Daan Kuiper

Effects of internal and external cytokinin concentrations on root growth and shoot to root ratio of Plantago major ssp pleiosperma at different nutrient conditions.

In Plantago major L. an enormous genetic variability is present for a large number of plant traits (Van Dijk and Van Delden, 1981; Kuiper, 1982, 1983; Kuiper and Smid, 1985). Differences in relative growth rates (RGR) for shoot and roots were observed among inbred lines of P. major. Inbred lines also differed largely in the rate of growth responses, when plants were transferred from a nutrient-rich growth solution (100%) to a 50 times diluted nutrient solution (2%) and vice versa. Quick growth responses in plants of an inbred line belonging to subspecies pleiosperma (Pilger) transferred from a 100% to a 2% solution (100–2% plants) were accompanied by a rapid decrease in shoot to root ratio (S/R). The rapidity of the responses in P. major ssp pleiosperma and preliminary determinations of the contents of several ions raised the question about the decisive role of the availability of minerals in growth regulation.

Actual cytokinin concentrations in plant tissue as an indicator for salt resistance in cereals

Growth rates of roots and shoots of hydroponically grown plants of a salt resistant variety of barley decreased rapidly after an exposure to 65 M m-3 sodium chloride. This growth rate reduction tended to be temporarily and it was accompanied by a lowered shoot to root ratio. At the same time growth reduction took place, the cytokinin concentrations in root and shoot tissue decreased rapidly too, as they were measured by an enzyme-linked immuno assay. The addition of 5·10-9M m-3 benzyladenine (BA) retarded the decreases of growth rates, shoot to root ratio and internal cytokinin concentrations.Growth rates of roots and shoot of identically grown plants of salt sensitive varieties of barley maintained their growth rates and shoot to root ratio after an exposure to NaCl for at least ten days in combination with unchanged levels of endogenous cytokinins. After ca 14 days NaCl induced severe decreases in RGR values, but not in shoot to root ratio. Addition of benzyladenine inhibited growth to some extent and enhanced the cytokinin concentration.It was concluded, that cytokinin concentrations measured directly after exposure to NaCl form a promising screening method for salt resistance. The addition of BA made salt resistance varieties behave as salt sensitive varieties.

Root functioning under stress conditions: An introduction

The only difference from the usual approach in plant sciences is that the experimental plants are exposed to suboptimal environmental conditions or even severe conditions, the so-called stress conditions.

Root temperature effects on growth and bud break of Rosa hybrida in relation to cytokinin concentrations in xylem sap.

The effects of three divergent root temperatures (11°C, 20°C and 26°C) on growth and bud break of Rosa hybrida were studied. Root morphology was changed considerably with root temperature. Roots at 11°C were white, succulent, short and sparsely branched, whereas at 26°C roots were long, brown, thin and branched. However, root dry weight was not affected by root temperature. Axillary bud break was earlier at higher root temperatures, resulting in a higher shoot dry weight. At higher temperatures, bottom breaks tended to appear earlier. Our hypothesis was that the effect of root temperature on growth and bud break of the shoot is mediated by cytokinin production in the roots and/or cytokinin translocation to the shoot. The concentration of zeatin riboside (ZR) in bleeding sap was determined during plant development. ZR was found to decrease slightly after bud break, but was not affected by the root temperature treatments, which falsified our hypothesis. Other processes may be involved in the effect of root temperature on shoot growth and bud break.

Bud break and cytokinin concentration in bleeding sap of Rosa hybrida as affected by the genotype of the rootstock

Summary Grafting Rosa hybrida Madelon on six rootstock genotypes revealed that growth of the scion was affected by the genotype of the rootstock If rootstocks would mediate scion growth via their cytokinin production, it might be possible to improve the performance of a rootstock by exogenous application of cytokinins. Indeed, benzyladenine (BA) application was found to stimulate the number of bottom breaks, mainly on the low-yielding rootstocks Vivaldi and Madelon. To test the hypothesis that a rootstock that induces earlier bud break of the scion supplies more cytokinins to the shoot, cytokinin levels in bleeding sap of Vivaldi and the vigorous rootstock Multic were followed during plant development. Bud break of the axillary shoots was not affected by the genotype of the rootstock, but bottom breaks appeared earlier when Madelon was grafted on Multic than on Vivaldi. The concentration of zeatin riboside (ZR) in bleeding sap of Madelon/Multic combination plants was high at axillary bud break, decreased when the axillary buds grew out, increased thereafter until the bottom breaks appeared, and decreased again. The ZR concentration in bleeding sap of Madelon/Vivaldi plants was considerably lower than that of Madelon/Multic plants, but showed more or less the same pattern. Apical dominance in rose combination plants during their development is discussed in terms of auxin and cytokinins.