Reductions in maize root tip elongation by salt and osmotic stress do not correlate with apoplastic .O2- levels”

DOLORES BUSTOS1, RAMIRO LASCANO1, ANA LAURA VILLASUSO2, ESTELA MACHADO2, GRACIELA RACAGNI2, MARÍA EUGENIA SENN1, ALICIA CÓRDOBA1, AND EDITH TALEISNIK1*

ANNALS OF BOTANY

Oxford Journals

Año: 2008 vol. 102 p. 551 - 559

0305-7364

Background and Aims Experimental evidence in the literature suggests that O2Experimental evidence in the literature suggests that O2 †2 produced in the elongation zone of roots and leaves by plasma membrane NADPH oxidase activity is required for growth. This study explores whether growth changes along the root tip induced by hyperosmotic treatments in Zea mays are associated with the distribution of apoplastic O2 the distribution of apoplastic O2 of roots and leaves by plasma membrane NADPH oxidase activity is required for growth. This study explores whether growth changes along the root tip induced by hyperosmotic treatments in Zea mays are associated with the distribution of apoplastic O2 the distribution of apoplastic O2 2 produced in the elongation zone of roots and leaves by plasma membrane NADPH oxidase activity is required for growth. This study explores whether growth changes along the root tip induced by hyperosmotic treatments in Zea mays are associated with the distribution of apoplastic O2 the distribution of apoplastic O2 Zea mays are associated with the distribution of apoplastic O22 †2.2. † Methods Stress treatments were imposed using 150 mM NaCl or 300 mM sorbitol. Root elongation rates and the spatial distribution of growth rates in the root tip were measured. Apoplastic O2 spatial distribution of growth rates in the root tip were measured. Apoplastic O2 Methods Stress treatments were imposed using 150 mM NaCl or 300 mM sorbitol. Root elongation rates and the spatial distribution of growth rates in the root tip were measured. Apoplastic O22 †2 was determined using nitro blue tetrazolium, and H2O2 was determined using 20, 70-dichlorofluorescin. blue tetrazolium, and H2O2 was determined using 20, 70-dichlorofluorescin. 2 was determined using nitro blue tetrazolium, and H2O2 was determined using 20, 70-dichlorofluorescin.2O2 was determined using 20, 70-dichlorofluorescin. † Key Results In non-stressed plants, the distribution of accelerating growth and highest O2Key Results In non-stressed plants, the distribution of accelerating growth and highest O2 †2 levels coincided along the root tip. Salt and osmotic stress of the same intensity had similar inhibitory effects on root elongation, but O2 the root tip. Salt and osmotic stress of the same intensity had similar inhibitory effects on root elongation, but O2 2 levels coincided along the root tip. Salt and osmotic stress of the same intensity had similar inhibitory effects on root elongation, but O22 †22 levels increased in sorbitol-treated roots and decreased in NaCl-treated roots. †Conclusions The lack of association between apoplastic O2Conclusions The lack of association between apoplastic O2 †2 levels and root growth inhibition under hyperosmotic stress leads us to hypothesize that under those conditions the role of apoplastic O2 stress leads us to hypothesize that under those conditions the role of apoplastic O2 2 levels and root growth inhibition under hyperosmotic stress leads us to hypothesize that under those conditions the role of apoplastic O22 †2 may be to participate in signalling processes, that convey information on the nature of the substrate that the growing root is exploring. in signalling processes, that convey information on the nature of the substrate that the growing root is exploring. 2 may be to participate in signalling processes, that convey information on the nature of the substrate that the growing root is exploring. Key words: Root tip growth, Zea mays, salt stress, reactive oxygen species, ROS.Root tip growth, Zea mays, salt stress, reactive oxygen species, ROS. INTRODUCTION Production of reactive oxygen species (ROS) appears to be a general characteristic of expanding plant cells and organs (Foreman et al., 2003; Peleg-Grossman et al., 2007; Potocky et al., 2007). A requirement for ROS for elongation of tip-growing cells has been demonstrated for root hairs using NADPH oxidase mutants (Foreman et al., 2003; Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 of tip-growing cells has been demonstrated for root hairs using NADPH oxidase mutants (Foreman et al., 2003; Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 Potocky et al., 2007). A requirement for ROS for elongation of tip-growing cells has been demonstrated for root hairs using NADPH oxidase mutants (Foreman et al., 2003; Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 of tip-growing cells has been demonstrated for root hairs using NADPH oxidase mutants (Foreman et al., 2003; Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 et al., 2003; Peleg-Grossman et al., 2007; Potocky et al., 2007). A requirement for ROS for elongation of tip-growing cells has been demonstrated for root hairs using NADPH oxidase mutants (Foreman et al., 2003; Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 Carol and Dolan, 2006); infection threads in symbiotic relationships (Peleg-Grossman et al., 2007) and pollen tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon et al., 2001), and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 and germinating seeds (Schopfer et al., 2001) can produce and extrude ROS. In maize, pharmacological treatments that reduce O2 and extrude ROS. In maize, pharmacological treatments that reduce O2 tubes (Potocky et al., 2007) also require ROS for active growth. Expanding organs such as embryonic axes (Puntarulo et al., 1988), growing roots (Jon e