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International audience; Inorganic phosphate (Pi) and zinc (Zn) are two essential nutrients for plant growth. In soils, these two minerals are either present in low amounts or are poorly available to plants. Consequently, worldwide agriculture has become dependent on external sources of Pi and Zn fertilizers to increase crop yields. However, this strategy is neither economically nor ecologically sustainable in the long term, particularly for Pi, which is a non-renewable resource. To date, research has emphasized the analysis of mineral nutrition considering each nutrient individually, and showed that Pi and Zn homeostasis is highly regulated in a complex process. Interestingly, numerous observations point to an unexpected interconnection between the homeostasis of the two nutrients. Nevertheless, despite their fundamental importance, the molecular bases and biological significance of these interactions remain largely unknown. Such interconnections can account for shortcomings of current agronomic models that typically focus on improving the assimilation of individual elements. Here, current knowledge on the regulation of the transport and signalling of Pi and Zn individually is reviewed, and then insights are provided on the recent progress made towards a better understanding of the Zn-Pi homeostasis interaction in plants.

Inorganic phosphate (Pi) and Zinc (Zn) are essential nutrients for normal plant growth. Interaction between these elements has been observed in many crop plants. Despite its agronomic importance, the biological significance and genetic basis of this interaction remain largely unknown. Here we examined the Pi/Zn interaction in two lettuce (Lactuca sativa) varieties, namely, “Paris Island Cos” and “Kordaat.” The effects of variation in Pi and Zn supply were assessed on biomass and photosynthesis for each variety. Paris Island Cos displayed better growth and photosynthesis compared to Kordaat under all the conditions tested. Correlation analysis was performed to determine the interconnectivity between Pi and Zn intracellular contents in both varieties. Paris Island Cos showed a strong negative correlation between the accumulation levels of Pi and Zn in shoots and roots. However, no relation was observed for Kordaat. The increase of Zn concentration in the medium causes a decrease in dynamics of Pi transport in Paris Island Cos, but not in Kordaat plants. Taken together, results revealed a contrasting behavior between the two lettuce varieties in terms of the coregulation of Pi and Zn homeostasis and provided evidence in favor of a genetic basis for the interconnection of these two elements.

The present study was fixed as objective to compare the response to water deficit (33% of field capacity, FC) stress of eight cultivars of Medicago sativa, originating from the Mediterranean basin. Comparison was performed on some key parameters such as growth, relative water content, leaf water potential, MDA tissue content, electrolyte leakage and proline and soluble sugar tissue concentrations. In all cultivars, water deficit stress reduced the whole plant growth, increased the root/shoot DW ratio and led to a significant decrease in leaf relative water content and leaf water potential. In water-stressed plants and for the majority of cultivars, proline and soluble sugar concentrations increased significantly. The Tamantit cultivar originating from Algeria showed the better tolerance to water deficit stress. Some criteria are concomitant with this tolerance: (1) a high biomass production under stress conditions when compared to other cultivars (2) the root preferential development, (3) the better ability to accumulate proline and soluble sugars, and (4) the aptitude to protect its photosynthetic apparatus against the oxidative stress generated by the water deficit stress. Ecotipo Siciliano, originating from Italy was the most sensitive cultivar. The increase of proline and soluble sugars concentrations upon water deficit stress particularly in the most tolerant cultivar suggested their involvement in the osmotic adjustment.Key words: Medicago sativa, intraspecific variability, water deficit stress, osmotic adjustment, MDA.