Department of Botany, Institute of Biosciences, University of São Paulo, CEP 05508-900, São Paulo, SP, Brazil.
J Plant Physiol. 2010 May 1;167(7):526-33. doi: 10.1016/j.jplph.2009.10.011. Epub 2009 Dec 1.
Leaves comprise most of the vegetative body of tank bromeliads and are usually subjected to strong longitudinal gradients. For instance, while the leaf base is in contact with the water accumulated in the tank, the more light-exposed middle and upper leaf sections have no direct access to this water reservoir. Therefore, the present study attempted to investigate whether different leaf portions of Guzmania monostachia, a tank-forming C(3)-CAM bromeliad, play distinct physiological roles in response to water shortage, which is a major abiotic constraint in the epiphytic habitat. Internal and external morphological features, relative water content, pigment composition and the degree of CAM expression were evaluated in basal, middle and apical leaf portions in order to allow the establishment of correlations between the structure and the functional importance of each leaf region. Results indicated that besides marked structural differences, a high level of functional specialization is also present along the leaves of this bromeliad. When the tank water was depleted, the abundant hydrenchyma of basal leaf portions was the main reservoir for maintaining a stable water status in the photosynthetic tissues of the apical region. In contrast, the CAM pathway was intensified specifically in the upper leaf section, which is in agreement with the presence of features more suitable for the occurrence of photosynthesis at this portion. Gas exchange data indicated that internal recycling of respiratory CO(2) accounted for virtually all nighttime acid accumulation, characterizing a typical CAM-idling pathway in the drought-exposed plants. Altogether, these data reveal a remarkable physiological complexity along the leaves of G. monostachia, which might be a key adaptation to the intermittent water supply of the epiphytic niche.
叶片构成了水槽凤梨属植物的大部分营养体，通常会受到强烈的纵向梯度影响。例如，虽然叶基与水槽中积累的水接触，但更暴露于光线下的中叶和上叶部分则无法直接接触到这个水库。因此，本研究试图探讨不同叶段在应对缺水时是否发挥不同的生理作用，因为缺水是附生环境中的主要非生物限制因素。为了确定每个叶片区域的结构与功能重要性之间的相关性，评估了 Guzmania monostachia （一种水槽形成的 C(3)-CAM 凤梨科植物）基部、中部和顶部叶片的内部和外部形态特征、相对含水量、色素组成和 CAM 表达程度。结果表明，除了明显的结构差异外，该凤梨科植物的叶片还表现出高度的功能专业化。当水槽中的水耗尽时，基部叶片丰富的水组织是维持顶部叶片光合作用组织稳定水分状态的主要储水器。相比之下，CAM 途径在顶部叶片中特异性增强，这与该部分更适合光合作用发生的特征相一致。气体交换数据表明，内部呼吸 CO2 的循环几乎可以解释所有夜间的酸积累，这表明在暴露于干旱的植物中存在典型的 CAM-休眠途径。总之，这些数据揭示了 G. monostachia 叶片的显著生理复杂性，这可能是对附生环境间歇性供水的关键适应。
