Roncal T, Ugalde U O, Irastorza A
Departamento de Química Aplicada, Facultad de Ciencias Químicas, Universiad del País Vasco, San Sebastián, Spain.
J Bacteriol. 1993 Feb;175(3):879-86. doi: 10.1128/jb.175.3.879-886.1993.
Addition of Ca2+ (1 to 10 mM) to submerged cultures of Penicillium cyclopium induces conidiation. Ca2+ induced an increase in cytosolic pH from approximately 7.00 to > 7.60 in less than 10 min, as determined with the fluorescent pH probe fluorescein. Measurement of the H(+)-ATPase activity in total membrane fractions did not show any stable activation in vivo as a result of Ca2+ treatment. By fluorescence ratio imaging microscopy, it was observed that vegetative hyphae exhibit a tip-to-base pH gradient, with the tip being more acidic. Ca2+ caused this gradient to dissipate within 10 min. The effect of several agents that are supposed to cause internal acidification, by different means, on conidiation was tested. Concentrations of these agents that did not significantly affect growth but inhibited Ca(2+)-induced conidiation also prevented the intracellular alkalinization observed after exposure to the cation. Calcium channel blockers (lanthanum, cobalt, verapamil, and nifedipine) were not able to inhibit Ca(2+)-induced conidiation, although their effect on calcium uptake was not evaluated. However, the combined results point towards externally bound Ca2+ as the primary agent of conidiation induction, causing changes in plasma membrane function which disrupt the pH gradient observed during apical growth.
向环孢青霉的深层培养物中添加Ca2+（1至10 mM）可诱导分生孢子形成。用荧光pH探针荧光素测定，Ca2+在不到10分钟内使胞质pH从约7.00升高至>7.60。对总膜组分中H(+)-ATPase活性的测定未显示Ca2+处理在体内有任何稳定的激活作用。通过荧光比率成像显微镜观察到，营养菌丝呈现出从顶端到基部的pH梯度，顶端酸性更强。Ca2+导致该梯度在10分钟内消失。测试了几种通过不同方式引起内部酸化的试剂对分生孢子形成的影响。这些试剂的浓度对生长无显著影响，但抑制Ca(2+)-诱导的分生孢子形成，同时也阻止了暴露于阳离子后观察到的细胞内碱化。钙通道阻滞剂（镧、钴、维拉帕米和硝苯地平）不能抑制Ca(2+)-诱导的分生孢子形成，尽管未评估它们对钙摄取的影响。然而，综合结果表明，外部结合的Ca2+是诱导分生孢子形成的主要因素，它会导致质膜功能发生变化，从而破坏顶端生长过程中观察到的pH梯度。
