Bases fisiológicas da propagação de cactos sob estresses abióticos

Abstract

The Cactaceae family is among the groups of plants best adapted to survival in extreme environments. This thesis explores the physiological mechanisms of tolerance to abiotic stresses in propagules of four cactus species. The first study evaluated the in situ longevity of seeds from different populations of Cereus jamacaru, Pilosocereus catingicola ssp. salvadorensis, and Xiquexique gounellei ssp. gounellei, as well as the role of the antioxidant defense system and compatible organic solutes in maintaining seed viability. All species demonstrated the ability to establish a short-term persistent seed bank; however, this capacity was affected by the seed formation environment. This was evident in C. jamacaru, where seeds produced in a drier area (precipitation < 400 mm) exhibited a rapid decline in viability throughout the storage period. Additionally, the antioxidant defense system played a crucial role in controlling lipid peroxidation and maintaining seed viability in situ. The second study investigated the impact of different drought regimes on seed hydration memory expression in two populations of P. catingicola. Seeds from the driest area showed greater expression of hydration memory and germinability at low water potentials when subjected to HD cycles. The cycles stimulated enzymatic activity and reduced the levels of hydrogen peroxide and malonaldehyde in the evaluated seeds. The third study reported viviparity in the species Cereus jamacaru and evaluated the incidence of viviparity in fruits produced in different climatic seasons. Furthermore, seeds produced by viviparous fruits had their responses to different qualities of light evaluated. Vivipary incidence was higher in fruits produced under high-water availability. Seeds from viviparous fruits exhibited greater germination capacity under far-red light, demonstrating differences in sensitivity to light and potential for germination in shaded environments. The fourth study sought to understand the dynamics of post-fire recovery of a population of the invasive cactus Opuntia ficus-indica by evaluating the predominant type of plants recruited in the area and the functional mechanisms of invasion success. Clones represented the predominant plant type recruited in the post-fire scenario, exhibiting elevated levels of cytokinins and gibberellins associated with their enhanced relative growth. Seed-derived plants contributed a smaller percentage to the total number of individuals recruited in the area, but observations of photosynthetic performance and vitamin E content revealed the ability of these individuals to contribute to population regeneration. The combination of both reproductive strategies proved to be an important component in the successful invasion of the species in areas of the Mediterranean ecosystem affected by fire, given the possibility of rapid expansion of vegetation cover and maintenance of the genetic variability of the affected population. Overall, the results presented in this thesis reveal a significant influence of environmental components on the physiology of cactus propagules, with the antioxidant defense system playing a fundamental role in controlling oxidative stress and photoprotection. The parental and current environment of seeds and other propagules interact, modulating the physiology and capacity for tolerance to abiotic stresses and defining the final response to the conditions found in their environments of occurrence.