J.E. Davey

Cytokinin translocation: Changes in zeatin and zeatin-riboside levels in the root exudate of tomato plants during their development

SummaryThe zeatin and zeatin riboside content of tomato (Lycopersicon esculentum Mill.) root exudates were determined at different stages of development. Zeatin riboside was found to be the major translocational form of cytokinin in the xylem during early vegetative growth. During flower bud formation this cytokinin decreased markedly in concentration so that, at anthesis, there was no appreciable difference in the zeatin and zeatin riboside concentration in the root exudate.

Endogenous cytokinins in the fruits of ripening and non-ripening tomatoes

Abstract Ripening fruits of a normal strain (Rutgers) of tomato (Lycopersicon esculentum Mill.) were found to contain lower levels of endogenous cytokinins than fruits of a non-ripening mutant rin. The cytokinin content of both strains was high at the light green (breaker) stage and decreased as the fruits senesced. This decrease was more pronounced in the normal fruits. The non-ripening rin not only contained higher levels of the free base cytokinins, zeatin and zeatin riboside, but also high levels of zeatin glucoside, a storage cytokinin. It is suggested that the high levels of endogenous cytokinins in rin fruits are involved in delaying the ripening process.

Endogenous Cytokinins in the Laminae and Galls of Erythrina latissima Leaves

The endogenous cytokinins which coeluted with Z, ZR, and ZG increased in the leaf laminae and in the galls of Erythrina latissima over the entire growing season. The highest concentrations were reached in autumn before the leaves senesced. In the galls 90% of the cytokinin activity was localized within the larvae, which made up only 1% of the tissue analyzed. While most of the activity in the leaf laminae was in the form of ZG, a storage or inactive form of the cytokinin, that in the larvae was in the form of the free bases, Z and ZR, regarded as the active form of the cytokinin. This, together with the fact that the cytokinins are very concentrated in the larvae, would ensure that the insect has the ability to mobilize its nutrient requirements even when the leaves may be exporting food reserves during autumn. It appears that the gall is indeed under the control of the parasite and that this control is maintained as a result of the active accumulation of cytokinins from the leaf laminae and, if necessary, their conversion to the active forms by the larvae.

Endogenous cytokinin levels and development of flower virescence in Catharanthus roseus infected with mycoplasmas

The development of virescent flowers as a result of the infestation of Catharanthus roseus plants by different “strains” of mycoplasmas could be correlated with marked changes in the levels of endogenous cytokinins within the flowers, mature leaves and roots of the plants. In all cases, the cytokinin levels in the roots and mature leaves decreased while that in the flowers increased. Three peaks of cytokinin activity which co-eluted with glucosylzeatin, ribosylzeatin and zeatin respectively were detected in these organs. No qualitative differences in the cytokinin complement of the infected plants were detected. At present it is not known whether or not the mycoplasmas used synthesize cytokinins which upset the cytokinin balance of Catharanthus roseus plants or are responsible for changes in the synthetic capacity and/or translocation pattern of the infested plants.

Ultrastructural aspects of reserve protein deposition during cotyledonary cell development in Lupinus albus

Summary The cotyledons of the white lupin ( Lupinus albus L.) are visible at approximately four weeks after anthesis. Compartmentalization of lipid and carbohydrate is evident at six weeks after anthesis. Between six and eight weeks after flowering cell division ceases and the cotyledons increase in size by cell expansion. During this period storage protein synthesis is initiated. Protein forms the major storage product in mature white lupin cotyledonary cells. It is deposited in vacuoles (protein bodies) which occupy a large volume of the cell at maturity. The transition from meristematic to storage cell is accompanied by lobing and enlargement of the cotyledonary cell nuclei and the proliferation of sheets of rough endoplasmic reticulum. During the early stages of protein synthesis two types of proteinaceous aggregation are distinguishable. One kind is membrane bound, and closely associated with the rough endoplasmic reticulum. The other type of proteinaceous aggregation does not appear to be membrane bounded and is only present for a limited period. It is not present at 12 weeks after anthesis. The presence of these aggregations and the observation that electron-dense protein-like vesicles are budded off the dictyosomes during protein synthesis in the white lupin, suggest that there may be different mechanisms by which protein can be synthesised in the cotyledonary cells. The proteinaceous aggregations may fuse to form a protein vacuole, or protein deposition may take place at the tonoplast. The accumulated protein becomes dispersed throughout the protein vacuole which eventually takes on a mottled appearance. At maturity the remaining organelles become compressed between the protein bodies.

Cytokinin Translocation in Xylem Sap of Herbaceous Plants

Summary Partition chromatography of the xylem sap of four herbaceous species, on Sephadex LH-20, in conjunction with the soybean bioassay, revealed the presence of two peaks of activity in each species. These peaks co-eluted with zeatin and its riboside. Within species the two peaks of activity usually elicited similar responses in the bioassay. These findings do not support the suggestion that zeatin-riboside is the major translocational form of cytokinin in the xylem. Qualitative changes during maturation and development of the plants can however not be eliminated.

Seasonal Changes in the Levels of Endogenous Cytokinins in the Willow Salix babylonica L.

Summary A seasonal study of the cytokinin levels in different parts of young plants of Salix babylonica revealed that for a better understanding of the role of these hormones in plant growth it is essential that a more comprehensive approach must be adopted. As would be expected a close relationship was found between the bark, leaf, xylem and root tissue analysed. It would appear as if the bark (which included the cambium, phloem, stem cortex and epidermis) in particular could play an important function in the regulation of cytokinin levels in different tissues at different times of the year.

Gall formation in Erythrina latissima

Summary The Chalcid galls that develop on the leaves of Erythrina latissima are morphologically consistent, suggesting that they either have an obligate fauna, or alternatively that one organism, probably a species of Eurytoma , dominates the whole system. Structurally the galls are as complex as Cynipid galls, consisting of four distinct zones. Of these the nutritive and protective zones are the most important as they provide the food for the developing larvae and protection for the pupae when they overwinter in the gall on the ground. It would appear as if the larvae within the galls exert a strong mobilizing effect and creates a strong sink which ensures the translocation of nutrients towards the galls. This is usually manifested in that the leaf greatly decreases in size with increased infestation.

Changes in the food reserves of viable and non-viable Protect compacta embryos during incubation

Summary Both viable and non-viable Protea compacta embryos show the same pattern of protein digestion during incubation. In the viable embryos however, the hydrolysis of proteins is accompanied by a much larger increase in free amino acids. Protein hydrolysis is followed by lipid digestion, probably by way of the glyoxylate pathway, and the accumulation of starch. Following this there is a rapid development of organelles. In non-viable embryos, digestion does not progress further than the hydrolysis of protein. It would appear as if pre-existing enzymes are associated with globoids, but that the majority of enzymes required for digestion, and in particular those required for lipid hydrolysis, are synthesized de novo .

Lipid Utilization in Viable and Non-Viable Protea compacta Embryos during Germination

Summary An inability to convert free fatty acids to carbohydrate appears to be the main obstacle to germination in non-viable Protea compacta seeds. This block to energy release is apparently due to the fact that no glyoxysomes develop, a situation that may be related to the state of the nuclei, and to inability of the embryos to produce growth promoting substances. Autoxidation of unsaturated fatty acids and the subsequent formation of free radicals during dry storage, do not appear to be responsible for the loss in seed viability.