# Effects of Glyoxylic Acid on Metabolism and Ripening of 'Rocha' Pears Treated with 1-MCP
## 1 Introduction  
The primary challenge of the fruit sector today is not only to extend the storability of perishable fruits but also to ensure the maintenance of fruit quality during postharvest storage, including during cross-border and long-distance shipping [1, 2]. To achieve this, the pear industry relies on 1-MCP and cold storage to delay senescence, thereby extending the fruit's availability throughout the year [3, 4]. However, despite its effectiveness in reducing postharvest decay, 1-MCP disrupts the normal ripening process after cold storage [5, 6]. Physiologically, 1-MCP competes with ethylene, the key hormone responsible for coordinating climacter fruit ripening, by binding to ethylene receptor proteins located in the endoplasmic reticulum membrane. This binding downregulates ethylene signaling and biosynthesis genes, thereby suppressing or delaying essential ripening responses [7, 8]. Consequently, the fruits remain unripe, failing to develop desirable textural, aromatic, and flavor attributes, which reduces their commercial value and leads to economic losses. The Portuguese 'Rocha' pear (_Pyrus communis_ L. '[PERSON]'), a Protected Designation of Origin (PDO) cultivar, generates around EUR 120 to 130 million per year, having a great positive impact on the Portuguese economic balance. It is a cultivar known worldwide for its exceptional flavor. With the increase in exportation, conservation strategies have been aimed at maintaining the availability of 'Rocha' pear throughout 10 months. At the moment, it is a cultivar particularly affected by the challenges posed by 1-MCP [5]. Currently, no alternative exists to replace this technology. However, achieving a balance between preventing postharvest disorders and ensuring proper ripening remains difficult. According to [PERSON] and [PERSON] [9], the optimal 1-MCP concentration necessary to prevent superficial scalp also prevents consistent ripening. As a result, the search for new strategies that mitigate 1-MCP's effects while preserving fruit's quality and marketability has become urgent. Over recent decades, multiple approaches have been explored to restore ripening in peers treated with 1-MCP. These methods have primarily focused on physical treatments, such as exposure to exogenous ethylene [10; 11], increasing the storage temperature, or a combination of both [12; 13]. However, these techniques have shown limited effectiveness in overcoming the ripening blockage caused by 1-MCP [7], and they often exhibit cultivar-specific responses. According to producers, exposure to non-chilling temperatures and/or exogenous ethylene in 'Rocha' pears fails to restore ripening and is also energy-intensive. Therefore, the identification of effective treatments to counteract the effects of 1-MCP in 'Rocha' pears is a critical necessity. Recent advancements in chemical genomics have identified specific organic compounds as regulators of fruit's development and ripening [14; 15; 16; 17]. Among these, GLA has emerged as a potential metabolic activator in fruit treated with 1-MCP [7; 18]. GLA is an organic acid belonging to the class of alpha-keto acids, acting as a key metabolic intermediate in various biochemical pathways, including the glyoxylate cycle and amino acid metabolism. Its chemical structure contains both an aldehyde (-CHO) and a carboxyl (-COOH) group, making it a highly reactive and biologically relevant compound [19; 20]. GLA is known to play various roles in plants' metabolism, particularly as an intermediate in the glyoxylate cycle, which is crucial for gluconeogenesis and the mobilization of stored lipids. Additionally, GLA has been associated with responses to oxidative stress and metabolic adjustments under environmental stress conditions [20]. While its precise role in ethylene synthesis has not been established, it may influence hormonal crosstalk and energy metabolism, potentially affecting postharvest physiological responses in fruit.