Silicon- and Boron-Induced Physio-Biochemical Alteration and Organic Acid Regulation Mitigates Aluminum Phytotoxicity in Date Palm Seedlings

Abstract

The current study aimed to understand the synergistic impacts of silicon (Si; 1.0 mM) and boron (B; 10 µM) application on modulating physio-molecular responses of date palm to mitigate aluminum (Al3+; 2.0 mM) toxicity. Results revealed that compared to sole Si and B treatments, a combined application significantly improved plant growth, biomass, and photosynthetic pigments during Al toxicity. Interestingly, Si and B resulted in significantly higher exudation of organic acid (malic acids, citric acids, and acetic acid) in the plant’s rhizosphere. This is also correlated with the reduced accumulation and translocation of Al in roots (60%) and shoots (56%) in Si and B treatments during Al toxicity compared to in sole Al3+ treatment. The activation of organic acids by combined Si + B application has significantly regulated the ALMT1, ALMT2 and plasma membrane ATPase; PMMA1 and PMMA3 in roots and shoots. Further, the Si-related transporter Lsi2 gene was upregulated by Si + B application under Al toxicity. This was also validated by the higher uptake and translocation of Si in plants. Al-induced oxidative stress was significantly counteracted by exhibiting lower malondialdehyde and superoxide production in Si + B treatments. Experiencing less oxidative stress was evident from upregulation of CAT and Cyt-Cu/Zn SOD expression; hence, enzymatic activities such as polyphenol oxidase, catalase, peroxidase, and ascorbate peroxidase were significantly activated. In the case of endogenous phytohormones, Si + B application demonstrated the downregulation of the abscisic acid (ABA; NCED1 and NCED6) and salicylic acid (SA; PYL4, PYR1) biosynthesis-related genes. Consequently, we also noticed a lower accumulation of ABA and rising SA levels under Al-stress. The current findings illustrate that the synergistic Si + B application could be an effective strategy for date palm growth and productivity against Al stress and could be further extended in field trails in Al-contaminated fields.

Supplemental Silicon and Boron Alleviates Aluminum-Induced Oxidative Damage in Soybean Roots

“…B, Si, and their combination can activate APX, CAT, and POD, which are the antioxidant enzymes responsible for scavenging H 2 O 2 under Al stress ( Figure 4 A–C). Consistent with our findings, Pontigo et al observed that Si significantly reduced lipid peroxidation induced by Al toxicity, and similarly, B application reduced oxidative damage to plants subjected to Al stress [ 42 , 45 , 46 ]. In summary, supplementation with B, Si, and their combination mitigated oxidative damage by reducing the accumulation of ROS and MAD and triggering the up-regulation of the antioxidant system ( Figure 3 and Figure 4 ).…”

“…This study revealed the inhibited root growth potential and parameters under Al toxicity (50 μM Al) ( Figure 1 ). Several mechanisms have been proposed for plant resistance to aluminum toxicity, and it has become evident that B and Si play an indispensable role in plant tolerance to aluminum toxicity [ 42 ]. In our current study, the B + Si combination and B and Si alone significantly reversed the root growth inhibition induced by Al toxicity ( Figure 1 C), which is consistent with earlier reports in citrus and date palm seedlings [ 36 ].…”

“…B and Si supplementation has been hypothesized to enhance plant antioxidant defense systems, thereby mitigating Al toxicity [ 42 , 45 ]. As stated above, MDA and H 2 O 2 levels were significantly elevated in soybean roots under Al stress ( Figure 3 A,B).…”

“…Moreover, higher root PCD levels and relative root length parallelled higher H 2 O 2 production ( Figure 1 A,C, Figure 2 A and Figure 3 B), indicating that Al-induced oxidative bursts play an active role in the induction of PCD. Moreover, B, Si, and their combination reduced MDA and H 2 O 2 levels and alleviated root growth inhibition under Al stress ( Figure 1 and Figure 2 ), suggesting that B, Si, and their combination mitigates Al toxicity by reducing the accumulation of ROS [ 36 , 42 , 46 ].…”

Boron alleviates the aluminum toxicity in buckwheat by regulating antioxidant defense system and maintaining osmotic balance

“…(Cakmak and Horst, 1991). In a study of date palm seedlings under Al stress, the boron treatment reduced MDA and superoxide production levels (Bilal et al, 2022). Our results show that whether the germinated buckwheat or the buckwheat in the seedling stage, Al stress signi cantly increased MDA content in roots as well as leaves (Fig.…”