Functional anatomy controls ion distribution in banana leaves: significance of Na⁺ seclusion at the leaf margins

Abstract

Typical salt stress symptoms appear in banana (Musa sp., cv. 'Grand Nain' AAA) only along the leaf margins. Mineral analysis of the dry matter of plants treated with increasing concentrations of KCl or NaCl revealed significant accumulation of Na + , but not of K + or Cl -, in the affected leaf margins. The differential distribution of the three ions suggests that water and ion movement out of the xylem is mostly symplastic and, in contrast to K + and Cl -, there exists considerable resistance to the flow of Na + from the xylem to the adjacent mesophyll and epidermis. The parallel veins of the lamina are enclosed by several layers of bundle sheath parenchyma; in contrast, the large vascular bundle that encircles the entire lamina, and into which the parallel veins merge, lacks a complete bundle sheath. Xylem sap containing a high concentration of Na + is 'pulled' by water tension from the marginal vein back into the adjacent mesophyll without having to cross a layer of parenchyma tissue. When the marginal vein was dissected from the lamina, the pattern of Na + distribution in the margins changed markedly. The distinct anatomy of the marginal vein plays a major role in the accumulation of Na + in the margins, with the latter serving as a 'dumping site' for toxic molecules.

Hydathode morphology and role of guttation in excreting sodium at different concentrations of sodium chloride in eddo

“…There are many salinity tolerance and response mechanisms in plants, such as ion homeostasis and compartmentalization, ion transport and uptake, and sodium excretion through hydathodes (Gupta & Huang, 2014;Klepper & Kaufmann, 1966;Shapira et al, 2009). In this study, our results show that hydathodes do not play a role in sodium homeostasis in eddo.…”

“…Then, samples were frozen quickly in droplets of 50% (v/v) dimethyl sulfoxide with liquid nitrogen and cracked cross-ways or longitudinally with a razor blade. After melting, the samples were rinsed in distilled water, et al, 2010;Shapira et al, 2009). Plants generally maintain low sodium levels in the cytoplasm and/or high potassium ion (K + ):sodium ion (Na + ) ratios that are considered to alleviate salt injury.…”

“…Shapira et al (2009) reported that banana leaves exuded guttation fluid under mild salinity (2 mM NaCl), but ceased exuding guttation fluid as the degree of salinity increased. Higher NaCl treatments were also shown to suppress guttation in barley (Shabala et al, 2010) and rice seedlings (Doi & Kasaku, 1953).…”

Variação sazonal da concentração de nutrientes em folhas de bananeiras, no Vale do Ribeira-SP

“…As maiores concentrações de Fe nas folhas das bananeiras foram observadas logo após época de maior acúmulo de chuva ( Figuras 1A e 3D), provavelmente devido a maior disponibilidade no solo ocasionado pelo excesso de chuva e condição de redução, como observado por Abreu, Fernandes e Ruivo (2007). Considerando as concentrações foliares adequadas de Fe recomendadas por Silva et al (2002) Shapira et al (2009), devido à anatomia da folha da bananeira, o maior acúmulo de sódio ocorre nas margens das folhas, assim a parte da folha amostrada no presente experimento, e indicada para avaliação do estado nutricional, não deve ser a amais adequada para a detecção do excesso de Na.…”

The Heterogeneity and Spatial Patterning of Structure and Physiology across the Leaf Surface in Giant Leaves of Alocasia macrorrhiza

“…Another hypothesis for dieback at leaf edges is the effect of toxic contents of guttation fluids driven by root pressure out of hydathodes in the leaf margins. Thus, previous studies suggested that damages in the leaf margins of banana leaves [64], [65] can occur due to the concentration of ions, including boron, in guttated xylem sap. However, this mechanism appears less likely to explain the damage observed in A. macrorrhiza .…”