Succulence and aquaporin expression during drought and recovery in the CAM epiphytic bromeliad Acanthostachys strobilacea (Schult. & Schult.f.) Klotzsch

Abstract

Due to climate change, drought-rewatering cycles might become more intense and frequent, potentially threatening epiphytic bromeliads as they are detached from the soil. Hence, research on drought-rewatering responses is essential to determine the resilience of these species to projected future environmental conditions. The tankless, CAM epiphytic bromeliad Acanthostachys strobilacea shows significant drought tolerance from its early developmental stages. Here, we investigated water storage remobilization and the expression of aquaporin genes in the succulent leaf tissues of juvenile A. strobilacea plants in response to a drought-rewatering cycle and their relation to metabolic status. Under greenhouse conditions, 3-month-old plants were subjected to 14 days without irrigation, followed by 1 day of rewatering. We conducted analyses of water status, leaf anatomy, photosynthetic rates, titratable acidity, metabolic profile, and aquaporin gene expression. Data on water status indicated drought-induced turgor loss, which could be mainly attributed to the collapse of the hydrenchyma (water-storage tissue). The water stored in these cells likely relocated to the photosynthetically active cells of the chlorenchyma, which may have helped maintain metabolic activity. Indeed, titratable acidity, gas exchange, and metabolic data showed intensified CAM activity after drought. Drought also increased proline and antioxidant contents but significantly reduced the expression of AsPIP1;1, AsPIP1;2-like, AsTIP2;2 and AsNIP2;2 genes. After 1 day of rewatering, turgor, CAM activity, and the expression of most aquaporin genes and most metabolite contents were fully restored to control levels. The rapid turgor recovery, even in the absence of leaf water-absorbing trichomes, was due to water storage in hydrenchyma cells upon rehydration. Additionally, the modulation of aquaporin expression likely reduced water loss during drought and aided turgor restoration after rewatering. These results can guide future research on the responses of epiphytic bromeliads to climate change, essential to developing conservation strategies.