Exogenous brassinosteroid alleviates calcium deficiency induced tip-burn by regulating calcium transport in Brassica rapa L. ssp. pekinensis.

Mini Chinese cabbage (Brassica rapa L. ssp. Pekinensis) plays an important role in the supply of summer vegetables on the plateau in western China. In recent years, tip-burn has seriously affected the yield, quality and commodity value of mini Chinese cabbage. Calcium (Ca ²⁺ ) deficiency is a key inducer of tip-burn. As a new type plant hormone, brassinolide (BR) is involved in regulating a variety of biotic and abiotic stresses. To explore the alleviation role of BR in tip-burn caused by Ca ²⁺ deficiency, a hydroponic experiment was conducted to study the relationship between BR and Ca ²⁺ absorption and transport. The results showed that foliar spraying with 0.5 µM BR significantly reduced tip-burn incidence rate and disease index of mini Chinese cabbage caused by Ca ²⁺ deficiency. Moreover, the dynamic monitoring results of tip-burn incidence rate showed that the value reached the highest on the ninth day after treatment. BR promoted the Ca ²⁺ transport from roots to shoots and from outer leaves to inner leaves by increasing the activities of Ca ²⁺ -ATPase and H ⁺ -ATPase as well as the total ATP content, which provided power for Ca ²⁺ transport. In addition, exogenous BR upregulated the relative expression levels of BrACA4, BrACA11, BrECA1, BrECA3, BrECA4, BrCAX1, BrCAS and BrCRT2, whereas Ca ²⁺ deficiency induced down-regulation. In conclusion, exogenous BR can alleviate the Ca ²⁺ -deficiency induced tip-burn of mini Chinese cabbage by promoting the transport and distribution of Ca ²⁺ .
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2023. Published by Elsevier Inc.)