Uptake and distribution of root‐applied or foliar‐applied ⁶⁵Zn after flowering in aerobic rice

Abstract

We investigated the uptake and distribution of zinc (Zn) either applied to the roots or to the leaves in rice during grain development. Plants of two aerobic rice cultivars were grown in a nutrient solution with either sufficient Zn or surplus Zn. Root treatment with 1 week's supply of both 65 Zn and unlabelled Zn was started at flowering or 15 days after flowering (DAF). Foliar treatment with 65 Zn applied to the flag leaf or to senescent leaves was carried out at flowering. When 65 Zn was applied to roots, plants continued to take up Zn after flowering, even beyond 15 DAF, irrespective of cultivar and Zn nutritional status of the plants. During the 1 week of supply of both 65 Zn and unlabelled Zn, which either started at flowering or 15 DAF, the absorbed 65 Zn was mainly distributed to roots, stem and grains. Little 65 Zn was allocated to the leaves. Following a week of 65 Zn supply directly after flowering, under sufficient Zn or surplus Zn, the proportions of total 65 Zn uptake allocated to the grains continued to change during grain filling (9-33%). This Zn mainly came from the roots but under sufficient Zn supply also from the stem. With 65 Zn applied to leaves (either the flag leaf or the lowest senescent leaf), both cultivars showed similar Zn distribution within the plants. About 45-50% of the 65 Zn absorbed was transported out of the 65 Zn-treated leaf. From that Zn, more than 90% was translocated to other vegetative organs; little was partitioned to the panicle parts and even less to the grains. These results suggest that in rice plants grown under sufficient or surplus Zn supply, most of the Zn accumulated in the grains originates from uptake by roots after flowering and not from Zn remobilisation from leaves.

Characterization of 68Zn uptake, translocation, and accumulation into developing grains and young leaves of high Zn-density rice genotype

“…After anthesis stage, both of the rice genotypes continued to uptake the root-supplied Zn with high accumulation occurring in the rice grains (Table 3). This was consistent with the findings of cotton (Constable et al, 1988), red spring wheat (Miller et al, 1994), and aerobic rice (Jiang et al, 2007). Of the total plant Zn, 50% (cotton), 10% (wheat), or 20% (rice) was taken up between anthesis and maturity.…”

“…Following absorption by the root, Zn is rapidly transported via the xylem to the shoot (Riceman and Jones, 1958). In rice plant, adequate Zn supply leads to a high proportion of Zn located in the shoots (especially stems), while with toxic level of Zn supply (150 µmol/L), a higher proportion of total Zn may accumulate in the roots (Jiang et al, 2007). Zn appears to be most mobile in all micronutrients and its remobilization is closely related to leaf senescence (Marschner, 1995;Uauy et al, 2006).…”

“…Although the literature is limit for Zn transport from stems and leaves to rice grains, it is argued that it is different from wheat and barely (Stomph et al, 2009). Jiang et al (2007) have investigated the uptake and distribution of Zn during rice grain development and suggested that most of the Zn accumulated in the grains originates from uptake by root after flowering and not from Zn remobilization from leaves, both under sufficient or surplus Zn supply. However, previous researches showed that foliar Zn fertilizer still could increase Zn content in rice (Broadley et al, 2007;Wissuwa et al, 2008), which suggested that Zn retranslocation in plant especially in late development stage may be also important for Zn density in rice.…”

Moving micronutrients from the soil to the seeds: Genes and physiological processes from a biofortification perspective

“…In this wheat study, flag leaf and lower leaves were the major sources of remobilized micronutrients, in contrast to results from rice, where stems accounted for the major source of Zn remobilized to grain [13]. In another rice study, the authors concluded that remobilization accounted for very little grain Zn, and that uptake after anthesis supplied the majority of Zn to grain, with most Zn passing through stems, and only a small amount passing through leaves [25]. It is possible that differences in plant anatomy between rice and wheat [26] account for these contrasting observations, and highlights the importance of conducting similar experiments in a variety of plant species.…”

Nutritionally Enhanced Staple Food Crops

“…On the other hand, in rice, xylemtransported Zn from uptake during seed filling might be more important for Zn accumulation in seed than phloem-transported Zn remobilized from leaves (Ziang et al 2007(Ziang et al , 2008. It would seem that contrary to wheat (Zee and O'Brian 1970), there is no xylem discontinuity in the rice plant (Zee 1972;Krishnan and Dayanandan 2003).…”