium andraeanum Lind, through callus cultures. The procedural sequence is as follows: callus induction on excised leaf fragments, callus subculture on solid and in liquid media, adventitious sprout formation in callus on solid media, and rooting of excised sprouts. Recently 20 adult genotypes were propagated by this method. [ABSTRACT FROM AUTHOR]

In this study, we explore the interplay between the plant hormones gibberellins (GA), brassinosteroids (BR), and Indole-3-Acetic Acid (IAA) in their collective impact on plant shade avoidance elongation under varying light conditions. We focus particularly on low Red:Far-red (R:FR) light conditions achieved by supplementing the background light with FR. We characterized the tomato internode response to low R:FR and, with RNA-seq analysis, we were able to identify some of the potential regulatory hormonal pathways. Through a series of exogenous pharmacological modulations of GA, IAA, and BR, we demonstrate that GA and BR are sufficient but also necessary for inducing stem elongation under low R:FR light conditions. Intriguingly, while IAA alone shows limited effects, its combination with GA yields significant elongation, suggesting a nuanced hormonal balance. Furthermore, we unveil the complex interplay of these hormones under light with low R:FR, where the suppression of one hormone's effect can be compensated by the others. This study provides insights into the hormonal mechanisms governing plant adaptation to light, highlighting the intricate and adaptable nature of plant growth responses. Our findings have far-reaching implications for agricultural practices, offering potential strategies for optimizing plant growth and productivity in various lighting environments., (© 2024 The Author(s). Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

Shade is a potential threat to many plant species. When shade-intolerant plants detect neighbours, they elongate their stems and leaves in an effort to maximise their light capture. This developmental programme, known as 'shade-avoidance' is tightly controlled by specialised photoreceptors and a suite of transcriptional regulators. The basic helix-loop-helix (bHLH) family of transcription factors are particularly important for shade-induced elongation. In recent years, it has become apparent that many members of this family heterodimerise and that together they form a complex regulatory network. This review summarises recent work into the structure of the bHLH network and how it regulates elongation growth. In addition to this, we highlight how photoreceptors modulate the function of the network via direct interaction with transcription factors. It is hoped that the information integrated in this review will provide a useful theoretical framework for future studies on the molecular basis of shade-avoidance in plants., (© 2020 The Authors. Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)