Crosstalk between sulfur and iron nutrition
Author(s)
Celletti, Silvia
Date Issued
June 27, 2016
Type
Doctoral Thesis
Abstract
Growth and development of plants mainly depend on the availability of water and nutrients in their
habitat. Increasing food production to face the rise of global population will require to exploit
uncultivated or abandoned arable land, some of which with unfavorable soil mineral composition or
availability, and to reduce the use of fertilizers for more sustainable practices. Therefore,
understanding the mechanisms underlying nutrients acquisition by plants and improving plant
nutrient use efficiency (NUE) is of social, economic, agricultural, and ecological importance.
The availability of nutrients in different soils and how it influences the physiology of the plants has
been widely described at the level of single nutrient. However, this picture is most likely
confounded by nutrient interactions. In nature it is unlikely that plants are exposed to a single
nutrient deficiency. Multiple nutrient deficiency situations are more likely to occur. For example,
agricultural soils are becoming depleted for important elements, such as sulfur (S), while iron (Fe),
although being highly abundant in the soil, is poorly available for uptake due to its insolubility in
the soil. Therefore, interactions among the various mineral elements need to be investigated
urgently in order to understand how the different sensing and signaling pathways activated in
response to changes in availability of one element are coordinately integrated with those of other
elements. The main problem in studying nutrient interactions is that, in some cases, stress responses
are antagonistic, while in other ones are either additive or synergistic, thus combined nutrient
deficiencies very often result as a new condition, that requires different responses from those
observed when plant response to deficiency of a single nutrient is described.
The aim of this thesis was to provide a comprehensive understanding of the molecular,
physiological, and biochemical interactions underlying S and Fe nutrition and how these two
essential nutrients are associated within the plant and one may impact the uptake, transport and
storage of another.
In particular, the present thesis deal with three key questions for this critical research area: 1) New
functions for S in improving plant efficiency to uptake, transport or accumulate Fe; 2) New
mechanisms underlying Fe homeostasis and how these are impacted by S; 3) Crop management
strategies that minimize Fe deficiency without additional input of Fe fertilizers.
Since monocots and dicots have, for the most part, distinct mechanisms for regulating Fe
acquisition, both Strategy I and Strategy II plants (tomato and durum wheat, respectively) were
considered.
As a result of the different approaches used in the research, several novel acquisitions have been
achieved from the analysis of S/Fe interaction.
As expected, it has to be assumed a complex regulatory system, wherein S and Fe starvation induce
partially overlapping and partially distinct response mechanisms, which coordinate plant response
to either or to joint starvations. A high degree of common and even synergistic response patterns as
well as nutrient specific responses were identified by the metabolomic approach in tomato.
Furthermore, it appears that tomato plants exposed to Fe deficiency are able to change S metabolic
balance mimicking S starvation responses through an increased sulfate uptake and root-to-shoot
translocation to meet the increased demand for ethylene and nicotianamine, allowing them to cope
with this stress.
On the other hand, the finding that in wheat plants changes in S accumulation were closely related
to plant capability to release phytosiderophores and correspondingly to accumulate Fe could be
significant to overcome a key challenge in plant Fe nutrition: the optimization of Fe acquisition and
allocation based on a sustainable new approach with low cost and decreased requirements for Fe
fertilizers.
Besides being a promising approach, whereby targeted application of one nutrient (S) could be used
to overcome the deficiency of another (Fe), it could be also a promising tool to increase the
micronutrient content (Fe) in food crops. This could lead to a decrease, in the long term, of
chemical inputs, getting healthier food and respecting the surrounding environment of the cultivated
crops, as well as the health of the agricultural workers.
Furthermore, the identification of the Fe availability level, below which durum wheat plants start an
expensive metabolic reorganization of S and several other elements, could be particularly important
not exclusively for the cost of the metabolic reorganization underlying the adaptive responses to the
Fe shortage but also for the grain quality that this process may affect. In fact, it is well known that S
is relevant for bread and pasta-making qualities through its effect on grain protein composition.
In conclusion, to extend these concepts, we need to develop a better understanding of how Fe/S
interactions take place at a mechanistic level and, for that, a multi-stage comprehensive approach is
necessary.
Additional information
Dottorato di ricerca in Scienze e tecnologie per la gestione forestale e ambientale