Comparison Of Physiological Responses To Drought Stress Induced By Polyethylene Glycol6000in Grass Pea(Lathyrus Sativus L.) And Pea(Pisum Sativum L.)

Grass pea (Lathyrus sativus L.) has been recognized as an important crop to be cultivated in arid and semi-arid areas for its extensive tolerance to drought and advantageous agronomic characters. Pea (Pisum sativum L.) which was reported to be less drought tolerant has a wild relative with grass pea. To elucidate the characteristics of grass pea in response to drought stress, we subjected7-day-old grass pea and pea seedlings to20%polyethylene glycol6000(PEG) for6d. Many morphological and physiological parameters were determined and analyzed in both leaves and roots of the two legumes, such as the levels of reactive oxygen species (ROS), malondialdehyde (MDA), proline, ethylene, several antioxidants as well as the activities and mRNA expression level of some antioxidant enzymes. The results are as follows:1. PEG inhibited the growth of both grass pea and pea. Remarkable declines were observed in the length and weight of shoot and root, leaf area, relative water content (RWC) and stomatal opening, in which the decline rates in pea were1.5-2times higher than that of grass pea. But the root/shoot ratio of grass pea and pea increased to2and1.7times of their respective controls. Moreover, curling or rolling of leaves as well as an increase of stoma density were found in grass pea, whereas leaves of pea failed to display these traits.2. The root vitality of grass pea increased to1.4times of control while it decreased slightly in the roots of pea after PEG treatment. O2·-, H2O2and malondialdehyde (MDA) accumulation increased in pea more than that in grass pea. At the same time, greater accumulation of proline were observed in grass pea (5times of control), with a higher amounts in roots, which helps to alleviate osmotic stress injury.3. It was found that the contents of ascorbic acid (ASC), ascorbate peroxidase (APX) and activities of the main antioxidant enzymes were increased significantly in grass pea, especially in the leaves, whereas the leaves and roots of pea showed less increases or kept unchanged. The mRNA expression level of Mn-SOD, CATand cytosolic APX showed a significant increase in grass pea leaves, whereas only Cu/Zn-SOD showed a remarkable increase in the leaves of pea. The expression level of these enzymes were lower in roots of the two species and no obvious changes were observed between control and treated groups.4. The production of ethylene was significantly enhanced to2times of control in leaves of both grass pea and pea, but no obvious changes were observed in the roots of the two legumes.From the results above we could see that under the same drought stress, grass pea exhibited better growth status and stronger defense responses than pea, revealing the high drought tolerance of grass pea. The strong tolerance of grass pea to drought was mainly relied on the adaptive changes in the morphology of leaves and roots, the enhanced root vitality, as well as the higher abilities of osmotic and antioxidant adjustment.