Leaf scald, caused by Monographella albescens, is a key disease affecting rice production worldwide. Alternative methods for leaf scald management are demanded by the growers and silicon (Si) application emerges as a promising way to decrease severity not only of leaf scald but also of other relevant rice diseases. Some evidence suggests that Si may preserve the photosynthetic performance of plants upon pathogen infection but the mechanistic basis for this remain unresolved. In the present study, mesophyll conductance (g_m) was calculated to suitably parameterize the responses of net carbon assimilation rate (A) to chloroplastidic CO₂ concentration (C_c) and to resolve the relative contributions of stomatal, mesophyll, and biochemical drawbacks to photosynthesis in rice plants challenged with M. albescens and how all of these facts may be influenced by Si application. Rice plants (cultivar “Primavera”) were hydroponically grown with 0 or 2 mM Si (− Si and + Si plants) and inoculated with M. albescens. Leaf scald-induced decreases in A were associated with roughly proportional decreases in CO₂ diffusion (lower stomatal conductance and g_m) and impaired photochemistry (e.g. reduced maximum electron transport rate) and biochemistry (e.g. RuBisCO activity) regardless of Si supply. The magnitude of these decreases were, overall, greater in − Si plants than in their + Si counterparts, and therefore a mitigating effect of Si on the preservation of the photosynthetic activity on diseased plants is evident. On infected leaves, g_m was not scaled with maximum carboxylation rate (V_cmax) − C_c and, as a consequence, C_c increased accordingly, but only in + Si plants. In conclusion, the supply of Si to rice plants played a central role in decreasing leaf scald symptoms and, as such, preserving to a certain extent their photosynthetic performance. This preservation was not linked to differential impairments on the stomatal function or biochemical steps of photosynthesis but rather with increased CO₂ diffusion throughout the mesophyll. This ultimately led to a lower photorespiration-to-gross photosynthesis ratio and less mesophyll limitations of photosynthesis in + Si plants than in their − Si counterparts during the infection process of M. albescens on rice leaves.

中文翻译：

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硅减轻白粉病菌侵染的水稻叶片光合作用的叶肉限制

叶烫伤，造成Monographella albescens，是影响全球水稻生产的主要疾病。种植者需要替代性的方法来控制叶锈病，硅（Si）的应用成为降低叶锈病和其他相关水稻疾病严重程度的一种有希望的方法。一些证据表明，硅可能在病原体感染后保留了植物的光合作用性能，但其机理基础尚未得到解决。在本研究中，计算叶肉电导（g _m）以适当地参数化净碳同化率（A）对叶绿体CO ₂浓度（C _c）的响应），并解决光合作用与挑战水稻气孔，叶肉和生化缺陷的相对贡献M. albescens以及如何将所有这些事实可以由硅应用的影响。水稻植株（品种“ Primavera”）与0或2 mM Si（-Si和+ Si植株）水培生长，并接种白僵菌。叶片烫伤引起的A降低与CO ₂扩散大致成比例的降低有关（气孔导度和g _m降低）和光化学（例如降低的最大电子传输速率）和生物化学（例如RuBisCO活性）受损，而与硅供应无关。总体而言，这些减少的幅度在-Si植物中比在+ Si植物中更大，因此，Si在减轻患病植物的光合活性方面具有缓解作用。在受感染的叶子上，g _m没有以最大羧化率（V _cmax）-C _c缩放，因此，C _c相应增加，但仅在+ Si植物中增加。综上所述，向水稻植物供应硅对减轻叶子上的鳞状症状起到了关键作用，因此在一定程度上保留了它们的光合性能。这种保存与气孔功能或光合作用的生化步骤的不同损伤无关，而与整个叶肉中CO ₂扩散的增加有关。这最终导致在+硅植物比其更低的光呼吸毛比光合作用比和光合作用的叶肉少局限性-期间的感染过程的Si同行M. albescens对水稻的叶子。