Phosphorus Accumulation and Toxicity in Leaves in Relation to Zinc Supply

Abstract

The relationship of zinc (Zn) deficiency to phosphorus (P) toxicity was examined in ‘Emerald’ okra [Abelmoschus esculentus (L.) Moench] grown for 21 days (D21) in complete nutrient solution and then transferred to treatments with two levels of P (P1, P2 = 250, 2,000 µM P) and four levels of Zn (Zn1, Zn2, Zn3, Zn4 = 0, 0.25, 1, 2 µM added Zn).No symptoms of “little leaf” or “rosetting” developed in any plants. “Mottle leaf” symptoms developed as chlorotic and necrotic patches in the interveinal areas of the older leaves of Zn1 plants at P1 and in Zn1, Zn2, and Zn3 plants at P2. Thus, increasing the level of P induced symptoms which were eliminated by adding Zn.Treatments had little effect on dry matter at D45 and D63: at D111, low Zn depressed dry weight of P1 tops and even more markedly depressed dry weight of P2 tops, roots, and fruits.Increasing solution P increased the concentration and amount of P in all plant parts at all harvests. At D45 it also depressed Zn concentrations in all parts of Zn1 plants but in no other Zn treatment and in no treatment at later harvests.At Zn1, leaves had relatively low concentrations of Zn and high concentrations of P. Increasing levels of Zn enhanced their Zn concentrations and depressed their P concentrations; at D45 and D63 they also depressed the concentrations and total amounts of P in tops and whole plants but increased them in roots. Thus Zn deficiency markedly enhanced P absorption by roots, transport to tops, and accumulation in leaves.Concentrations of magnesium in plant organs responded to treatments in the same way as did P but to a smaller degree, particularly in the leaves. No other element measured (Ca, K, Na, Fe, Cu, Mn) responded in the same way.The development and intensity of symptoms in old leaves correlated closely with P concentrations. Leaves with faint symptoms had 0.8% P; those with marked symptoms had > 1.5% P; and dead leaves had nearly 5% P. The intensification of symptoms is attributed to accumulation of P to toxic levels in leaves.It is suggested that Zn deficiency interferes with P metabolism enhancing the amounts of P absorbed by roots and transported to tops: under conditions of high P supply, P accumulates to toxic levels in leaves inducing or accentuating symptoms resembling Zn deficiency. This effect of Zn on P metabolism in roots seems to explain previously puzzling observations in which P treatments enhanced symptoms of Zn deficiency without any reduction in Zn contents of plant tops: there is no need to invoke any effect of P in inactivating Zn in leaves.

Growth and Nutrient Uptake by Barley (Hordeum vulgare L. cv Herta): Studies Using an N-(2-Hydroxyethyl)ethylenedinitrilotriacetic Acid-Buffered Nutrient Solution Technique (I. Zinc Ion Requirements)

“…Our results, and those of others, support the suggestion by Loneragan et al (1982) that Zn deficiency interferes with the control of ion uptake in a general way. In a companion paper (Welch and Norvell, 1993), we present evidence that Zn plays a role in the maintenance of root cell membranes, as first reported by Welch et al (1982).…”

Zinc-enriched fertilisers as a potential public health intervention in Africa

“…It may also be possible to breed lower PA concentrations into the grains of staple crops and the benefits of even marginal reductions in grain PA concentration on Zn bioavailability could be large at population scales (Joy et al 2014). Interestingly, it has been reported that Zn-enriched fertilisers can decrease concentrations of PA in cereal grains while Zn deficiency may lead to increased P uptake and accumulation in plants (Loneragan et al 1982;Erdal et al 2002).…”

Disponibilidade de zinco para milho em resposta à localização de fósforo no solo

“…Citam-se a baixa velocidade de translocação do Zn das raízes para a parte aérea (Souza et al, 2006); o efeito de diluição do Zn na parte aérea, pelo crescimento da planta, em resposta à adição do P (Marinho & Igue, 1972) ou o distúrbio metabólico nas células da planta, provoca do pelo desequilíbrio entre P e Zn (Loneragan et al, 1982). Souza et al (2006) constataram interação negativa entre P e Zn em mudas de cacaueiro, princi palmente nas raízes, o que resultou na redução da translocação de Zn para as folhas.…”

“…Souza et al (2006) constataram interação negativa entre P e Zn em mudas de cacaueiro, princi palmente nas raízes, o que resultou na redução da translocação de Zn para as folhas. Loneragan et al (1982) relataram que a deficiência de Zn estimula não só a taxa de absorção de P pelas raízes como também a translocação de P para a parte aérea. Este estímulo é específico para o Zn, não sendo verificado para outros micronutrientes.…”