The interplay between polyamines (PAs) and nitrogen (N) is emerging as a key factor in plant response to abiotic and biotic stresses. The PA/N interplay in plants connects N metabolism, carbon (C) fixation, and secondary metabolism pathways. Glutamate, a pivotal N-containing molecule, is responsible for the biosynthesis of proline (Pro), arginine (Arg) and ornithine (Orn) and constitutes a main common pathway for PAs and C/N assimilation/incorporation implicated in various stresses. PAs and their derivatives are important signaling molecules, as they act largely by protecting and preserving the function/structure of cells in response to stresses. Use of different research approaches, such as generation of transgenic plants with modified intracellular N and PA homeostasis, has helped to elucidate a plethora of PA roles, underpinning their function as a major player in plant stress responses. In this context, a range of transgenic plants over-or under-expressing N/PA metabolic genes has been developed in an effort to decipher their implication in stress signaling. The current review describes how N and PAs regulate plant growth and facilitate crop acclimatization to adverse environments in an attempt to further elucidate the N-PAs interplay against abiotic and biotic stresses, as well as the mechanisms controlling N-PA genes/enzymes and metabolites.

Greenhouse horticulture is a cornerstone of year-round vegetable production. However, escalating climate change is intensifying abiotic stressors (i.e., elevated temperatures, increased vapor pressure deficits, water shortage, and modified solar radiation), threatening both crop productivity and postharvest performance. This review synthesizes current knowledge on how these climatic shifts impact greenhouse microclimate, pest and disease patterns, energy and water requirements, as well as crop development in the Mediterranean region. This study focuses on three major crops (tomato, cucumber, and sweet pepper), which prevail in the regional protected cultivation sector. Among the climate-induced stressors examined, elevated temperature emerges as the primary environmental constraint on greenhouse productivity. In reality, however, a combination of climate-induced stressors is at play, acting simultaneously and often synergistically. Among crops, cucumber generally displays the highest sensitivity to climate-induced shifts, whereas sweet pepper tends to be the most resilient. Next, adaptive strategies are explored, including precision irrigation, structural retrofitting measures, renewable energy integration, Decision Support Systems, and climate-resilient cultivars. Regional case studies revealed diverse country-specific counteractive innovations. As key elements of inclusive climate adaptation, supportive policy frameworks and a practical agenda of targeted research priorities are outlined. In conclusion, the sustainability of greenhouse horticulture under a changing climate demands integrated, technology-driven, and region-focused approaches.