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Abstract Background The mesocotyl connects the coleoptilar node and the basal part of the seminal root of maize (Zea mays) seedling. The mesocotyl pushes the shoot of the seedling out of the soil during seed germination; thus, its growth is highly related to deep-sowing tolerance. Although many studies on the maize mesocotyl have been carried out at physiological and molecular levels, the proteomic changes associated with cellular and physiological activities during mesocotyl growth are still unknown. Results In the present study, the maize hybrid Zhengdan 958 was used to study mesocotyl growth and accompanying protein changes. The dark-grown etiolated mesocotyls exhibited a slow-fast-slow feature, with significant changes in the levels of indole-3-acetic acid (IAA) and cellulose and the activity of peroxidase (POD). In particular, POD activity increased with mesocotyl growth, showing higher activity at the mature (lower) end of the mesocotyl. For the proteomic analysis, soluble proteins were extracted from etiolated mesocotyls dark-grown for 48 h, 84 h, and 132 h, corresponding to the initial, rapid, and slow growth periods, respectively, and subjected to separation by two-dimensional gel electrophoresis (2-DE). As a result, 88 differentially abundant proteins (DAPs) were identified using MALDI-TOF-TOF analysis. At 48 h, most DAPs were stress proteins, heat shock proteins and storage proteins; at 84 h, oxidation/reduction proteins, carbohydrate biogenesis-related proteins and cytoskeleton-related proteins were highly accumulated; at 132 h, the most striking DAPs were those involved in the synthesis and modification of the cell wall and the biogenesis of carbohydrates. Gene ontology (GO) analysis showed that changes in the abundance and proportion of DAPs were consistent with cellular and physiological activities and biological processes during mesocotyl growth. The accumulation of nine DAPs of interest was verified by immunoblotting and RT-qPCR. Conclusions The present study revealed that the protein patterns in 2-D gels differed greatly with mesocotyl growth. At different growth periods, a specific set of DAPs participate in various biological processes and underlie the cellular and physiological activities of the mesocotyl. These results contributed to the understanding of mesocotyl growth and the cultivation of maize lines with deep-sowing tolerance.

Either ethylene or carbon dioxide stimulated the growth of oat mesocotyls in darkness, although the effect was much greater for carbon dioxide. Maximum elongation was obtained in the presence of both gases. Ethylene also induced lateral expansion of the mesocotyl: the volume of the mesocotyl was increased more in air with added ethylene than in air depleted of ethylene. Ethylene also stimulated mesocotyl growth under red light. gibberellin only slightly increased mesocotyl length under red light and acted cooperatively with ethylene in the promotion of growth. The oat mesocotyl is a unique organ in terrestrial plants because ethylene simultaneously stimulates not only longitudinal growth but also lateral expansion. The ecological significance of oat mesocotyl growth in relation to the response to ethylene and carbon dioxide is discussed. [ABSTRACT FROM AUTHOR]

The effects of continuous red and far-red light and of brief light pulses on the growth kinetics of the mesocotyl, coleoptile, and primary leaf of intact oat ( Avena sativa L.) seedlings were investigated. Mesocotyl lengthening is strongly inhibited, even by very small amounts of P, the far-red light absorbing form of phytochrome (e.g., by [P]≈0.1% of total phytochrome, established by a 756-nm light pulse). Coleoptile growth is at first promoted by P, but apparently inhibited later. This inhibition is correlated in time with the rupturing of the coleoptile tip by the primary leaf, the growth of which is also promoted by phytochrome. The growth responses of all three seedling organs are fully reversible by far-red light. The apparent lack of photoreversibility observed by some previous investigators of the mesocotyl inhibition can be explained by an extremely high sensitivity to P. Experiments with different seedling parts failed to demonstrate any further obvious interorgan relationship in the light-mediated growth responses of the mesocotyl and coleoptile. The organspecific growth kinetics, don't appear to be influenced by P destruction. Following an irradiation, the growth responses are quantitatively determined by the level of P established at the onset of darkness rather than by the actual P level present during the growth period. [ABSTRACT FROM AUTHOR]

Fluence rate response curves for light-induced inhibition of mesocotyl growth and promotion of coleoptile growth in etiolated Avena sativa L. (cv. Victory) were developed. The irradiation time was 24 h. Fluence rates between 10 and 10 nmol ms and 30 wavelengths between 563 and 1,093 nm were used. The main conclusions are as follows: 1. Both organs exhibit a low fluence rate response as well as a high fluence rate response. 2. The mesocotyl response is more sensitive to light than the coleoptile response. 3. The low fluence rate response of the mesocotyl shows a threshold of sensitivity at about 10 nmol ms (i.e., total fluence of 5·10 nmol m during the experiment) in the red and a saturation (about 70% inhibition of growth) at 10 nmol ms (50 nmol m). 4. The action spectrum for the low fluence rate response parallels the P absorption spectrum. Alterations induced by screening are discussed. 5. The action spectrum demonstrates an exponential decrease in apparent photoconversion cross-section (P→P) up to about 800 nm. Between 800 and 1,093 nm the photoconversion cross-section is only weakly dependent on wavelength. 6. The action spectrum for the high fluence rate response shows a broad peak in the red, a trough at 723 nm, and a sharp peak at 740-750 nm. [ABSTRACT FROM AUTHOR]