Dry Priming of Maize Seeds Reduces Aluminum Stress

Abstract

Aluminum (Al) toxicity is directly related to acidic soils and substantially limits maize yield. Earlier studies using hormones and other substances to treat the seeds of various crops have been carried out with the aim of inducing tolerance to abiotic stress, especially chilling, drought and salinity. However, more studies regarding the effects of seed treatments on the induction of Al tolerance are necessary. In this study, two independent experiments were performed to determine the effect of ascorbic acid (AsA) seed treatment on the tolerance response of maize to acidic soil and Al stress. In the first experiment (greenhouse), the AsA seed treatment was tested in B73 (Al-sensitive genotype). This study demonstrates the potential of AsA for use as a pre-sowing seed treatment (seed priming) because this metabolite increased root and shoot growth under acidic and Al stress conditions. In the second test, the evidence from field experiments using an Al-sensitive genotype (Mo17) and an Al-tolerant genotype (DA) suggested that prior AsA seed treatment increased the growth of both genotypes. Enhanced productivity was observed for DA under Al stress after priming the seeds. Furthermore, the AsA treatment decreased the activity of oxidative stress-related enzymes in the DA genotype. In this study, remarkable effects using AsA seed treatment in maize were observed, demonstrating the potential future use of AsA in seed priming.

Fig 1. Growth comparison of 5-day-old maize seedlings (B73).

Unprimed and AsA-primed maize seeds that germinated in optimum soil (A) and unprimed and AsA-primed maize seeds that germinated in acidic soil with aluminum stress (B).

Fig 2. Length of roots and shoots of 5-day-old maize seedlings (B73).

Different uppercase letters denote significant differences between roots (dark gray). The significant differences between shoots (light gray) are shown by different lowercase letters (p < 0.05).

Fig 3. Quantification of aluminum in 5-day-old maize seedlings (B73).

Different uppercase letters denote significant differences between roots (dark gray). The significant differences between shoots (light gray) are shown using different lowercase letters (p < 0.05).

Fig 4. COMT1, ZmMYB31 and ZmMYB42 expressions in the roots of 5-day-old maize seedlings (B73).

Different uppercase letters denote significant differences between COMT1 gene expressions (dark gray). The expression differences of the transcription factors ZmMYB31 (light gray) and ZmMYB42 (white) are shown using different lowercase letters (p < 0.05).

Fig 5. COMT1, ZmMYB31 and ZmMYB42 expressions in the shoots of 5-day-old maize seedlings (B73).

Different uppercase letters denote significant differences between COMT1 gene expressions (dark gray). The expression differences of the transcription factors ZmMYB31 (light gray) and ZmMYB42 (white) are shown using different lowercase letters (p < 0.05).

Fig 6. Differences in the maize cob sizes of DA plants.

Maize cobs that originated from unprimed seeds (A) and maize cobs that originated from AsA-primed seeds (B).

Fig 7. Hydrogen peroxide (dark gray) and malondialdehyde (light gray) quantification.

The similar letters above the bars denote means that are not significantly different at a confidence level of 95%. FM = fresh matter.

Fig 8. Spectrophotometric analysis of the ascorbate content of the maize leaves (Mo17; DA) and grains (DA).

Similar letters above the bars denote means that are not significantly different at a confidence level of 95%. Ascorbate content in μM.g^-1 fresh matter.

Fig 9. Visualization of enzyme activity in maize leaves determined from 10% polyacrylamide gels.

(A) Visualization of catalase activity (CAT). (B) Visualization of ascorbate peroxidase activity (APX). (C) Visualization of glutathione reductase activity (GR).

Fig 10. Spectrophotometric analysis of guaiacol-type peroxidase (GPOX) activity in maize leaves.

Similar letters denote means that are not significantly different at a confidence level of 95%.