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Senescence and reserve mobilization are integral components of plant development, are basic strategies in stress mitigation, and regulated at least in part by cytokinin. In the present study the effect of altered cytokinin metabolism caused by senescence-specific autoregulated expression of the Agrobacterium tumefaciens IPT gene under control of the P(SAG12) promoter (P(SAG12)-IPT) on seed germination and the response to a water-deficit stress was studied in tobacco (Nicotiana tabacum L.). Cytokinin levels, sugar content and composition of the leaf strata within the canopy of wild-type and P(SAG12)-IPT plants confirmed the reported altered source-sink relations. No measurable difference in sugar and pigment content of discs harvested from apical and basal leaves was evident 72 h after incubation with (+)-ABA or in darkness, indicating that expression of the transgene was not restricted to senescing leaves. No difference in quantum efficiency, photosynthetic activity, accumulation of ABA, and stomatal conductance was apparent in apical, middle and basal leaves of either wild-type or P(SAG12)-IPT plants after imposition of a mild water stress. However, compared to wild-type plants, P(SAG12)-IPT plants were slower to adjust biomass allocation. A stress-induced increase in root:shoot ratio and specific leaf area (SLA) occurred more rapidly in wild-type than in P(SAG12)-IPT plants reflecting delayed remobilization of leaf reserves to sink organs in the transformant. P(SAG12)-IPT seeds germinated more slowly even though abscisic acid (ABA) content was 50% that of the wild-type seeds confirming cytokinin-induced alterations in reserve remobilization. Thus, senescence is integral to plant growth and development and an increased endogenous cytokinin content impacts source-sink relations to delay ontogenic transitions wherein senescence in a necessary process.

A rapid methodology for the simultaneous analysis of a large number of cytokinins is presented. The cross-reactivity of a mixture of polyclonal antibodies against zeatin riboside and isopentenyladenosine was exploited in a protocol that can be used for immunoaffinity purification of 23 additional cytokinins. Ligands include the cytokinin bases zeatin, dihydrozeatin, isopentenyladenine, benzyl-adenine and kinetin, and their corresponding nucleoside, nucleoside-5'-monophosphate, and 9-glucoside derivatives, as well as cis-zeatin, cis-zeatin riboside, the 2-methylthiol derivatives of isopentenyladenosine and zeatin riboside, and benzyl-adenine-3-glucoside. Mixtures of cytokinins could be retained with high recoveries of all the components. Immunoaffinity purification of extracts of Arabidopsis thaliana (L.) Heynh. and Solarium tuberosum L. gave fractions clean enough, as verified by gas chromatographymass spectrometry (GC-MS), to allow analysis of endogenous cytokinins using a single high-performance liquid chromatography (HPLC) step with on-line UV-spectrum detection. The detection limit was 4-6 pmol. The procedure described forms a routine assaying technique that is faster and simpler, yet yields better qualitative and quantitative information than the commonly used procedure of immunoassaying of HPLC fractions.

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Indol-3yl-acetic acid (IAA) was identified in Phaseolus vulgaris L. Shoot tissue of seedlings, exposed to light for 5 days, had a higher level of IAA than etiolated seedlings of the same age. The content of IA A increased in green seedlings during light treatment for 5-12 days. No increase could be measured in dark-grown seedlings. Inhibitory substances appeared at different Rf-values. The main part was identical to the inhibitor-)? complex and occurred in a higher amount in light-grown seedlings than in etiolated taller ones. One part of the inhibitor-complex appeared to be abscisic acid (ABA). It is suggested that both IAA and acid inhibitors may play an important role in the control of stem growth and differentiation, although light effects on other hormones and regulatory systems cannot be ignored.

