Cell Wall Invertase and Sucrose Synthase Regulate Pollen Tube Growth through Sucrose Metabolism

The development of polarized pollen tubes, which transport sperm nuclei to egg cells through female tissues, is a defining process in plant sexual reproduction. Despite its importance, the molecular mechanisms regulating pollen tube growth remain incompletely understood. This study investigated the regulatory roles of cell wall invertase (CWIN) and sucrose synthase (SUS) in tomato pollen tube development and examined how heat stress affects these pathways. Biochemical analyses were conducted to quantify CWIN and SUS activities in pollen tubes, using transgenic tomato lines with suppressed expression of either CWIN inhibitors or CWIN itself. Suppression of the CWIN inhibitor significantly enhanced both CWIN and SUS activities, leading to increased sucrose hydrolysis and accelerated pollen tube growth. In contrast, direct inhibition of CWIN reduced enzyme activities, limited sucrose hydrolysis, and impaired pollen tube development. Heat stress further decreased CWIN and SUS activities, resulting in slower pollen tube elongation. These results demonstrate that CWIN plays a central regulatory role in coordinating CWIN–SUS activity by controlling the supply of hydrolyzed sugars required for pollen tube growth. Overall, this study provides new mechanistic insight into carbohydrate metabolism during pollen tube development and highlights potential targets for improving reproductive performance in crops under heat stress conditions. Keywords: cell wall invertase; sucrose synthase; pollen tube; sucrose metabolism; heat stress.