Abstract:

The rare earth element lanthanum （La） as a heavy metal can cause stress damage to crops at high concentrations. In order to explore the mitigative effect of exogenous cysteine （Cys） on La stress in naked oats （Avena nuda） and its physiological mechanism， the effects of spraying Cys （0.0， 0.5， 1.0， 2.5， 5.0 mmol·L^-1） at heading stage on the metabolism of reactive oxygen species （ROS） and osmotic regulation in leaves of naked oats under 400 mg·kg^-1 La stress， were studied in a pot experiment. Measurements made included agronomic yield traits and the absorption and accumulation of La at crop maturity. It was found that the increase in superoxide anion content in naked oat leaves under La stress was alleviated by spraying 0.5-2.5 mmol·L^-1 Cys. Spraying 0.5-5.0 mmol·L^-1 Cys significantly alleviated increase in hydrogen peroxide and malonaldehyde contents in leaves of naked oat under La stress， and improved the shoot biomass， grains per spike， grain weight per spike， and grain yield of naked oats， but had no significant effect on plant height and 1000-grain weight. Spraying 0.5-5.0 mmol·L^-1 Cys significantly reduced the activities of superoxide dismutase and peroxidase， and ascorbic acid and carotenoid contents， and increased ascorbic acid peroxidase activities， glutathione and phytochelatin contents in leaves of naked oats under La stress. Spraying 0.5 and 1.0 mmol·L^-1 Cys significantly increased catalase （CAT） activity， while spraying 2.5 and 5.0 mmol·L^-1 Cys significantly decreased CAT activity. Spraying 0.5-5.0 mmol·L^-1 Cys significantly alleviated the decrease of soluble protein and soluble sugar contents in naked oat leaves under La stress， and further improved the proline content. Spraying 2.5 mmol·L^-1 Cys had the best effect. With increase in the spraying concentration of Cys， the enrichment capacity and absorption and accumulation of La in root， stem and leaf of naked oat under La stress were significantly increased， by 4.5%-41.3% and 4.4%-41.2%， respectively， but there was no significant effect on the transport of La to different parts of the naked oat plant. The above results showed that although exogenous Cys increased the absorption and enrichment of La in naked oats， the oxidative damage to cells and inhibition of agronomic yield traits caused by La stress was alleviated by regulation of the ROS scavenging system and promotion of the accumulation of osmoregulatory substances， thus enhancing the tolerance of naked oats to La stress.

Key words: cysteine, naked oat, La stress, physiological mechanism