Cytokinin Metabolism in Phaseolus vulgaris L.: I: VARIATIONS IN CYTOKININ LEVELS IN LEAVES OF DECAPITATED PLANTS IN RELATION TO LATERAL BUD OUTGROWTH

A stable isotope dilution method employing a deuterium-labelledinternal standard and combined gas chromatography-mass spectrometryhas been used to quantify the accumulation of di-hydrozeatin-O-ß-D-glucosidein the primary leaves of decapitated, disbudded bean plants.This cytokinin accumulated at a rate of 11 ng g^–1 fr.wt. d^–1 (eq. to an increase of 50 ng d^–1 per leaf),reaching a maximum of c. 500 ng g^–1 after 40 d from decapitation.This accumulation appeared to parallel the gradual increasein leaf fresh weight, and did not occur in detached leaves,in leaves of intact plants, or in leaves of plants that weredecapitated but not disbudded. When secondary lateral buds wereallowed to grow out from decapitated and initially disbuddedplants, the levels of dihydrozeatin-O-ß-D-glucosidein the primary leaves rapidly declined to a value similar toor lower than that found in leaves of intact plants. A similardecline in dihydrozeatin-O-ß-D-glucoside levels wasseen over 5 d in detached leaves of plants which had been decapitatedand disbudded for 15 d; this effect was reduced but not preventedwhen the leaves were supplied with inorganic nutrients. Theseresults are discussed in relation to the metabolism and distributionof cytokinins in the whole plant.     

Ethylene and 1 -Aminocyclopropane-1-Carboxylic Acid Production in flacca, a Wilty Mutant of Tomato, Subjected to Water Deficiency and Pre-treatment with Abscisic Acid

Neill, S. J., McGaw, B. A. and Horgan, R. 1986. Ethylene and1-aminocyclopropane-l-carboxylic acid production in flacca,a wilty mutant of tomato, subjected to water deficiency andpretreatment with abscisic acid —J. exp. Bot. 37: 535–541. Plants of Lycoperstcon esculentum Mill. cv. Ailsa Craig wildtype and flacca (flc) were sprayed daily with H²O or 2?10^–2mol m^–3 abscisic acid (ABA). ABA treatment effected apartial phenotypic reversion of flc shoots; leaf areas wereincreased and transpiration rates decreased. Leaf expansionof wild type shoots was inhibited by ABA. Indoleacetic acid (IAA), ABA and l-aminocyclopropane-l-carboxylicacid (ACC) concentrations were determined by combined gas chromatography-massspectrometry using deuterium-labelled internal standards ABAtreatment for 30 d resulted in greatly elevated internal ABAlevels, increasing from 1?0 to 4?3 and from 0?45 to 4?9 nmolg^–1 fr. wt. in wild type and flc leaves respectively.Endogenous IAA and ACC concentrations were much lower than thoseof ABA. IAA content ranged from 0?05 to 0?1 nmol g^–1 andACC content from 0?07 to 0?24 nmol g^–1 Ethylene emanationrates were similar for wild type and flc shoots. Wilting of detached leaves induced a substantial increase inethylene and ACC accumulation in all plants, regardless of treatmentor type. Ethylene and ACC levels were no greater in flc leavescompared to the wild type. ABA pretreatment did not preventthe wilting-induced increase in ACC and ethylene synthesis. Key words: ABA, ACC, ethylene, wilting, wilty mutants     

Effect of water stress on metabolism of abscisic acid in Populus robusta× schnied and Euphorbia lathyrus L.

Abstract. Dihydrophaseic acid (DPA) has been identified in leaves from Euphorbia lathyrus L and Populus robusta x schnied. The formation of DPA from abscisic acid (ABA) was demonstrated using ¹⁴C-ABA. Measurements of ABA, DPA and phaseic acid (PA) concentrations were made in Euphorbia subjected to drought and waterlogging and in Populus subjected to rhythmic water stress. The results are consistent with the proposition that ABA concentrations are controlled by de novo biosynthesis and by metabolism via the PA /DPA pathway. The findings are discussed in relation to effects of the type of stress and its duration and to behaviour during stress relief.     

