How do plants reverse, at night, aluminum-induced dehydration?

• Grant number: 23/09043-6
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Effective date (Start): November 01, 2023
• Effective date (End): October 31, 2025
• Field of knowledge: Agronomical Sciences - Agronomy - Crop Science
• Principal Investigator: José Lavres Junior
• Grantee: Brenda Mistral de Oliveira Carvalho
• Host Institution: Centro de Energia Nuclear na Agricultura (CENA). Universidade de São Paulo (USP). Piracicaba , SP, Brazil

Abstract

The most evident symptom of aluminum (Al) toxicity is the inhibition of root growth, which can be accompanied by anatomical damage to the xylem, reduced hydraulic conductivity of the roots (Lpr), increased lipid peroxidation, and suppression of aquaporin genes (AQPs). Furthermore, Al toxicity causes a reduction in stomatal conductance (gs), relative water content (RWC), and leaf water potential (¨w) at midday (¨md). Interestingly, the low leaf hydration observed during the day is not accompanied by low ¨w in the pre-dawn (¨pd). Somehow, these plants reverse the dehydration caused by Al during the night. Considering that morphological and anatomical damages are irreversible, it is possible that more instantaneous changes, such as molecular and biochemical ones, occur at night. AQPs genes are affected by the circadian rhythm of plants and are involved in the improved hydration observed during the night in Arabidopsis thaliana. The suppression of PIP1;1 and PIP2;1 genes was observed during the day in Citrus x limonia exposed to Al, and their expression during the night has never been analyzed in Al-sensitive plants. It is possible that during the night, Al has a differentiated effect on these and other PIP subfamily genes. The transmembrane water transport is also affected by increased lipid peroxidation, one of the first effects of Al toxicity. Experiments in which the effects of Al were not studied have shown that lipid peroxidation affects transmembrane water transport. For example, in Cucumis sativus, exogenous H2O2 reduces Lpr up to six times, and a high concentration of H2O2 reversibly blocks Lpr in Zea mays. Therefore, it is possible that nighttime rehydration is partially explained by the reduction of lipid peroxidation during this period. In general, organ hydration is influenced by the osmotic potential (¨À) of tissues and the accumulation of osmolytes in cells. For instance, decreased ¨À is associated with drought tolerance, and Al-tolerant plants exhibit higher osmolyte accumulation in root and leaf cells. So far, there are no reports of nocturnal osmotic adjustment in Al-sensitive plants, and this process could increase water absorption and organ hydration during the night. In this context, we selected C. x limonia, a woody and Al-sensitive plant, to test if nighttime rehydration is associated with (1) increased expression of PIP subfamily AQPs genes, (2) reduced ¨À and increased osmolyte concentration, and (3) reduced lipid peroxidation in roots and leaves.