Striker G G, Insausti P, Grimoldi A A, Vega A S
IFEVA-CONICET, Facultad de Agronomía, Universidad de Buenos Aires, Avenida San Martín 4453. CPA 1417 DSE Buenos Aires, Argentina.
Plant Cell Environ. 2007 May;30(5):580-9. doi: 10.1111/j.1365-3040.2007.01639.x.
The objective of this work was to study the existence of a trade-off between aerenchyma formation and root mechanical strength. To this end, relationships among root anatomical traits and mechanical properties were analysed in plant species with contrasting root structural types: Paspalidium geminatum (graminaceous type), Cyperus eragrostis (cyperaceous type), Rumex crispus (Rumex type) and Plantago lanceolata (Apium type). Variations in anatomical traits and mechanical strength were assessed as a function of root diameter by exposing plants to 0, 7, 15 and 30 d of control and flooded conditions. For each species, the proportion of root cortex was positively associated with the increment of root diameter, contributing to the increase in root porosity under both control and flooded conditions. Moreover, cell lysis produced an additional increase in root porosity in most species under flooded conditions (except R. crispus). Both structural types that presented a uniseriate layer (epidermis) to cope with compression (Rumex and Apium types) were progressively weakened as root porosity increased. This effect was significant even when the increment of root porosity was solely because of increased root diameter (R. crispus), as when both processes (root diameter and cell lysis) added porosity to the roots (P. lanceolata). Conversely, structural types that presented a multiseriate ring of cells in the outer cortex (graminaceous and cyperaceous types) maintained mechanical strength over the whole range of porosity, in spite of lysogenic processes registered in the inner cortex. In conclusion, our study demonstrates a strong trade-off between aerenchyma formation and mechanical strength in root structural types that lacked a multiseriate ring of tissue for mechanical protection in the outer cortex. The results suggest that this ring of tissue plays a significant role in maintaining the mechanical strength of roots when flooding induces the generation of additional aerenchyma tissue in the root cortex.
这项工作的目的是研究通气组织形成与根系机械强度之间的权衡关系。为此，对具有不同根系结构类型的植物物种进行了根系解剖特征与力学性能之间关系的分析：双穗雀稗（禾本科类型）、莎草（莎草科类型）、皱叶酸模（酸模类型）和窄叶车前（芹菜类型）。通过将植物置于对照和淹水条件下0、7、15和30天，评估解剖特征和机械强度随根直径的变化。对于每个物种，根皮层比例与根直径的增加呈正相关，在对照和淹水条件下均有助于增加根孔隙率。此外，在淹水条件下，大多数物种（除皱叶酸模外）细胞溶解导致根孔隙率进一步增加。两种具有单层（表皮）以应对压缩的结构类型（酸模和芹菜类型）随着根孔隙率的增加而逐渐减弱。即使根孔隙率的增加仅仅是由于根直径的增加（皱叶酸模），或者当两种过程（根直径和细胞溶解）都增加了根的孔隙率时（窄叶车前），这种影响也很显著。相反，在外皮层具有多层细胞环的结构类型（禾本科和莎草科类型）在整个孔隙率范围内保持机械强度，尽管在内皮层中记录到了溶生过程。总之，我们的研究表明，在缺乏用于外层机械保护的多层组织环的根系结构类型中，通气组织形成与机械强度之间存在强烈的权衡关系。结果表明，当淹水诱导根皮层中产生额外的通气组织时，这种组织环在维持根系机械强度方面起着重要作用。
