Growth, Physiological, Biochemical, and Transcriptional Responses to Drought Stress in Seedlings of Medicago sativa L., Medicago arborea L. and Their Hybrid (Alborea)

Eleni Tani,Penelope Bebeli,Xristina Vaharidi,Effie Sarri,Evangelia Chronopoulou,Εleni Abraham,Nikolaos Labrou,Maria Psychogiou,Alexia Tornesaki,Μaria Goufa

doi:10.3390/agronomy9010038

Abstract

Medicago sativa L. is a tetraploid perennial forage legume of great agronomical interest. The increasing need for its use under water-deficit conditions as well as low-input systems demands further improvement of its drought tolerance. On the other hand, Medicagoarborea L. is a perennial leguminous shrub, which is knownas a drought-tolerant species. In the present study, drought stress responses of the aforementioned medicago species, along with their hybrid, named Alborea, were comparatively assayed at the morphological, physiological, biochemical, and transcriptional levels. In particular, transcript abundance of representative genes that: (a) control ion transport, intracellular Na+/H+ antiporters(NHX1) and rare cold inducible2A (RCI2A); (b) have an osmotic function Δ1-pyrroline-5-carboxylate synthetase 1 (P5CS1); and (c) participate in signaling pathways and control cell growth and leaf function stress-induced mitogen-activated protein kinases kinases (SIMKK), Zinc Finger (ZFN), apetala2/ethylene-responsive element binding (AP2/EREB), basic leucine zipper (bzip) and Medicago sativa Helicase 1(MH1) were evaluated. Under well-watered conditions, the studied population of Alborea showed the highest stem elongation rate and photosynthetic rate that were dramatically reduced under drought conditions compared to M. sativa and M. arborea. Under drought conditions, the studied population of M. arborea showed less reduction of relative water content, all gas-exchange parameters, less lipid peroxidation, and more antioxidant capacity. Moreover, transcriptional analysis demonstrated that the population of M. arborea exhibited significantly higher transcript levels of drought-responsive genes in both leaves and roots under drought stress conditions. M. sativa has better antioxidant capacity than Alborea and had a higher induction of stress-related genes, thus it performs better than Alborea under drought conditions. Among the studied genes, it seems that AP2/EREB play a critical role in the response of the studied population to drought stress.

Highlights

Drought is one of the most important environmental stresses limiting crop yields and productivity all over the world [1]
The morphological parameters were significantly reduced under drought stress (Table 2) compared to the control. Significant interaction for both seedling height and Stem elongation rate (SER) was detected between entries (M. sativa, M. arborea, Alborea) and dates of drought stress indicating a different response of the entries during the drought treatment (Figure 1a,b)
The SER of Alborea’s population was rapidly declined by about 98% after three weeks of water deficit, whereas the SER of population of M. sativa and M. arborea was gradually reduced by about 90% and 75% respectively (Figure 1b)

Summary

Introduction

Drought is one of the most important environmental stresses limiting crop yields and productivity all over the world [1]. As the world’s population is increasing rapidly, the amount of available agricultural land is shrinking mainly due to habitat use and climate change. It is of great importance to exploit drought-affected land to meet the increasing world food demand and energy needs [2]. Plants react to the water deficit by the regulation of different physiological and biochemical processes such as water relation, gas exchange, photosynthesis, and the metabolism of organic compounds [3] as well as by adjustments of the membrane system [4]. Water deficit severely affects the photosynthesis process in all its phases mainly due to decrease of CO2 diffusion to the chloroplast and to metabolic constraints [5]. Plants accumulate compatible solutes such as proline that can stabilize proteins, to facilitate water absorption by decreasing the cytoplasmic osmotic potential, and to remove excess levels of Reactive Oxygen Species (ROS) maintaining cellular redox balance [1,6]

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