The role of nitrogen nutrition in high-temperature tolerance of the kelp, Laminaria saccharina (Chromophyta)
The role of nitrogen nutrition in high-temperature tolerance of the kelp, Laminaria saccharina (Chromophyta)
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DOI：
10.1111/j.0022-3646.1997.00800.x
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发表时间：
1997-10-01
影响因子：
2.9
通讯作者：
Gerard, VA
中科院分区：
文献类型：
--
作者：
Gerard, VA
通过比较来自纽约长岛海峡 (LIS) 的耐热生态型和来自缅因州大西洋 (ATL) 海岸的海带海带 (Laminaria saccharina (L.) Lamour) 的高温耐受机制。更高的耐热性并不归因于光合装置更高的热稳定性：LIS和ATL植物表现出相似的高温对光合能力（P-max）和量子产率（估计为可变叶绿素荧光与最大叶绿素荧光的比率，F-v/F-m）的短期影响。由于 LIS 植物的氮和蛋白质含量始终高于 ATL 植物，因此研究了氮营养与高温耐受性之间的相互作用。当在高氮供应和最佳温度（12℃）下生长时，LIS植物比ATL植物具有更高的光系统II反应中心（RCII）密度、两种卡尔文循环酶（核酮糖二磷酸羧化酶加氧酶[RUBISCO]和NADP依赖性甘油醛-3-磷酸脱氢酶[G3PDH]）的活性以及更高的P-max和F-v/F-m。此外，单个 ATL 植物表现出 RCII 密度和酶活性与氮和/或蛋白质含量的密切相关性。反过来，RCII 密度和酶活性的变化在很大程度上解释了植物间 P-max 和 F-v/F-m 的差异。在最佳条件下生长的单个 LIS 植物中，这些参数之间的关系通常很弱或缺乏，这显然是因为大量的氮消耗导致光合装置组件的储备过多。将富含氮的 LIS 和 ATL 植物暴露在超最佳温度（22 摄氏度）下 4 天，导致光合机构 (tau) 的最短周转时间增加和 P-max 降低，但对 F-v/F-m、RCII 密度、PSU 大小（叶绿素 a/RCII）或酶活性没有一致的影响。然而，当植物同时受到氮限制和热胁迫时，LIS 和 ATL 种群表现出截然不同的反应。限氮ATL植物的所有光合参数响应高温而急剧下降，导致每日净固碳率出现负值。相比之下，LIS植物的PSU尺寸有所减小，但其他参数（包括每日固碳量）保持在与最佳温度下限氮植物相似的水平。总体而言，LIS植物积累和维持高氮储备的能力似乎对于耐热性至关重要，因此对于在同时低氮供应和超优温度的夏季生存至关重要。 ATL植物也经历了夏季氮供应量低但没有超优温度的情况，不会积累大量的氮成分储备，并且无法耐受综合胁迫。由于低氮供应通常与高温海洋系统中的高温同时发生，因此藻类生产力的大规模下降（例如在厄尔尼诺事件期间）可能是由于氮限制和热应激的相互作用造成的。
Mechanisms of high-temperature tolerance in the kelp Laminaria saccharina (L.) Lamour, were examined by comparing a heat-tolerant ecotype from Long Island Sound (LIS), New York, and a population from the Atlantic (ATL) coast of Maine. Greater heat tolerance was not attributable to greater thermal stability of the photosynthetic apparatus: LIS and ATL plants exhibited similar short-term effects of high temperature on photosynthetic capacity (P-max) and quantum yield (estimated as the ratio of variable to maximum chlorophyll fluorescence, F-v/F-m). As LIS plants had consistently higher N and protein content than ATL plants, the interaction between nitrogen nutrition and high-temperature tolerance was examined. When grown under high N supply and optimal temperature (12 degrees C), LIS plants had a higher density of photosystem II reaction centers (RCII), higher activity of two Calvin cycle enzymes (ribulose bisphosphate carboxylase oxygenase [RUBISCO] and NADP-dependent glyceraldehyde-3-phosphate dehydrogenase [G3PDH]), and higher P-max and F-v/F-m than ATL plants. Individual ATL plants, furthermore, exhibited close correlations of RCII density and enzyme activity with N and/or protein content. Variation in RCII density and enzyme activity, in turn, largely accounted for plant-to-plant differences in P-max and F-v/F-m. Relationships among these parameters were generally weak or lacking among individual LIS plants grown under optimal conditions, apparently because luxury N consumption resulted in excess reserves of photosynthetic apparatus components. Exposure of N-replete LIS and ATL plants to a superoptimal temperature (22 degrees C) for 4 days caused an increase in the minimum turnover time of the photosynthetic apparatus (tau) and a decrease in P-max, but had no consistent effect on F-v/F-m, RCII density, PSU size (chlorophyll a/RCII), or enzyme activities. When plants were subjected to concurrent N limitation and heat stress, however, LIS and ATL populations exhibited quite different responses. All photosynthetic parameters of N-limited ATL plants declined sharply in response to high temperature, resulting in a negative rate of daily net C fixation. In contrast, LIS plants showed a reduction in PSU size, but maintained other parameters, including daily C fixation, at levels similar to those of N-limited plants at optimal temperature. Overall, the ability of LIS plants to accumulate and maintain high N reserves appears to be critical for heat tolerance and, therefore, for survival during summer periods of simultaneous low N supply and superoptimal temperature. ATL plants, which also experience low summer N supply but not superoptimal temperatures, do not accumulate large reserves of nitrogenous components and are unable to tolerate the combined stress. Because low N supply often co-occurs with high temperatures in temperature marine systems, large-scale declines in algal productivity, such as during El Nino events, are probably due to the interactive effect of N limitation and heat stress.