Baldet Pierre, Hernould Michel, Laporte Frédéric, Mounet Fabien, Just Daniel, Mouras Armand, Chevalier Christian, Rothan Christophe
UMR 619 Physiologie et Biotechnologie Végétales, Institut National de la Recherche Agronomique, Universités Bordeaux 1 et 2, Centre de Recherche de Bordeaux, BP 81, F-33883 Villenave d'Ornon Cedex, France.
J Exp Bot. 2006;57(4):961-70. doi: 10.1093/jxb/erj082. Epub 2006 Feb 17.
Changes in photoassimilate partitioning between source and sink organs significantly affect fruit development and size. In this study, a comparison was made of tomato plants (Solanum lycopersicum L.) grown under a low fruit load (one fruit per truss, L1 plants) and under a standard fruit load (five fruits per truss, L5 plants), at morphological, biochemical, and molecular levels. Fruit load reduction resulted in increased photoassimilate availability in the plant and in increased growth rates in all plant organs analysed (root, stem, leaf, flower, and fruit). Larger flower and fruit size in L1 plants were correlated with higher cell number in the pre-anthesis ovary. This was probably due to the acceleration of the flower growth rate since other flower developmental parameters (schedule and time-course) remained otherwise unaffected. Using RT-PCR, it was shown that the transcript levels of CYCB2;1 (cyclin) and CDKB2;1 (cyclin-dependent kinase), two mitosis-specific genes, strongly increased early in developing flower buds. Remarkably, the transcript abundance of CYCD3;1, a D-type cyclin potentially involved in cell cycle regulation in response to mitogenic signals, also increased by more than 5-fold at very early stages of L1 flower development. By contrast, transcripts from fw2.2, a putative negative regulator of cell division in tomato fruit, strongly decreased in developing flower bud, as confirmed by in situ hybridization studies. Taken together, these results suggest that changes in carbohydrate partitioning could control fruit size through the regulation of cell proliferation-related genes at very early stages of flower development.
源器官和库器官之间光合产物分配的变化显著影响果实发育和大小。在本研究中，对低果负载（每穗一个果实，L1植株）和标准果负载（每穗五个果实，L5植株）条件下生长的番茄植株（Solanum lycopersicum L.）进行了形态学、生物化学和分子水平的比较。果负载降低导致植株中光合产物可用性增加，且所分析的所有植株器官（根、茎、叶、花和果实）的生长速率提高。L1植株中较大的花和果实大小与花前子房较高的细胞数量相关。这可能是由于花生长速率加快，因为其他花发育参数（进程和时间进程）在其他方面未受影响。使用RT-PCR表明，CYCB2;1（细胞周期蛋白）和CDKB2;1（细胞周期蛋白依赖性激酶）这两个有丝分裂特异性基因的转录水平在发育中的花芽早期强烈增加。值得注意的是，CYCD3;1（一种可能参与响应促有丝分裂信号的细胞周期调控的D型细胞周期蛋白）的转录丰度在L1花发育的非常早期阶段也增加了5倍以上。相比之下，番茄果实中假定的细胞分裂负调控因子fw2.2的转录本在发育中的花芽中强烈减少，原位杂交研究证实了这一点。综上所述，这些结果表明碳水化合物分配的变化可能通过在花发育的非常早期阶段调控细胞增殖相关基因来控制果实大小。
