Background

Stomata in rice control a number of physiological processes by regulating gas and water exchange between the atmosphere and plant tissues. The impact of the structural diversity of these micropores on its conductance level is an important area to explore before introducing stomatal traits into any breeding program in order to increase photosynthesis and crop yield. Therefore, an intensive measurement of structural components of stomatal complex (SC) of twenty three Oryza species spanning the primary, secondary and tertiary gene pools of rice has been conducted.

Results

Extensive diversity was found in stomatal number and size in different Oryza species and Oryza complexes. Interestingly, the dynamics of stomatal traits in Oryza family varies differently within different Oryza genetic complexes. Example, the Sativa complex exhibits the greatest diversity in stomatal number, while the Officinalis complex is more diverse for its stomatal size. Combining the structural information with the Oryza phylogeny revealed that speciation has tended towards increasing stomatal density rather than stomatal size in rice family. Thus, the most recent species (i.e. the domesticated rice) eventually has developed smaller yet numerous stomata. Along with this, speciation has also resulted in a steady increase in stomatal conductance (anatomical, g_max) in different Oryza species. These two results unambiguously prove that increasing stomatal number (which results in stomatal size reduction) has increased the stomatal conductance in rice. Correlations of structural traits with the anatomical conductance, leaf carbon isotope discrimination (∆¹³C) and major leaf morphological and anatomical traits provide strong supports to untangle the ever mysterious dependencies of these traits in rice. The result displayed an expected negative correlation in the number and size of stomata; and positive correlations among the stomatal length, width and area with guard cell length, width on both abaxial and adaxial leaf surfaces. In addition, g_max is found to be positively correlated with stomatal number and guard cell length. The ∆¹³C values of rice species showed a positive correlation with stomatal number, which suggest an increased water loss with increased stomatal number. Interestingly, in contrast, the ∆¹³C consistently shows a negative relationship with stomatal and guard cell size, which suggests that the water loss is less when the stomata are larger. Therefore, we hypothesize that increasing stomatal size, instead of numbers, is a better approach for breeding programs in order to minimize the water loss through stomata in rice.

Conclusion

Current paper generates useful data on stomatal profile of wild rice that is hitherto unknown for the rice science community. It has been proved here that the speciation has resulted in an increased stomatal number accompanied by size reduction during Oryza’s evolutionary course; this has resulted in an increased g_max but reduced water use efficiency. Although may not be the sole driver of water use efficiency in rice, our data suggests that stomata are a potential target for modifying the currently low water use efficiency in domesticated rice. It is proposed that Oryza barthii can be used in traditional breeding programs in enhancing the stomatal size of elite rice cultivars.

中文翻译：

---

栽培和野生稻种气孔特征的自然多样性。

 背景

水稻中的气孔通过调节大气和植物组织之间的气体和水交换来控制许多生理过程。在将气孔性状引入任何育种计划以提高光合作用和作物产量之前，这些微孔的结构多样性对其电导水平的影响是一个需要探索的重要领域。因此，对跨越水稻一级、二级和三级基因库的二十三个稻种的气孔复合体（SC）的结构成分进行了深入的测量。

 结果

不同稻种和稻复合体的气孔数量和大小存在广泛的多样性。有趣的是，稻科中气孔性状的动态在不同稻遗传复合体中存在不同的差异。例如，苜蓿复合体在气孔数量方面表现出最大的多样性，而药用复合体的气孔大小则更加多样化。将结构信息与水稻系统发育相结合表明，水稻家族中的物种形成倾向于增加气孔密度，而不是气孔大小。因此，最新的物种（即驯化水稻）最终发育出较小但数量较多的气孔。除此之外，物种形成还导致不同稻种的气孔导度（解剖学， g _max ）稳定增加。这两个结果明确证明，增加气孔数量（导致气孔尺寸减小）增加了水稻的气孔导度。结构性状与解剖电导、叶片碳同位素辨别（Δ ¹³ C）以及主要叶片形态和解剖性状的相关性为解开水稻中这些性状的神秘依赖性提供了强有力的支持。结果显示气孔的数量和大小呈预期的负相关；叶背面和正面的气孔长度、宽度和面积与保卫细胞长度、宽度呈正相关。此外，发现g _max与气孔数和保卫细胞长度呈正相关。 水稻品种的 Δ ¹³ C 值与气孔数呈正相关，这表明随着气孔数的增加，水分流失也增加。有趣的是，相比之下，Δ ¹³ C 始终显示出与气孔和保卫细胞大小的负相关关系，这表明当气孔较大时，水分流失较少。因此，我们假设增加气孔大小而不是数量是育种计划的更好方法，以最大限度地减少水稻气孔的水分损失。

 结论

当前的论文生成了有关野生稻气孔特征的有用数据，这些数据迄今为止对水稻科学界来说是未知的。这里已经证明，在稻的进化过程中，物种形成导致了气孔数量的增加，同时尺寸的减小；这导致g _max增加，但水利用效率降低。尽管可能不是水稻用水效率的唯一驱动因素，但我们的数据表明，气孔是改变目前驯化水稻用水效率较低的潜在目标。有人提出， Oryza barthii可用于传统育种计划，以增强优良水稻品种的气孔大小。