Open Access

ARTICLE

The Physiological Mechanisms Underlying N₂-Fixing Common Bean (Phaseolus vulgaris L.) Tolerance to Iron Deficiency

Abdelmajid Krouma^1,2,*

1 Faculty of Sciences and Techniques, University of Kairouan, Sidi Bouzid, 9100, Tunisia
2 Laboratory of Ecosystems and Biodiversity in Arid Land of Tunisia, Faculty of Sciences, University of Sfax, Sfax, Tunisia

* Corresponding Author: Abdelmajid Krouma. Email: -kairouan.tn

(This article belongs to the Special Issue: Abiotic and Biotic Stress Tolerance in Crop)

Phyton-International Journal of Experimental Botany 2023, 92(7), 2133-2150. https://doi.org/10.32604/phyton.2023.029048

Received 29 January 2023; Accepted 03 March 2023; Issue published 29 May 2023

Abstract

Iron is an essential element for plants as well as all living organisms, functioning in various physiological and biochemical processes such as photosynthesis, respiration, DNA synthesis, and N₂ fixation. In the soil, Fe bioavailability is extremely low, especially under aerobic conditions and at high pH ranges. In contrast, plants with nodules on their roots that fix atmospheric nitrogen need much more iron. To highlight the physiological traits underlying the tolerance of N₂-fixing common bean to iron deficiency, two genotypes were hydroponically cultivated in a greenhouse: Coco nain (CN) and Coco blanc (CB). Plants were inoculated with an efficient strain of Rhizobium tropici, CIAT899, and received a nutrient solution added with 0 µM Fe (severe Fe deficiency, SFeD), 5 µM Fe (moderate Fe deficiency, MFeD) or 45 µM Fe (control, C). Several physiological parameters related to photosynthesis and symbiotic nitrogen fixation were then analyzed. Iron deficiency significantly reduced whole plant and nodule growth, chlorophyll biosynthesis, photosynthesis, leghemoglobin (LgHb), nitrogenase (N₂ase) activity, nitrogen, and Fe nutrition, with some genotypic differences. As compared to CB, CN maintained better Fe allocation to shoots and nodules, allowing it to preserve the integrity of its photosynthetic and symbiotic apparatus, thus maintaining the key functional traits of the plant metabolism (chlorophyll biosynthesis and photosynthesis in shoots, leghemoglobin accumulation, and nitrogenase activity in root nodules). Plant growth depends on photosynthesis, which needs to be supplied with sufficient iron and nitrogen. Fe deficiency stress index (FeD-SI) and Fe use efficiency (FeUE) are two physiological traits of tolerance that discriminated the studied genotypes.

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