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首页> 外文期刊>Marine biology >Buffer sensitivity of photosynthetic carbon utilisation in eight tropical seagrasses
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Buffer sensitivity of photosynthetic carbon utilisation in eight tropical seagrasses

机译：八种热带海草光合碳利用的缓冲敏感性

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摘要

Some of the mechanisms involved in inorganic carbon (Ci) acquisition by tropical seagrasses from the western Indian Ocean were described by Bjork et al. (Mar Biol 129:363-366, 1997). However, since then, it has been found that an additional, buffer-sensitive, system of Ci utilisation may operate in some temperate seagrasses (Hellblom et al. in Aquat Bot 69:55-62, 2001, Hellblom and Axelsson in Photos Res 77:173-191, 2003); this buffer sensitivity indicates a mechanism in which electrogenic H~+ extrusion may form acidic diffusion boundary layers, in which either HCO_3~--H~+ is co-transported into the cells, or where HCO_3~- is converted to CO_2 (as catalysed by carbonic anhydrase) prior to uptake of the latter Ci form. Because a buffer was used in the 1997 study, we found it important to reinvestigate those same eight species, taking into account the direct effect of buffers on this potential mode of Ci acquisition in these plants. In doing so, it was found that all seagrass species investigated except Cymodocea serrulata were sensitive to 50 mM TRIS buffer of the same pH as the natural seawater in which they grew (pH 8.0). Especially sensitive were Halophila ovalis, Halodule wrightii and Cymodocea rotundata, which grow high up in the inter-tidal zone (only ca. 50-65% of the net photosynthetic activity remained after the buffer additions), followed by the submerged Enhalus acoroides and Syringodium isoe-tifolium (ca. 75% activity remaining), while Thalassia hemprichii and Thalassodendron ciliatum, which grow in-between the two zones, were less sensitive to buffer additions (ca. 80-85% activity remaining). In addition to buffer sensitivity, all species were also sensitive to acet-azolamide (AZ, an inhibitor of extracellular carbonic anhydrase activity) such that ca. 45-80% (but 90% for H. ovalis) of the net photosynthetic activity remained after adding this inhibitor. Raising the pH to 8.8 (in the presence of AZ) drastically reduced net photosynthetic rates (0-14% remaining in all species); it is assumed that this reduction in rates was due to the decreased CO_2 concentration at the higher pH. These results indicate that part of the 1997 results for the same species were due to a buffer effect on net photosynthesis. Based on the present results, it is concluded that (1) photosynthetic Ci acquisition in six of the eight investigated species is based on carbonic anhydrase catalysed HCO_3~- to CO_2 conversions within an acidified diffusion boundary layer, (2) C. serrulata appears to support its photosynthesis by extracellular carbonic anhydrase catalysed CO_2 formation from HCO_3~- without the need for acidic zones, (3) H. ovalis features a system in which H~+ extrusion may be followed by HCO_3~--H~+ co-transport into the cells, and (4) direct, non-H~+-mediated, uptake of HCO_3~- is improbable for any of the species.
机译：Bjork等人描述了热带印度洋从西印度洋获取无机碳（Ci）的一些机制。 （Mar Biol 129：363-366，1997）。但是，从那时起，人们发现在某些温带海草中可能会使用一种额外的，对缓冲液敏感的Ci利用系统（Hellblom等人，Aquat Bot 69：55-62，2001； Hellblom和Axelsson，Photos Res 77）。 ：173-191，2003）；这种缓冲液敏感性表明了一种机制，其中电生H〜+挤压可形成酸性扩散边界层，其中HCO_3〜--H〜+共转运到细胞中，或其中HCO_3〜-转化为CO_2（经催化） （碳酸酐酶）吸收）。由于在1997年的研究中使用了缓冲液，因此，考虑到缓冲液对这些植物中Ci潜在获取方式的直接影响，我们发现对这8个物种进行重新研究很重要。这样做时，发现所有被调查的海草物种（除锯齿夜蛾）均对50 mM TRIS缓冲液敏感，该缓冲液的pH值与其生长的天然海水相同（pH 8.0）。尤为敏感的是椭圆形嗜盐菌，Whalodule wrightii和Cymodocea rotundata，它们在潮间带高高生长（添加缓冲液后仅保留了约50-65％的净光合作用活性），其次是淹没的钩状a虫和丁香。异叶ween叶（保留约75％的活性），而在两个区域之间生长的Thalsia hemprichii和Thalassodendron纤毛对缓冲液添加的敏感性较低（保留约80-85％的活性）。除了对缓冲液敏感外，所有物种还对乙酰唑胺（AZ，一种胞外碳酸酐酶活性的抑制剂）敏感。加入该抑制剂后，仍然保持45-80％的净光合作用活性（但对卵形嗜血杆菌为90％）。将pH值提高到8.8（在存在AZ的情况下）大大降低了净光合速率（所有物种中剩余的0-14％）；可以认为，速率的降低是由于在较高的pH值下CO_2浓度降低。这些结果表明，同一物种在1997年的结果中有一部分是由于对净光合作用的缓冲作用。根据目前的结果，可以得出以下结论：（1）在八种被调查物种中的六种中，光合作用Ci的获得是基于碳酸酐酶催化的酸化扩散边界层内HCO_3〜CO_2的转化，（2）Ser。通过细胞外碳酸酐酶催化HCO_3〜-形成CO_2来支持其光合作用，而无需酸性区；（3）卵形隐孢子虫具有H〜+挤出后可以跟随HCO_3〜--H〜+共转运的系统进入细胞，并且（4）对于任何物种，都不可能直接，非H〜+介导地摄取HCO_3〜-。

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