Effects of climate change on productivity of cereals and legumes; model evaluation of observed year-to-year variability of the CO2 response

The effect of elevated [CO₂] on the productivity of spring wheat, winter wheat and faba bean was studied in experiments in climatized crop enclosures in the Wageningen Rhizolab in 1991–93. Simulation models for crop growth were used to explore possible causes for the observed differences in the CO₂ response. Measurements of the canopy gas exchange (CO₂ and water vapour) were made continuously from emergence until harvest. At an external [CO₂] of 700 μmol mol^?1 Maximum Canopy CO₂ Exchange Rate (CCERmax) at canopy closure was stimulated by 51% for spring wheat and by 71% for faba bean. At the end of the growing season, above ground biomass increase at 700 μmol mol^?1 was 58% (faba bean), 35% (spring wheat) and 19% (winter wheat) and the harvest index did not change. For model exploration, weather data sets for the period 1975-88 and 1991–93 were used, assuming adequate water supply and [CO₂] at 350 and 700 μmol mol^?1. For spring wheat the simulated responses (35–50%) were at the upper end of the experimental results. In agreement with experiments, simulations showed smaller responses for winter wheat and larger responses for faba bean. Further model explorations showed that this differential effect in the CO₂ response may not be primarily due to fundamental physiological differences between the crops, but may be at least partly due to differences in the daily air temperatures during comparable stages of growth of these crops. Simulations also showed that variations between years in CO₂ response can be largely explained by differences in weather conditions (especially temperature) between growing seasons.     

Metabolism of [14C]Indole-3-Acetic Acid by Coleoptiles of Zea mays L.

Reverse-phase high-performance liquid chromatography was usedto analyse [¹⁴C]-labelled metabolites of indole-3-acetic acid(IAA) in coleoptile segments of Zeo mays seedlings. After incubationfor 2 h in 10^–2 mol m^–3 [2-¹⁴C]IAA, methanolic extractsof coleoptiles contained between six and ten radioactive compounds,one of which co-chromatographed with IAA. The metabolic productsin coleoptile extracts appeared to be similar to those in rootextracts, with an oxindole-3-acetic-acid-like component as theprincipal metabolite, but the rate of metabolism was slowerin coleoptile than in root segments. Decarboxylation did notappear to play a major role in the metabolism of exogenous IAAduring the short incubation periods. Moreover, external IAAconcentration had little effect on the pattern of metabolism.Coleoptile segments were also supplied with [¹⁴C]IAA from agardonor blocks placed at the apical ends, and agar receiver blockswere placed at the basal ends. After incubation for 4 h, theidentity of the single radioactive compound in the receiverblocks was shown to be IAA by both reverse-phase high-performanceliquid chromatography and gas chromatography-mass spectrometrytechniques. Key words: Zea mays, Coleoptile, High-performance liquid chromatography, Indole-3-acetic acid     

Measurement of the Rates of Oxindole-3-Acetic Acid Turnover, and Indole-3-Acetic Acid Oxidation in Zea mays Seedlings

Nonhcbcl, H. M. 1986. Measurement of the rates of oxindole-3-aceticacid turnover and indole-3-acetic acid oxidation in Zea maysseedlings.—J. exp. Bat. 37: 1691–1697. Oxindole-3-acetic acid is the pnncipal catabolite of indole-3-aceticacid in Zea mays seedlings. In this paper measurements of theturnover of oxindole-3-acetic acid are presented and used tocalculate the rate of indole-3-acetic acid oxidation. [³H]Oxindolc-3-acetic acid was applied to the endosperm of Zeamays seedlings and allowed to equilibrate for 24 h before thestart of the experiment. The subsequent decrease in its specificactivity was used to calculate the turnover rate. The averagehalf-life of oxindole-3-acetic acid in the shoots was foundto be 30 h while that in the kernels had an average half-lifeof 35 h. Using previously published values of the pool sizesof oxindole-3-acetic acid in shoots and kernels from seedlingsof the same age and variety, and grown under the same conditions,the rate of indole-3-acetic acid oxidation was calculated tobe I-I pmol plant^–1 h^–1 in the shoots and 7·1pmol plant^–1 h^–1 in the kernels. Key words: Oxindole-3-acetic acid, indole-3-acetic acid, turnover, Zea mays     

