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Phosphate (Pi) is pivotal for plant growth and development. Pi deficiency triggers local and systemically regulated adaptive responses in Arabidopsis thaliana. Inhibition of primary root growth (PRG) and retarded development of lateral roots (LRs) are typical local Pi deficiency-mediated responses of the root system. Expression of Pi starvation-responsive (PSR) genes is regulated systemically. Here, we report the differential influence of iron (Fe) availability on local and systemic sensing of Pi by Arabidopsis. P-Fe- condition disrupted local Pi sensing, resulting in an elongated primary root (PR). Altered Fe homeostasis in the lpsi mutant with aberration in local Pi sensing provided circumstantial evidence towards the role of Fe in the maintenance of Pi homeostasis. Reporter gene assays, expression analysis of auxin-responsive genes (ARGs) and root phenotyping of the arf7arf19 mutant demonstrated the role of Fe availability on local Pi deficiency-mediated LR development. In addition, Fe availability also exerted a significant influence on PSR genes belonging to different functional categories. Together, these results demonstrated a substantial influence of Fe availability on Pi deficiency-mediated responses of ontogenetically distinct traits of the root system and PSR genes. The study also provided evidence of cross-talk between Pi, Fe and Zn, highlighting a complex tripartite interaction amongst them for maintaining Pi homeostasis.

Zinc (Zn) is an essential micronutrient which affects plant growth and development in deficiency and can be toxic when present in excess. In Arabidopsis thaliana , different families of cation transporters play pivotal roles in Zn homeostasis. In the present study, we evaluated the effects of Zn in its deficiency (0 μM; Zn-) and excess (75 μM; Zn++) on various morphophysiological and molecular traits. Primary root length was reduced in Zn- seedlings, whereas there were significant increases in the number and length of lateral roots under Zn- and Zn++ conditions, respectively. Concentration of various macro- and microelements showed variations under different Zn regimes and notable among them was the reduced level of iron (Fe) in Zn++ seedlings compared to Zn+. Certain members of the ZIP family (ZIP4, ZIP9, and ZIP12) showed significant induction in roots and shoots of the Zn- seedlings. Their suppression under Zn++ condition indicated their transcriptional regulation by Zn and their roles in the maintenance of its homeostasis. Zn-deficiency-mediated induction of HMA2 in roots and shoots suggested its role in effluxing Zn into xylem for long-distance transport. Attenuation in the expression of Fe-responsive FRO2 and IRT1 in Zn- roots and their induction in Zn++ roots provided empirical evidence toward the prevalence of a cross talk between Zn and Fe homeostasis. Variable effects of Zn- and Zn++ on the expression of subset of genes involved in the homeostasis of phosphate (Pi), potassium (K), and sulfur (S) further highlighted the prevalence of cross talk between the sensing and signaling cascades of Zn and macronutrients. Further, the inducibility of ZIP4 and ZIP12 in response to cadmium (cd) treatment could be harnessed by tailoring them in homologous or heterologous plant system for removing pollutant toxic heavy metals from the environment.

Anthocyanins are the largest and best studied group of plant pigments. However, not very much is known about the fate of these phenolic pigments after they have accumulated in the cell vacuoles of plant tissues. We have previously shown that magnesium treatment of ornamentals during the synthesis of anthocyanins in the flowers or foliage caused an increase in the pigment concentration. In this study, we characterized the effect of magnesium on the accumulation of anthocyanin in red cell suspension originating from Vitis vinifera cv. Gamay Red grapes. Magnesium treatment of the cells caused a 2.5- to 4.5-fold increase in anthocyanin concentration, with no substantial induction of the biosynthetic genes. This treatment inhibited the degradation of anthocyanins occurring in the cells, and changed the ratio between different anthocyanins determining cell color, with an increase in the relative concentration of the less stable pigment molecules. The process by which magnesium treatment affects anthocyanin accumulation is still not clear. However, the results presented suggest at least part of its effect on anthocyanin accumulation stems from inhibition of the pigments' catabolism. When anthocyanin biosynthesis was inhibited, magnesium treatments prevented the constant degradation of anthocyanins in the cell suspension. Future understanding of the catabolic processes undergone by anthocyanins in plants may enable more efficient inhibition of this process and increased accumulation of these pigments, and possibly of additional phenolic compounds.

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