A study of the phytotoxic effects of the aerial parts of Senecio westermanii Dusén (Asteraceae) on Lactuca sativa L. and Allium cepa L. seeds

The objective of this study was to evaluate the effects of the ethanolic crude extracts and fractions of the species Senecio westermanii Dusén on Lactuca sativa L. (lettuce) and Allium cepa L. (onion) seeds. We assessed the germination, growth, root respiration and photosynthesis of the target species in Petri dishes (9.0 cm diameter) containing filter paper n°6. The study was conducted using 50 seeds per plate and held in 4 replicates per concentration of each sample. In the germination there was an inhibitory effect of fractions hexane (FH) and chloroform (FCl) at concentrations of 500 and 1000 µg/mL. There was a reduction in the radicle growth of lettuce by 14 to 24% and a reduction of hypocotilum by 14 to 28%. As for the radicle of the onion was up 74% reduction to the FCl and the coleoptile was 24 and 45% reduction for FH and FCl, respectively. Inhibitory effects in the root respiration of lettuce were detected in all the samples analyzed, with results ranging from 16 to 83%. For the seeds of A. cepa, there was an encouragement for the FCl and ethyl acetate fractions (FAE), with results ranging from 94 to 142% and 76 to 150%, respectively. With regard to the photosynthesis of L. sativa, there was no significant difference between the control, and as for the A. cepa, there was a strain in inhibition concentrations of 250 and 500 µg/mL, which ranged from 27 to 68%. The samples of S. westermanii caused changes in the target species and thus can be used as a natural herbicide.

Effects of the plant steroidal hormone, 24-epibrassinolide, on the mitotic index and growth of onion (Allium cepa) root tips

The purpose of the present study was to determine the effects of the steroidal plant hormone, 24-epibrassinolide (BL), on the mitotic index and growth of onion (Allium cepa) root tips. The classical Allium test was used to gather and quantify data on the rate of root growth, the stages of mitosis, and the number of mitoses in control and BL-treated groups of onions. Low doses of BL (0.005 ppm) nearly doubled the mean root length and the number of mitoses over that of controls. Intermediate doses of BL (0.05 ppm) also produced mean root lengths and number of mitoses that were significantly greater than those of the controls. The highest dose of BL (0.5 ppm) produced mean root lengths and number of mitoses that were less than control values, but the differences were not statistically significant. Examination of longitudinally sectioned root tips produced relatively similar results. This study confirms the suppositions of previous authors who have claimed that exogenously applied BL can increase the number of mitoses in plants, but failed to show cytogenetic data. This is the first report detailing the effects of BL on chromosomes and the cell cycle.

Evaluation of cytotoxic potential of latex of Calotropis procera and Podophyllotoxin in Allum cepa root model

In the present study we have utilized the Allium cepa root tip meristem model to evaluate the cytotoxic and anti-mitotic activities of latex of Calotropis procera (DL) and podophyllotoxin. Standard cyto-toxic drug cyclophosphamide and non-cytotoxic drugs cyproheptadine and aspirin served as controls. Like cyclophosphamide, both DL and podophyllotoxin significantly inhibited the growth of roots and mitotic activity in a dose-dependent manner. However, podophyllotoxin was more potent in this regard and produced root decay. Cyproheptadine and aspirin, on the other hand, showed a marginal effect on the root growth and mitotic activity at much higher concentrations