Proline metabolism in cherry tomato exocarp in relation to temperature and solar radiation

Abstract

SummaryGiven the importance of proline and its metabolism in resistance to abiotic stress, the objective of this work was to study the influence of temperature and solar radiation on proline metabolism in the exocarp fraction of cherry tomato fruits. Solanum lycopersicum cv. Naomi plants were grown in an experimental greenhouse. Three fruit samples were taken over the entire production period. The first sampling was at the beginning of harvest [85 d after transplanting (DAT)], the second at mid-harvest (160 DAT), and the third at the end of harvest (229 DAT). Temperature and solar radiation values peaked during the third sampling, which coincided with an increase in lipid peroxidation (lipoxygenase activity) and malondialdehyde content, indicating the presence of oxidative stress during this period. However, yield values did not vary during the production cycle of cherry tomatoes. An increase in proline content was found at 229 DAT, with two enzymes responsible for proline synthesis: Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine-δ-aminotransferase (OAT). In contrast to previous work, proline dehydrogenase (PDH), which degrades proline, also increased its activity during this period. Under these conditions, the accumulation of proline, and proline degradation by PDH, could be considered to be a mechanism for resistance to stress by eliminating O2 and forming H+ ions. This would limit any major formation of reactive oxygen species (ROS), and thus cell necrosis, reducing losses in productivity.