Nutrient stoichiometry of linked catchment‐lake systems along a gradient of land use

1. Catchments export nutrients to aquatic ecosystems at rates and ratios that are strongly influenced by land use practices, and within aquatic ecosystems nutrients can be processed, retained, lost to the atmosphere, or exported downstream. The stoichiometry of carbon and nutrients can influence ecosystem services such as water quality, nutrient limitation, biodiversity, eutrophication and the sequestration of nutrients and carbon in sediments. However, we know little about how nutrient stoichiometry varies along the pathway from terrestrial landscapes through aquatic systems. 2. We studied the stoichiometry of nitrogen and phosphorus exported by three catchments of contrasting land use (forest versus agriculture) and in the water column and sediments of downstream reservoirs. We also related stoichiometry to phytoplankton nutrient limitation and the abundance of heterocystous cyanobacteria. 3. The total N : P of stream exports varied greatly among catchments and was 18, 54 and 140 (molar) in the forested, mixed‐use and agricultural catchment, respectively. Total N : P in the mixed layers of the lakes was less variable but ordered similarly: 35, 52 132 in the forested, mixed‐use and agricultural lake, respectively. In contrast, there was little variation among systems in the C : N and C : P ratios of catchment exports or in reservoir seston. 4. Phytoplankton in the forested lake were consistently N limited, those in the agricultural lake were consistently P limited, and those in the mixed‐use lake shifted seasonally from P‐ to N limitation, reflecting N : P supply ratios. Total phytoplankton and cyanobacteria biomass were highest in the agricultural lake, but heterocystous (potentially N fixing) cyanobacteria were most abundant in the forested lake, corresponding to low N : P ratios. 5. Despite large differences in catchment export and water column N : P ratios, the N : P of sediment burial (integrated over several decades) was very low and remarkably similar (4.3–7.3) across reservoirs. N and P budgets constructed for the agricultural reservoir suggested that denitrification could be a major loss of N, and may help explain the relatively low N : P of buried sediment. 6. Our results show congruence between the catchment export N : P, reservoir N : P, phytoplankton N versus P limitation and the dominance of heterocystous cyanobacteria. However, the N : P stoichiometry of sediments retained in the lakes was relatively insensitive to catchment stoichiometry, suggesting that a common set of biogeochemical processes constrains sediment N : P across lakes of contrasting catchment land use.     

Abscisic Acid Production and Water Relations in Wilty Tomato Mutants Subjected to Water Deficiency

Neill, S. J. and Horgan, R. 1985. Abscisic acid production andwater relations in wilty tomato mutants subjected to water deficiency.—J.exp. BoL 36: 1222-1231. Abscisic acid (ABA) concentrations were determined in shootsof Lycopersicon esculentum Mill. cv. Ailsa Craig wild type andthe three wilty mutants notabilis (not), flacca (flc) and sitiens(sit). ABA content of unstressed wild type leaves was 1.5 nmolg^–1 fr. wt.; concentrations in not, flc and sit were 49,26 and 15% of this respectively. Gradual water stress was imposed on potted plants and a morerapid stress imposed on detached leaves. Leaves of the wildtype and not responded to both stresses by increasing theirABA content but leaves of flc and sit did not produce any moreABA under stress. Transpiration rates of flc plants were three times greater thanthose of the wild type and stomatal resistances correspondinglylower. Stomata of both flc and the wild type responded to darknessand externally supplied ABA by closing. However, only wild typestomata responded to water stress by dosing; those of flc leavesremained open until the leaves were severely desiccated. Thus,there was some relationship between the lack of stomatal responseto water stress and the failure to synthesize ABA. Key words: ABA, biosynthesis, stomata, water shortage, wilty mutants     

Cytokinins and the Growth Responses of Seedlings of Betula pendula Roth. and Acer pseudoplatanus L. to Nitrogen and Phosphorus Deficiency

Deficiencies in the supply of nitrogen and phosphorus broughtabout the cessation of shoot extension and the formation ofterminal resting buds in seedlings of Acer pseudoplatanus maintainedunder long days, whereas seedlings of Betula pendula maintainedunder the same conditions continued extension growth of themain axis over a long period, although they showed symptomsof nitrogen deficiency, including a reduced chlorophyll content.The endogenous cytokinin levels of the base/nucleoside fractionin leaves of B. pendula were significantly lower in the nitrogen-deficientplants than in the controls only 3 d after transfer to deficientconditions. Similar, though less marked, changes were observedin response to phosphorus deficiency. Changes in the levelsof cytokinin activity in the nucleotide fraction in responseto nitrogen deficiency were much less marked. No significantchanges in cytokinin levels of the base/nucleoside or nucleotidefractions could be detected in leaf material from seedlingsof A. pseudoplatanus, even after a nitrogen or phosphorus deficiencytreatment of 4 weeks. Application of exogenous benzyladenineto seedlings of B. pendula subjected to nitrogen deficiencyresulted in a rapid regreening and to outgrowth of inhibitedlateral buds after only 2 d.