Proline enhances growth, productivity and anatomy of two varieties of Lupinus termis L. grown under salt stress

• Proline can alleviate the adverse effects of soil salinity on Lupinus termis L. plants.
• Growth and yield of Lupinus termis L. plants are maximized by proline under salinity stress.
• Leaf photosynthetic pigments are maintained by proline application under soil salinity.
• Increased alkaloids with salinity are reduced by exogenous proline.
• Stem anatomical traits are improved by proline application under salinity stress.

To assess the ameliorative effects of exogenous proline application on salinity stress, 20, 35 and 50-day old seedlings of two lupine varieties (i.e., Giza 1 and Giza 2) grown on a saline soil (i.e., 6.35 – 6.45 dS m- 1) were sprayed with 0 (tap water as a control), 3, 6 or 9 mM proline. This study was conducted in two seasons of 2012/2013 and 2013/2014. All proline levels caused a significant increase in growth characteristics, physiological attributes, yields and anatomical traits of both lupine varieties compared to the control. Among proline concentrations, 6 mM proline led to the highest levels of plant growth, leaf photosynthetic pigments, total soluble sugars, endogenous proline and yields, and represented the best anatomical characteristics of the two lupine varieties. In contrast, the 6 mM proline level caused the lowest levels of alkaloids under salinity stress. Giza 2 variety was found to generate better growth and yield, thus reflecting more salt-tolerance than Giza 1 variety. This study highlights the potential ameliorative effects of proline in mitigating the adverse effects of salinity stress in growing plants. To enhance lupine plant growth and productivity in saline soils, we recommend the use of proline as a commercial formulation.