Abstract
Mature leaves of field-grown eddo plants were used for observing hydathode morphology by light and scanning electron microscopies. There were approximately five hydathode pores on the adaxial surface of each leaf tip. A ring structure with two borders around the pore was detected in this study. Further observations revealed a large cavity underneath the pores. The cavity was directly connected to vascular bundles that lacked a bundle sheath, via intercellular spaces among loosely organized parenchyma cells. Many crystal cells were present around the cavity and vascular bundles. To evaluate the role of guttation in sodium excretion under salinity stress, eddo plants were grown in hydroponic solutions containing 0, 1, 4, 8, and 12 mM sodium chloride (NaCl) for 7 d. As the NaCl concentration in the hydroponic solution increased, the sodium contents increased in leaf blades, petioles, and roots but remained unchanged in corms. The sodium concentration in the guttation fluid increased; however, the volume of guttation fluid decreased with increasing NaCl concentrations. Therefore, sodium elimination via guttation decreased with increasing NaCl concentrations. The ratios of the sodium content in guttation fluid to that of leaf blades, leaves, and whole plants decreased with increasing NaCl concentrations. The ratios of potassium to sodium contents in leaves, roots, and guttation fluid also decreased as the NaCl concentration increased. These results indicate that guttation did not eliminate sufficient sodium to play a role in adjusting sodium homeostasis and the ratios of potassium to sodium contents in eddo plants under saline conditions.
Highlights
Eddo [Colocasia esculenta (L.) Schott var. antiquorum Hubbard & Rehder], a member of the taro group, is an important edible crop in the Araceae family
Hydathodes are present at the tip, on the adaxial and/or abaxial surface, and along the margin of leaves in a wide range of plant species (Chen & Chen, 2005; Lersten & Curtis, 1991; Maeda & Maeda, 1987; Taiz & Zeiger, 2006)
The hydathode pores are arranged along the leaf tip on the adaxial surface (Figures 1(c) and 2(a)), and not along the margin or on the adaxial or abaxial surfaces of leaf blade (Figure 2(e) and (f))
Summary
Eddo [Colocasia esculenta (L.) Schott var. antiquorum Hubbard & Rehder], a member of the taro group, is an important edible crop in the Araceae family. Sodium exudation through guttation flow has been shown to increase considerably in some plants under saline conditions (Maathuis et al, 2014). Guttation was shown to cease under increasing salinity in rice seedlings (Doi & Kasaku, 1953) and barley seedlings (Shabala et al, 2010). At present, it is unknown how much sodium is excreted in guttation fluid through hydathodes in eddo. To understand the mechanisms of salinity tolerance and solute movement in eddo, it is important to analyze the morphology of hydathodes and evaluate their role in sodium excretion via guttation fluid. We subjected eddo plants to varying degrees of NaCl stress to evaluate the role of guttation in distributing and balancing sodium
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