Analysis of reduced and oxidized antioxidants in Hevea brasiliensis latex reveals new insights into the regulation of antioxidants in response to harvesting stress and tapping panel dryness

Latex diagnosis (LD) is applied to optimize the natural rubber production and prevent tapping panel dryness (TPD), a physiological syndrome affecting latex production in Hevea brasiliensis. The reduced thiol content (RSH) is one of the biochemical parameters associated with the risk of TPD. However, RSH is difficult to interpret because of the influence of the environment. In order to better understand the regulation of antioxidants and to better interpret RSH, a key parameter of LD, this study analysed in latex both oxidised and reduced forms of ascorbic acid (AsA) and glutathione, and their cofactors as well as other latex diagnosis parameters in response to harvesting stress (tapping and ethephon stimulation) and TPD occurrence. The content of antioxidants in latex had a high variability among five rubber clones. The concentration in AsA was about ten times higher than GSH in laticifer, GSH accounting for about 50% of RSH. For short-term harvesting stress, RSH increased with tapping frequency and ethephon stimulation. TPD is associated with high latex viscosity and bursting of lysosomal particles called lutoids, as well as for several rubber clones with lower RSH and GSH contents. These results suggest that a high level of RSH shows the capacity of laticifer metabolism to cope with harvesting stress, while a drop in RSH is the sign of long stress related to lower metabolic activity and TPD occurrence. RSH remains an essential physiological parameter to prevent TPD when associated with reference data under low and high harvesting stress. This study paves the way to understand the role of AsA and GSH, and carry out genetic studies of antioxidants.