Wild and Domesticated Opuntia as a Model for Evaluating Abiotic Stress in the Physiology and Biochemistry of Succulent Plants

Plants of the genus Opuntia are cacti that grow under natural conditions, with scarce humidity, drastic changes in daytime and nighttime temperatures, and poor soils. Their fruits are a food source in certain regions of the world, and their modified stems (cladodes) have diverse uses, including human consumption—especially when young, tender, and succulent (“nopalitos”) —livestock feed, and raw material for various products. There are approximately 300 species and dozens of variants of this genus, identified as wild, semi-domesticated, or domesticated. The physiological and biochemical responses to abiotic stress in these species are diverse but are related to their Crassulacean acid metabolism and the level of domestication. The morphological modifications in fruits, seeds, and cladodes of the genus Opuntia during domestication appear to be the sum of numerous significant biochemical-physiological changes, but generally of small magnitude. Thus, evaluating wild, semi-domesticated, and domesticated Opuntia species allows us to understand the physiological and biochemical processes along a natural gradient (original and modified by natural and artificial selection and by the cultivation environment) and their alteration by abiotic stress of any kind. This review summarizes our main advances in considering the genus Opuntia as a model for evaluating abiotic stress in the physiology and biochemistry of succulent plants. Furthermore, it shows high relevance, especially in the context of climate change, because Opuntia species are key to food security in arid zones.