Influences of High Temperature Stress on Activity of Cell Defense Enzymes andMembrane Permeability in Leaves of Spinach Genetic Diversity and Relationship of Spinach Germplasm Revealed by AFLPs Two Isozymes of Glutamine Synthetase Observed in Spinach Leaves Genetic Diversity and Relationship of Spinach Germplasm Revealed by AFLPs Chlorophyll Metabolism of Spinach Leaves under Seawater Stress