Stress Responsive Zinc-finger Protein Gene of Populus euphratica in Tobacco Enhances Salt Tolerance Cloning and Expression Analysis of a B-box-type Zinc-finger Protein Gene PhBBX8 in Petunia hybrida Transformation of Zinc Finger Protein Transcription Factor Gene (ZxZF) and Preliminary Evaluation of Drought Tolerance in Populus × euramericana Cloning and Expression Analysis of a B-box-type Zinc-finger Protein Gene PhBBX8 in Petunia hybrida