Aloni Roni, Barnett John R
Department of Botany, George S. Wise Faculty of Life Sciences, Tel Aviv University, 69978, Tel Aviv, Israel.
School of Plant Sciences, The University of Reading, Whiteknights, PO Box 221, RG6 6AS, Reading, UK.
Planta. 1996 Apr;198(4):595-603. doi: 10.1007/BF00262647. Epub 2017 Mar 18.
The differentiation of phloem anastomoses linking the longitudinal vascular bundles has been studied in stem internodes of Cucurbita maxima Duchesne, C. pepo L. and Dahlia pinnata Cav. These anastomoses comprise naturally occurring regenerative sieve tubes which redifferentiate from interfascicular parenchyma cells in the young internodes. In all three species, severing a vascular bundle in a young internode resulted in regeneration of xylem to form a curved by-pass immediately around the wound. The numerous phloem anastomoses in these young internodes were not involved in this process, the regenerated vessels originating from interfascicular parenchyma alone. Conversely, in mature internodes of Dahlia, the regenerated vessels originated from initials of the interfascicular cambia, and their phloem anastomoses did not influence the pattern of xylogenesis. On the other hand, in old internodes of Cucurbita, in which an interfascicular cambium was not yet developed, the parenchyma cells between the bundles had lost the ability to redifferentiate into vessel elements, and instead, regenerated vessels were produced in the phloem anastomoses. Thus, the wounded region of the vascular bundle was not bypassed via the shortest, curved pathway, but by more circuitous routes further away from the wound. Some of the regenerated vessels produced in the phloem anastomoses were extremely wide, and presumably efficient conductors of water. It is proposed that the dense network of phloem anastomoses developed during evolution as a mechanism of adaptation to possible damage in mature internodes by providing flexible alternative pathways for efficient xylem regeneration in plants with limited or no interfascicular cambium.
对连接纵向维管束的韧皮部吻合组织的分化进行了研究，涉及的植物有笋瓜（Cucurbita maxima Duchesne）、西葫芦（C. pepo L.）和大丽花（Dahlia pinnata Cav.）。这些吻合组织由天然存在的再生筛管组成，这些筛管从幼嫩节间的束间薄壁组织细胞重新分化而来。在这三个物种中，切断幼嫩节间的一个维管束会导致木质部再生，从而在伤口周围立即形成一条弯曲的旁路。这些幼嫩节间大量的韧皮部吻合组织并未参与此过程，再生的导管仅起源于束间薄壁组织。相反，在大丽花的成熟节间，再生的导管起源于束间形成层的原始细胞，其韧皮部吻合组织不影响木质部发生的模式。另一方面，在笋瓜的老节间，其中束间形成层尚未发育，束间的薄壁组织细胞已失去重新分化为导管分子的能力，取而代之的是在韧皮部吻合组织中产生再生导管。因此，维管束的受伤区域不是通过最短的弯曲路径被绕过，而是通过离伤口更远的更迂回的路径。在韧皮部吻合组织中产生的一些再生导管极其宽大，大概是高效的水分传导者。有人提出，在进化过程中形成的密集韧皮部吻合组织网络，作为一种适应机制，通过为束间形成层有限或没有束间形成层的植物中的高效木质部再生提供灵活的替代途径，来应对成熟节间可能受到的损伤。