The content of indoleacetic acid (IAA) was determined in dry and germinating seeds of French bean (Phaseolus vulgaris), sugar maie (Zea mays), and Scots pine (Pinus silvestris). IAA was found in both the dry and the soaked seeds of the three species examined. The amount of IAA per gram fresh weight was extremely different in the three species whereas the variation between different harvests of the same species was small. Maize contained the highest level of IAA and bean the smallest. The time of imbibition was of decisive importance for the level of IAA. In all three species the content of IAA increased considerably during the initial 4 hours of swelling. The highest level of IAA was found in seeds that had swelled for 24 to 48 hours, during which period the radicies began to emerge from the seed coat. Later, during the period of npid root growth, the content of IAA declined.Auxin is an important plant growth hormone which is active in the regulation of most growth processes in plants. However, its role in the germination of seeds is largely unknown. While it is well known that gibberellins and cytokinins are of importance for the germination processes (2, 10, 13) some authors assume that auxin is of no importance for the mobilization of nutrients or for the early metabolic and growth processes in the embryo (e.g. [25,26]).Most of the present evidence of the roles of plant hormones in the germinative processes is based on the effects of external application of compounds to the seeds. The general finding is that exogenously applied auxin has no promotive effect on germination. This may be the basis of the belief that auxin is of no or little importance for germination. It is also possible that no promotive effect is found as the seeds may already contain a level of endogenous auxin optimal for germination.So far, relatively few attempts have been made to characterize and identify the endogenous auxins in seeds during the germination and to relate quantitative changes to growth and developmental processes. Zea mays is a shining exception (e.g. [24]).This paper is a report of analyses of the amounts of endogenous IAA in dry and swelling seeds. A comparison has been made among three different species which belong to different taxonomic groups and which also differ in the kind of nutritive reserves they possess. The species studied were Zea mays, Phaseolus vulgaris, and Pinus silvestris. The seeds were soaked under conditions that were suitable for germination of each particular species. IAA content was determined by the indole-a-pyrone fluorescence method (21). Extraction and Purification. Seeds weighing 10 g before treatment were homogenized in a Sorvall homogenizer (bean and maize) or in a mortar (pine) in ice-cold methanol (10 ml/g plant material). To each homogenate was added another portion of methanol (10 ml/g plant material). The sterilization and soaking of the seeds resulted in a slight difference in the methanol concentration between different homogenates: soaking time: 0 hr = 98%; 4 hr = 97.5%; 24...

Germination experiments on isolated embryos and intact achenes from Rosa rugosa L. var. rubra revealed the existence of both coat‐induced and embryo dormancy. Studies were made on the quantitative changes in abscisic acid (ABA) of achenes during both a stratification period at 4°C and a subsequent germination period at 20°C. Controls were run in parallel at 17°C. Dormant, unimbibed achenes contained large amounts of ABA. The level fell rapidly during the early stages of stratification at 4°C, mainly due to leakage, and then the decline levelled off. The reduction of ABA content during germination was less and followed a tri‐phasic pattern. Under the control conditions, the ABA level also fell although still faster, the amounts present being consistently below those detected in the corresponding cold‐stratified samples. The content of alkali‐hydrolysable ABA was low and not affected either by the duration or by the temperature of stratification. The investigation shows that termination of dormancy is not simply a consequence of a fall in the content of endogenous ABA and supports the current debate questioning the central role of ABA in regulation of dormancy breakage and of germination.

Abseisic acid content at defined levels of bud dormancy and frost tolerance in two contrasting populations of Picea abies grown in a phytotron -Physiol Plant 87: 203-210.Seedlings of a southern (Romanian) and a northern (Swedish) population of Picea abies were cultivated under continuous light and 20°C for 10 weeks. To arrest growth, induce terminal bud dormancy and promote frost tolerance the seedlings were then exposed to 16 h nights for 12 weeks, with gradually lower temperature during the last 6 weeks. Samples for estimating the abscisic acid content of the needles were taken just before the onset of the night treatment, at day 3 of the treatment, and then with one, and later 2 week, intervals. From the second week onwards (third week for frost tolerance) bud dormancy and frost tolerance were assessed at the same time as abscisic acid (ABA) determinations. Phosphate-buffered saline extracts were purified on mini-columns (in some eases immunoaffinity colums) and quantified by HPLC. The degree of dormancy was estimated by transferring the seedlings to growth conditions and determining the number of days until growth was resumed. The frost tolerance of the needles exposed to -10°C and -20°C was classified in 6 classes. The frost tolerance of the terminal buds was estimated as the number of seedlings that showed some growth after 6 weeks in growth conditions. The night treatment rapidly induced terminal bud dormancy in both populations, but the release of dormancy occurred earlier in the northern population. The needles and the terminal buds became highly frost tolerant more rapidly in the northern than in the southern population and before the temperature decrease. TTie degree of dormancy began to decline before full frost tolerance was obtained in the southern population and this decline continued in both populations, while frost tolerance remained at a high level. The southern population showed a transient peak in ABA content at day 3. Although the ABA content of the northern population was lower than in the southern before the 16-h night treatment, it increased in the northern population during the treatment period, in particular after the temperature decrease. latitig frost hardiness could be identified. One way to approach the identification of these genes may he to Frost hardiness is of decisive itnportance for the sur-identify the components of hardiness. Another may he vival, growth and reprodtiction of Scandinavian forest to study the steps from the perception of the signal from trees. Breeding would he facilitated if the genes regu-the environment up to the time when the highest degree