G.G. Dimalla

The effect of temperature on the germination and endogenous cytokinin and gibberellin levels of pecan nuts

Summary Incubation of pecan embryos at 30 °C resulted in an increase in the level of endogenous cytokinins and gibberellins and also gave optimum germination. A much slower rate of hormone production occurred with incubation at 20 °C and this is possibly correlated with the poor germination obtained at this temperature. Incubation at 4 °C partly substituted for the high temperature germination requirement and resulted in hormonal changes very similar to those recorded at 30 °C. Kinetin and gibberellin acid were also found to substitute partially for the high temperature requirement. These results suggest that endogenous hormones may play an important role in the mobilization of lipid food reserves to supply the energy required for germination.

Cytokinins in the root-knot nematode, Meloidogyne incognita

Abstract Adult nematodes, egg masses and hatched larvae were found to contain cytokinins which are apparently accumulated from the host plant tissue. Most activity in the adult nematode co-chromatographed with cytokinin glucosides, while in the larvae the free bases were the only cytokinins present. It would appear as if the cytokinin glucosides are hydrolysed during the life cycle of the parasite and that substantial amounts of cytokinin are released during the hatching process.

Cytokinins from soils

SummarySubstances that coeluted with zeatin and zeatin riboside were extracted from soils supporting plants growing in symbiotic association with microorganisms.

Regulation of Germination of Pecan, Carya illinoensis

Summary The seed of the pecan Carya illinoensis is non-dormant and will germinate at any time after harvest if incubated under favourable environmental conditions. The surrounding shell is freely permeable to water and gases but retards germination by mechanically restricting radicle elongation. This mechanical effect can be nullified by incubating the nut at optimum temperature, which is shown to be between 30 and 35 °C. At these temperatures germination is uniform, rapid, and complete within 20 days.

Pecan nut germination — A review for the nursery industry

Abstract The shell of the pecan nut is freely permeable to water and gases, but retards germination by mechanically restricting growth of the radicle. This mechanical effect, which is pronounced at 20°C, can be overcome by germinating nuts between 30° and 35°C. Cool, moist stratification can substitute for the high-temperature germination-requirement in that following stratification nuts germinate equally well at 20°, 25° and 30°C. During stratification or incubation at high temperature, cytokinin and gibberellin levels increase in the embryo. This increase in endogenous promoter levels is closely correlated with the digestion of food reserves necessary for the resumption of embryo growth.

Influence of ethylene on cytokinin pools in tuberizing potatoes

Abstract Low concentrations of ethylene partly inhibit tuberization and result in the formation of “hybrid” swellings which contain limited amounts of starch. It would appear as if ethylene treatment results in an accumulation of cytokinin glucosides which may be inactive in the tuberizing process.

Penetration and Distribution of Dimethyl Sulfoxide-35S in Potato Tubers

Whole and cut potato tubers were immersed in 25% DM35SO for different lengths of time and then sectioned and autoradiographed. Penetration of DMSO is restricted by the periderm, but takes place relatively rapidly through buds and cut surfaces When entering through cut surfaces, it is most rapidly distributed via the xylem while most of the absorbed DMSO is in the parenchyma adjacent to the cut. Eventually DM35SO becomes distributed throughout the entire tuber with the exception of the phloem, which remains unlabeled. Our results confirm that DMSO distribution follows an apoplastic route and that the phloem of potato tubers exists as an interconnected symplastic network in which DMSO and the presence of sugars are incompatible.

The Effect of the Antibiotic Hadacidin on the Growth and Cytokinin Levels of Stem Explants

Summary In the present experiments the antibiotic hadacidin was found to inhibit cell division. The levels of endogenous cytokinins in almond and willow explants increased significantly under these conditions. This increase was most noticeable in the bark. These results suggest that an accumulation of these hormones in plant tissue could be related to a retardation of active growth rather than being a normal accompaniment of cell division as was previously suggested. While the present data confirm earlier reports that rootless shoots can produce cytokinins, there seems to be insufficient evidence to conclude that this production is associated with cambial activity.

Metabolism of dimethyl sulfoxide in sprouting potato tubers.

Abstract Whole and cut potato tubers treated with high and low dosages of DMSO respond with a favorable increase in sprouting. DMSO was metabolized to dimethyl sulfide and dimethyl sulfone. A large proportion of the applied DMSO remained unchanged. The major metabolite was dimethyl sulfide suggesting that simple reduction is the preferred route of metabolic breakdown. Growing sprouts were apparently the major site of DMSO metabolism and their development was unaffected by high dosages.

The Effect of Temperature on the Mobilisation of Food Reserves of Pecan Nuts

Summary Lipid mobilisation in the pecan embryo apparently follows a similar pattern irrespective of whether the nuts are incubated at 30°C or stratified. The only difference between the two treatments is that at the low temperature about sixty days are required to attain a similar degree of lipid hydrolysis as is reached within three days at an incubation temperature of 30°C. During incubation at both high and low temperatures the lipid reserves are converted to starch which accumulates in amyloplasts. These ultrastructural observations in part explain why pecan nuts stratified for sixty days develop the capacity to germinate well at ambient temperatures. While endogenous hormones may at some stage be involved in lipid hydrolysis it is nevertheless significant that the levels of gibberellins and cytokinins within the embryos incubated at 30°C only increased after lipid hydrolysis was well under way. It is thus possible that these changes are not related to lipid hydrolysis but more directly with the increased activity of the developing radicles.