Kalachanis Dimitrios, Chondrogiannis Christos, Petropoulou Yiola
Laboratory of Plant Physiology, Department of Biology, University of Patras, 26504 Patras, Greece.
School of Natural Sciences, Botany, Trinity College Dublin, D02 PN40 Dublin, Ireland.
Plants (Basel). 2024 Oct 14;13(20):2867. doi: 10.3390/plants13202867.
Fruit photosynthesis occurs in an internal microenvironment seldom encountered by a leaf (hypoxic and extremely CO-enriched) due to its metabolic and anatomical features. In this study, the anatomical and photosynthetic traits of fully exposed green fruits of L. were assessed during the period of fruit production (summer) and compared to their leaf counterparts. Our results indicate that leaf photosynthesis, transpiration and stomatal conductance drastically reduced during the summer drought, while they recovered significantly after the autumnal rainfalls. In acorns, gas exchange with the surrounding atmosphere is hindered by the complete absence of stomata; hence, credible CO uptake measurements could not be applied in the field. The linear electron transport rates (ETRs) in ambient air were similar in intact leaves and pericarps (i.e., when the physiological internal atmosphere of each tissue is maintained), while the leaf NPQ was significantly higher, indicating enhanced needs for harmless energy dissipation. The ETR measurements performed on leaf and pericarp discs at different CO/O partial pressures in the supplied air mixture revealed that pericarps displayed significantly lower values at ambient gas levels, yet they increased by ~45% under high CO/O ratios (i.e., at gas concentrations simulating the fruit's interior). Concomitantly, NPQ declined gradually in both tissues as the CO/O ratio increased, yet the decrease was more pronounced in pericarps. Furthermore, net CO assimilation rates for both leaf and pericarp segments were low in ambient air and increased almost equally at high CO, while pericarps exhibited significantly higher respiration. It is suggested that during summer, when leaves suffer from photoinhibition, acorns could contribute to the overall carbon balance, through the re-assimilation of respiratory CO, thereby reducing the reproductive cost.
由于其代谢和解剖学特征，果实光合作用发生在叶片很少遇到的内部微环境中（缺氧且二氧化碳极度富集）。在本研究中，对夏季果实生产期间完全暴露的青果的解剖学和光合特征进行了评估，并与相应的叶片进行了比较。我们的结果表明，夏季干旱期间叶片光合作用、蒸腾作用和气孔导度急剧下降，而秋季降雨后它们显著恢复。在橡子中，与周围大气的气体交换因完全没有气孔而受阻；因此，无法在田间进行可靠的二氧化碳吸收测量。在环境空气中，完整叶片和果皮中的线性电子传递速率（ETR）相似（即当维持每个组织的生理内部大气时），而叶片的非光化学猝灭（NPQ）显著更高，表明对无害能量耗散的需求增加。在供应的空气混合物中不同二氧化碳/氧气分压下对叶片和果皮圆盘进行的ETR测量表明，在环境气体水平下，果皮显示出显著较低的值，但在高二氧化碳/氧气比下（即模拟果实内部的气体浓度）它们增加了约45%。同时，随着二氧化碳/氧气比的增加，两个组织中的NPQ都逐渐下降，但在果皮中下降更为明显。此外，在环境空气中，叶片和果皮段的净二氧化碳同化率都很低，在高二氧化碳条件下几乎同等增加，而果皮表现出显著更高的呼吸作用。有人认为，在夏季，当叶片遭受光抑制时，橡子可以通过重新同化呼吸产生的二氧化碳来促进整体碳平衡，从而降低生殖成本。
