Direct effects of aluminum in leaves of sensitive plants, maintenance of leaf hydration in tolerant plants, and role of aluminum in roots of accumulating plants

Author(s)

Brenda Mistral de Oliveira Carvalho

• Document type: Doctoral Thesis
• Press: Rio Claro. 2023-04-10.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2023-03-31
• Advisor: Gustavo Habermann

Abstract

The first symptom of aluminum (Al) toxicity is the root growth inhibition, and may reduce shoot growth, leaf hydration and photosynthetic performance. Most of the absorbed Al is retained in root system. Thus, it is unknown if Al effects in aboveground organs is a consequence of the stunted root or a direct effect of the minor Al concentration reaching the mesophyll. On the other hand, some plants grow in the presence of high Al concentrations showing no symptoms. These tolerant plants are divided into Al-accumulating and non-accumulating species, and the latter stores more than 1000 mg Al per kg of dry leaves. Some mechanisms of tolerance are well described in the literature, but it is still not clear how these plants maintain leaf hydration when exposed to Al. Proline, an osmoprotectant amino acid, reduces osmotic potential () and improves water uptake in plant exposed to drought. Proline accumulation was already observed in plants exposed to Al, but only in Al-sensitive ones, and leaf hydration was not measured. Interestingly, some Al-accumulators show increased root growth when exposed to Al. Although Al alters root auxin concentration in sensitive plants, this association in Al-accumulating plants has received less attention. Within this context, we aimed to test the following hypotheses: (H1) Al reduces photosynthetic performance when applied directly on leaves of Al-sensitive plants, (H2) proline accumulation is associated with the maintenance of leaf hydration in Al-tolerant plants, and (H3) auxin accumulation is involved in Al-induced increased root growth in Al-accumulating plants. To test H1, we grew Citrus x limonia (Al-sensitive) in nutrient solution ‘without’ Al and exposed the shoots to increasing Al concentrations through injection in the petiole (24 h) and spraying (60 days). Photosynthetic performance decreased and root growth was not affected in both experiments, and shoot growth decreased in the long-term experiment. Therefore, we confirmed that Al reduces photosynthetic performance when applied directly on leaves. To test H2, we grew Pinus sylvestris (Al-tolerant) in nutrient solution with increasing Al concentrations for 45 days. As expected, Al did not interfere in photosynthetic performance and RWC, but proline concentration increased in roots and new shoots, while water potential decreased between seven and 14 days. These results indicate that proline accumulation may be involved in osmotic adjustment of P. sylvestris exposed to Al. To test H3, we grew Camellia sinensis (Al-accumulator) in nutrient solution with increasing Al concentrations and measured auxin (IAA), biometric data, root surface area, and RWC throughout 90 days. We evidenced that IAA accumulation in roots is associated to Al-induced root growth, which leads to increased root surface area and improved leaf hydration. (AU)

• FAPESP's process: 18/15359-8 - Direct effects of Al in leaves of sensitive and Al-accumulating species and al role in roots of Al-accumulating species
• Grantee: Brenda Mistral de Oliveira Carvalho
• Support Opportunities: Scholarships in Brazil - Doctorate