Abstract
Main conclusionEffects of a low aluminum (Al) dose were characterized. The Al supplement inhibited root growth but enhanced leaf growth in maize lines with different Al sensitivities.High levels of Al are phytotoxic especially in acidic soils. The beneficial effects of low Al levels have been reported in some plant species, but not in maize. Maize is relatively more sensitive to Al toxicity than other cereals. Seedlings, at the three leaf stage, of four Chinese maize foundation parent inbred lines with different Al tolerances, were exposed to complete Hoagland’s nutrient solution at pH 4.5 supplemented with 48 μM Al3+ under controlled growth conditions, and then the Al stress (AS) was removed. The leaf and root growth, root cell viability, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ions (K+, Ca++ and Mg++), photosynthetic rate and chlorophyll, protein and malondialdehyde contents in tissues were assayed. In conclusion, a low Al dose inhibits root growth but enhances leaf growth in maize. The Al-promoted leaf growth is likely a result of increased protein synthesis, a lowered Ca++ level, and the discharge of the growth-inhibitory factors. The Al-promoted leaf growth may be a ‘memory’ effect caused by the earlier AS in maize. Al causes cell wall rupture, and a loss of K+, Ca++ and Mg++ from root cells. CAT is an auxiliary antioxidant enzyme that works selectively with either SOD or POD against AS-related peroxidation, depending on the maize tissue. CAT is a major antioxidant enzyme responsible for root growth, but SOD is important for leaf growth during AS and after its removal. Our results contribute to understanding how low levels of Al affect maize and Al-resistant mechanisms in maize.
Highlights
Aluminum (Al) is the third most abundant chemical element in the earth’s crust (Pilon-Smits et al 2009)
The root growth rate was significantly reduced under Al stress (AS) (Fig. 1e)
The leaf growth rate in all of the maize lines was accelerated under AS, starting at 24 h after AS and increasing more significantly with the duration of AS (Fig. 1f)
Summary
Aluminum (Al) is the third most abundant chemical element in the earth’s crust (Pilon-Smits et al 2009). It is phytotoxic, especially in acidic soils with a pH in the 4.5–5.0 range (Matsumoto 2000). To detoxify AS-caused ROS, plants employ enzymatic antioxidants, majorly including superoxide dismutases (SOD), peroxidases (POD) and catalases (CAT) (Boscolo et al 2003; Inostroza-Blancheteau et al 2012). Whether these three enzymes contribute or selectively cooperate during the detoxification of AScaused ROS remains unknown
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