ASHS 2025 Conference

The development of genotypes resilient to abiotic stresses like drought has a pivotal role over the impacts of climate extremes on global food security. Recent studies suggest that modulating the activity of polyamine oxidases (PAOs) in crop species could enhance stress tolerance. Given the limited data on how altered PAOs expression (either overexpression or silencing) affects physiological and anatomical traits that may contribute to plant resilience, the aim of the present study is to investigate phenotypic variability - focusing on leaf structure and function - in tomato genotypes with modified polyamine metabolism under deficient irrigation. Three tomato genotypes were cultivated in a greenhouse, one reference (cv. Moneymaker) and two transgenic lines of the reference genotype with silenced expression of the genes encoding the homologous enzymes SlPAO3 and SlPAO4 of PAO. Two irrigation regimes were applied: Control (100% field capacity, FC) and Drought (20% FC). Following the development of new leaves under drought conditions (long-term acclimation), anatomical features of the leaves and petioles, as well as gas exchange parameters, were assessed. Results showed that, regardless of genotype, water deficit led to a reduction in leaf area, reflecting a decrease in transpiring surface, an adaptation of leaf function under limited water availability. The slpao3 plants, regardless of the irrigation regime, exhibited a smaller total vascular tissue area per petiole cross-section compared to both the reference genotype and the slpao4 plants. However, during acclimation to drought stress, an increase in vascular tissue area was observed only in the slpao3 plants. These findings align with previous studies highlighting the involvement of polyamines in xylem differentiation processes. Long-term acclimation resulted in a reduction in xylem vessel size and an increase in vessel density, irrespective of genotype, indicating an adjustment of hydraulic traits to meet the water demands of acclimated leaves. Petiole vascular characteristics, leaf area, and gas exchange parameters, independent of genotype and treatment, showed strong correlations among them. These results confirm a coordination presence between hydraulic function and photosynthetic response. Further research is needed to clarify how this coordination influences water transport and use efficiency, and to explore whether modulation of PAOs activity could serve as an effective strategy to enhance plant resilience to environmental stresses.