Kiwifruit sensitivity to boron: impact on physiological and molecular responses

Boron (B) is an essential micronutrient critical for crop growth and productivity. However, excessive boron concentrations can impair plant development, and detoxification remains a significant challenge. Understanding genetic variability and identifying tolerance mechanisms are crucial for developing boron-resistant cultivars. This study explores the physiological and molecular responses of two <i>Actinidia</i> species, namely kiwifruit (<i>A.chinensis</i>) and kiwiberry (<i>A.arguta</i>), to varying levels of excess B. Under excessive B conditions, B accumulation followed the order roots< stems< leaves, with maximum concentrations of 68.6 mg/kg, 105 mg/kg, and 160.7 mg/kg in <i>AC</i>, and 68.2 mg/kg, 107 mg/kg, and 196.9 mg/kg in <i>AA</i>, respectively. B toxicity symptoms appeared in <i>AA</i> when B levels exceeded 50 mg/kg, leading to a 15-20% reduction in dry weight across roots, stems, and leaves. <i>AC</i> exhibited greater sensitivity, with a 20-30% reduction in dry biomass. Both species showed significant declines in chlorophyll a and b content under B stress, with alterations in the chlorophyll a/b ratio and increased oxidative stress. Additionally, stress-responsive genes, including <i>1-aminocyclopropane-1-carboxylate synthase</i> (<i>Actinidia10066</i>) and <i>xyloglucan endotransglucosylase/hydrolase</i> (<i>Actinidia11948</i>), were downregulated in response to B stress, suggesting potential disruptions in growth and development. These findings provide valuable insights into the differential physiological and molecular responses to excess boron in <i>Actinidia</i> species, laying a foundation for functional genomics research and the development of boron-tolerant kiwifruit cultivars.