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.

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.

The nature and role of metabolic leakage from root-knot nematode galls and infection by Rhizoctonia solani.

A severe root rot of tomato caused by Meloidogyne incognita and Rhizoctonia solani was associated with nutrient mobilization into gall tissue and root exudation. Root decay did not develop when root exudates were continuously removed by leaching. When leachates were collected from M. incognita-infected and control roots and applied to roots of tomatoes inoculated with R. solani alone, roots receiving leachates from M. incognita-infected roots developed a severe rot while roots receiving leachates from control roots were free of decay. During the fourth and fifth weeks following nematode infection, an increased mobilization of (1)C labelled compounds to nematode-infected roots occurred. Higher counts of water soluble nonvolatile (1)C labelled exudates leaked from nematode-infected roots than from control roots at each weekly sampling period. Higher concentrations of Ca, Mg, Na, K, Fe, and Cu were found in exudates from nematode-infected roots than from the control roots. During the first 14 days following nematode infection, carbohydrates were the major organic constituents in exudates leaking from nematode-infected roots. Fourteen days after nematode infection, nitrogenous compounds become the major organic constituents leaking from roots. Shifts in C/N ratio of root exudates from nematode-infected roots were associated with parasitic development of R. solani in tomato roots.