Effects of Potassium Deficiency on Ascorbate-Glutathione Cycle Related to Leaf Senescence in Cotton.

In order to explore the changes in ascorbate-glutathione cycle in relation to leaf senescence under potassium (K) deficiency, field experiments were conducted in 2012 and 2013 using two cotton (Gossypium hirsutum L.) cultivars with contrasting K sensitivity (Simian 3, low-K-tolerant cultivar and Siza 3, low-K-sensitive cultivar) under two K levels (0 and 150 kg K₂O ha⁻¹). Results showed that K deficiency enhanced the early season flowering rate and yellow leaf ratio. The premature senescence of leaf subtending the cotton boll (LSCB) induced by K deficiency was characterized by early chlorophyll degradation. Although higher content of ascorbic acid (ASC) existed in the K-deficient leaf, higher hydrogen peroxide content was observed, which caused higher malondialdehyde content. Although lower dehydroascorbate reductase activity was observed under K deficiency, high ASC content was attributed to lower ascorbate peroxidase activity. The differences between Siza 3 and Simian 3 in response to K deficiency were that glutathione reductase activity decreased markedly only in Siza 3, but not in Simian 3.