Putrescine-mediated growth improvement and antioxidant response in pistachio (Pistacia vera L.) seedlings of ‘Badami Riz-e-Zarand’

Early vegetative ontogeny of Pistacia vera L. seedlings critically governs subsequent arboreal architecture, canopy ontogenesis, and agronomic productivity. This controlled-environment investigation systematically evaluated foliar-applied putrescine (0, 0.25, 0.5, 1 mM) on morphometric, photochemical, metabolic, and oxidative stress indices in uniform 10-cm 'Badami Riz-e-Zarand' seedlings. Putrescine elicited concentration-dependent morphogenic optima at 0.5 mM, inducing +160% longitudinal shoot extension, +36% radial stem hypertrophy, +65% foliar primordia proliferation +156% assimilatory surface expansion, and +293% dry biomass accrual. Photochemical efficiency peaked concomitantly, with chlorophyll a/b and carotenoid augmentation (+92% total Chl,) paralleling carbohydrate anabolism (+146% reducing sugars, +102% starch,) and diminished fresh:dry mass ratio, signifying enhanced lignocellulosic consolidation. Osmoregulatory homeostasis was fortified via -67% electrolyte exudationو +65% proline hyperaccumulation, and -49% lipid hydroperoxidative catabolism. Antioxidative enzymatic cascades exhibited exponential induction (+319% peak catalase activity, encompassing superoxide dismutase, peroxidase, and ascorbate peroxidase, thereby effectuating ROS scavenging homeostasis. Quadratic dose-response modeling confirmed 0.5 mM as the inflectional optimum across 18 physiological determinants, with 1 mM eliciting parabolic attenuation. These data substantiate exogenous putrescine (0.5 mM) as a potent biostimulant, orchestrating integrated morpho-physiological synergies that accelerate juvenile vigor, photosynthetic quantum yield, osmotic poise, membranal integrity, and redox homeostasis in P. vera seedlings. This mechanistic framework underpins precision horticultural interventions for optimized canopy establishment and sustained orchard productivity.