Adams William W, Watson Amy M, Mueh Kristine E, Amiard Véronique, Turgeon Robert, Ebbert Volker, Logan Barry A, Combs Andrew F, Demmig-Adams Barbara
Department of Ecology & Evolutionary Biology, University of Colorado, Boulder, CO 80309-0334, USA.
Photosynth Res. 2007 Nov-Dec;94(2-3):455-66. doi: 10.1007/s11120-006-9123-3. Epub 2007 Jan 9.
The potential role of foliar carbon export features in the acclimation of photosynthetic capacity to differences and changes in light environment was evaluated. These features included apoplastic vs. symplastic phloem loading, density of loading veins, plasmodesmatal frequency in intermediary cells, and the ratio of loading cells to sieve elements. In initial studies, three apoplastic loaders (spinach, pea, Arabidopsis thaliana) exhibited a completely flexible photosynthetic response to changing light conditions, while two symplastic loaders (pumpkin, Verbascum phoeniceum), although able to adjust to different long-term growth conditions, were more limited in their response when transferred from low (LL) to high (HL) light. This suggested that constraints imposed by the completely physical pathway of sugar export might act as a bottleneck in the export of carbon from LL-acclimated leaves of symplastic loaders. While both symplastic loaders exhibited variable loading vein densities (low in LL and high in HL), none of the three apoplastic loaders initially characterized exhibited such differences. However, an additional apoplastic species (tomato) exhibited similar differences in vein density during continuous growth in different light environments. Furthermore, in contrast to the other apoplastic loaders, photosynthetic acclimation in tomato was not complete following a transfer from LL to HL. This suggests that loading vein density and loading cells per sieve element, and thus apparent loading surface capacity, play a major role in the potential for photosynthetic acclimation to changes in light environment. Photosynthetic acclimation and vein density acclimation were also characterized in the slow-growing, sclerophytic evergreen Monstera deliciosa. This evergreen possessed a lower vein density during growth in LL compared to HL and exhibited a more severely limited potential for photosynthetic acclimation to increases in light environment than the rapidly-growing, mesophytic annuals.
评估了叶片碳输出特征在光合能力适应光照环境差异和变化方面的潜在作用。这些特征包括质外体与共质体韧皮部装载、装载叶脉密度、中间细胞中的胞间连丝频率以及装载细胞与筛管分子的比例。在初步研究中，三种质外体装载植物（菠菜、豌豆、拟南芥）对光照条件变化表现出完全灵活的光合响应，而两种共质体装载植物（南瓜、毛蕊花）虽然能够适应不同的长期生长条件，但从低光（LL）转移到高光（HL）时，其响应更有限。这表明糖输出的完全物理途径所施加的限制可能成为共质体装载植物LL适应叶片碳输出的瓶颈。虽然两种共质体装载植物都表现出可变的装载叶脉密度（LL中低，HL中高），但最初表征的三种质外体装载植物均未表现出此类差异。然而，另一种质外体植物（番茄）在不同光照环境下持续生长期间，叶脉密度表现出类似差异。此外，与其他质外体装载植物不同，番茄从LL转移到HL后，光合适应并不完全。这表明装载叶脉密度和每个筛管分子的装载细胞，即表观装载表面容量，在光合适应光照环境变化的潜力中起主要作用。生长缓慢的硬叶常绿植物龟背竹也对光合适应和叶脉密度适应进行了表征。与HL相比，这种常绿植物在LL生长期间叶脉密度较低，并且与快速生长的中生一年生植物相比，其光合适应光照环境增加的潜力受到更严重的限制。
