Hydrogen sulphide: a versatile tool for the regulation of growth and defence responses in horticultural crops

The improvement of plant growth and productivity under biotic and abiotic stress conditions, as well as the reduction of post-harvest losses, are of paramount significance to meet the increasing demand for food by a growing World population. Hydrogen sulphide (H2S) has recently appeared as a key contributor towards this goal through its bioactive role in the regulation of plant defence responses. In this review, we provide an up-to-date overview of recent literature concerning the biosynthesis and regulation of H2S within plant cells, as well as its involvement in a series of plant physiological processes. More specifically, H2S is actively associated with several horticultural plant growth and developmental processes, tolerance responses following exposure to stress factors, as well as in post-harvest fruit physiology. The H2S-mediated enhancement of tolerance to several abiotic stress factors is highlighted, with particular emphasis on the priming effects of H2S on the anti-oxidant capacity, redox regulation and signalling, and transcriptional regulation of cellular defence components in plants. Moreover, H2S has been reported to be associated with seed germination, increased growth, and root organogenesis, while also enhancing the post-harvest performance and anti-oxidant capacity of fruit. The present review proposes a practical role for H2S in horticultural crop physiology, further supporting the notion that H2S acts as a key signalling molecule in plants, possibly acting by "cross-talk" with other secondary plant cell messengers.