By cultivating tipburn-susceptible plants in modified Hoagland’s medium containing of gradient exogenous calcium (Ca2+), we have shown that Ca2+ deficiency is one of the main causes of tipburn in Chinese cabbage (Brassica rapa L. ssp. pekinensis). The effect of endogenous plant Ca2+ concentrations on tipburn was also studied in a doubled haploid (DH) population consisting of 100 individuals, but no correlation was found. We then examined the expression of 12 Ca2+ transporter genes that function in cytosolic Ca2+ homeostasis in both tipburn-susceptible and tipburn-resistant plants under normal and tipburn-inducing conditions. Expression patterns for most of these genes differed between the two types of plants. Salicylic acid (SA) accumulated in response to conditions of calcium deficiency in our study, and both total SA and SA β-glucoside (SAG) in tipburn-susceptible plants was ∼3-fold higher than it was in resistant plants following Ca2+ deficiency treatment. Also, the changes observed in SA levels correlated well with cell death patterns revealed by trypan blue staining. Therefore, we speculate that the cytoplasmic Ca2+ fluctuation-induced downstream signaling events, as well as SA signaling or other biological events, are involved in the plant defense response to tipburn in Chinese cabbage.

中文翻译：

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内源性水杨酸对大白菜 (Brassica rapa L. ssp. pekinensis) 缺钙性烧灼感的影响

通过在含有梯度外源钙 (Ca2+) 的改良 Hoagland 培养基中培养易烧灼感的植物，我们已经表明 Ca2+ 缺乏是大白菜 (Brassica rapa L. ssp. pekinensis) 烧灼感的主要原因之一。还在由 100 个个体组成的双单倍体 (DH) 群体中研究了内源性植物 Ca2+ 浓度对tipburn 的影响，但未发现相关性。然后，我们检查了在正常和诱导尖端灼伤的植物中的 12 个 Ca2+ 转运蛋白基因的表达，这些基因在对尖端灼伤易感植物和抗尖端灼伤植物中的细胞质 Ca2+ 稳态中起作用。大多数这些基因的表达模式在两种植物之间有所不同。在我们的研究中，水杨酸 (SA) 在钙缺乏条件下积累，在缺钙处理后，茎尖烧伤易感植物中的总 SA 和 SA β-葡萄糖苷 (SAG) 比抗性植物中的总 SA 和 SA β-葡萄糖苷 (SAG) 高约 3 倍。此外，观察到的 SA 水平变化与台盼蓝染色揭示的细胞死亡模式密切相关。因此，我们推测细胞质 Ca2+ 波动诱导的下游信号事件，以及 SA 信号或其他生物事件，参与了大白菜对尖烧的植物防御反应。