Effects Of Drought Stress On Barley Seedling Roots With Different Drought Resistance

Object: The objectives of this study were to investigate the effects of different drought treatments on the growth and development of barley with different drought resistance and to explore the physiological effect of rhizosheath under soil drought stress.Methods: Four barley cultivars Xinyin D9, Kenpi 6 as tolerant and Z027S078 T, Berenice as sensitive to drought were grown in pots in which the soil water content was maintained at 85% of field capacity(FC), 55% of FC, 45% of FC and 35% of FC by weighing and irrigating with distilled water daily, respectively. Morphological indexes, absorption capacity and the content of osmoprotectants, reactive oxygen species and malondialdehyde, and the activity of antioxidant enzymes were investigated in this study.Results: The results shows that :(1) The longest seminal root and the number of tips are decreased with the decreasing of soil water content, the number of forks, root/shoot ratio showed a rising trend in general and the root hair density raised at first and then decreased.(2) The active absorption area showed a decreasing trend while root activity raised at first and then decreased.(3) The content of proline and the activity of antioxidant enzymes in drought-tolerant cultivar was higher than that in sensitive one, while the degree of cell damage and the intracellular levels of reactive oxygen species were lower.(4) The soil drought can facilitate the formation of rhizosheath and increase in the length and quantity of root hair to some extent and we speculated that the rhizosheath was not only determined by the length of root hair, but it was also correlated with the amount distribution of root hair length.(5) There had no significant correlation between Xinyin D9 and Kenpi 6(P=0.780), however, a negative and significant correlation was observed among Berenice(P=0.001), Z027S078T(P<0.001) and Xinyin D9 in rhizosheath size. Rhizosheath size showed a significant positive correlation with the protective enzyme CAT and SOD(P<0.001), but it was significantly negative correlated with Pro(P<0.001) and MDA(P=0.001).Conclusion:(1) Under the condition of soil drought stress, root system can inhibit the root elongation and promote the lateral growth of root in soil.(2) There is a certain complementary effect between root activity and active absorption area.(3) The performance of drought-tolerant cultivars is superior to the sensitive one in face of soil drought stress, when it comes to antioxidant enzyme activity, membrane integrity and intracellular levels of ROS.(4) There may be formed a buffer zone called rhizosheath in which the soil water content is relatively high between root and bulk soil to prevent the cell from dehydration. In that case, the rhizosheath can maximum maintain the integrity of lipid and membrane and won’t be the obstacle to root sensing the stress signal. So the plant not only reduce the damage of root cell, but also receipt the primary signal of soil drought and trigger a serious of antioxidant system by a complex secondary signal transduction net.