Contrasting Incorporation of 2H from 2H2O into ABA, Xanthoxin and Carotenoids in Tomato Shoots

Nonhebel, H. M. and Milborrow, B. V. 1987. Contrasting incorporationof ²H from ²H²O into ABA, xanthoxin and carotenoids in tomatoshoots.—J. exp. Bot. 38: 980–991. The incorporation of ²H into abscisie acid, xanthoxin, ß-carotene,lutein, lutein epoxide and violaxanthin in tomato shoots incubatedfor 6 d in 70% ²H₂O was compared to investigate whether thesecompounds are precursors of abscisie acid. On average, 5% ofabscisie acid molecules became labelled with a single ²H atomand 21% with from 3 to 14 atoms of ²H. However, mass spectralanalysis of endogenous xanthoxin extracted from the same plants,in darkness, under nitrogen, and derivatized to the pentafluorobenzyloximeshowed incorporation of only single ²H atoms, ruling out xanthoxinas an abscisie acid precursor. Normal-phase HPLC analysis oftomato shoot extracts showed four major carotenoid peaks; ß-carotene,lutein, lutein epoxide and violaxanthin. Calculations basedon the measured carotenoid pool sizes and on the calculatedminimum pool size of the ABA precursor predicted that at least6·8% of violaxanthin molecules or 7·9% of luteinepoxide molecules should become labelled with from 3 to 14 ²Hatoms if these molecules are precursors of abscisie acid. However,mass spectral analysis of xanthoxin derived from purified violaxanthinand lutein epoxide showed no molecules with more than a single²H atom, with detection limits of less than 1% and 0·2%respectively. Similarly, mass spectra of ß-caroteneand lutein did not show any ²H. We conclude that these carotenoidsare not precursors of abscisie acid. Key words: Abscisic acid, xanthoxin, carotenoids     

Incorporation of 2H from 2H2O into ABA in Tomato Shoots: Evidence for a Large Pool of Precursors

Tomato shoots were supplied simultaneously with S-[¹⁴C]abscisicacid and ²H₂O for 4 h. After a further 6 h incubation no deuteriumhad been incorporated into abscisic acid (ABA) extracted fromwilted or turgid shoots although up to 93% of the ABA had beensynthesized in the presence of ²H₂O as shown by the dilutionof [¹⁴C]ABA. This provides substantial evidence for a largepool of ABA precursors. When tomato shoots were incubated for6d in 80% ²H₂O between 20% and 32% of ABA molecules became labelledwith from 1 to 14 deuterium atoms. From this data the minimumsize of the precursor pool was calculated to be approximately35 times that of ABA. In addition, ABA from wilted plants containedsignificantly less deuterium than that from turgid plants suggestinga second or an enlarged pool of precursor in wilted plants. Key words: Abscisic acid, precursor pool, ²H incorporation     

SHORT COMMUNICATION Factors Affecting Protoplast Culture ofCucumis melo'Green Delica'

Hypocotyls, cotyledons and etiolated half-expanded leaves ofCucumismelo‘Green Delica’ were used as explants for protoplastisolation and culture. Protoplasts isolated from cotyledonsand etiolated half-expanded leaves cultured in Durand, Potrykusand Donn (DPD) medium supplemented with 0.9 µMbenzylaminopurine(BAP), 3.6 µM2,4-dichlorophenoxyacetic acid (2,4-D) and1% sucrose, using the agarose bead culture method, were ableto form cell walls and subsequently go through cell division.Pretreatment of half-expanded leaf explants in the dark for14 d provided the best material for protoplast isolation andcell division. Approximately one third of protoplasts from etiolatedhalf-expanded leaves formed microcolonies. For hypocotyl protoplasts,none of the treatments used were suitable to induce cell division.There was no significant difference between sucrose, glucose,and sucrose plus glucose, in culture media on the plating efficiencyof leaf protoplasts ofC. melo‘Green Delica’; however,bigger colonies were formed in media supplemented with 1% sucrose.No shoot or whole plant regeneration was achieved. However,the methods reported here provide further information onC. meloprotoplastculture.Copyright 1998 Annals of Botany Company Cucumis melo,protoplast culture, 2,4-D, BAP, yeast extract, casein hydrolysate.