We previously reported that the seedlings of a mangrove, Rhizophora mucronate (Rhizophoraceae; formerly R. stylosa), exhibited very low survivability when cultured in the absence of NaCl. This suggests that R. mucronate is an obligate halophyte (plant that absolutely requires salt for survival), but the possible mechanism for the apparent salt requirement in R. mucronate remains unclear. In the present study, we examined the possibility that R. mucronate utilizes Na⁺ as a co-transport ion for the uptake of nutrient ions, as is known for the seagrass Zostera marina. To minimize the influence of individual differences in ion uptake activities among sample plants, we adopted a modified split-root method. In this method, the root system of an individual R. mucronate seedling was split into two halves by making a longitudinal cutting into the lower halves of their hypocotyl. Then, each half was respectively immersed in a culture medium that did or did not contain 240 mM NaCl, and the rates of nutrient (phosphate, nitrate, and ammonium ions) uptake in the presence or absence of Na⁺ were measured in a single seedling and compared. The results demonstrated that ion uptake in R. mucronate was, in contrast to the case with Z. marina, not hindered in the absence of Na⁺, suggesting that nutrient uptake in R. mucronate is not dependent on Na⁺. Based on this and other results, possible alternative mechanism(s) for the apparent Na⁺-requirement observed in R. mucronate seedlings are discussed.

我们以前曾报道过，在没有NaCl的情况下培养时，红树林的毛根霉（Rhizophoraceae；原名R. stylosa）的幼苗表现出非常低的存活率。这表明粘酸罗氏沼虾是专性的盐生植物（绝对需要盐才能生存的植物），但对粘酸罗氏沼虾明显的盐分需求的可能机制仍不清楚。在本研究中，我们研究了丁酸克鲁维酵母利用Na ⁺作为吸收营养离子的共转运离子的可能性，这对于海草Zostera滨海区是众所周知的。为了最大程度地减少样本植物之间离子吸收活性中个体差异的影响，我们采用了改进的分裂根法。在该方法中，通过纵向切割其下胚轴的下半部分，将单个丁酸假单胞菌幼苗的根系分成两半。然后，将每半分别浸入含有或不含240 mM NaCl的培养基中，并在单个幼苗中测量存在或不存在Na ⁺的养分（磷酸盐，硝酸盐和铵离子）的吸收速率。并进行比较。结果表明，与Z. marina的情况相反，在没有Na ⁺的情况下，丁酸丁香中的离子吸收没有受到阻碍。提示粘酸罗非鱼的营养吸收与Na ⁺无关。基于此结果和其他结果，讨论了在芥酸丁香幼苗中观察到的明显Na ^+需求的可能替代机制。