[Hollow-bearing characteristics of Populus euphratica in the lower reaches of Tarim River, China].

We analzyed the hollow ratio of tree trunks, tree hole parameters, and its distribution characteristics among different DBH and tree height classes in a long-term monitoring plots of Populus euphratica forest at the Argan section in the lower reaches of Tarim River. The results showed that P. euphratica in the study area had a high hollow ratio, in that trees with hollowness accounted for 56% of the total individuals, with a absolute value of 159 tree·hm-2. The hollow ratio of P. euphratica showed significant difference among different DBH classes and tree height classes. The hollow ratio was positively correlated with DBH, and negatively correlated with tree height. The density of P. euphratica with hollowness was 560 ind·hm-2 and 2 ind·tree-1. Most of tree holes appeared on the tree trunk (57.1%) and mainly in the middle of the trunk (31.3%). The hole with a diameter of 5-15 cm accounted for the largest proportion (38.2%). The total number of tree holes, the number of tree holes per tree, and the diameter of holes were positively correlated with DBH and negatively correlated with tree height. The distribution of different tree hole types among different DBH classes and tree height classes was different, with inconsistent changing trends. The distribution of tree holes showed significant difference acorss orientations, with most of which mainly toward the west. The occurrence rate of tree hollow in P. euphratica desert riparian forest was more serious. The larger the DBH of poplar tree was, the more obvious the degree of hollow. Therefore, it is of great significance to strengthen the conservation of young poplar trees and to restore degraded desert riparian forests.

An ERF transcription factor from Tamarix hispida, ThCRF1, can adjust osmotic potential and reactive oxygen species scavenging capability to improve salt tolerance.

Ethylene-Responsive Factors (ERFs) are plant-specific transcription factors (TFs) involved in multiple biological processes, especially in abiotic stress tolerance. However, the ERFs from woody halophytes that are involved in salt stress have been little studied. In the present investigation, we characterized a subfamily member of ERF TFs from Tamarix hispida, ThCRF1, which responds to salt stress. ThCRF1 is a nuclear protein that binds to the motifs including TTG, DRE and GCC-box. Transient transformation was performed to generate T. hispida overexpressing ThCRF1 and RNA interference (RNAi)-silenced ThCRF1 to analyze its function using gain- and loss-of-function methods. Overexpression of ThCRF1 in T. hispida significantly improved tolerance to salt-shock-induced stress; by contrast, RNAi-silence of ThCRF1 significantly decreased tolerance to salt-shock-induced stress. Further experiments showed that ThCRF1 induces the expression of genes including those encoding pyrroline-5-carboxylate synthetase (P5CS), trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP), superoxide dismutase (SOD) and peroxidase (POD), which lead to enhanced proline and trehalose levels and increased SOD and POD activities. These results were further confirmed by studying transgenic Arabidopsis plants overexpressing ThCRF1. Therefore, the results suggested that ThCRF1 improves tolerance to salt-shock-induced stress by enhancing trehalose and proline biosynthesis to adjust the osmotic potential, and by improving SOD and POD activities to increase reactive oxygen species scavenging capability.