Rapid industrialization, urbanization, and mine tailings runoff are the main sources of heavy metal contamination of agricultural land, which has become one of the major constraints to crop growth and productivity. Finding appropriate solutions to protect plants and agricultural land from heavy metal pollution/harmful effects is important for sustainable development. Phytoremediation and plant growth-promoting rhizobacteria (PGPR) are promising methods for this purpose, which both heavily rely on an appropriate understanding of the anatomical structure of plants. Specialized anatomical features, such as those of epidermis and endodermis and changes in the root vascular tissue, are often associated with heavy metal tolerance in legumes. This review emphasizes the uptake and transport of heavy metals by legume plants that can be used to enhance soil detoxification by phytoremediation processes. Moreover, the review also focuses on the role of rhizospheric organisms in the facilitation of heavy metal uptake, the various mechanisms of enhancing the availability of heavy metals in the rhizosphere, the genetic diversity, and the microbial genera involved in these processes. The information presented here can be exploited for improving the growth and productivity of legume plants in metal-prone soils.

Soybean has great potential as a high-quality leguminous forage, and research increasingly focuses on improving its forage quality. In addition to stem structural traits, petiole structure appears to be an important contributor to whole-plant digestibility. In this study, petiole anatomy of grain and forage soybean cultivars was analyzed using a stereological method. Volume densities (Vv) of petiole tissues were calculated and compared between grain and forage cultivars and along the petiole length, from the proximal to distal segments. Comparisons between cultivars originally grown for grain and forage revealed no significant differences in petiole anatomical parameters related to digestibility. They did not differ significantly in the proportions of lignified tissues (xylem and sclerenchyma) or parenchyma. Grain cultivars had higher Vv of petiole phloem, which supports more effective transport of photosynthetic products from the leaf blade to the grains. Lower proportions of epidermis and collenchyma, tissues forming a mechanical barrier to microbial penetration, were observed in grain cultivars rather than in forage cultivars. The most favorable combination of petiole anatomical traits, regarding digestibility, was observed in the forage cultivar ‘Tyrone’. This cultivar had the most desirable proportion of thin- and thick-walled cells, the lowest Vv of epidermis and collenchyma the highest Vv of parenchyma and the lowest Vv of xylem and sclerenchyma. The results indicate that grain cultivars also have potential to provide high-quality forage. Alongside stem traits, greater attention should be directed to the management of lignified tissues in petioles, which are important components of total herbage and influence its digestibility.