One of the longest standing theories and, therein-based, regulation-model of plant root development, posits the inhibitory action of auxin (IAA, indolylacetic acid) on elongation growth of root cells. This effect, as induced by exogenously supplied IAA, served as the foundation stone for root growth regulation. For decades, auxin ruled the day and only allowed hormonal side players to be somehow involved, or in some way affected. However, this copiously reiterated, apparent cardinal role of auxin only applies in roots immersed in solutions; it vanishes as soon as IAA-supplied roots are not surrounded by liquid. When roots grow in humid air, exogenous IAA has no inhibitory effect on elongation growth of maize roots, regardless of whether it is applied basipetally from the top of the root or to the entire residual seedling immersed in IAA solution. Nevertheless, such treatment leads to pronounced root-borne ethylene emission and lateral rooting, illustrating and confirming thereby induced auxin presence and its effect on the root — yet, not on root cell elongation. Based on these findings, a new root growth regulatory model is proposed. In this model, it is not IAA, but IAA-triggered ethylene which plays the cardinal regulatory role — taking effect, or not — depending on the external circumstances. In this model, in water- or solution-incubated roots, IAA-dependent ethylene acts due to its accumulation within the root proper by inhibited/restrained diffusion into the liquid phase. In roots exposed to moist air or gas, there is no effect on cell elongation, since IAA-triggered ethylene diffuses out of the root without an impact on growth.

The promotion of Climate Literacy is a central concern of our time. To achieve this ability, one can draw on different content areas. One possible area is Nature-Based Solutions (NBS), such as Vertical Greening Systems (VGS), and their effectiveness in mitigating climate change. However, VGS is not yet an established topic in environmental education, even if the pro-environmental effectiveness of VGS has been proven from a scientific point of view and this topic is close to everyday life. To facilitate the transfer of knowledge from research to school, this paper presents an example of a possible procedure. This procedure starts with a narrative review of the scientific literature on VGS. Then, the main results of this review are related to the Sustainable Development Goals, Climate Literacy, and general educational goals to capture its educational relevance. Finally, a flow chart for a teaching sequence is developed, with the phase sequence derived from the performed narrative review. Thus, a parallelism between the structure of a scientific review and an action-oriented environmental education becomes visible. To what extent this parallelization may be generalized, and whether teaching based on it is effective, will have to be tested.

Land plants perceive gravity and respond to it in an organ-specific way; shoots typically direct growth upwards, roots typically downwards. Historically, at least with respect to maize plants, this phenomenon is attributed to three sequential processes, namely graviperception, the transduction of the perceived signal, and the graviresponse, resulting in a typical (re)positioning of the organ or entire plant body relative to the gravivector. For decades, sedimentation of starch-containing plastids within the cells of special tissues has been regarded as the primary and initiating process fundamental for gravitropic growth (starch-statolith hypothesis). Based on Popper’s falsification principle, uncompromising experiments were executed. The results indicate that the model of graviperception based on amyloplast sedimentation does not apply to maize seedlings.

The elongating leaves of young rye seedlings do not show a gravitropic response when placed horizontally. However, after treatment with ethylene, either supplied exogenously via ethephon or by application of its precursor 1‐aminocyclopropane‐1‐carboxylic acid (ACC), gravicompetence is seen. The inhibition of ethylene perception by 1‐methylcyclopropene (MCP) prevents gravicompetence. Young rye leaves provide a useful model system in which to identify the components of the gravity sensing or response systems, the presence of which govern gravicompetence.

A recent study demonstrated that gravi‐incompetent coleoptile‐less seedlings of rye exhibit gravi‐competence after exogenous application of ethylene. Treatments and conditions which induce and interfere with this phenomenon were analysed in more detail. Aminocyclopropane‐1‐carboxylic acid (ACC) as a precursor of ethylene has similar gravicompetence‐inducing effects and also appropriate conditions of light, which strongly enhances ethylene synthesis. Both effects can be inhibited by the ethylene‐perception blocking agent methylcyclopropene (MCP) or inhibitors of ethylene synthesis such as aminovinylglycine (AVG), indicating that light exerts its gravicompetence‐generating effect via induced/enhanced ethylene synthesis. Gain in gravicompetence is accompanied by the induced/enhanced occurrence of calreticulin and lipoxygenase as detected by 2D‐gels and Q‐TOFF‐analyses. Previously gravicompetent, light‐grown coleoptile‐less seedlings are characterized by gravi‐incompetent growth during subsequent horizontal gravistimulation when perception of ethylene is inhibited by MCP. The results demonstrate that continuous perception of ethylene is an indispensable step, permanently required for the regulation of gravitropic growth in germinating primary shoots of rye, either within the process of graviperception and/or of the transduction of the gravi‐signal.