PHYTOTOXICITY OF SICYOS DEPPEI DURING TOMATO GERMINATION AND ITS EFFECTS ON THE ROLE OF ABA AND CELL WALL ENZYMES

Sicyos deppei is a harmful weed that grows in central Mexico, decreasing crop productivity by allelochemical release via lixiviation of the aerial organs through raining. Sicyos deppei aqueous leachate is phytotoxic to tomato seed germination causing various metabolic alterations, such as high levels of abscisic acid, which delay germination and inhibit radicle growth. To determine whether abscisic acid catabolism was involved in the delay of germination caused by S. deppei, tomato seeds were exposed to diniconazole, an ABA catabolism-inhibitor, and subsequently the activity of cell wall-degrading enzymes (endo-beta-mannanase, alpha-galactosidase, exo-polygalacturonase, and beta-1,3-glucanase) was estimated in the presence of ABA, diniconazole and S. deppei aqueous leachate. Results showed that during germination, there is a delay in ABA degradation and the activity of the four cell wall-degrading enzymes evaluated was inhibited. Cell cycle was analyzed to characterize the inhibition of radicle growth during post-germination in the roots of treated seedlings. The phytotoxic aqueous leachate of S. deppei interfered with it, altering the expression of two cell cycle marker genes CDKB2;1 and CycB2;1, thereby reducing cell division. In summary, the delay in tomato germination through S. deppei leachate reflects first that there is a delay in ABA catabolism, and second there is an alteration of cellular processes that interfere with cell cycle and inhibit radicle growth during postgermination.