关键词: 杨树, 耐涝性, 根, 解剖结构, 超微结构

Abstract:

Waterlogging stress, one of the most important abiotic stresses, has induced a huge losses of poplar woody products in plain river network area of China. In order to elucidate flood-tolerance mechanism of poplar, two poplar species Populus deltoides ‘Lux’ ex I-69/55 (flood-tolerant) and P. simonii (flood-susceptible) were adopted as the materials to investigate influences of waterlogging stress on cell structure of primary roots. The flooding treatment was conducted on seedlings of the two species with height of 90-100 cm for 14 days, followed by 3 days drainage and recovery. During the study, phenotype of all the seedlings was observed every day, and root segmentsat 2.0-3.5 cm from the root tip of fine roots of the two species were sampled on day 0,1,3,7 and 14 of waterlogging stress. Responses of anatomy and ultrastructure of these roots to waterlogging stress were investigated by using methods of paraffin section and transmission electron microscope. Results showed: 1) Decreased stem growth, retarded leaf initiation and development, chlorosis and abscission of leaves, as well as development of hypertrophied lenticels all occurred in both of the two species under flooding treatment. With the waterlogging stress prolonged, most hypertrophied lenticels of P. simonii turned brown and became rotten, whereas they maintained normal fine in P. deltoides ‘Lux’ ex I-69/55. At the end of the study, survival rate of the latter were five times that of the former. 2) Waterlogging stress induced formation of aerenchyma in the primary root of the two species. Comparing to P. simonii, P. deltoides ‘Lux’ ex I-69/55 formed its aerenchyma slower. On the 3^rd day of waterlogging stress, some cortical cells began to collapse and formed few irregular small cavities in roots of P. simonii. After flooded for seven days, more serious collapse, continuing increase and enlargement of cavities, as well as loose structure were observed in cortical cells of root of P. simonii. Whereas, in P. deltoides ‘Lux’ ex I-69/55, the cortical cells displayed only slight collapse and few irregular small cavities on the 7^th day of waterlogging stress. Till day 14 of flooding treatment, much more cortical cells collapsed and fused into numerous irregular big cavities in P. simonii, which resulted in separation between cortical cells and pericycle cells. However, the structare in P. deltoides ‘Lux’ ex I-69/55 still maintained the relative integrity. 3) After flooded for three days, obvious plasmolysis occurred in cortical cells of root of P. simonii, accompanied with destruction and decrease of mitochondria, endoplasmic reticulum and Golgi apparatus, as well as disappearance of starch grain and increase of osmophores. On the 7^th day of flooding treatment, P. simonii displayed more serious plasmolysis and severe destruction in mitochondria and other organelles in root cortical cells. Whereas, normal cortical cells and numerous organelles were still observed in root of P. deltoides ‘Lux’ ex I-69/55 root, except for slight plasmolysis. By day 14 of waterlogging stress, cracked cell wall, as well as seriously destroyed and decreased mitochondria were observed in cortical cells of root of P. simonii roots, and nucleus and other organelles were not found. Whereas, P. deltoides ‘Lux’ ex I-69/55 still had complete cell structure and numerous organelles, especially mitochondria. These results indicated that normal hypertrophied lenticels, fine aerenchyma, as well as numerous structural stable mitochondria played a vital role for poplar under waterlogging stress.

Key words: poplar, waterlogging tolerance, root, anatomical structure, ultrastructure