Balance zinc and iron in plants

Nutrient imbalances can negatively impact crop health and agricultural productivity. The trace elements zinc and iron are taken up by the same transporters in plants, so zinc deficiency can lead to excessive iron absorption. How does the plant deal with this imbalance? Researchers at Meiji University in Japan reveal that autophagy, the process of intracellular self-degradation, may have an unexpected role in restoring the zinc-iron balance in plants.

A balance of nutrients and minerals in the soil is essential for optimal plant growth. A deficiency or excess of specific nutrients can have adverse effects on the growth and health of plants, thus affecting the overall quality and quantity of agricultural products. Nutritional imbalances have become more and more frequent, given the excessive contamination with heavy metals from industrial activities.

Zinc, an essential trace element, is important for a number of important life processes. Interestingly, the absorption and transport of zinc and iron, another essential nutrient, are facilitated by a common group of proteins known as zinc and iron regulated transporter-type proteins (ZIPs). This means that a disturbance of this zinc-iron “swing” can thus lead to symptoms induced by their respective deficiencies. That is, if a soil does not contain enough zinc, ZIPs cope by increasing their iron absorption, which leads to an increase in reactive oxidative species and chlorosis (yellowing of the leaves). Conversely, an excess of zinc leads to a decrease in iron absorption. How is the intracellular balance of these nutrients restored in such situations?

Exploring the likely mechanisms of zinc-iron balance or “homeostasis,” researchers at Meiji University, Japan, explored the potential role of autophagy, a process of self-degradation and recycling, in restoring zinc-iron balance in plant cells. Describing their study, published in Trends in plant scienceCorresponding author and professor Dr Kohki Yoshimoto said: “While most studies have addressed the role of nutrient uptake and transport, we are proposing a new model for how autophagy delivers ions. zinc and iron motives in zinc starvation and excessive zinc stress, respectively; thus, balancing the intracellular zinc-iron rocker to accommodate a wide range of environmental zinc concentrations. “

Autophagy has already been shown to increase zinc availability in plant systems. In Arabidopsis, a plant model system, atg mutants, which are deficient in autophagy responses, have lowered zinc levels and exhibit severe chlorosis. Additionally, zinc deficiency is known to trigger autophagy, which replenishes mobile zinc ions for plant growth. In autophagy deficient mutants, however, this activation is impaired, leading to classic symptoms of zinc deficiency.

Excess zinc is also toxic to plants, and autophagy is the savior in such cases as well. Plants show symptoms of iron deficiency under conditions of excess zinc. Autophagy is activated under conditions of excess zinc to replenish mobile iron ions from non-mobile forms such as iron-bound proteins. Autophagy improves the bioavailability of iron and suppresses symptoms of iron deficiency.

Shifting from the role of autophagy in zinc-iron homeostasis, the researchers proceeded to elucidate the mechanisms for detecting the nutrients responsible for activating autophagy. The transcription factors bZIP19 and bZIP23, belonging to the basic leucine pathway family, detect changes in intracellular zinc levels and thus regulate the expression of transport proteins on the cell membrane. Researchers believe that these proteins could be the regulators that turn the autophagic response on or off depending on the state of the zinc. A similar mechanism can also come into play in iron deficiency conditions with excess zinc to restore iron levels.

Overall, autophagy functions as a feedback mechanism that can respond to stress induced by zinc deficiency or excess and, therefore, alter the bioavailable fraction of nutrients in plant cells.

Dr Yoshimoto said: “Our model offers a new perspective on metal homeostasis in plants. This can contribute to the development of new cultivation techniques and hardy crop varieties that resist fluctuations in nutrient levels. In addition, our results can also be applied to humans. health to resolve symptoms induced by zinc deficiency, a major problem in developing countries.

Provided by Meiji University