Abstract
Legumes develop root nodules that harbor endosymbiotic bacteria, rhizobia. These rhizobia convert nitrogen to ammonia by biological nitrogen fixation. A thorough understanding of the biological nitrogen fixation in legumes and its regulation is key to develop sustainable agriculture. It is well known that plant hormones affect nodule formation; however, most studies are limited to model legumes due to their suitability for in vitro, plate‐based assays. Specifically, it is almost impossible to measure the effects of exogenous hormones or other additives during nodule development in crop legumes such as soybean as they have huge root system in soil. To circumvent this issue, the present research develops suitable media and growth conditions for efficient nodule development under in vitro, soil‐free conditions in an important legume crop, soybean. Moreover, we also evaluate the effects of all major phytohormones on soybean nodule development under identical growing conditions. Phytohormones such as abscisic acid (ABA) and jasmonic acid (JA) had an overall inhibitory effect and those such as gibberellic acid (GA) or brassinosteroids (BRs) had an overall positive effect on nodule formation. This versatile, inexpensive, scalable, and simple protocol provides several advantages over previously established methods. It is extremely time‐ and resource‐efficient, does not require special training or equipment, and produces highly reproducible results. The approach is expandable to other large legumes as well as for other exogenous additives.
Highlights
Nitrogen is an essential element for plant growth, development and productivity
The results presented describe a set of optimum growth and treatment conditions for soil-free soybean nodulation and effects of phytohormones on it, which will be useful for the community at large
The hairy roots were generated from trifoliate leaf containing upper part of soybean plants by applying nitrogen free media, which is an established protocol for the study of soybean nodulation [39,40]
Summary
Nitrogen is an essential element for plant growth, development and productivity. Improving the nitrogen amount available to plants results in significant increases in crop yields. Present in huge quantities in the atmosphere (78% of earth’s atmosphere), this nitrogen is not available to the plants, unless fixed by biological nitrogen fixation This biological nitrogen occurs by the activity of specialized groups of bacteria, which exists as symbionts with the roots of leguminous plants in specialized structures called root nodules. Active NFRs stimulate downstream signaling pathways through nuclear Ca2+ oscillations and Ca2+ spiking to begin nodule organogenesis from the cortical cells [4,5]. All these signaling and organogenesis events are significantly affected by the hormonal balance inside the leguminous plants, which is triggered by the Nod signals produced by bacteria [6]
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