Macler B A
Department of Botany, University of California, Berkeley, California 94720.
Plant Physiol. 1986 Sep;82(1):136-41. doi: 10.1104/pp.82.1.136.
The red alga Gelidium coulteri Harv. photosynthetically fixed [(14)C] bicarbonate at high rates under defined conditions in unialgal laboratory culture. The fixation rate and flow of photosynthate into various end products were dependent on the nitrogen status of the tissue. Plants fed luxury levels of nitrogen (approximately 340 micromolar) showed fixation rates several-fold higher than those seen for plants starved for nitrogen. The addition of NO(3) (-) or NH(4) (+) to such starved plants further inhibited fixation over at least the first several hours after addition. The majority of (14)C after incubations of 30 minutes to 8 hours was found in the compounds floridoside, agar and floridean starch. In addition, amino acids and intermediate compounds of the reductive pentose phosphate pathway, glycolytic pathway and tricarboxylic acid cycle were detected. Nitrogen affected the partitioning of labeled carbon into these compounds. Plants under luxury nitrogen conditions had higher floridoside levels and markedly lower amounts of agar and starch than found in plants limited for nitrogen. Amino acid, phycobiliprotein and chlorophyll levels were also significantly higher in nitrogen-enriched plants. Addition of NO(3) (-) to starved plants led to an increase in floridoside, tricarboxylic acid cycle intermediates and amino acids within 1 hour and inhibited carbon flow into agar and starch. Carbon fixation in the dark was only 1 to 7% of that seen in the light. Dark fixation of [(14)C]bicarbonate yielded label primarily in tricarboxylic acid cycle intermediates, amino acids and polysaccharides. Nitrogen stimulated amino acid synthesis at the expense of agar and starch. Floridoside was only a minor component in the dark. Pulse-chase experiments, designed to show carbon turnover, indicated a 2-fold increase in labeling of agar over 96 hours of chase in the light. No increases were seen in the dark. Low molecular weight pools, including floridoside, decreased 2- to 5-fold over this period under both light and dark conditions. Nitrogen status did not influence turnover. There was little or no organic carbon released into the culture medium over this period. The results are consistent with biosynthetic pathways to floridoside and agar that share the common intermediate UDP-d-galactose. It is hypothesized that synthesis of floridoside is regulated by nitrogen and light at the enzymic level.
红藻卡特利石花菜（Gelidium coulteri Harv.）在单种藻实验室培养的特定条件下，能以较高速率光合固定[¹⁴C]碳酸氢盐。固定速率以及光合产物向各种终产物的分配取决于组织的氮素状况。供给过量氮素（约340微摩尔）的植株，其固定速率比缺氮植株高出数倍。向缺氮植株添加硝酸根离子（NO₃⁻）或铵离子（NH₄⁺），至少在添加后的最初几个小时内会进一步抑制固定作用。在30分钟至8小时的孵育后，大部分¹⁴C存在于花苷、琼脂和红藻淀粉等化合物中。此外，还检测到了磷酸戊糖途径、糖酵解途径和三羧酸循环的氨基酸及中间化合物。氮素影响标记碳在这些化合物中的分配。处于高氮条件下的植株，其花苷水平较高，而琼脂和淀粉的含量则明显低于缺氮植株。富含氮素的植株中，氨基酸、藻胆蛋白和叶绿素水平也显著更高。向缺氮植株添加NO₃⁻会导致1小时内花苷、三羧酸循环中间产物和氨基酸增加，并抑制碳流向琼脂和淀粉。黑暗中的碳固定量仅为光照下的1%至7%。黑暗中[¹⁴C]碳酸氢盐的固定主要产生于三羧酸循环中间产物、氨基酸和多糖。氮素以牺牲琼脂和淀粉为代价刺激氨基酸合成。花苷在黑暗中只是次要成分。旨在显示碳周转的脉冲追踪实验表明，在光照下追踪96小时，琼脂的标记增加了2倍。黑暗中未见增加。包括花苷在内的低分子量库在这段时间内，无论在光照还是黑暗条件下都减少了2至5倍。氮素状况不影响周转。在此期间，几乎没有有机碳释放到培养基中。这些结果与花苷和琼脂的生物合成途径一致，它们共享共同的中间产物UDP - D -半乳糖。据推测，花苷的合成在酶水平上受氮素和光照调节。
