Ethylene: Fine-tuning plant growth and development by stimulation and inhibition of elongation

Plant architecture is determined by a subtle balance between growth stimulation and inhibition conferring optimal plasticity in response to environmental changes. Ethylene is a gaseous hormone which plays an essential role in a myriad of plant developmental processes, both by stimulation and inhibition of growth. Ethylene can promote root hair formation, flowering, fruit ripening and abscission, as well as leaf and petal senescence and abscission. Its role is dependent on the environmental conditions, and the plant developmental stage, besides also being species dependent. Within a plant and even within a given organ, the effect of ethylene treatment can differ, depending on endogenous and environmental cues. Moreover, ethylene signalling and response are a part of an intricate network in cross-talk with other hormones. In this review, current insights in the role of ethylene on growth processes and the influence of these different factors are discussed.